Assessment of the Energy Efficiency of Individual Means of Transport in the Process of Optimizing Transport Environments in Urban Areas in Line with the Smart City Idea

Abstract

One of the fundamental goals of contemporary mobility is to optimize transport processes in urban areas. The solution in this area seems to be the implementation of the idea of sustainable transport systems based on the Smart City concept. The article presents a case study—an assessment of the possibilities of changing mobility habits based on the idea of sustainable urban transport, taking into account the criterion of energy consumption of individual means of transport. The analyses are based on a comparison of selected means of transport occurring in the urban environment according to several key parameters for the optimization and efficiency of transport processes, i.e., cost, time, travel comfort, and impact on the natural environment, while simultaneously linking them to the criterion of energy consumption of individual means of transport. The analyzed parameters currently constitute the most important group of challenges in the area of shaping and planning optimal and sustainable urban transport. The presented research was used to indicate the connections between various areas of optimization of the transport process and the energy efficiency of individual modes of transport. Analyses have shown that the least time-consuming process of urban mobility is associated with the highest level of CO₂ emissions and, at the same time, the highest level of energy efficiency. However, combining public transport with other means of transport can meet most of the transport expectations of city residents, also in terms of energy optimization. The research results presented in the article can contribute to the creation of a strategy for the development of the transport network based on the postulates of increasing the optimization and efficiency of individual means of transport in urban areas. At the same time, recognizing the criterion of energy intensity of means of transport as leading in the development of sustainable urban mobility. Thus, confirming the important role of existing transport systems in the process of shaping and planning sustainable urban mobility in accordance with the idea of Smart City.

1. Introduction

Transport is one of the most important human needs due to the spatial differentiation of resources, population centres, workplaces, and various types of services. The internal transport system is becoming increasingly important due to the constant growth of urban areas. Creating the basis for the implementation of the concept of smart cities, in which mobility is the basic emptiness to improve the quality of life of citizens. However, the concept of smart cities itself refers to many aspects of “life” in urban areas. It is the broadly understood urban mobility that is the key area in the functioning of the promoted Smart City concept. Ensuring high quality of the transport system is a serious challenge facing smart cities and requires a multi-criteria approach in line with the principles of sustainable development. The main goal of such solutions is to provide city residents with access to various means of transport while maintaining the postulate of optimization and efficiency. Solutions improving the efficiency of urban mobility include initiatives such as car sharing, car policing, the use of applications enabling the transport of people (Uber, Bolt, etc.), or the use of e-scooters or city bikes. It should be remembered that the proper functioning of urban mobility consists of many interconnected components and different communication environments. Moreover, sustainable urban mobility should be integrated to the greatest extent possible with the development plans of individual cities, such that they create a coherent and mutually supporting system [1,2,3,4]. Considering that the efficiency of transport in cities is determined by the level of efficiency of technical infrastructure, the expenditures and costs incurred by city authorities on broadly understood communication, which includes the operation of public transport vehicles, infrastructure maintenance, removal of the effects of accidents, environmental fees, costs incurred by individual users in connection with the failure to adapt the transport system to the needs of residents [5,6,7]. It is emphasized that the introduction of changes most often reflects the needs of individual vehicle users, although investing in more attractive public transport for residents or using several means of transport operating within the transport system may be much more effective in the long term. Therefore, the authors of this article used appropriate research tools to conduct a multi-criteria analysis of the transport system of a given metropolis. Assuming that the presented research will be used to develop a sustainable urban mobility plan and a development strategy oriented towards transit in urban areas [8]. Recognizing that the travel characteristics of urban residents, and consequently the choice of transport mode in a city, depend on many factors, among which travel time and comfort, as well as environmental considerations, play a significant role.

In this context, an interesting research problem is the assessment of the relationship between intervention for transport optimization and the demand for energy efficiency. This issue is all the more significant if we assume that energy management should be the central instrument for creating sustainable development of urban transport. Due to the lack of discussions and research in an interdisciplinary approach, combining the demands for transport optimization with the criterion of energy consumption of individual means of transport.

The aim of the article is to assess the energy efficiency of individual means of transport in the process of optimizing transport environments in urban areas in accordance with the Smart City idea. In order to achieve the indicated goal, selected means of transport were analyzed according to selected parameters in terms of optimization and increasing the efficiency of urban transport, taking into account the criterion of energy consumption of individual means of transport. The research emphasizes the sustainability of the transport process through the multi-variant use of individual means of transport included in the current transport system of the analyzed city. The novelty of this article is the use of multi-criteria assessment to analyze mobility processes based on real data covering individual case studies. The obtained results based on computational experiments provide comprehensive information on the potential benefits resulting from the use of various solutions based on the idea of sustainable mobility and the identification of current limitations related to their implementation. The empirical research approach allowed the authors to indicate directions for improvements—i.e., the use of public transport in the implementation of the transport process. This approach can contribute to achieving more effective mobility focused on reaching the city center while taking into account the criterion of energy efficiency of individual means of transport. At the same time, taking into account the traveller’s preferences in terms of the natural environment, shortening the travel time, and improving travel comfort. The content of the presented considerations gives a new perspective and provides the necessary knowledge in the area of sustainable urban transport based on the variant selection of the means of transport. To our knowledge, this is the first approach to this topic, which includes a synthetic analysis of not one, but several means of transport within the same transport task for urban mobility, in particular on the optimization and efficiency of the transport process itself in connection with the assessment of the energy intensity of individual means of transport. The presented study therefore fills a gap in the literature on the subject, thus creating an incentive for further research in the following areas: (I) energy efficiency, (II) optimization of urban transport, (III) sustainable urban mobility plans, (IV) the Smart City concept, and (V) transit-oriented development strategies in urban areas.

The article was organized as follows. Section 2 presents a detailed description of the research approach based on the latest literature on the subject. This part presents the main findings related to the subject of work and summarises the contribution of the diploma thesis to the state of scientific knowledge. Section 3 describes the research methodology used. This part formulated mathematical models describing the analyzed systems and presented input data and assumptions adopted for the needs of the research. Section 4 presents the results of the experiment and their interpretation. This chapter focuses on the presentation of research results and the assessment of the functioning of individual systems. In addition, a discussion of the results that is devoted to an in-depth and critical analysis of the obtained results in terms of their reality and significance was presented. In turn, Section 5 includes research conclusions, indicating their restrictions, practical application, and future research directions in this field.

2. Review of the Literature in the Context of the Research Problem: Smart City—Sustainable Transport Development in Urban Areas

The outline of the Smart City idea is presented in theory as a creative-thinking community [9,10]. The concept of Smart City determines the urbanized area, which uses IT technologies as well as advanced and innovative technologies to improve the quality of life of its inhabitants and create an environmentally balanced city [11,12,13]. Another area of Smart City functioning is focused on sustainable development [14,15,16]. At the base of Smart City lies the use of new thinking paradigms using real-time coordination tools. The contemporary idea of sustainable development can be seen in every aspect of the lives of inhabitants of urbanized areas [17]. This intelligent city is identified as ensuring the appropriate conditions for residents to be happy to meet their needs [18,19,20]. One of the features of an intelligent city is high efficiency. Thanks to knowledge-based, creative activities, intelligent cities are oriented towards the results and sustainable development [21,22,23]. The philosophy of intelligent cities should be interpreted as an intellectual ability, which is taken into account in the form of innovative aspects [24,25,26]. The purpose of implementing the concept of an intelligent city is to improve efficiency by monitoring data and providing more effective services for city residents, including optimization of existing infrastructure [27,28,29]. The development of an intelligent city requires a comprehensive approach, including advanced infrastructure, technology convergence, intelligent management systems, active public participation, sustainable development, and global cooperation. The integration of these six levels is the key to creating intelligent, balanced, and efficient urban systems. Researchers define an intelligent city as a six-level structure [30,31,32]. Evolution levels show the development of cities at every level through established relationships and improvements that take place to achieve an innovative, technologically balanced, intelligent city. This includes such elements as follows:

• Intelligent economy—cities should be characterized by high productivity, an innovative atmosphere, and flexibility of the labour market.
• Intelligent mobility—thanks to the ICT sector, the city is a network of quick connections connecting all city resources.
• Intelligent environment—an intelligent city optimizes energy consumption, including the use of renewable energy sources, undertakes actions to reduce emissions to the environment, and also manages resources by the principle of sustainable development.
• Wise people—the initiators of changes in cities should be their inhabitants, who, with appropriate technical support, can avoid excessive energy and pollution consumption and strive to improve the quality of life.
• Smart Living—the city should provide its residents with a friendly environment, in particular by guaranteeing them wide access to public services, technical and social infrastructure, high-level safety and protection, appropriate cultural and recreational facilities, as well as care for the environment and green areas.
• Intelligent management—the development of this aspect requires the creation of an appropriate city management system, developing procedures that require cooperation between local authorities and other city users, as well as the use of modern technologies in the functioning of the city.

Although the Smart City concept consists of six dimensions [33,34,35], sustainable mobility plays a key role in the success of this concept. There already exist solutions that can contribute to the gradual improvement of the current situation and the achievement of the intended goals [9]. Effective management of transport in traditional and mobility in urban areas is undoubtedly one of the most important issues of the idea of a Smart City. It should be noted that cities are places with a particularly high concentration of the flow of people and goods [36,37]. Therefore, there are also problems with transport. The needs and expectations of various transport users, companies, or residents can be contradictory. In addition, the effects of transport activity can have a significant impact on the natural environment, the public sphere, the urban landscape, etc. Therefore, it is necessary to conduct a policy of sustainable development of transport systems [38,39,40]. The main goal of such a policy should be transport, which is available and meets the needs of residents in the field of mobility. Transports that enable the city’s economic development, including creating a suitable business environment for local entrepreneurs, are environmentally friendly and do not negatively affect the quality of life. It seems that it is very difficult to achieve all these goals at the same time. A certain solution, as it is, is the integration of various transport systems (including the development of solutions based on the use of several means of transport) and restrictions on the use of private cars [41]. The sustainable transport development policy is based on the recommendations contained in several international and national documents, including those developed by the European Conference of Transport Ministers (ECMT) and the Organization of Economic Cooperation and Development (OECD) [42,43,44]. One of the areas to which the most attention is paid is the broadly understood sustainable urban mobility. Thus, it is a key element for effective planning of the transport process.

In the era of climate change, progressive urbanization, and crowds of cities, modern cities face the challenge of developing solutions based on the idea of intelligent transport and implementation of sustainable mobility, which aims to manage urban transport in an effective, environmentally responsible, and socially responsible way [45]. The need to implement solutions in the field of sustainable mobility is becoming a priority. Intensive socio-economic development of cities, especially in the second half of the 20th century, and the resulting problems mentioned above led to a public debate on stopping environmental degradation [46,47,48]. This was reflected in numerous program documents, of which the most noteworthy is certainly the report of the World UN Commission for Environment and Development from 1987 [49] entitled “Our Common Future”, which defines the concept of sustainable development as the ability to develop the potential of cities without harming future generations. Information on the need and benefits of implementing sustainable urban mobility can also be found in the European Green Deal and the “Ready for 55” legislative package, for example, by promoting efficient and environmentally friendly forms of urban transport [49]. It is important to emphasize that the challenges related to mobility in urban transport include problems with congestion and parking, longer travel time, inadequate public transport, barriers in non-motorized transport, loss of public space, high maintenance costs, environmental impact and energy consumption, accidents and safety of road users, spatial planning, commodity transport in urban areas in urban areas [50,51,52]. The concept of ensuring sustainable urban mobility involves creating a mobility system in the urban area, which at the same time improves the availability of areas and services (stimulating the local economy) and contributes to improving the quality of the environment and the quality of life of the inhabitants.

To sum up, intelligent cities are a concept that assumes the interaction of citizens, local authorities, enterprises, and other institutions at all stages of their functioning. The main purpose of the concept is to use the available space and resources as effectively as possible, with the support of technology and direct participation of citizens [53,54,55]. It is therefore determined that the measure of the city’s intelligence is the structure of the local economy, the level of mobility solutions, and resource management, including the transport system. However, sustainable transport, in order to become the key to implementing the Smart City concept, must include research on the energy consumption of individual means of transport in response to postulates that, in the opinion of citizens, bring them measurable benefits [56].

Against this background, the authors present an analysis of the multi-criteria assessment of individual means of transport within the promoted idea of Smart City, using a case study of a selected metropolis. In this case, the research is based for the first time on the connection of four criteria: travel costs, travel time, environmental friendliness, and travel comfort with energy efficiency. The considerations aim to draw attention to the essence of the problem and emphasize the significant role of existing transport systems in striving to implement the Smart City concept. At the same time, taking into account the postulate of sustainable development of transport systems and the analysis of energy efficiency.

3. Materials and Methods

3.1. Justification for the Selection of the Place of Analysis—Selection of the City’s Transport System

The transport system of one of the cities, Krakow, in Central and Eastern Europe, was analyzed. The choice of destination was not accidental and was dictated by the fact that the analyzed city ranks 80th out of 118 cities located in the Smart City index. In addition, the diversity of means of transport in the analyzed transport system is representative of most cities in this region of Europe. The researchers’ process itself was divided into individual stages. The first step was the diagnosis of the current urban transport system, the second stage included the formulation of the problem as a multi-critical problem of sequencing of variants, which includes four steps: description of the decision-making situation, heuristic construction of variants supported by traffic simulation, the third stage was the review and assessment of sequencing of multi-criteria variants, the fourth step was to perform experiments. Computing and sensitivity analysis, the fifth step concerns the summary of calculation experiments.

3.2. Challenges of Sustainable Transport in the Selected Urban Agglomeration

Transport planning should prioritize the needs of residents. The development of efficient and effective sustainable transport systems should be based on an analysis of the city’s existing transport system. One of the main challenges in achieving more sustainable urban mobility is to reduce the number of trips by private cars at the expense of increasing the share of public transport. One of the consequences of the much larger participation of cars in the daily travels of the inhabitants is the phenomenon of congestion. Clothes of several minutes on the main transport routes are everyday life in highly urbanized areas. Currency has a direct impact on the deterioration of air quality, increasing the noise level and environmental degradation. Therefore, they are a highly undesirable phenomenon, but not one that cannot be limited or eliminated to some extent. Intelligent urban mobility solutions can help. More effective management of available means of transport can have a positive impact on the balanced nature of the transport process to achieve this goal. It is not enough to encourage society to change preferences from private cars to public transport. The benefits of promoting alternative means of transport and giving them a greater role on the streets of the city should be demonstrated. Given the fact that urban space is limited, it must be managed effectively.

To this end, analyzes and defines the most effective means of transport by analyzing the transport process from the move (distance between 10 and 15 km) to the city centre: the attractiveness of individual means of transport was assessed based on the four above-mentioned criteria: travel costs, travel time, outflow for the natural environment, and comfort.

Each assessment was assigned separately based on collected data. The analyzed means of transport for the selected transport process were as follows:

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combustion and electric passenger cars,

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public transport,

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suburban railway,

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bicycles (private),

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shared transport (car-sharing, scooter, and bicycle operators).

There are many publications in the literature on the benefits of electric scooters in urban mobility and their importance in first- and last-mile transport [57]. However, due to the legal restrictions introduced in Poland, they were omitted from further analysis, focusing instead on the analysis of electric bicycles and shared vehicles.

Then the distance traveled by the person who was the source of this analysis was determined. To assess individual means of transport, it was first necessary to define selected criteria based on which the passage would be evaluated. It should be emphasized that during the transport process, it is possible to use many means of transport. Data on costs, travel time, environmental friendliness, and comfort were used to determine how the choice of individual means of transport affects the efficiency of mobility. Groups of the best variants were created and selected, and the selection of the best indicated combinations and cases that met the most accepted criteria.

3.3. Basic Analysis Conditions

Due to the high level of urbanization of the area and the analyzed city, the number of vehicles entering the city centre every day is an important communication problem. According to the available data on weekends, this problem may affect up to 250,000 cars. Therefore, the challenge for the analyzed transport system in the coming years will be to reverse the visible trend and minimize the number of vehicles entering the city centre. Due to the scale of the problem, it was decided that the study would focus on the travelling of people living outside Krakow or in its immediate vicinity, from such places as Wieliczka (16.5 km), Skawina (18 km), Zabierzów (15.7 km), or Zielonki (8.7 km), as presented in Figure 1. To determine the medium distance covered to the city centre, it was established that the journey would start with the most urbanized towns around Krakow. The average daily distance was then calculated for the destination point of the city centre, i.e., the Krakow market. Distances from these towns to the centre of Krakow are in three cases over 15 km and were determined using a tool in the form of Google Maps navigation. The average distance to the city centre from the above-mentioned places is about 14.7 km. Because the transport process takes place in both directions, it can be assumed that the average distance over and from Krakow by the inhabitants of the towns located near Krakow is 29.4 km. This value was used in further considerations, e.g., to determine the cost of a specific journey or its duration.

3.4. Justification for the Selection of Individual Criteria for Analysis of Mobility

The assessment criteria should reflect the needs and goals that relate to the functioning of society in the surroundings of the urbanized area. For the mobility of a given city to be considered intelligent, it should not be based solely on the assessment of one criterion often cited in the literature on the subject and appearing at the time of reaching the city centre. This is a very important indicator, but not the only one that defines innovation and high efficiency. Therefore, in the case of intelligent urban mobility, the selection criteria should be wider to take into account more factors that contribute to travelling by a given type of transport. As already mentioned, the first criterion is the travel time parameter. This is one of the factors most often taken into account when choosing a means of transport. With this provision, citizens living in larger cities may prioritize other factors, e.g., cost. For example, the cost of electric cycling will be disproportionately lower than the cost of travelling by car. Depending on the level of expenses, such a criterion may determine the effectiveness of a given type of transport. However, the price for performing transport work depends on many factors. These include such determinants as the distance and the type of energy used (gasoline, electricity, etc.). The third criterion is environmental efficiency. All actions aimed at reducing the intensity of urban mobility emissions are highly desirable today. The environmental efficiency of a given means of transport can be measured, for example, using its carbon footprint. It may vary significantly depending on different means. The car is considered the least environmentally friendly means of transport, mainly due to the type of energy consumed and the high travel demand. However, bicycles are considered the most environmentally friendly means of transport. Shared mobility in the form of buses, trains, trams, and bicycles is crucial in the fight for environmentally friendly transport. The last criterion taken into account in this work is the comfort of travel during the transport process. The comfort of reaching a specific place is also an important factor in the quality assessment of the individual means of transport by society. Depending on the type of transport, this assessment may vary significantly. It is therefore one of the factors that should be taken into account in the overall analysis. Factors other than the type of transport can also be influenced by comfort. For example, climatic factors, such as temperature and rainfall, will have a significant impact on the assessment of comfort, e.g., while cycling.

The last criterion that has been linked to the issue of optimizing the transport process is energy efficiency. Minimizing and assessing energy consumption must respect the limitations of data availability. It is easy to see that minimizing energy consumption in the process of optimizing the urban transport system is based on the decomposition of the optimal task: maximizing pedestrian and bicycle traffic, minimizing car traffic, and optimizing public transport. In their analyses, the authors presented several connections with postulates regarding transport optimization. Particular emphasis should be placed on the issue related to the relationship between low efficiency and energy efficiency.

To sum up, it should be mentioned that all of the above criteria can affect the assessment of transport availability, the departure of private cars, the balance of transport, or limiting CO₂ emissions. Key postulates as part of the idea of sustainable transport are consistent with the Smart City concept.

3.5. Available Means of Transport

Based on the daily observation of the way the residents of the analyzed transport system moved in the experiment, all available public transport was taken into account. It should be emphasized that in addition to public transport, it is possible to travel quickly by an extensive tram network, and also by the agglomeration rail. In the case of shared mobility, several car-sharing operators operate in the city, and the city is undergoing a reconstruction of its bike network. Because the analysis focuses on a significant distance, it was decided to take into account the electric driving bicycles in the study; the possibility of using cars in the form of private cars, shared cars, and taxis is also taken into account. However, the cars were divided into those where electricity and those driven by a traditional internal combustion engine are used to drive. To sum up, the analysis included such means of transport as buses, trams, suburban railways, cars, and electric bikes.

4. Results and Discussion

Multi-Criteria Analysis

(a)

time criterion

The first of the criteria studied concerns travel time. To assess the type of transport in terms of this parameter, it is necessary to define in advance how individual types of transport will be compared. To maintain the logicality of the research, it was assumed that the assessment of the speed of a given means of transport would be based on medium speeds achieved by the tested vehicles in the city. It was assumed for calculations that the daily distance to travel is 29.4 km. Analysis of the data is contained in Figure 2 and Figure 3. It indicated that two communication peaks could directly increase the travel time.

The data analysis in Figure 1 shows that during rush hour, the time of travel to the centre of Krakow is between 30 and 40 min. In other cases, this process is estimated at 20 min. Then it was decided to calculate the average speed for 5 standard business days (11–12.05 and 15–17.05) during peak hours as a representative value for further consideration. In the case of passenger cars, it was decided to adopt a weighted two-speed average for value in the middle and peripheral areas. Weighing the average was the ratio of the distance to the total number of travel (pattern 1—explanations of the formula and adopted variables in Appendix A) [8]:

$$\mathit{v}={\displaystyle \frac{{\mathit{w}}_1·{\mathit{v}}_1+{\mathit{w}}_2·{\mathit{v}}_2}{{\mathit{w}}_1+{\mathit{w}}_2}}$$

(1)

where:

• ${\mathit{w}}_1-$ weight for the center, ${\displaystyle \frac{5}{12}}$,
• ${\mathit{v}}_1-$ speed for the centre, ${\displaystyle \frac{\mathbf{k}\mathbf{m}}{\mathbf{h}}}$,
• ${\mathit{w}}_2-$ weight on the outskirts of the city, ${\displaystyle \frac{7}{12}}$,
• ${\mathit{v}}_2$—speed on the outskirts of the city, ${\displaystyle \frac{\mathbf{k}\mathbf{m}}{\mathbf{h}}}$.

The average driving speed calculated according to the criteria adopted above was 31 km/h. Based on this value, you can calculate the daily travel time by a combustion car, which is 57 min over a distance of 29.4 km. In the case of electric cars and taxis, you should take into account the possibility of using the bus lane. With this reservation, as the number of electric cars increases, the principle will probably be lifted for the use of electric cars on these lanes. However, currently, an electric vehicle can use belts for public transport. It is estimated that the use of bus lanes leads to an increase in speed by about 10–20%. Assuming the average value of travel shortening by 15%, the time of taxi and electric vehicles is 51 min, which gives an average speed of 34.6 km/h.

Public transport speeds and times were determined based on the current timetable. On this basis, the average driving speed was calculated. In the case of buses, as in the case of trams, four lines were selected to determine the criterion for running from interchange points to the city centre, and then their average travel time and average speed were determined, taking into account the average delay for buses, which was taken at the level of 15 min.

In the case of suburban railways, it was decided to use the same calculation method as in the case of public transport. As for the last tested means of transport, i.e., an electric bike, to determine the average movement speed, factors such as the prevailing weather conditions and the presence of other driveways on the road were taken into account. In theory, it is assumed that the average speed is estimated at 25 km/h, but in practice, it is lower due to the need to stop at intersections or lights. Therefore, it was decided to limit the cyclist’s speed to 20 km/h.

The collective analysis of estimated medium speeds for individual means of transport is presented in

Table 1. Collective table of average travel speeds for various means of transport.

Means of Transport	Average Movement Speed, km/h
Internal combustion passenger car	31
Electric passenger car	34.60
Taxi services	34.60
A car from a car-sharing service	31/34.6
Tram	18.61
Bus	16.06
Train	41.09
Electric bike	20

Source: own.

and Figure 4.

(b)

The energy consumption of individual means of transport

Energy consumption should be of fundamental importance in the optimization of public transport, both in the process of planning transport systems, mobility, and fleets, as well as in supporting projects, management, and organization of urban transport within the promoted idea of Smart City. At the international level, the most popular combination of energy consumption by different means of transport is the adoption of data provided by the International Energy Agency (IEA). This agency follows various scientific studies on the energy consumption of individual means of transport in the urban environment. Figure 4 shows how much energy several of the most popular means of urban transport consume in the analyzed city in the system of MJ per passenger kilometer of the route. This indicator is useful if we want to know how much energy we will use when using a given means of transport. In order to maintain logical consistency, the analyzed energy expenditures were averaged and summarized in Figure 5.

As indicated by the analysis of data presented in Figure 4, the lowest energy consumption occurs in the case of the transport process, which takes place using a bicycle. In the case of mechanized means of transport with engines, the lowest energy consumption occurs when using a means of transport in the form of a tram, urban railway, or public transport buses. On the other hand, the highest level of energy consumption occurs in the case of using individual means of transport, such as passenger cars and city taxis.

(c)

Ecological criterion

The environmental criterion refers to the impact of urban mobility on the environment. To properly assess the degree of impact of a given means of transport on the environment, it was found that it is necessary to identify and then determine the parameters for each type of vehicle tested, which would allow an uncomplicated emission assessment by calculating the carbon footprint. The assessment and comparison regarding this criterion will result from the size of the generated carbon trace. The lower value of this parameter means a higher result in the environmental criterion. A bag was used to determine CO₂ emissions: (pattern 2—explanations of the formula and adopted variables in Appendix B)

$$E={\displaystyle \frac{E_{CO2}·+S_{pśr}·}{L}}$$

(2)

where:

• $E-$ emissions into the atmosphere per person, kg CO₂/100 km,
• $E_{CO2}$—CO₂ emissions into the atmosphere per 1 litre of gasoline/1 kWh of current, [kg CO₂/L]/Current [kg CO₂/KWh].
• L—number of people in the vehicle,
• $S_{pśr}$—average fuel/electricity consumption [l/100 km]/[kwh/100 km].

To determine the carbon trace of a given means of transport, it is necessary to know the CO₂ emissions to the atmosphere caused by the use of the vehicle for calculations. It was assumed that the amount of CO₂ emitted to the atmosphere is calculated per passenger. All final values obtained for the intensity of the emission of a given type of transport are presented in

Table 2. A summary table of CO₂ emissions into the atmosphere for selected means of transport.

Means of Transport	Emissions per Passenger, kg CO2/100 km
Internal combustion passenger car	6.61
Electric passenger car	6.18
Taxi services	6.61/6.18
A car from a car-sharing service	6.61/6.18
Tram	4.50
Bus	1.31
Train	4.70
Electric bike	0.63

Source: own.

and Figure 6.

(d)

Comfort criterion

The next examined criterion is the comfort of travel. It should be mentioned that. Depending on your preferences and lifestyle, people may individually and subjectively perceive comfort and exchange factors that determine quality. In this case, three parameters were analyzed as measures of travel comfort:

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congestion of means of transport,

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transport availability,

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the impact of weather conditions on travel comfort.

The survey method was used -the research program covered a group of 100 respondents, and a scale of 1 to 10 for a given means of transport was adopted: 1 was the lowest possible rating for a given means of transport, and 10 was the highest.

Table 3. Assessment of the comfort of movement due to various factors.

Means of Transport	Availability	Weather	Congestion	Average Rating
Private car	10	9	9	9.30
Taxi services	8	9	9	8.66
Car-sharing services	8	9	9	8.66
Bus	8	6	6	6.66
Tram	7	6	7	6.66
Train	5	7	8	6.66
Bicycle	10	4	10	8

Source: own.

and Figure 7 present collective results in the field of travel comfort.

(e)

Assessment of the use of several means of transport under the idea of sustainable transport

Once we have data on the means of transport described in the four criteria, we can start implementing them in a way that is consistent with the concept of intelligent urban mobility for the selected metropolis for analysis. The final result will answer the question of how the choice of individual means of transport affects the journey in terms of cost, time, ecology, and comfort. It is assumed that it will be necessary to use at least two modes of transport during the trip. This condition has been set because this work should answer questions about the validity of using several means of transport in the city. Therefore, cases where only one means of transport is used are not taken into account.

The analysis included eight modes of transport. Possible travel cases are presented. Each of them requires at least one transfer to another means of transport. It was also necessary to determine what part of the total distance would be covered by a given means of transport. It was decided that the shortest possible distance covered by a vehicle should not exceed 25% of the total distance. The longest possible distance is 75 [%] of the distance travelled. A maximum of two transfers could be made during the journey. The number of possible transfers was limited to two to reduce the number of possible combinations. The scoring itself was based on pre-defined criteria and the data associated with them. Having data for the criteria allows you to assess the quality of the trip. The rating of the trip for each criterion was determined in two ways. For the time being, the financial and environmental aspects, the data collected was used to determine the final results in terms of cost, time, and carbon dioxide emissions into the atmosphere. For each criterion, the final result was presented as the sum of the products of the individual parameters and the duration of the trip. In the case of the comfort rating, the final result was presented as a weighted average of the sub-ratings. The weighting of the average is based on the percentage of distance travelled using transport.

At the beginning of the work on the implementation of the available data, all the possible combinations in terms of movement were determined. It should be noted that the order in which the given means of transport appear does not affect the final result. Thus, combinations with the same group of vehicles but in a different order were not duplicated. The available combinations do not include trips made with two private cars, i.e., an internal combustion engine car and an electric car. It has been explained that it is pointless to consider such cases from the point of view of commuting to the city, as their use would require a car to be parked outside the place of residence. Cases where the only means of transport is the tram and hired cars. It was found that this mode of transport is practically unavailable for people commuting from outside the city limits. Taking into account these restrictions, the number of available trip combinations was 155.

Moving on to the evaluation of trip types, Figure 8, Figure 9, Figure 10, Figure 11, Figure 12, Figure 13 and Figure 14 show all available cases broken down by the factors considered. Individual combinations have not been marked on the graphs in order to maintain the clarity of the graphs [8]. The most favourable cases will be distinguished later in the paper. The graphs provide information on the average speed of travel, costs incurred, carbon dioxide emissions, and comfort ratings for the relevant connections.

Each of the above graphs shows the distribution of the different ways of travelling around the city, depending on the criteria taken into account. On this basis, you can select the best-rated combinations and, as mentioned above, narrow down the group of available combinations. To reduce the number of cases, it was decided to set limits for the criteria. In this way, thresholds are created on the abscissa and ordinate axes, which determine whether a particular type of movement is taken into account or not. These values are set to ensure that the cases with the highest criteria indicators are subjected to further analysis. To determine the cut-off values, it was decided that they should be the same for the criteria described, regardless of the graph. The limits are, therefore, as follows:

-

in Figure 7, the lower speed limit is 35 km/h, and the maximum travel cost is EUR 1628 per year,

-

in Figure 8, the lower speed limit is 25 km/h, and the emission level is a maximum of 3 kg/CO₂ per year,

-

in Figure 9, the lower speed limit is 35 km/h, and the comfort of commuting is not less than 8.33,

-

in Figure 10, the upper cost limit is EUR 1628 per year, and the emission intensity is a maximum of 3 kg/CO₂ per year,

-

in Figure 11, the upper cost limit is EUR 1628 per year, and the comfort of commuting is a score not lower than 8.33,

-

in Figure 12, the emission is a maximum of 3 kg/CO₂ per year, and the commuting comfort is a score not lower than 8.33,

-

in Figure 13, the highest emission indicators of over 6 kg/100 km are associated with the highest energy consumption of 2 MJ/km.

A separate table (

Table 4. The most advantageous ways of commuting, taking into account the criteria of speed and cost of travel.

Type of Transport	Trip Division, %	Speed, km/h	Cost, EURO	Emission, kg CO2/Person	Comfort	Energy Consumption, MJ/km
train–car sharing–car	50–25–25	36.05	1446	5.80	7.80	1.530
electric car–train–car sharing	50–25–25	35.32	1261	5.99	8.48	0.772
electric car–train–taxi	50–25–25	36.22	1520	5.99	8.48	0.772
train–car sharing–electric car	50–25–25	36.90	1334	5.62	7.82	0.772
train–electric car–taxi	50–25–25	37.85	1593	5.62	7.82	0.921
car–train	50–50	36.05	567	5.80	7.98	1.530
electric car–train	50–50	37.85	345	5.44	7.98	0.312
train–car sharing	75–25	38.68	1407	5.25	7.16	1.232
train–bicycle	75–25	35.82	440	3.68	6.99	0.473
train–tram	75–25	35.47	428	4.65	6.66	0.588
train–car	75–25	38.57	529	5.25	7.32	1.070
train–electric car	75–25	39.47	417	5.07	7.32	0.461
electric car–train	75–25	36.22	271	5.81	8.64	0.258

Source: own.

,

Table 5. The most advantageous methods of access take into account the criteria of speed and environmental friendliness of the journey.

Type of Transport	Trip Division, %	Speed, km/h	Cost, EUR	Emission, kg CO2/Person	Comfort
bus–tram–electric car	50–25–25	26.95	292	2.85	7.32
bus–train	50–50	28.57	365	2.48	6.66
train–bicycle	50–50	30.54	245	2.67	7.33
bicycle–train	72–25	25.28	123	1.65	7.65

Source: own.

,

Table 6. The most advantageous methods of access take into account the criteria of speed and travel comfort.

Type of Transport	Trip Division, %	Speed, km/h	Cost, EUR	Emission, kg CO2/Person	Comfort
bus–tram–electric car	50–25–25	36.22	1520	5.99	8.48
bus–train	50–25–25	35.32	1261	5.99	8.48
train–bicycle	75–25	36.22	271	5.81	8.64

Source: own.

,

Table 7. The most advantageous methods of transport, taking into account the cost criteria and the ecological nature of the journey.

Type of Transport	Trip Division, %	Speed, km/h	Cost, EUR	Emission, kg CO2/Person	Comfort
bus–tram–electric car	50–25–25	26.95	292	2.85	7.32
bus–tram–train	50–25–25	22.95	303	2.42	6.66
bus–tram–bicycle	50–25–25	17.68	252	1.41	6.99
bus–tram–electric car	50–25–25	21.33	985	2.80	7.32
bus–train–car	50–25–25	26.95	230	2.84	7.32
bus–train–bike	50–25–25	23.30	315	1.46	6.99
bus–bike–car sharing	50–25–25	20.78	1231	2	7.49
bus–bike–taxi	50–25–25	21.68	1490	2	7.49
bus–bike–car	50–25–25	20.78	353	2	7.65
bus–bicycle–electric car	50–25–25	21.68	242	1.83	7.65
bus–train	50–50	28.57	365	2.48	6.66
bus–tram	50–50	17.33	240	2.37	6.66
bus–bike	50–50	18.03	515	0.44	7.33
train–bicycle	50–50	30.54	1053	2.67	7.33
tram–bicycle	50–50	19.30	120	2.56	7.33
bicycle–train	50–50	30.54	245	2.66	7.35
bus–tram	75–25	16.69	240	2.11	6.66
bus–car sharing	75–25	19.80	1219	2.71	7.16
bus–train	75–25	22.32	303	2.15	6.66
bus–taxi	75–25	20.70	1478	2.71	7.16
bus–bike	75–25	17.05	252	1.14	6.99
bus–car	75–25	19.80	341	2.71	7.32
bus–electric car	75–25	20.70	230	2.71	7.32
train–bike	75–25	25.28	123	1.65	7.65
bicycle–car sharing	75–25	22.75	1040	2.20	8.16
bicycle–taxi	75–25	23.65	1299	2.20	8.16
bicycle–train	75–25	25.27	123	1.65	7.66
bike–bus	75–25	19.01	60	0.80	7.66
bicycle–tram	75–25	19.65	60	1.60	7.66
bicycle–car	75–25	22.75	161	2.20	8.32

Source: own.

,

Table 8. The most advantageous ways of commuting, taking into account the cost and travel comfort criteria.

Type of Transport	Trip Division, %	Speed, km/h	Cost, EUR	Emission, kg CO2/Person	Comfort
electric car–bus–car sharing	50–25–25	29.06	1198	5.14	8.48
electric car–bus–taxi	50–25–25	29.96	1457	5.14	8.48
electric car–tram–car sharing	50–25–25	29.70	1198	5.94	8.48
electric car–tram–taxi	50–25–25	30.60	1457	5.94	8.48
electric car–train–car sharing	50–25–25	35.32	1261	5.99	8.48
electric car–train–taxi	50–25–25	36.22	1520	5.99	8.48
electric car–bicycle –car sharing	50–25–25	30	1212	4.97	8.81
electric car–bicycle–taxi	50–25–25	30.90	1470	4.97	8.81
bicycle–car sharing–car	50–25–25	25.50	1345	3.76	8.49
bicycle–car sharing–electric car	50–25–25	26.40	1280	3.58	8.49
car–bus	75–25	27.26	544	5.50	8.64
car–train	75–25	33.52	606	6.35	8.64
car–tram	75–25	27.90	544	6.30	8.64
car–bike	75–25	28.20	556	5.33	8.97
electric car–train	75–25	36.22	271	5.81	8.64

Source: own.

and

Table 9. The most advantageous methods of access take into account ecological criteria and travel comfort.

Type of Transport	Trip Division, %	Speed, km/h	Cost, EUR	Emission, kg CO2/Person	Comfort
bicycle–car	75–25	22.75	161	2.20	8.33
bicycle–electric car	75–25	23.65	50	2.02	8.33

Source: own.

) has been created for each graph, giving a complete overview of the analyzed case.

When choosing the most advantageous journeys in terms of time and money, you can distinguish between journeys made by the following:

-

bicycle–train,

-

train–car/electric car,

-

train–tram.

These three combinations are the most effective in terms of time limiting and incurring costs for the implementation of the transport process. Considering the other two criteria (environmental aspect and comfort), which did not play a leading role in this case, it should be stated that the transport process of a bicycle with a train or a train with a car may be a response to the postulates of sustainable mobility in the Smart City concept.

However, if you want to leave the smallest carbon trail, you should use a variant covering urban public transport in the form of trains and a tram, supplemented with the use of electric bikes, which ensure relatively fast movement with a minimum carbon footprint.

If we take into account the comfort criterion, then the highest score is obtained by a private car. Due to the greater space and lack of sharing space with many passengers, however, this transport process may be replaced by services using passenger cars (taxi, car sharing). Higher speed and use of private transport are associated with an increase in CO₂ emissions per person. To sum up, high comfort in combination with the quick performance of the transport process can be achieved by combinations including cars, taxis, car-sharing services, and trains.

In terms of economic criteria, the use of a bicycle is the cheapest means of transport. In addition, by comparing other means of transport in combination with an electric bike, you can achieve the most satisfactory results in terms of the environment. Variants that have both a low emission coefficient and ensure adequate travel comfort are a combination of a car and an electric bike. The types of transport, which are considered the most economical and convenient, include:

-

electric car–bike/train/tram/bus,

-

car–bike/train/tram/bus.

Analyzing the aspect of energy efficiency in the case of the most advantageous methods of access, taking into account the criterion of speed and friendliness to the traveler’s environment, it should be stated that it is possible to maintain high parameters for these variables with simultaneous low energy consumption. An example of such a solution is the use of an electric car–train in the transport process.

Depending on the preferences adopted for analyses, based on the above analyses, it was identified what means of transport is the most effective in terms of the adopted criteria of the highest rated communication connections covering the analyzed transport system is presented in

Table 10. Top-rated transport connections from the vicinity of Krakow to its centre.

Type of Transport	Trip Division, %	Speed, km/h	Cost, EUR	Emission, kg CO2/Person	Comfort	Energy Consumption, MJ/km
train–bicycle	75–25	35.82	440	3.68	6.99	0.472
car–train	50–50	36.05	567	5.80	7.98	1.530
electric car–train	50–50	37.85	345	5.44	7.98	0.312
train–tram	75–25	35.47	428	4.65	6.66	0.587
train–car	75–25	38.47	529	5.25	7.32	1.070
train–electric car	75–25	39.47	417	5.07	7.32	0.461
bus–train	50–50	28.57	365	2.48	6.66	0.830
electric car–taxi–train	50–25–25	36.22	1520	5.99	8.48	0.772
car–train–car sharing	50–25–25	35.32	1261	5.99	8.48	1.990
bicycle–car	75–25	22.75	161	2.20	8.33	0.705
bicycle–electric car	75–25	23.65	50	2.02	8.33	0.048
bicycle–train	75–25	25.27	123	1.65	7.66	0.197
bike–bus	75–25	19.01	60	0.80	7.66	0.307
bicycle–tram	75–25	19.65	60	1.60	7.66	0.175
bus–bike	50–50	18.03	120	0.44	7.33	0.555
train–bicycle	50–50	30.54	245	2.67	7.33	0.335
tram–bicycle	50–50	19.30	120	2.56	7.33	0.290
car–bus	75–25	27.26	544	5.50	8.64	2.242
car–train	75–25	33.52	606	6.35	8.64	2.132
car–tram	75–25	27.90	544	6.30	8.64	2.110
car–bike	75–25	28.20	556	5.33	8.97	1.995
electric car–train	75–25	36.22	271	5.81	8.64	0.163
electric car–tram	75–25	30.60	209	5.76	8.64	0.140
electric car–bicycle	75–25	30.95	221	4.79	8.97	0.025

Source: own.

.

The analysis of the data contained in Table 10 shows that the vast majority of analyzed variants concern transport processes using two means of transport. On the other hand, transport processes in which three means of transport are used are in a decisive minority due to lower results in the scope of individually analyzed parameters. The graphical presentation of the analysis of the four selected criteria (travel speed, costs, comfort, and CO₂ emissions in connection) with the energy efficiency criterion for the 24 analysed variants of the transport process is presented in Figure 15 and Figure 16.

Data analysis indicates that none of the analyzed variants of using several means of transport achieve the highest values in each of the analyzed criteria. For example, choosing a variant of the transport process based on the low-emission criterion reduces speed and extends travel time, which may contribute to the deterioration of comfort. The most emission-producing means of transport perform the transport process the fastest. Therefore, travel comfort is associated with higher CO₂ emissions. The use of bicycles and trains in the transport process ensures low CO₂ emissions and cost-effectiveness at a reasonable travel speed and good comfort. On the other hand, the use of a combustion or electric car in combination with a train ensures high comfort and short travel time, but the average values of environmental and cost indicators are not fully beneficial. However, linking the described dependencies with the energy intensity criterion in the variant of using two means of transport allowed for the indication of variants of transport solutions such as: electric car–train, which can lead to the optimization of the transport process in the form of maintaining the low-emission parameter, appropriate travel speed, or a high travel comfort indicator. It is important to emphasize, however, that low energy intensity can also be expensive. An example is the use of three means of transport in the transport process, such as: electric car–taxi–train. In addition, studies have confirmed the dependence of CO₂ emissions on the degree of energy intensity of individual means of transport.

5. Conclusions

Sustainable urban transport is an idea of a communication system based on economic benefits that minimizes the harmful impact of vehicles on the environment, taking into account the criterion of travel comfort and high travel speed [56]. It focuses on the implementation of the transport process, including using not one but several means of transport, usually two or three. Apart from the above-mentioned postulates, it also seems important to assess the energy consumption of individual means of transport that make up the implementation of the transport process. Although sustainable transport primarily assumes limiting the devastation of urban space by replacing individual transport with public transport. What is becoming increasingly important in this matter may turn out to be the estimation of changes in the energy consumption of transport solutions based on the variant combining individual transport modes with public transport means within the framework of existing transport systems. The analyses presented above allowed for the following conclusions to be presented:

• The assessment of energy consumption of individual means of transport may play an important role in the optimization processes of existing transport systems in cities. This is conducted to demonstrate the need to transform individual transport towards electromobility and to increase the role of transport processes based on the combination of two or three means of transport in the process of meeting transport needs in urban areas.
• The implementation of the fastest urban mobility process is associated with the highest level of CO₂ emissions. The exception is the use of bicycles and city trains in the transport process. This allows for maintaining high-cost efficiency with reasonable travel speed and appropriate comfort.
• Analyses of selected variants of transport connections involving two or three means of transport indicate that high CO₂ emissions are not always associated with high energy intensity–energy consumption (MJ/km). However, studies clearly indicate high energy consumption by means of individual transport, such as a passenger car equipped with a combustion engine. This is the basis for a discussion on the broader implications of solutions based on the idea of electromobility in the area of urban transport systems.
• In most variants, bikes and trains are perceived as the most effective means of transport. The combination of these two means of transport provides daily access to the city centre, which can be indicated as meeting most transport expectations of city residents. This connection seems to be the optimal solution in the context of the transport process, in line with the idea of sustainable transport.
• The analyzed variants of using individual means of transport are not able to guarantee the highest standards in each of the criteria studied. High values in one criterion usually lead to worse parameters in other categories. However, it is possible to identify several types of variants of using two means of transport, which can be assessed satisfactorily in terms of the four analyzed criteria.
• Services provided by public transport are part of a wide range of favourable transport options, mainly due to their low environmental impact. They can complement a smaller number of journeys due to lower speeds and comfort. However, taxi services and car rentals are very low in financial terms. Compared to other means of transport, the cost of using these services is relatively higher than in the case of public transport. The authors put forth the thesis that these two means of transport may be complementary to meet everyday transport needs.
• Due to the high complexity and scope of the problems presented, it is also not possible to indicate the most effective variant used for individual means of transport. Nevertheless, transport connections have been identified, which are an interesting alternative and can be a large exchange for the use of private cars, which is one of the demands of implementing sustainable transport solutions in many cities as part of shaping and planning sustainable mobility.
• The presented results indicate that individual transport is not the best solution for specific selection criteria. In turn, the use of an electric bike as one of the elements of the transport process is a direction that is worth promoting as an alternative, of course, provided that you have an appropriate link and point infrastructure. In addition, the development of railway connections within the urban agglomeration may constitute one of the main strategies for the development of sustainable transport. If it is not possible to give up individual transport as one of the means of transport, the analysis shows that the use of several other means of transport, depending on our priorities, can partially reduce problems related to environmental pollution while maintaining travel comfort and speed, which is one of the main goals of developing solutions within the philosophy of sustainable development and the Smart City concept.

To sum up, in addition to an ecological and well-organized transport system, the idea of Smart City should be largely based on shared transport with reduced emissions and energy consumption. This concept allows residents to use various means of transport, including car sharing, taxis, bicycles, urban rail, etc., at a convenient time, without having to purchase them. The sharing economy focuses on use, not possession. This solution can also meet the mobility needs of users, similarly to your own car, but is less costly than an individual purchase of an electric vehicle. This is because private vehicles are not used for most of the day, while an electric car shared in car sharing (for minutes) can replace up to 12 such vehicles in 1 day.

The authors argue that the key postulate in this matter seems to be the shaping and planning of sustainable mobility based on existing transport systems. By improving their optimization and efficiency without incurring unnecessary costs for their transformation in the form of outlays on point and linear infrastructure. For example, to meet the postulates of electromobility or to fully implement solutions based on the idea of intelligent transport.

The presented research was based on pre-adopted assumptions. The question remains whether the above-mentioned conclusions can be directly implemented in other metropolises in Central and Eastern European countries. It should be emphasized that despite the differences between the urban areas of individual metropolises, the proposed optimization model can lead to a more sustainable transport system by, among other things, reducing the carbon footprint, improving comfort, and increasing the speed of the transport process. This is something mentioned by researchers from other cities in Poland [58,59] and Europe [60]. Therefore, the considerations presented in the article proved to be a lasting and convincing concept, indicating a sustainable and clear direction of change, also in terms of social policy, increasing the transparency and social acceptance of management based on the Smart City idea. However, full implementation requires broader analysis and research covering the architecture of the transport system of a given metropolis. In order to obtain the synergy effect in the implementation of the proposed solutions in practice, in the area of use of all available means of transport.

Like any study, this one also has its limitations. Certainly, much broader analyses will soon be needed, including the growing opportunities to improve the energy efficiency of transport through planned changes in the field of electromobility and intelligent transport systems. Particular attention should also be paid in the future to include analyses of the impact of the development and use of renewable energy sources in order to minimize energy demand. Moreover, the authors postulate that further research in this area should also focus on extending the analysis to the entire urban transport system, including freight transport, with particular emphasis on final energy consumption. It also seems necessary to take into account in the analysis a broader adaptation of a coherent family of criteria and preference models for the case of assessing urban logistics variants, including in-depth research in the area of transport ergonomics, in particular vibration comfort [61]. The issues mentioned above have been omitted in this study due to their wide thematic scope. It also seems important to compare the implementation of infrastructure investments with the financing options available to local authorities in individual cities. Ultimately, their decisions may accelerate or slow down the pace of implementation of the presented concept. However, they will certainly be the subject of a broader analysis by the authors in the future.

In summary, the considerations presented in this article certainly do not fully exhaust the topic related to the assessment of the energy efficiency of individual means of transport in the process of optimizing transport environments in urban areas in accordance with the Smart City idea. However, they make a significant contribution to research on the transformation of urban mobility in a direction consistent with the optimization of transport processes in urban areas, taking into account the criterion of energy intensity.