Critical Risk Factors Affecting Time and Cost in Highway Construction: A Global Systematic Literature Review

Abstract

This study presents a systematic literature review of critical risk factors affecting the time and cost performance of highway construction projects. Drawing from 83 peer-reviewed studies across multiple geographic regions, the paper identifies recurrent drivers of project delay and cost overrun in highway construction. The most frequently reported risks include (1) financial constraints, (2) political regulatory issues; (3) land-acquisition and right-of-way delays; (4) design and scope changes; (5) utilities relocation/conflicts; (6) materials and equipment shortages; (7) contractor-related issues; (8) planning and scheduling weaknesses; (9) labour and personnel issues; and (10) weather conditions. These risk factors collectively highlight the importance of robust planning, proactive stakeholder coordination, and the integration of risk-informed decision-making tools. The findings emphasize the need for targeted risk mitigation during early project stages and provide a foundation for refining risk assessment frameworks and future research directions in transport infrastructure development.

1. Introduction

The construction of roads plays a pivotal role in developing a nation’s transportation system, serving as a fundamental component of economic infrastructure. Road networks and highways are essential for addressing national and regional socio-economic challenges, as their development and condition directly influence factors such as gross domestic product (GDP), price levels, and the efficient use of roads across economic sectors. As shown by Datta [1] for India’s Golden Quadrilateral where improved highways reduced firms’ input inventories by about one week of production and eased transport obstacles. Ghani, Goswami and Kerr [2] further show that for India’s Golden Quadrilateral, districts within 10 km of the upgraded highway experienced roughly 50% higher manufacturing output over the 2000–2009 period, driven by surging entry and post-entry scaling, alongside improved allocative efficiency and higher wages. As Pérez [3] highlights, transportation infrastructure acts as a critical link between production and consumption centres, making it indispensable to a country’s economic growth and stability. At the same time, highway project delivery is exposed to uncertainties across planning, procurement, and construction that frequently result in cost growth and schedule delays. Accordingly, guidance from the highway/transportation infrastructure industry, specifically TRB’s NCHRP Report 658, recommends addressing risk explicitly from the outset, integrated into project development and monitored throughout delivery [4].

However, the technical and operational condition of roads deteriorates over time due to various factors, including weather conditions, material aging, and increasing vehicle loads. (see FHWA [5]; Paterson [6]; Llopis-Castelló et al. [7]. With rising population demands and the subsequent growth in freight and passenger traffic, the need for strategic expansion, upgrading, and maintenance of road networks has become increasingly evident. Addressing these demands requires collaborative efforts between government and private partners as shown in global analyses, with illustrative evidence from the United States (GAO [8]; Mallett [9]). In addition, highway projects are inherently complex. Although Yang and Frangopol [10] develop their framework for civil infrastructure in general, they emphasise that the dynamic nature of the construction industry and the interdependence of multiple project components create high uncertainty requiring management throughout planning, design, construction, and operation. Highways, as linear, capital- and maintenance-intensive assets, demand substantial financial, material, and labour inputs over their full lifecycle, including planning and design, construction, rehabilitation/reconstruction, and routine maintenance, particularly under constrained budgets (OECD/ITF) [11].

In highway construction projects, uncertainties and risks arise at every lifecycle stage; systematic risk management is essential to maintain costs and quality and to achieve scheduled completion Vishwakarma et al. [12]. During the estimation stage, systematic risk identification and evaluation improve the treatment of uncertainty in cost prediction (Birnie & Yates) [13]. Furthermore, Zwikael and Ahn [14] show that project risk-management planning moderates the impact of risk on overall project success.

While risk-based thinking has yielded benefits, it also raises challenges and controversies that demand careful attention from decision-makers (Ball) [15]. In highway projects, complexity, scope change, and exposure to cost and schedule risk make risk management particularly demanding; accordingly, practitioners should identify, assess, and mitigate key risks and apply appropriate analysis tools throughout the project development process (TRB, NCHRP Report 658) [4].

According to ISO 31000:2018 [16], the risk-management process comprises risk assessment (identification, analysis, evaluation) and risk treatment (mitigation/response), with ongoing communication, consultation, monitoring, and review. This paper addresses the above challenges by conducting a systematic literature review to identify critical and frequently discussed risks affecting highway construction projects. This study develops a comprehensive taxonomy of highway-construction risk factors, identifies the principal risks reported in the global literature across diverse countries, and determines those most critical to project cost and schedule performance.

Research Objectives

The main objectives of Systematic Literature Review are:

• To identify and recommend a comprehensive classification system for risk factors associated with highway construction projects.
• To identify the key risk factors associated with highway construction projects.
• To determine the most critical risks affecting road/highway construction project cost and time performance.

2. Fundamentals of the Systematic Literature Review

2.1. Description of the Systematic Literature Review

This study employed a systematic literature review (SLR) drawing on the Evidence for Policy and Practice Information and Co-ordinating Centre’s (EPPI-Centre) methodological guidance for evidence synthesis [17]. Reporting adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [18]. The SLR was implemented using EPPI-Reviewer [19], the EPPI-Centre’s software developed at University College London (UCL), United Kingdom, to manage study records, conduct screening, and support data extraction and synthesis, thereby ensuring a transparent and systematic review process.

2.2. Methodology

2.2.1. Methodology of SLR

The scope of this review was guided by well-defined conceptual frameworks, including relevant key concepts, synonyms, and free terms. To ensure extensive coverage of the subject matter, multiple sources were explored. These included: Electronic bibliographic databases, Internet search engines, Organization-specific websites, Physical copies of books and journals, Conference proceedings, Peer-reviewed journal papers, and Professional reports and scientific articles relevant to risk management, cost-time optimization, and risk assessment techniques in highway construction.

The references of each identified paper were also screened for further relevant studies to ensure completeness. Prior to screening and analysing the retrieved documents, all search results were imported into the EPPI-Reviewer 4 tool. This tool was instrumental in facilitating the systematic processes of screening, coding, storing, and synthesizing the collected data to generate comprehensive insights.

The review methodology followed a structured approach, broken into two primary stages:

(1)

Title/Abstract Screening: Initial screening of studies to identify relevance based on predefined criteria.

(2)

Full-Text Screening: Detailed review and synthesis of studies that met the inclusion criteria during the title/abstract screening phase.

The methodological quality of the included studies was assessed using the MMAT; the full MMAT Quality Appraisal Report for all 83 included studies is provided in the Supplementary Materials S2.

To ensure the systematic literature review was conducted effectively and transparently, a detailed and rigorous research protocol was developed. The protocol serves as a documented action plan, outlining the following elements:

(1)

Research Questions: Clearly defined questions guiding the review process.

(2)

Eligibility Criteria: Development of inclusion and exclusion criteria to ensure the relevance and quality of selected studies.

(3)

Search Terms and Sources: Identification of relevant keywords, synonyms, and databases to comprehensively capture the literature.

(4)

Scope of the Review: Conceptual definitions and boundaries to ensure focus and coherence.

The full protocol including the detailed search terms used to generate the dataset for the systematic literature review is provided in Supplementary Material S1.

This systematic review was preregistered on the Open Science Framework (OSF) under DOI https://doi.org/10.17605/OSF.IO/KTWJG.

Search Question

This review seeks to address the following primary research question:

• What is the evidence supporting the use of risks management/optimisation (framework) in highway construction?
• What is the evidence supporting the use of risk optimization methods for highway construction?

Summary of Figure 1: Literature Selection Process

Figure 1. Search process of database—schematic diagram of the systematic literature review.

Figure 1 presents the schematic overview of the literature search and selection process employed in this review.

The process commenced with the identification of 1295 potential studies. After applying title/abstract screening, full-text eligibility assessments, and inclusion criteria, 83 studies were selected for detailed analysis.

2.2.2. Methodology of Identifying the Most Common Risk Factors in Highway Projects

The methodology adopted in this paper adheres to the SLR process particularly emphasizing structured data extraction and frequency-based analysis.

A total of 83 peer-reviewed studies were analysed using predefined inclusion and exclusion criteria. Studies were screened for relevance based on their empirical focus on risk factors in road and highway construction.

Each study was assessed for methodological rigor and categorized based on geographical regions, data collection method, and identified risk types. Frequencies were calculated to determine the most commonly cited risk factors.

The analysis of the most significant factors contributing to delays and cost overruns utilized the basic statistical concept of “frequency percentage.” As a result, the ranked list of frequently discussed risk factors is presented later in the Results (see Section 3). Additionally, calculations of percentage values based on the frequency analysis were performed for each significant factor.

To determine the prevalence of each factor within the reviewed literature, the frequency index was calculated using the formula below:

Frequency (%) = (Frequency of Occurrences/Total Number of Documents) × 100

2.2.3. Methodology for Producing the Recommended Classification Standard

The recommended risk-classification standard (presented later in the Results; see Section 3) was produced through a rules-based consolidation process. The approach was anchored to widely used guidance (ISO 31000 [16]; TRB’s NCHRP Report 658 [4]) and was also informed by prior highway/construction risk taxonomies reported in the literature. In particular, definitions and factor groupings were synthesised and harmonised from El-Sayegh and Mansour [20]; Hasina and Fazil [21]; Infrastructure Risk Group [22]; Nguyen et al. [23]; Deshpande and Valunjkar [24]; Heravi and Hajihosseini [25]; Msomba et al. [26]; Azhagarsamy et al. [27]; Sharaf and Abdelwahab [28]; and Ogbu and Adindu [29].

To ensure consistency, original risk labels were extracted verbatim from each eligible study, after which obvious synonyms and near-duplicates were combined. A single primary category by root cause was then assigned to each label, so that causes were prioritised over consequences. Where a label could plausibly belong to more than one category, simple tie-break rules were applied in this order: (i) cause before consequence (e.g., “delay in approvals” classified under Political/Regulatory rather than under scheduling effects); (ii) policy/regulatory action before administrative timing (e.g., “change in law” treated as Political/Regulatory rather than a generic management delay); and (iii) site/geotechnical before broad environment where subsurface or ground conditions were involved. Coding was conducted independently and then reconciled; any inconsistencies were resolved through discussion prior to finalisation. Through this protocol, a standards-informed and repeatable classification was achieved without altering the substantive meaning of the original sources.

3. Results and Analysis of Key Risk Factors

3.1. Classification of Highway Construction Risks

Consistent with established classifications, construction-project risks are commonly grouped into internal and external categories (Zhi [30]; Tah & Carr [31]; Aleshin [32]; El-Sayegh [20]. Internal risks include design and technical issues, managerial shortcomings, and stakeholder/communication problems (El-Sayegh) [20], whereas external risks encompass political instability, macroeconomic fluctuations, legal and regulatory constraints, and environmental and social pressures (Zhi) [30]. El-Sayegh and Mansour [33] distinguish between internal and external risks in highway projects, find internal risks to be more significant, and provide risk-allocation guidance assigning responsibilities to clients, contractors and consultants together with mitigation measures.

Effective risk management plays a pivotal role in enabling organizations to navigate uncertainties and enhance performance. The internationally recognized ISO standards for risk management serve as a robust framework for implementing effective strategies. These standards provide organizations with tools to better identify threats, monitor risks, and allocate resources efficiently, thereby increasing the likelihood of achieving project goals. However, given the dynamic nature of the construction industry, risk management strategies often require continuous improvement and adaptation to address evolving challenges.

3.1.1. Challenges in Risk Classification Across Literature

The classification of construction project risks and their sources has been extensively studied over the years, with numerous scholars contributing to its development

One of the most significant challenges in conducting a comprehensive review of highway construction project risks lies in the inconsistency in how risks are categorized across different sources. It is observed that the various studies adopt distinct (i.e., different) frameworks for classifying risks, often shaped by disciplinary focus, regional considerations, or project-specific factors. This lack of uniformity introduces ambiguity, especially for multi-dimensional risks that could feasibly belong to more than one category.

For example, Hasina & Fazil [21] classify expropriation/nationalization and permit/approval delays as Political, whereas El-Sayegh and Mansour [33] place analogous approval/NOC/right-of-way/expropriation delays under Technical

Similarly, in the Infrastructure Risk Group [22] framework, “adverse weather” is categorized as an external event under construction risk (implementation phase), reflecting its immediate disruptive impact on site activities. Studies such as Nguyen et al. [23] and Deshpande and Valunjkar [24] and align weather risk with construction-related challenges affecting site operations and scheduling. In contrast, Heravi and Hajihosseini [25] and Msomba et al. [26] classify severe weather conditions under force majeure, emphasizing its role as an exceptional event beyond human control. El-Sayegh and Mansour [33] and Azhagarsamy et al. [27]—treat weather as an environmental risk. This perspective situates weather within broader ecological and environmental frameworks, associating it with climate effects, sustainability considerations, and regulatory challenges, rather than immediate construction process disruptions.

This ambiguity underscores the need for a more flexible, source-independent classification model, especially when synthesizing findings from multiple sources. It also reinforces the importance of transparency in how researchers define and apply risk categories in literature reviews and empirical investigations.

To synthesise a varied literature, this paper first documents how prior studies classify risks and then proposes a harmonised taxonomy. This ordering clarifies sources of ambiguity and provides the rationale for the recommended scheme.

Table 1 presents 16 risk factor examples identified across multiple studies, along with the diverse categories they were associated with. The table clearly shows that there is the adoption of a local taxonomy of terms by different researchers, leading to ambiguity in how terms are defined and applied.

Table 1. Examples of inconsistent categorisation of risk factors in the literature.

Repeated Risk Factor	Reported Category	References	Proposed as the Standardised Category for This Risk Factor	Justification (for the “Standardised Category” Recommendation (or Not))
1. Weather (and Extreme Weather)	Construction-related	Construction Risk (Implementation Phase)—External Events—Infrastructure Risk Group [22], Nguyen et al. [23], Deshpande and Valunjkar [24]		Secondary (impact): Weather is an external cause, the construction impacts (delays, lost productivity, cost overruns, rework) happen afterward as consequences, not because of the construction process itself.
	Environmental	El-Sayegh and Mansour [33], Azhagarsamy et al. [27]	Yes (for Weather)	Ordinary/adverse weather is a climatic/environmental condition expected to impact site conditions/productivity.
	Force majeure	Heravi and Hajihosseini [25], Msomba et al. [26] Schramek and McCormack [34], Vogel and Moore [35], Ponce de Leon et al. [36]	Yes (for Extreme Weather)	In contractual and risk-management practice, extreme weather (e.g., record temperatures, rainfall and wind speeds are leading to wildfires, severe storms and floods) is treated as an event beyond the parties’ reasonable control, often a force-majeure trigger, because it exceeds the normal adverse weather conditions that baseline construction planning is expected to accommodate. (Hogan Lovells [37], Mastt [38])
2. Force Majeure	Construction-related	Deshpande and Valunjkar [24]		Secondary (impact): Force majeure affects construction, but it is not caused by construction activities.
	Environmental	Hasina and Fazil [21] [24]		Some force majeure events (storms, floods) are environmental in nature, but not all e.g., war and terrorism
	Force majeure—As a Category itself	Msomba et al. [26], Sharaf & Abdelwahab [28], Heravi and Hajihosseini [25] [28]	Yes	Multiple Academic Risk Management Studies, International standards classify force majeure as its own category of risk as it refers to extraordinary events (earthquakes, floods, wars, pandemics) beyond the control of any party.
	Safety/Incidents	Infrastructure Risk Group [22]		Secondary (impact)
	Site	El-Sayegh and Mansour [33], Ogbu and Adindu [29]		Secondary (impact): Force majeure events may impact a site, but they are not site-specific risks, they are higher-level uncontrollable risks.
3. Change in law/Change in laws and regulations	Political	El-Sayegh and Mansour [33] [2], Hasina & Fazil [21], Msomba et al. [26] Infrastructure Risk Group [22], Heravi and Hajihosseini [25]	Yes	The primary cause is government policy. Change in law is fundamentally a government or legislative action, it arises from policy decisions, legal reforms, or regulatory updates Multiple Academic Risk Management Studies, standard contract frameworks (FIDIC).
	Construction-related	Azhagarsamy et al. [27]		Secondary (impact): delays, cost overruns
4. Design changes/Design error/Defective design	Construction-related	Deshpande and Valunjkar [24], Nguyen at al. [23]		Secondary (impact): rework or delays
	Design	Hasina and Fazil [21], Msomba et al. [26], Sharaf and Abdelwahab [28], Ogbu and Adindu [29]	Yes	The terms design changes, design error, defective design all originate from design processes, e.g., incomplete surveys, inaccurate assumptions, or poor drafting. Multiple Academic Risk Management Studies.
	Technological	Hasina and Fazil [21]		Secondary (impact)
5. Land acquisition	Political	Azhagarsamy et al. [27]	Yes	The acquisition process depends on government approvals, expropriation decisions, and administrative clearances.
	Construction-related	Deshpande and Valunjkar [24]		Secondary (impact)
	Legal	Heravi and Hajihosseini [25]		Secondary (impact)
	Social	Hasina and Fazil [21]		Secondary (impact)
	Schedule/Planning	Msomba et al. [26]		Secondary (impact)
	Site	Sharaf & Abdelwahab [28]		Secondary (impact)
6. Delays in expropriations	Political	Hasina and Fazil [21]	Yes	Expropriation is a government-led legal process where private land is taken for public use
	Technical	El-Sayegh and Mansour [33]		Delays in expropriations stem from government/legal processes, not technical challenges e.g., engineering failures.
7. Fire	Force majeure	Msomba et al. [26], Sharaf & Abdelwahab [28]	Yes	Major, uncontrollable fires
	Safety/Incidents	Azhagarsamy et al. [27], Infrastructure Risk Group [22]	Yes	Fires caused by negligence or unsafe work practices belong in “Safety/Incidents”
8. Delay in payments	Economic	Deshpande & Valunjkar [24], Hasina & Fazil [21]		Economics relate to macro factors like inflation or currency rates
	Commercial/ Contractual	El-Sayegh and Mansour [33]		Describe related effects (e.g., disputes, poorly managed contracts)
	Financial	Sharaf & Abdelwahab [28], Ogbu and Adindu [29], Azhagarsamy et al. [27]	Yes	Multiple Academic Risk Management Studies. This is fundamentally about money availability, cash flow problems, funding shortages, client/owner financial constraints/financial management.
	Management	Msomba et al. [26]		Describe related effects project oversight problems (e.g., admin inefficiency, scheduling delays)
9. Inadequate site investigation	Construction-related	Deshpande and Valunjkar [24], Msomba et al. [26]		Deals with execution issues and on-site activities (delays, rework, congestion, labour problems) rather than the pre-construction survey stage.
	Environmental	El-Sayegh and Mansour [33]		Referring to pollution, ecological damage, regulatory compliance, climate effects, etc. e.g., Protected wetlands, site contamination may influence the investigation
	Technical	Azhagarsamy et al. [27]		Covers design and engineering complexity or technological aspects, not about surveying or ground studies.
	Contractor/Subcontractors	Hasina and Fazil [21]		Secondary consequences: performance issues or failures by parties might cause inadequate investigation
	Site	El-Sayegh and Mansour [33], Ogbu and Adindu [29], Infrastructure Risk Group [22]	Yes	“Inadequate site investigation” is about missing or incomplete geotechnical/soil studies, that’s a site-level risk (directly tied to subsurface conditions) Multiple Academic Risk Management Studies.
10. Inflation	Economic	Infrastructure Risk Group [22], Sharaf and Abdelwahab [28], Hasina and Fazil [21]	Yes	Economic in nature, reflect a general rise in prices across the economy (macro-level).
	Financial	Msomba et al. [26], Heravi and Hajihosseini [25], Azhagarsamy et al. [27]		Focuses more on project-specific cash flow, funding, and liquidity issues (e.g., delayed payments, insufficient project financing)
	Operation & maintenance	Nguyen et al. [23]		Deals with long-term upkeep and lifecycle costs, not the root cause of inflation or market-wide price changes
11. Delay in approvals	Political	Hasina and Fazil [21]	Yes	Approvals (permits, clearances, licenses) almost always depend on government agencies or regulatory bodies. Delays usually stem from bureaucracy, policy changes, or slow government processes.
	Technical	El-Sayegh and Mansour [33]		Approval is not a technical issue (like design complexity or engineering).
	Construction-related	Sharaf & Abdelwahab [28], Nguyen et al. [23]		covers execution issues on-site; approvals happen before or parallel to construction.
	Schedule/ Planning	Deshpande and Valunjkar [24]		Secondary (impact): Delays affect the schedule, but the root cause is the political approval process.
	Environmental	Infrastructure Risk Group [22], Hasina and Fazil [21]		Some approvals are environmental permits, but the delay itself is caused by government process.
12. Poor performance of contractor	Construction-related	Deshpande and Valunjkar [24], Msomba et al. [26]		Covers execution risks like site delays etc.
	Schedule/Planning	Msomba et al. [26]		Secondary (impact): Poor performance impacts the schedule
	Contractor/Subcontractors	Sharaf and Abdelwahab [28], Hasina & Fazil [21], Ogbu & Adindu [29]	Yes	Specifically addresses the competence, resources, and management of contractors.
	Organizational	Azhagarsamy et al. [27]		Refers to the project owner or overall management structure.
13. Change of tax; Taxation risk; Changes in tax regulation	Political	Infrastructure Risk Group [22]	Yes	Tax changes are driven by government policy and regulation.
	Economic	Sharaf and Abdelwahab [28], Hasina and Fazil [21]		Macro/strategic risk. Macro conditions such as recession, demand slump, inflation, policy or structural supply shock, war-driven shortages across many inputs.
14. Commodity/material price escalation risk	Economic	Deshpande and Valunjkar [24], Hasina and Fazil [21]		Economic is macro/strategic risk such as recession, demand slump, inflation, policy or structural supply shock, war-driven shortages.
	Financial	Azhagarsamy et al. [27]	Yes	Commodity price (market) risk that might be driven by supply/demand shocks, logistics, foreign exchange, sanctions, etc.
15. Exchange rate fluctuations	Economic	Infrastructure Risk Group [22], Sharaf and Abdelwahab [28], Hasina and Fazil [21]		Exchange—rate swings are market-price movements, so financial market risk.
	Financial	Nguyen et al. [23]	Yes	Financial because it directly affects the movement and settlement of funds (financial/market risks that hit cash flows, valuations, and balance sheets, price moves in currency pairs)
16. Claims and disputes	Construction related	Sharaf and Abdelwahab [28]		It’s a contractual entitlement issue
	Commercial/Contractual	Msomba et al. [26], El-Sayegh and Mansour [33]	Yes	Claims and disputes are fundamentally about exercising or contesting contract rights/obligations (time, money, scope, variations, EOT, LDs, payment).
	Management	Deshpande and Valunjkar [24]		Management is usually a driver/mitigation issue (poor contract admin, weak change control), not the claim itself.

Within Table 1, the utilisation of the terms by the original authors has been considered in order to propose an unambiguous (or Standard) risk category definition. The first three columns report examples on how prior studies classify the risks, the subsequent columns identified a recommended “Standardised Category” (i.e., the causal or main driver) for each risk factor and the justifications for the selected category being classified as “The Standard” or not. Note: A “yes” in the “Standardised Category” column denotes a recommended primary classification. Any additional category listed for the same risk is secondary, indicating where the risk chiefly manifests or is administered (i.e., the main impact and operational responsibility).

For example: The repeated Risk Category Factor “16. Claims and disputes”. The Standard is recommended to be “Commercial/Contractual” as Claims and disputes concern the exercise or contestation of contract rights/obligations (time, money, scope, variations, extensions of time (EOTs), liquidated damages (LDs), payment).

3.1.2. Recommended Classification

Risk categories are analytically useful but not mutually exclusive, boundaries are porous because many hazards have multi-causal provenance and cut cross functions. Accordingly, each risk is classified by its primary driver (the root cause that determines responsibility and mitigation). Table 2 (“Recommended Classification”) sets out the categories with illustrative factors, providing a consistent basis for the analysis that follows.

Table 2. Recommended Classification.

No.	Category	Risk Factors (Significant Examples—Not Exhaustive, Primary Category Recommended to Remove Historic Ambiguity)
1	Political	Political pressure/interference; War, terrorism or hostilities; Change of tax/taxation risk/changes in tax regulation; Protestor influence; Public inquiry; Government relations; Threat of war; Changes in Rules and Regulations; Changes in laws and policies affecting the project; Political instability of the government (unfavorable political environment); Delay in approvals: Delay or refusal of project approval and permit by government departments (excessive approval procedures); Outbreak of hostilities (wars, revolution, riots, and terrorism); Corrupt local government officials demand bribes or unjust rewards; High level of bureaucracy of the authority; Expropriation and nationalization of assets/facilities without reasonable compensation; Government’s improper intervention during construction; Poor relations with related government departments, Government restrictions on foreign companies (e.g., import/export restrictions, mandatory technology transfer, differential taxation of foreign firms, etc.); Termination of concession by government; Influential economic events; Sanction; Local citizens issue; Interference of local politicians; Delayed statutory clearances/Delays in obtaining NOCs (No Objection Certificates); Delay in environmental and forest clearance; Delay in land acquisition; Insufficient right of way.
2	Technical	Technical feasibility, Engineering capability, Quality and integrity of design; Insufficient technology/skills/techniques; Technical (Design): Inadequate design; Inadequate specification; Complexity of project; Misinterpretation of traffic data.
3	Construction related	Replacement of consultant; On site congestion; Defective design; Incompetent subcontractor; Unavailability of land; Improper construction methods; Unsafe working conditions; Unexpected Surface conditions; Access conditions; Differing site condition; Security problems; Unidentified utilities; Unrealistic time estimates by the contractor; Low productivity of personnel; Equipment and machines; Defective construction materials; Lack of project close supervision by the client; Conflicts; Defective work; Failure of work; Changing need; Rework; Project delay; Disputes between labours; Changing sequences in construction activity; Non availability of resources; Revision of design; Availability of camp for labours; Change in quantities of work; In Time work permissions for executing work; Safety of workers; Stoppage of work due to Medical outbreak; Unforeseen geological conditions; Approval delay in construction period; Unavailability of material and labour; Environmental compliance; Change in construction procedure; Delay in material procurement; Poor quality of material; Excessive labour and material movement; Lower work quality, Dewatering due to change in water table, Insufficient resource availability
4	Legal	Statutory non-compliance (statutory breaches); Litigation/arbitration; Enforceability, IP infringement, Data protection/privacy breaches where applicable including when a contract dispute escalates to litigation/arbitration. Note: it could be argued that all legal items are escalations within all the other Categories. However, within the highways construction industry these are classified as being “of risk to be escalated to the legal teams”, due to ease of categorisation by Risk Managers. In reality it can be argued that there should be no “legal” risk category as issues should be attributed to the other categories.
5	Environmental	Adverse weather, Incomplete environmental analysis; Historic/brownfield sites; Disposal of construction waste; Contaminated soils; Effect on wetlands; Climate effects; Permitting and approvals; Environmental and geotechnical: Environmental factors; Subsurface conditions; Geotechnical survey; Dewatering; In-accurate survey; Site Contamination; Perceived Environmental Impacts of Project; Adverse environmental impacts of the project; Pollution associated with construction activities (dust, harmful gases, noise, solid and liquid wastes, etc.); Strict environmental regulations and requirements; Poor environmental regulations and controls; Changes in environmental standards and permitting; Poor preliminary assessment and evaluation of environmental impacts of the project; Failure to obtain environmental approval; Natural disasters; Management of large construction waste; Pollution and safety rules; Forest clearance; Any natural obstructions.
6	Social	Criminal Acts; Cultural Differences; Bribes; Public opposition to the project (public objections, social grievances); Differences in social, cultural, and religious backgrounds; Insecurity and crime (theft, vandalism, and fraudulent practices); Strikes and labour disputes; Poor public relations with local contacts; Unfavourable social environment; Societal conflict and/or public unrest; Poor public decision-making process; Disturbances to public activities.
7	Economic	Inadequate cost planning; Cost overrun; Unavailability of funds; Inflation; Political changes; Economic crisis; Project-funding problems; Unpredicted changes in interest rates; Unfavourable economic situations in the country (instability of economic conditions); Market demand changes; Recession; Demand slump; Policy or structural supply shock; War-driven shortages across many inputs.
8	Financial	Inadequate project funding; Labour and material cost; Interest rate changes; Bankruptcy of major participants/Sponsor bankrupt; Time of payments; Advance payment; Project time extension; Delay from clients; Increment for staff benefits; Raw material prices/Unprecedented price in raw materials; Fluctuations in Estimated finance than expected; Delay in payments; Cash flow problems; Unavailability of critical resources in the local market; Change of input resource prices; Limited capital; Need for land appraisal; Financial problems due to environmental protection,; Change in value of granted lands due to inflation; Change in value of granted lands due to development; Financing cost–related risks: Insufficient equity contribution; Preferential debt unavailability; Exchange rate risk: Exchange rate fluctuations/Variation rate of exchange; Fluctuations in currency exchange and/or difficulty of convertibility; Inability to service debt; High compensation demands; Unsettled and lack of project funding; Change in material prices/material price escalation; Poor financial market or unavailability of financial instrument resulting in difficulty of financing (Financing availability & market liquidity risk).
9	Commercial/ Contractual	Ambiguities in contract formation; Project labour agreements; Claims and disputes/Inadequate claim administration; Contract Strategy: Unrealistic timelines; Ignored risks; Poorly tailored contract forms; Third-party liability; Conflict in contract documents.
10	Logistical	Logistical Disruption: Late procurement; Late manufacture; Disrupted transport/delivery; Security holdups, Insufficient/inadequate storage; Congestion; Inability to dispose of waste.
11	Management	Poor allocation of resources; Poor motivation; Lack of or insufficient managerial skills; Lack of risk management; Unsatisfactory conduct of status review meetings; Poor labour planning; Lack of decision making; Inadequate project planning resource; Project management risks: Lack of coordination/communication; Delays in preparation of submittals; Delays in the approvals of submittals; Inefficient dispute resolution; Untimely inspection and testing; Inadequate inspection and testing; Poor relationship between parties; Documents and process directed as per agreement for mitigation of risk; Project team discussions on risk; Use of WBS and project milestones to help identify project risks; Documented process for identifying project risks, Inefficient planning.
12	Schedule/Planning	Financial delays; Construction delays; Delay in material transportation; Delay in site possession; Delay of mobilization; Inefficient delivery method; Inappropriate contract awards; Poor contractor and supplier selection; Inadequate project planning; Inappropriate pricing; Length project development period; Inadequate contingency planning; Indecision; Poor estimation process/Improper estimation of time and cost.
13	Resources (Plants, Equipment, Materials)	Breakdown of plant; Unavailability of raw material required for plant; Poor equipment management & planning; Equipment quality; Equipment breakdown, Condition; Availability of Equipment; Storage; Maintenance; Mobilization; Material damage; Material storage.
14	Human resources	Labour accidents; Lack of specialized staff; Inexperienced staff; Lack of coordination; Unskilled labours and poor labour productivity; Low labour productivity; Labour availability; Inadequate (under and over) Recruitment.
15	Force majeure	Severe weather condition (according to contract law definition); Fire; Earthquake; Flood; Tornado; Hurricanes; War; Revolution; Natural disasters; Terrorism; Riots; Government actions or prohibitions; Strikes; Explosions.
16	Safety/Incidents	Safety and security; Poor safety procedures; Non availability/no use of safety equipment and tools at site; Death/injuries at site due to accidents; Non availability of proper medical facilities at site; Accidental: Damage to equipment’s; Labour injuries; Equipment and material fire and theft; Removal of structures; Shifting of utilities; HSE incident; Asset failure; Fire; Industrial action.
17	Design (Design and Scope Changes/Errors)	Design quality; Changes in scope of work/client; Inadequate survey data; Lack of experience of design team; Inaccurate quantity estimates by the design team; Unclear scope of work; Inaccurate assumption on technical data; Inadequate technical staffs; Design error and omission; Road alignment; Traffic flow; Alignment availability; Change in design; Scope vagueness; Shortage of information; Improper feasibility study; Complexity of project design; Design changes by owner or his agent during construction; Insufficient data collection and survey before design; Mistakes and delays in producing design documents; Misunderstanding of owner’s requirements by design engineer; Poor use of advanced engineering design software; Unclear and inadequate details in drawings; Incomplete project design; Defective or Incomplete design; Discrepancy between actual quantities and contract quantities; Incompetent supervision/poor project management; Corruption/unethical practices.
18	Technological	Emerging disruptive technologies; Obsolescence; Poor constructability; Complexity of design; Technology changes; Delay in design; Inadequate study and insufficient data before design; Unclear and inadequate details in design drawings and specifications; Unanticipated engineering and design changes.
19	Contractor/ Subcontractors	Subcontractor bankrupt; Subcontractor quality; Subcontractor delay; Frequent change of subcontractors; Poor performance of contractor/Inadequate contractor experience; Inappropriate construction methods; Incompetent project team; Ineffective project planning and scheduling; Poor communication and coordination between owner and consultant; Poor site management and supervision; Unreliable subcontractors; Inappropriate contractor’s policies; Poor financial control on site; Poor project planning and control; Lack of experience; Defective work/Reworks, Poor estimating.
20	Site/Site Environment and Location/Site Access & Conditions	Site facilities; Site security; Site mobilization; Existing traffic; Unexpected underground utilities; Archaeological finds; Unforeseen soil conditions; Inadequate safety measures; Feasibility of construction methods; Inadequate construction quality; Restrictive site conditions; Geo-technical risks/ground conditions; Frustrated site access; unexpected site costs; Slow mobilization, poor ground/water table; Building foundations, sewers, contamination, archaeology/unexploded ordnance; Wildlife and other environmental; Demolition problems; Inadequate site investigation; Diversion of existing traffic.
21	Organizational	Suboptimal decision processes; Invalid assumptions; Organization risk; Coordination risk/Poor coordination; Intense competition at tender stage; Efficiency of managers or supervisors; Lack of specified arbitrators; Change of supervisors; Improper distribution of roles and responsibility; Conflict between executives; Stakeholders disputes over changes; Contractor problem and inadequate experience.
22	Operation and maintenance	Operation cost overrun; Operator default; High maintenance costs; Underestimated maintenance frequency (premature deterioration); Government-requested change in output specifications; Tort liability.
23	Performance-related risks	Performance reliability; Not achieving required quality; Not meeting stakeholders’ expectations; Poor quality; Poor supervision; Excessive settlement; Damage, Site nuisance (noise, light, vibration); Systems integration problems.
24	Consultant-related risks	Lack of consultant experience in construction projects; Conflicts between consultant and design engineer; Delay in approving major changes in scope of work by consultant; Delay in performing inspection and testing; Inadequate project management assistance; Late in reviewing and approving design document; Poor communication and coordination between owner and contractor.

The recommended risk-classification scheme in Table 2 was developed by synthesising and harmonising risk taxonomies reported in prior studies, resolving overlapping terms, removing historical ambiguities, drawing on and reconciling definitions and factor groupings from El-Sayegh and Mansour [33]; Hasina and Fazil [21]; Infrastructure Risk Group [22]; Nguyen et al. [23]; Deshpande and Valunjkar [24]; Heravi and Hajihosseini [25]; Msomba et al. [26]; Azhagarsamy et al. [27]; Sharaf and Abdelwahab [28]; and Ogbu and Adindu [29]. In line with Section 2.2.3, Table 2 presents the recommended, rules-based classification that harmonises labels from the reviewed highway studies and assigns one primary category by root cause.

Note: Although this study focuses primarily on a systematic literature review of critical risk factors specific to highway construction projects, it is important to note that several references cited in Table 2 under the “Recommended Classification” pertain to risk classifications within general construction. For instance, Hasina and Fazil [24] address construction risk factors more broadly and are not limited to highway projects. These broader sources have been incorporated where relevant, given their contribution to understanding foundational risk categorization frameworks applicable across infrastructure sectors.

An additional point to consider is that Design-related risks may be treated either as a subset of technical and engineering risks or as a separate category, depending on the structure and level of detail adopted in the risk register. For smaller projects, design-related risks can be merged with technical risks under a single category of “Technical and Engineering Risks.” In the case of megaprojects, however, design risks are better maintained as a distinct category to ensure sufficient attention is given to their impact on project time and cost outcomes.

While Table 2 consolidates the classification scheme, it is neither exhaustive nor mutually exclusive. As illustrated in Figure 2, many risks can have multi-causal origins and manifest across functions, creating legitimate overlaps. To balance comparability with realism, each risk is assigned a primary classification determined by the main causal driver. Accordingly, Table 2 should be read as a baseline, extensible scheme, not a closed list; overlaps are expected and documented rather than treated as errors.

Figure 2. Risk category overlap map.

Figure 2 visualises common overlaps among risk categories, showing only triadic overlaps as illustrative examples. Nodes represent categories, edges indicate frequently co-occurring pairwise links within each triad. (e.g., Financial–Economic–Political; Legal–Political–Commercial/Contractual; Management–Schedule/Planning–Organizational, Environmental–Site/Site–Environment–Safety/Incidents; Design–Technical–Construction related; Construction related–Schedule/Planning–Contractor/Subcontractors, Technical–Technological–Resources, Operation & Maintenance–Management–Performance-related, and Logistical–Resources–Schedule/Planning).

3.1.3. Identification of Critical Risks Associated with Time and Cost for Highway Construction

According to ISO 31000:2018 [16], risk identification is an iterative process of finding, recognizing and describing risks (including their sources, events, causes and potential consequences), with results recorded and reported as part of the risk-management process.

This section examines key aspects of the risk management framework, focusing on the identification of critical risk factors discussed by previous researchers and the existing risk assessment models applied in highway construction projects.

The comprehensive systematic literature review (Figure 1) resulted in the identification of 83 key articles. Table 3 presents key risk factors leading to highway and road construction project delay and cost overrun. (organised primarily by alphabetical country, then year).

Table 3. Factors leading to highway and road construction project delay and cost overrun.

№	Author(s)	Year	Location	Method of Identifying Risks	Key Risk Factors
1	Rivera et al. [39]	2020	Across 25 developing countries	Data gathered from previous studies by qualitative perceptions collected from surveys.	The lack of experience of the construction manager, inadequate planning/scheduling, expropriation for the construction of the project, changes in the design, poor communication between construction parties, shortage of equipment, force majeure, contract modification, delays in execution of progress billing, shortage of construction materials, delayed payment to contractors, poor labour productivity.
2	Mashal and Mathur [40]	2023	Afghanistan	Literature review, Questionnaire survey	Delay in progress payment by owner, variations in quantities, lack of modern equipment, delay in approval of completed work by client, security (external related), poor communication and coordination with other parties, lack of material in market, change orders by owner during construction, corruption and bribery.
3	Creedy et al. [41]	2010	Australia (Queensland)	NGT, Multivariate linear regression analysis, Delphi techniques,	Design and scope change, Insufficient investigations and latent conditions, Deficient documentation, specification and design, Owner project management costs, Services relocation, Constructability, Price escalation, Right-of-way costs, Contractor risks, Environment.
4	Hasan et al. [42]	2014	Bahrain	Field survey, Questionnaire	Lack of planning, shortage of manpower and materials, suspension of work, budget availability and delay in decision making, lack of experience, Services and utilities.
5	Zayed et al. [43]	2008	China	Questionnaire survey	Political, financial, emerging technology and resource risks (shortage of skilled workers, availability of specialty equipment, and delays of materials supply).
6	Tian et al. [44]	2021	China	Field investigation, expert scoring/expert survey within a risk-matrix	Collapse (disaster risk), Risk of bridge lifting (project risk), Instability at tunnel portal excavation (project risk), Pressure of construction (social risk), Large-scale equipment management (management risk). Also, several High risks, including landslide, water damage, debris flow, falling from height in bridge works, bridge high-slope excavation, tunnel water-inrush, management system/personnel issues, and material transport constraints.
7	Ramírez et al. [45]	2018	Colombia	Risk Criticality Index, RFMEA), Expert surveys (Cronbach’s alpha and Spearman correlation), MCS, CSRAM, Case study model of actual road project	Delays in the delivery of material and equipment, Effect of social and cultural factors, Acquisition of land, Geological problems on site, Defective/incomplete design, Effect of rain on construction activities, Mismanagement and poor site supervision by the contractor, Subcontractor scheduling conflicts, Contractual problems, Inefficient planning and programming by the contractor.
8	Sharaf and Abdelwahab [28]	2015	Egypt	Questionnaire survey	Delay in making decisions, land acquisition and interference from the project owner, design change.
9	Aziz et al. [46]	2016	Egypt	Questionnaire survey	Owner’s financial problems, Shortages of equipment, Inadequate contractor experience (work), Shortage of construction materials, Equipment failure (breakdown), Design errors due to unfamiliarity with local conditions and environment, Soil investigation is the first step in decision of the design of road with traffic capacity, loads on road, number of layers of pavement, Poor subcontractor performance delays, Rework due to change of design or deviation order; Poor site management and supervision by the contractor.
10	El-Maaty et al. [47]	2017	Egypt	Questionnaire survey, Fuzzy logic approach, Regression Analysis	Schedule Overrun: Contractor’s technical staff is insufficient and ineligible to accomplish the project, difficulties in financing the project by the contractor, lack of equipment efficiency, shortage of equipment, shortage of construction materials. Cost Escalation: inadequate preparation of the project concerning planning and execution, inadequate planning for project costs and lack of cost follow-up, lack of communication between project parties, increase in construction material prices, Contractor’s failure to conduct a technical study before bidding.
11	Khodeir et al. [48]	2019	Egypt	Questionnaire survey	Incorrect Sewer location during construction, Delay in Material Approval, Late Delivery of Material to Site, Inefficient Quality control, Poorly Installed Sewers, Wrongly Installed Sewer size, Delivery Problems in Sewer pipe length, Technology changes, Unsuitable Soil Filled Around Sewers, Inadequate supervision system, Low subcontractor performance, Poor Water Insulation Application on Site, Shortage of construction equipment, Poor subcontractor’s performance, Shortage of construction materials.
12	El-Kholy [49]	2019	Egypt	Modular Neural Network Paradigm, MAPE	Core construction project risks: schedule risks, cost risk (cost overruns).
13	Issa et al. [50]	2021	Egypt	Field survey	Lack of pre-studies & shortage of project data/documents/details during design stage, Delay in applying the next layer of the road leads to erosion of the existing layer, Poor grading of the granular soil, Discontinuity or delay in crushed stones supply.
14	Wubet et al. [51]	2021	Ethiopia	Questionnaire survey, Relative Importance Index (RII), Statistical Analysis: ANOVA, Kendall’s W	Shortage of finance/cash flow problems, Inadequate planning, Lack of access to foreign currency, Delay in possession of the construction site (Right of Way), Frequent breakdown of equipment, Delay in delivery of material and equipment; Financial failure, Inflation, Delay in payments, Poor commitment and coordination within contractor teams.
15	Carbonara et al. [52]	2015	Europe-based (multi-country)	Delphi Survey, Multiple-Case Study (8 real motorway PPP projects in UK, Greece, Netherlands, and Belgium)	Demand/Usage Risk (the uncertainty in future traffic volume and usage levels, which heavily affects the revenue stream of PPP motorway projects), Cost overrun; Financial closure risk, Interest rate increase, Inflation, Debt servicing risk, Force majeure risks, Regulatory risks (e.g., changes in legislation).
16	Fani Antoniou [53]	2021	Greece	Two hypothetical projects	Weather conditions, late land acquisition, utility networks and traffic control.
17	Patil et al. [54]	2013	India	Questionnaires survey	Land Acquisition, Environmental Impact of the project, financial closure, Change orders by the client, Poor site management and supervision by contractor.
18	Pathan & Pimplikar [55]	2013	India	Case-study analysis, Quantification via cash-flow modelling	Interest-rate (PLR) fluctuation, Revenue inadequacy/traffic risk, Force-majeure shocks, Technical/scope change risks, Regulatory/third-party delays, Legal/arbitration risk, Policy/contract risks.
19	Katkar et al. [56]	2015	India	Expert opinion	Environmental Permission, Emotional Issue, Land Acquisition, Political, Quality, Time, Money, Machinery, Rebound development around road analysis, Labor, Natural Obstruction, Knowledge level of lead group.
20	Honrao et al. [57]	2015	India	Questionnaire survey, Statistical indices	Difficulties in obtaining work permits and land acquisition, utilities are unidentified or incorrectly located, external environment related delay causes (traffic diversion, hot weather effect on execution activities, scarcity of materials in the market), owner interference during execution, ineffective construction methods by contractor, delay in solving design problems (major change of design during construction by consultant, bad project cost estimation).
21	Makam and Rao [58]	2015	India	Questionnaire survey, Regression analysis using SPSS (version not reported in the original study), Data analysis based on 230 NHDP highway project reports	Land acquisition delays, shifting of utilities (water mains, electrical, and telephone lines), inadequate Detailed Project Reports (DPRs), contractual disputes and poor contract management, law and order issues in certain states, geological surprises and adverse weather, capacity constraints (labour, equipment, and materials).
22	Vishwakarma [12]	2016	India	Likert scale, RII	Funds/Money, Time/delay in project, Local disturbances (law & order), Uncertain land acquisition cost, Issues related to obtaining Railway permits, Issues related to obtaining Government permits, Construction in hilly region, Unanticipated damage during construction, Utilities not relocated on time, Heritage issues.
23	Vasishta [59]	2018	India (Andhra Pradesh region)	Questionnaire survey, RII Analysis	Lack of coordination, Selection of inappropriate equipment, Insufficient technology/skills/techniques, Lack of communication, Inadequate construction quality.
24	Thombare and Ambre [60]	2019	India	Questionnaire survey, Case study, Risk-analysis tools	Delay in approvals, change in law/policy, cost overrun, dispatch/traffic constraints (revenue shortfall), land acquisition & compensation issues, enforceability of contracts, construction schedule risk, financial closing risk.
25	Rajput et al. [61]	2020	India	Questionnaire survey	Improper planning, delay in land acquisition, delay in project approval and permits, delay in making progressive payments, inaccurate cost estimate, delay in inspections, corruption at different levels, price increase of materials, shortage of equipment, machinery and tools, shortage of skilled manpower, frequent breakdown of equipment, and difficulties in financing.
26	Deshpande and Valunjkar [24]	2020	India	Questionnaire survey, Fuzzy Logic Toolbox	Delay in land acquisition, needs requested by stakeholders, unavailability of land and funds, disputes and claims, construction delays, force majeure, cost overruns, delay in owners’ payment, delay in site possession.
27	Azhagarsamy et al. [27]	2021	India	Questionnaire survey, RII, SPSS, real case study.	Rework due to error in execution; Inadequate specification; Inadequate design; Diversion of existing traffic; Land acquisition; Inadequate site investigation; High compensation demands; Lack of risk management; Unskilled labour/poor labour productivity; Lower work quality.
28	Danisworo et al. [62]	2018	Indonesia (Jakarta)	Questionnaires survey, Interviews	The Contract Specifications explaining the Employer’s Requirement are not clear and detail, the duration of the Contract is not appropriate, Delay in utility relocation, Delay in land acquisition, Issue of interface design, Request changes to work methods/designs from clients/external parties, Delay payment, Changes to Central Government Regulations, Changes to Regional Regulations, Lack of preparation in estimated costs.
29	Thapanont et al. [63]	2018	Internationally, Thailand	Questionnaire survey, Interviews	Incomplete drawings, lack of equipment efficiency or financial status of contractors, delay in relocating existing infrastructure structures, less of project engineer experiences, and delay in relieving environmental impact.
30	Mousavi et al. [64]	2011	Iran (Tehran)	Highway project risk identification information (key project documents)	Changes in design, Delay of material supply, Lack of experience in inspection and forwarding, Defective design, errors and rework, Lack of attention to contract requirements, Unsuitable weather conditions, Inadequate specifications, Failure in transmitting data from preliminary design to final Design, International relations, Health, Safety and Environment (HSE) matters, Change in scope of work, Lack of experienced workers, Technical problems, Economical inflation, Delay in paying and receiving project’s invoices, Political factors change.
31	Heravi and Hajihosseini [25]	2012	Iran	Case study: Tehran-Chalus Toll Road project	Inaccurate prediction of rate of inflation can increase project costs, Political risk, problems with land acquisition and compensation were important in the construction stage, leading to a significant delay in site delivery as well as projects’ schedule.
32	Ghorbani et al. [65]	2014	Iran	Questionnaire survey	Inflation risk, limited capital, improper design, ‘inadequate study and insufficient data, change in the value of granted lands due to development, termination of concession by the Government and financial problems due to environmental protection. Financial risk as the most important risk for the construction of the highway PPP project in Iran.
33	Jahanger [66] [	2013	Iraq (Baghdad)	Questionnaire survey	Mistakes, discrepancies in design documents, ineffective planning, and poor scheduling of the project by the contractor.
34	Al-Hazim and Salem [67]	2015	Jordan	Case-based analysis approach, Expert input, Percentage ranking	Terrain conditions (including difficult access, land acquisition issues, utility relocation delays, and lack of civil services), Weather conditions (extreme heat, rain, and seasonal disruptions), Variation orders (changes made after the project starts), Availability of labour (labour shortages or inefficiencies), Mistakes in design (leading to rework and scope changes).
35	Seboru [68]	2015	Kenya	Questionnaires survey	Payment by client, slow decision making and bureaucracy in client organization, inadequate planning and scheduling, and rain.
36	Isah and Kim [69]	2022	Korea	Assessment of Risk Impact on Road Project Using Deep Neural Network	Design (Changes in scope, Incomplete and omission in design, Inadequate specification, Financial and economic Inflation, Exchange rate fluctuation, Delay in payment by the client, Construction Technical and execution issues, Material delay, Shortage of technical and skilled labor on site, Politics and environment, Change of government laws and regulations, Delay in permission and approval Contract management, Delay in settling claims, Contract risk management by sub-contractor, Weather, Extreme weather condition.
37	Aboubaker et al. [70]	2017	Libya	Questionnaire survey, descriptive statistics (SPSS), EFA, Cronbach’s Alpha	Delays in the conversion and transfer of utility services by the competent authorities (such as power lines, water, etc.), difficulty in budget availability for the project, original contract duration is too short, delay in progress payments by the owner, effects of subsurface (underground) conditions.
38	Kamanga et al. [71]	2013	Malawi, South Africa, Botswana and Swaziland	Questionnaire survey	Shortage of fuel, Insufficient contractor cash-flow/difficulties in financing projects, Shortage of foreign currency for importation of materials and equipment, Slow payment procedures adopted by the client in making progress payments, Insufficient equipment, Delay in relocating utilities, Shortage of construction materials such as bitumen, cement and steel, Delay in paying compensations to land owners, Shortage of technical personnel, Delay in site mobilization.
39	Ghazali [72]	2009	Malaysia	Literature review, extensive interviews with key personnel	High: Initial toll-tariff decided by the government. Medium: Over-loaded freight transportation, Leakage of dangerous material/cargo on road surface, Traffic congestion, Change of road network. Low: Environmental pollution to water-supply quality, Flood/fog, Sudden increase in toll-tariff, Change of government policy, Poor road signs and delineator, Road side hazard, Inefficient road-safety device, Poor road surface.
40	Wafa and Singh [73]	2010	Malaysia (State of Perak)	Questionnaire survey, Collection of road project’s data	Lack of materials, lack of workers, change of design, financial problems and lack of machinery.
41	Karunakaran et al. [74]	2019	Malaysia (Klang Valley)	Pilot survey and Questionnaire survey	Improper planning, weather, poor site management, poor site investigation, underground utilities, land acquisition, accessibility problems at site, improper construction method, late payment for completed work progress, lack of experienced contractor, site accident (safety issues), machinery failure, late delivery of material to site, late salary to labour, lack of equipment.
42	Razi et al. [75]	2019	Malaysia (East Coast region of Malaysia)	Expert Interviews, Questionnaire survey, AHP, Sensitivity analysis	Technical: Unforeseen ground conditions, Existing utilities issue, Insufficient drawings and specification, Frequent design change. Natural hazards: Flood, Heavy rain, Heat wave. Economic and financial: Fund risk inflation risk. Contractual: Lack of contract clarity, Inappropriate contract, Improper estimation. Socio-politics: Land acquisition issue, Changes in government law and regulations, Changes in politics and environment. Organizational: Lack coordination between parties, Inadequate planning and scheduling in project team, Unclear job roles and responsibility. Resources: Shortage of material on site, Late delivery of material and equipment, Shortage of technical skill personnel, Shortage of workers.
43	Manavazhi et al. [76]	2002	Nepal	Survey method	Organizational weaknesses, suppliers’ defaults, governmental regulations, and transportation delays.
44	Hemant GAİN [77]	2021	Nepal	Questionnaire survey	Project Schedule Risk, Safety, Health, and Environmental Risks, Cost Overrun/Budget Risk, Financial and Economic Risk, Force Majeure Risk, Political, Legal, and Social Risks, Organizational Management Risk, Contractual Risks, Quality Standard Risks, Technical Design Risks.
45	Chileshe and Awotunde [78]	2010	Nigeria	Questionnaire survey, Likert scale, RII, TII	Top by likelihood of occurrence: Contaminated soil & unstable soil condition, Design changes & inaccurate design details, Defective material & material shortages. Top by degree of impact: Defective material & material shortage, Poor quality control & poor performance control, Design changes & inaccurate design details.
46	Ekung et al. [79]	2015	Nigeria (East-West Coastal Highway project)	Expert Validation, Survey, 3-point Likert scale, Risk Matrix	Government lack of political will, Change in government, Corruption and financial fraud, Insufficient design details, Incompetent design team, Ground Condition, Unstable market conditions, Flood/coastal surge risks, Exceptional Inclement Weather, Militant insurgency.
47	Fabi and Awolesi [80]	2015	Nigeria (Lagos State)	Questionnaire survey, Descriptive statistics (mean rankings), ANOVA, SPSS	Risks in the management process. Lack of accepted industry model for risk analysis, Human/organizational resistance (reluctance or inability to adopt modern risk management practices), Lack of dedicated resources (insufficient tools, training, and systems for managing risk), Prevalence of rule-of-thumb approaches (reliance on informal methods rather than structured techniques).
48	Ogbu and Adindu [29]	2019	Nigeria	Questionnaire survey	Safety and security, force majeure, geotechnical risks/ground conditions, payments delay/cash flow problems, change of input resource prices and interest rate changes/cost of funds, lack of experience, poor estimating, defective/incomplete design, incompetent supervision and corruption/unethical practices.
49	Pantelidis [81]	2011	Not specified	Literature Review, Critical Analysis	Insufficient consideration of geology and geomorphology, Neglect of climatic conditions, Limited focus on consequence categories, Questionable suitability of consequence factors.
50	Mahamid [82]	2013	Palestine	Questionnaire survey	Financial status of the contractors, payment delays by the owner, the political situation, segmentation of the West Bank, poor communication between construction parties, lack of equipment efficiency and high competition in bids.
51	Cruz and Marques [83]	2013	Portugal (Portuguese road concessions)	Case Study	Political interference, optimism bias in demand forecasts, and the absence of active regulators—factors lead to frequent renegotiations of contracts and substantial public compensations to concessionaires. The inability to manage increasing uncertainties in forecasts has prompted the government to adopt availability payment schemes to mitigate public losses.
52	Emam et al. [84]	2015	Qatar	Questionnaire survey	Long response times from utility agencies; major changes in design during construction; ineffective planning and scheduling; ineffective control of progress; and changes in the scope of projects.
53	Elawi et al. [85]	2016	Saudi Arabia	Real time quantitative performance analysis, Quantitative comparison	Land acquisition, contractor’ lack of expertise, re-designing, line services (haphazard underground utilities), Clashes with other Ministries, Design conflicts between owners, Variation in estimated quantities between designer and GC (General Contractor), Differences in opinions from the Ministry of Traffic, Deliberate delay in construction by the GC, Change of consultant during project execution.
54	Andrić et al. [86]	2019	Silk Road (China with Central Asia, India, Middle East, Western Asia and Europe)	Expert judgment, Fuzzy sets, Fuzzy logic, Fuzzy matrices	Delay in supplying materials, increases in material prices, poor quality of materials, delays in equipment delivery, increases in the costs of equipment use, and economic risk.
55	Perera et al. [87]	2009	Sri Lanka	Multiple case-study, semi-structured interviews, documentary and archival evidence, cross-case comparison	Defective design; Late approvals; Late handing over of the site; Tentative drawings; Unforeseen site ground conditions; Relations with neighbourhood (community issues); Public security and safety; Inflation; Scope change
56	Msomba et al. [26]	2018	Tanzania	Questionnaire survey	Inadequate project preparation (project planning), delayed payment by the client (inadequate funding), delayed compensation of land and properties, delayed reallocation of utilities (telecommunication and power lines), delayed approvals for various substantial claims and poor performance of contractor.
57	Karaman and Köseoğlu [88]	2021	Turkey	Questionnaire survey, Decision Matrix	Economic crisis, Embargo and war, Acceleration demand of project by employer or government, Labour force issues (inefficiency, poor workmanship), Slope flows (site risk), Falling from height and material fall.
58	El-Sayegh and Mansour [33]	2015	UAE	Questionnaire survey	Inefficient planning, unexpected underground utilities, quality and integrity of design, delays in the approvals of submittals, delays in expropriations, delays in obtaining no object certificates (NOCs) from authorities, poor coordination, inadequate safety measures, delay in payments, material, labour, and equipment resourcing.
59	Ayeni et al. [89]	2023	UK	Expert interviews, questionnaire survey—Likert scales, analysis in Excel/SPSS, RII	Client-related: delay in decision-making/order issuance; variation/changes in design; delay in revising/approving design documents. Consultant-related: delay in approval of drawings; delay in design preparation/late design revisions; frequent design changes or errors. Contractor-related: delay in providing utilities; construction mistakes/defects and rework; delay in subcontractor works. External: adverse weather; delays/issues with permissions & statutory approvals; changes in material types/specifications.
60	Chapman [90]	2024	UK	Secondary analysis of public evaluations (National Highways POPE and related sources) for 138 schemes; descriptive statistics	Inflation, poor oversight of the delivery of major road schemes, lack of data on performance and failure to aggregate data to identify the main trends or reasons for cost overruns and the lack of project management expertise and inhouse capability to be an intelligent customer, issues with risk management practices, methods of procurement and delivery capability.
61	Grunow [91]	1963	USA	PERT, CPA	Management-level uncertainties and scheduling risks: delays due to lack of manpower, right-of-way acquisition issues, bureaucratic approval delays, disruptions from changes in political leadership, inaccurate or uncertain time estimates for project activities.
62	Vidalis and Najafi [92]	2002	USA (Florida)	Review of completed FDOT highway projects, Expert interviews	Design issues (including incomplete or inaccurate designs), changed conditions (referring to unforeseen site or project scope changes during construction).
63	Molenaar [93]	2005	USA (Washington State)	CEVP (Cost Estimating Validation Process), Probability & Impact estimates, Monte Carlo Simulation, Sensitivity Analysis	Market conditions, ROW acquisition problems, Change in seismic criteria, Inadequate design/design uncertainty for interchanges, Geotechnical conditions, Local arterial improvements and access, Rail lines, Off- and on-site wetlands, ROW value and impact, Bridge foundations, Storm water treatment and/or quantities, Changes in permitting, Natural hazards, Traffic demand, Staging areas, NEPA/404 merger process, Environmental impact statement, Utility issues, Work window, Auxiliary lanes, WSDOT program management, Labor disruptions.
64	Shiraki et al. [94]	2007	USA (Los Angeles Highway network)	System Risk Curves, Probabilistic Seismic Hazard Analysis, MCS	Seismic risk (earthquakes can cause systemic disruption across highway network).
65	Gransberg and Riemer [95]	2009	USA (Oklahoma)	Historical project data of 462 completed ODOT highway projects, FHWA, Absolute error metrics	Inaccurate quantity estimates in engineer’s pre-bid documentation, which can lead to unbalanced bids by contractors, inefficiencies in pricing, increased cost exposure for both contractors and owners, manipulation of quantities to create hidden contingencies, distorting actual project costs.
66	Li and Madanu [96]	2009	USA (Indiana)	Indiana real data Case study, MCS, Beta probability distributions, Shackle’s model, Latin Hypercube stratified sampling	Uncertainty in construction, rehabilitation, and maintenance costs, variability in traffic growth rates, fluctuating discount rates.
67	Gharaibeh and Shirazi [97]	2009	USA	Risk-based modelling approach founded on Kaplan and Garrick’s theory	Risk of premature infrastructure failures in highway projects, which can lead to significant financial liabilities for contractors offering warranties.
68	Le et al. [98]	2009	USA	Quantitative Evaluation Mechanism (level of definition)	Poorly defined scope can lead to: increased project costs, schedule delays, quality issues.
69	Bhargava et al. [99]	2011	USA (Indiana)	Ex post facto analysis using historical data from INDOT projects, Statistical modelling, MCS, Multinomial logit models	Cost overruns. Factors contribute to the probability and magnitude of cost escalation: Project size, Work category (e.g., expansion, bridge, pavement), Area type (urban vs. rural), Highway classification (NHS vs. non-NHS), Time delays between project proposal, design, and letting, Contract type and geographic location.
70	Strong & Shane [100]	2012	USA (Iowa)	Survey Validation, Descriptive statistics, Likert scale	Top risks leading to crashes during mobile highway operations and maintenance: Improper traffic control systems near work zones, High speed limits on highways near mobile work zones.
71	Anastasopoulos et al. [101]	2012	USA (Indiana)	Analysed 1722 Indiana highway projects	Project cost (contract bid amount), project type, planned project duration, and the likelihood of adverse weather.
72	Tran & Molenaar [102]	2014	USA	Questionnaire survey	Scope risk, third-party and complexity risk, construction risk, utility and ROW, level of design and contract risk, management risk, regulation and railroad risk.
73	Hanna et al. [103]	2015	USA	Literature Review, Survey, Review of court cases and legal precedent related to each risk	Design adequacy (including incomplete or erroneous designs and constructability issues), specification interpretation, third-party delay, changed conditions (unforeseen site conditions, unsuitable subgrade material), claims process (inefficiencies and disputes due to unclear change order procedures).
74	Tran and Bypaneni [104]	2016	USA	Correlation coefficients, Simulation techniques	Cost Uncertainty.
75	Diab et al. [105]	2017	USA	Opinion survey, Questionnaire survey.	Late and erroneous surveys, inadequate constructability reviews, inexperienced project manager.
76	Bypaneni and Tran [106]	2018	USA	Expert feedback, analysed 274 real-world highway projects, Risk scoring, Cronbach’s alpha test, Correlation analysis	Delays in completing in railroad agreements, project complexity, uncertainty in geotechnical investigation, delays in a right-of-way (ROW) process, unexpected utility encounter, work-zone traffic control, challenges to obtaining environmental documentation, delays in delivery schedules.
77	Castro-Nova et al. [107]	2018	USA	Expert Survey Questionnaire	Landslides, Subsidence (subsurface voids), Contaminated material, Prediction of subsurface conditions due to inaccessible drilling locations, Sensitiveness of public considerations (parks, historic building, etc.), Karst formations, Slope instability.
78	Gaikwad et al. [108]	2021	USA	Review & analysis of bid dispersion and estimate accuracy from 305 D-B/BV highway projects, Interviews	Inaccuracy in engineering cost estimates, High bid dispersion among contractors (Innovation and differing scopes in design proposals, Varying risk appetites of design-build teams); Misalignment of best-value procurement with actual practice (risk of ineffective implementation of best-value principles). Three main root causes of bid dispersion and estimate inaccuracy: Ineffective communication of project goals to design-builders, Innovative and value engineering techniques not accounted for in estimates, Lack of a robust risk-based cost estimation program.
79	Tummalapudi et al. [109]	2022	USA	Questionnaire survey, Case studies	Difficulties in attaining the required documentation, claims and litigations, managing multiple funding sources, a lack of urgency from local utilities/entities, and the lack of sufficient DOT project staff.
80	Nguyen et al. [23]	2018	Vietnam	Quantitative survey, Qualitative semi structured interviews	Land Unavailability, Design Changes Required by Public Authority, Insufficient Traffic Volume, Toll Rates Are Too Low to Generate the Expected Return, Major Maintenance Required More Often Than Estimated, Inflation, Insufficient Equity Contribution, Interest Rate Risk.
81	Lam [110]	1999	Worldwide	Case studies	Changes by owner’s request, which includes unexpected external stakeholders’ involvement, extra road/bridge capacity request, adding wetland mitigation, forcing contractors to work at night, and any other extra work; Error in Right-of-Way, Land acquisition delay.
82	Kaliba et al. [111]	2009	Zambia	Literature review, Interviews, Questionnaire survey, Analysis of real project case data	Environmental, Equipment, Financial, Human Resource, Management, Material, Planning/Design, Regulatory/Administrative.
83	Ariyanto et al. [112]	2020	Study is based in Indonesia. Study is presented as a systematic review applicable internationally.	Literature review	Finance, Contractor Experience, Client Service, Material, Duration, Finance, Construction Method, Structure Construction, Project Management Contract, K3, Government.

It can be seen from Table 3, that data within the literature is available for many countries, gathered over many years, with multiple key risk factors being identified. It should be noted that while Tran and Bypaneni [103] primarily focuses on analysing cost uncertainty as an aggregated risk outcome, rather than explicitly identifying discrete risk factors their work is cited here to acknowledge cost uncertainty as a significant aggregated risk factor impacting highway project outcomes.

Figure 3 illustrates the global annual distribution of publications addressing risk factors in highway construction projects, based on the 83 reviewed studies included in this systematic review (Table 3). The trend highlights a significant increase in research output from 2009 onwards, with a notable peak in 2015. This growth reflects the expanding research attention towards identifying and managing risks affecting time and cost performance in highway construction across diverse geographic locations over the past two decades.

Figure 3. Global distribution of reviewed publications on highway construction risk factors (1963–2024).

Figure 4 illustrates the geographic distribution of the analysed publications by country, based on the 83 studies summarised in Table 3. The figure highlights that research on highway construction risk factors spans a wide range of global regions, with the highest concentration of studies originating from the USA and India. Contributions from other regions such as Egypt, Nigeria, Malaysia and internationally scoped studies further reflect the global interest and diversity of perspectives addressing risk management in highway construction projects. The distribution in Figure 4 reflects how locations were reported by the source papers and is not used to weight the risk rankings; it documents publication coverage rather than the strength of effects by region.

Figure 4. Geographic distribution of publications by country. Note: Countries are coded as reported by the original studies (Table 3). “Europe” denotes multi-country/region-level analyses within Europe; “Worldwide” covers cross-regional studies; “Not specified” indicates no location stated.

Figure 5 presents a global map showing the distribution of the reviewed publications by country, as summarised in Table 3. This map visually highlights the international scope of research addressing risk factors in highway construction projects. Notably, the highest concentrations of studies are seen in the USA and India, followed by significant contributions from China, Egypt, and Malaysia. The distribution underscores that while research attention is strongest in certain regions, the topic has attracted interest from a diverse range of countries worldwide.

Figure 5. Global map of publications by country based on reviewed studies.

3.2. Key Risk Factors (Frequency Analysis)

This subsection reports the frequency analysis and ranking of risk factors contributing to delays and cost overruns in highway construction, based on 83 sources. Table 4 summarizes the 10 most frequently cited risks, their source references, frequency of occurrence, and proportional representation in the dataset.

Table 4. Frequency and percentage of key risk factors in highway construction.

Risk Factors	Frequency	Percentage
1. Financial/Economic Issues	42	50.6%
2. Design and Scope Changes	39	47.0%
3. Material Issues	31	37.3%
4. Contractor-Related Issues	28	33.7%
5. Political/Regulatory	27	32.5%
6. Land Acquisition Delays	25	30.1%
7. Equipment Issues	22	26.5%
8. Utilities Relocation/Conflicts	21	25.3%
9. Planning and Scheduling	20	24.1%
10 (a) Labour/Personnel Issues	18	21.7%
10 (b) Weather Conditions	18	21.7%

Among the 83 studies, the most frequently cited risks are Financial Issues (50.6%) and Design/Scope Changes & Errors (47.0%). A second cluster—Material Issues (37.3%), Contractor-Related Issues (33.7%), and Political/Regulatory (32.5%)—appears in roughly one-third of studies, with Land Acquisition Delays (30.1%) closing this ≥30% group. Mid-20% citations include Equipment Issues (26.5%), Utilities Relocation/Conflicts (25.3%), and Planning & Scheduling (24.1%). Labour/Personnel and Weather Conditions are joint 10th at 21.7% each.

4. Implications and Relevance of Findings

The identification of the most frequently cited risk factors (namely financial constraints design and scope changes, and material issues extends beyond academic interest and serves as a strategic resource for a wide range of industrial stakeholders involved in highway construction. For policymakers and government agencies, these findings highlight the need for institutional reforms in areas such as procurement processes, land acquisition protocols, and financial oversight mechanisms to enable simplification and/or de-risk activities in these areas. For project managers, engineers, and contractors, the results provide a prioritization framework that supports proactive risk planning, enabling more effective allocation of resources during the early project stages, where risk mitigation has the greatest influence on outcomes. Additionally, the recurring nature of external risks, such as adverse weather and bureaucratic inefficiencies, across diverse geographic regions signals the presence of deep-rooted systemic vulnerabilities that must be addressed through adaptive planning and governance innovations.

In short, these risks are the first things to consider when allocating budget and time. The ranked risks are intended to be used as a front-end checklist when planning highway projects. Project managers should seed the risk register from this list, assign owners, and time-phase contingency against the highest-ranked items. Public owners should size contingency and schedule float with these risks in mind and bring forward early actions (e.g., right-of-way, permitting, utility coordination). Contractors should reflect the same risks in pricing, programmes, and contract clauses.

Importantly, these findings are not merely retrospective; they serve as the foundation for future studies and risk modelling & simulation through unambiguously defining the terminology for classifying risks.

Risk Managers should ensure that they appropriately consider all 10 of the identified risks within highways projects.

Future work should utilise the insights gained from this literature review and frequently used factor to develop practical, targeted solutions for improving project delivery in the highway sector. These findings inform a computational model for budget and schedule planning, the model and results will be presented separately.

The following section briefly outlines the main limitations of this review and how the results should be interpreted in practice.

5. Limitations

This review provides a prioritised list of risks for highway projects, but several limits should be noted. The synthesis is based on published studies that vary in method and metrics, as a result, effect sizes are not directly comparable.

First, the ranking reflects how often risks are reported as “critical” in published studies; it does not estimate a single, comparable effect size across settings. The analysis relies on factors the original authors labelled “critical,” which may reflect local context and publication emphasis. Second, the included studies use different methods and measures, making direct comparison of impact strength difficult. Third, the recommended classification in Table 2 required harmonising labels across sources, a rules-based protocol was followed, yet some judgement was still involved. Fourth, findings reflect the contexts of the original studies (countries, delivery models, time periods), so some risks may be more important in certain settings than others. Fifth, the synthesis relies on published literature, which may over-represent topics that are more frequently studied or published in English. Sixth, no new primary data were collected; the results summarise what prior studies already identified as critical. Taken together, these limits mean the findings are best used for prioritising planning attention, budget, schedule, contingency, and early actions, rather than as universal impact coefficients.

6. Conclusions

This paper applied a systematic literature review methodology to identify the most critical risk factors contributing to project delays and cost overruns in highway and road construction. The most prevalent risk categories were found to be (1) financial constraints, (2) political regulatory issues; (3) land-acquisition and right-of-way de-lays; (4) design and scope changes; (5) utilities relocation/conflicts; (6) materials and equipment shortages; (7) contractor-related issues; (8) planning and scheduling weaknesses; (9) labour and personnel issues; and (10) weather conditions. These findings underline the need for targeted risk management strategies, particularly during the early phases of project planning and procurement. The data-driven evidence presented here provides a foundational basis for enhancing risk assessment models and informing policy and practice in infrastructure project management. Practically, the ranked risks in Table 4 are the first items to consider when allocating budget and time, sizing contingency and schedule float, and sequencing early actions (e.g., right-of-way, permitting, and utility coordination). For methodological qualifications, see Chapter 4 (Implications and Relevance of Findings) and Chapter 5 (Limitations).

When combined with our previous study (Zhasmukhambetova et al. [113]), the present analysis provides the empirical foundation for a predictive model that quantifies and forecasts project duration and cost by incorporating multidimensional risk factors. Future work will extend these combined results by applying the risk assessment and analysis techniques identified in Zhasmukhambetova et al. [113], and by developing, calibrating, and validating a model applicable to highway and road construction projects to improve risk understanding, quantification, risk-time-cost optimization and management.