Equestrian Bridges and Underpasses

Abstract

Areas with well-developed networks of equestrian routes attract riders, contributing to tourism development and boosting the economy. As the most critical elements of equestrian routes are road, railway, and watercourse crossings, the construction of bridges and underpasses that meet equestrian needs is crucial. Due to the lack of clear, standardised guidance for the design of equestrian bridges and underpasses, a systematic literature review was conducted to identify and select manuals deal with equestrian bridge and/or underpass design. The selection criterion required that the manual be currently valid, written in English, and published online with open access, ensuring easy accessibility for engineers and policymakers. This paper summarises, compares, and comments on the design parameters of equestrian bridges and underpasses listed in the analysed manuals, which must be considered to achieve optimal solutions for both horse and rider. It also provides an overview of general recommendations and best practices for specific design parameters. In the absence of a manual offering comprehensive, standardised guidelines for the design of equestrian bridges and underpasses, this paper may assist policymakers, developers, and designers in creating a trail network suitable for equestrians.

1. Introduction

Ensuring and improving available outdoor infrastructure increases people’s connection to nature and the time they spend in nature, contributing to health and well-being.

Horse riding is a moderate- to high-intensity outdoor physical activity that can be important for improving social well-being and mental and physical health [1,2,3]. Although the benefits of horse riding are well known, access for riders is limited, even in countries with a developed equine industry (for example, less than 22% of the Public Right of Way Network in England, 21% in Wales and 1% in Northern Ireland is accessible to horse riders) [2,4,5,6].

Alongside pedestrians and cyclists, horse riders are a particularly vulnerable group of road users [7]; therefore, when designing equestrian infrastructure, special attention should be given to crossings. Bridges or underpasses at road or rail crossings minimise the number of potential conflicts between vehicles or trains and trail users and provide maximum safety. Waterways can be crossed at ground level by fords or above ground by bridges [8]. Bridges and underpasses on trails used by equestrians must be planned to take account of animal behaviour [9,10,11] and the fact that equestrians need more space than pedestrians or cyclists [12]. If a footbridge or underpass is part of a trail suitable for equestrians, it should be designed to provide sufficient space for horses and riders, have a suitable surfacing and take into account safety requirements that are different from those for pedestrians/cyclists.

Although the design of multi-use trails, where equestrians share the path with pedestrians and cyclists, is nowadays preferred [2,3,8], most manuals on pedestrian bridge design do not acknowledge this issue. Only few pedestrian bridge manuals do recognise equestrian use. CD 355 [13] defines a pedestrian bridge as a bridge or part of a bridge specifically designed for use by pedestrians, cyclists and/or equestrians. A similar definition can be found in the LRFD Guide Specification for Design of Pedestrian Bridges [14], which states that typical pedestrian bridges are designed and intended primarily to carry pedestrians, cyclists and equestrians. These manuals contain recommendations for the design of bridges and bridge facilities for equestrian use.

In the absence of bridge design manuals that comprehensively address the specifics of equestrian traffic, manuals for the design of equestrian trails and facilities on them were reviewed in the hope of gathering specific information that should be taken into account when designing bridges and underpasses used by equestrians. Most manuals for the design of equestrian trails exist in countries with a developed equestrian industry (e.g., UK, USA, Australia, Spain, etc.), e.g., [2,3,9,12,15,16,17,18,19,20,21,22,23], but only some of these deal with bridges and/or underpasses used by equestrians, providing only partial information on their design.

From the above, it is clear that there is a lack of clear, standardised guidance for the design of equestrian bridges and underpasses, highlighting a current research gap.

The main motivation of the research and the aim of this article is to provide an overview of manuals dealing with the design of footbridges and underpasses that are (also) suitable for equestrians and to summarise, compare and give critical commentary on the most important design parameters.

2. Materials and Methods

This study uses a systematic literature review to identify and select manuals on the design of bridges and underpasses suitable for equestrians. The systematic process flow of the study is shown in Figure 1.

The selection of manuals addressing the design of footbridges and underpasses suitable for equestrians (

Table 1. Selection of standards, manuals, and guidelines.

Manual	Publisher	Year
Equestrian Design Guidebook for Trails, Trailheads, and Campgrounds [11]	Recreational Trails Program of the Federal Highway Administration, Department of Transportation, USA	2007
Enabling Equestrian Access in Northern Ireland [2]	British Horse Society Ireland, UK	2022
Advice on Specifications and Standards recommended for equestrian routes in England and Wales [17]	British Horse Society, UK	2025
Advice on Bridges, gradients and steps in England and Wales [18]	British Horse Society, UK	2025
Advice on Width, area and height on routes used with horses [19]	British Horse Society, UK	2025
Equestrian access factsheets [20]	British Horse Society Scotland, UK	2018
CD 353 Design criteria for footbridges [13]	Highways England, UK	2020
CD 143 Designing for walking, cycling and horse-riding [24]	Highways England, UK	2021
Horse Trail Infrastructure Guidelines for peri-urban precincts in Australia [12]	Horse SA, Australia	2019
Horse Trail Infrastructure Guidelines for peri-urban precincts [22]	Horse SA, Australia	2010
Western Australian Horse Trail Management Guidelines [23]	Government of Western Australia, Australia	2025
LRFD Guide Specification for Design of Pedestrian Bridges [14]	American Association of State Highway and Transportation Officials, USA	2009
Design and Construction Guidelines—Trail Design Guidelines [21]	San Diego County, USA	2005

) is based on the following criteria:

• The manual defines its criteria for equestrian bridge and/or underpass design, such as clear widths and heights, slopes, approaches, ramps, stairs, parapets, loads, etc.;
• The manual is currently valid (not withdrawn);
• The manual is written in English and published online with open access, making it easily accessible and available to engineers and policymakers.

The following text provides a brief introduction to the analysed manuals, while

Table 2. Parameters of bridge design listed in the analysed manuals.

Manual	Clear Width/Height	Slope	Parapet/ Infill/Kickboard	Structural Material	Ramps/ Approaches	Steps	Surfacing	Loads
[11]	+/+	+	+/−/−	+			+	+
[2]	+/+	+	+/+/+		+/−	+	+	+
[17]	+/+	+	+/+/+			+		+
[18]	+/+	+	+/+/+			+
[19]		+
[20]	+/−		+/+/+
[13]	+/+		+/+/− *				+
[24]
[12]			+/+/−				+
[22]	+/−		+/−/−		−/+		+
[23]	+/−	+					+
[14]								+
[21]	+/−	+	+/−/−				+

* refers to CD 377 [25].

and

Table 3. Parameters of underpass design listed in the analysed manuals.

Manual	Clear Width/Height	Surfacing	Approaches	Cross-Sectional Design	Lightening
[11]
[2]	+/+
[17]	+/+
[18]
[19]	+/+				+
[20]	+/−
[13]
[24]	+/+	+
[12]	−/+	+
[22]	+/+	+	+		+
[23]				+
[14]
[21]

present an overview of the listed bridge and underpass design parameters in those manuals.

The Equestrian Design Guidebook for Trails, Trailheads, and Campgrounds is a manual that provides guidelines and instructions for the design of equestrian trails, including bridges [11]. The manual was prepared in cooperation with the Recreational Trails Program of the Federal Highway Administration, U.S. Department of Transportation. It contains guidelines for the selection of bridge location, bridge width, slope, construction materials and other important parameters for bridge performance. In addition to the guidelines, the importance of consulting with local riders was emphasised.

Advice on Specifications and Standards recommended for equestrian routes in England and Wales [17], Advice on Bridges, gradients and steps in England and Wales [18], Advice on Width, area and height on routes used with horses [19]. Enabling Equestrian Access in Northern Ireland [2] and Equestrian access factsheets [20] are manuals published by the British Horse Society (BHS) which deal with the design of equestrian routes, bridges and underpasses on equestrian routes in England, Scotland, Wales and Northern Ireland, including information on clearances, gradients, loads, steps, ramps etc.

CD 353 Design criteria for footbridges [13], published by Highways England, contains mainly geometric and user-related requirements for the design of footbridges used by pedestrians, cyclists and equestrians which applies to the design of footbridges in England, Scotland, Wales and Northern Ireland. In the case of parapets, it refers to CD 377 [25].

CD 143 Designing for walking, cycling and horse-riding [24], published by Highways England, provides requirements and advice for the design of walking, cycling and horse-riding facilities on and/or adjacent to the motorway and all-purpose trunk road network in England, Scotland, Wales and Northern Ireland. Details of subways on horse-riding routes are given, while CD 143 refers to CD 353 for the design of bridges.

In the absence of Australian standards for the design of equestrian trails or associated infrastructure, the Horse SA, Australia, published Horse Trail Infrastructure Guidelines for peri-urban precincts [22] in 2010 and Horse Trail Infrastructure Guidelines for peri-urban precincts in Australia [12] in 2019. The manuals contain information on the planning, design, construction and maintenance of equestrian trail networks and provide basic design information on bridges and underpasses on equestrian trails. The manual [22] is more detailed than [12] in relation to bridges and underpasses. Western Australian Horse trail Management Guidelines [23], published in 2025 by the Department of Local Government, Sport and Cultural Industries, Government of Western Australia, also provide general principles and advice for equestrian trails to meet the needs of users, manage potential degradation of natural and cultural values and meet high sustainability standards. This manual contains some information on the design of bridges and underpasses.

LRFD Guide Specification for Design of Pedestrian Bridges [14] is an edition of the American Association of State Highway and Transportation Officials (AASHTO) relevant to the United States. The purpose of the guide is to provide guidance for the design and construction of pedestrian bridges that are intended for pedestrians, cyclists and equestrians and are not for road traffic. In the section dedicated to bridge loads, bridge loads due to horses and equestrians are listed.

The Design and Construction Guidelines—Trail Design Guidelines [21], published by San Diego County were created for the development of equestrian trails to improve safety, reduce accidents, protect users, etc. Consistent with the County of San Diego’s vision and standards, this manual applies to all local entities as well as private investors. Use of the manual as a guide for planning and developing better and safer trails is encouraged. Although most of the guidelines relate to trail performance, some of them also apply to bridges.

3. Bridge Design Parameters

By definition, bridges are structures that span a physical obstacle (water, valley, road or railway, etc.). Bridges over roads or railways are also known as overpasses.

Bridges can be an interesting addition to trails, but they are expensive to build and maintain and can have a significant impact on the environment. When building a new trail, it is important to remember that bridges are the single most expensive item in the cost of trail construction. Therefore, special attention should be paid to the placement and design of bridges on the trail.

This chapter provides an overview of the general principles and specific parameters for equestrian bridge design as defined in the analysed manuals.

3.1. General on Bridge Design

When planning bridges on trails used by equestrians, special care should be taken to ensure that they are adapted to the experience on the trail and to the classification of the trail. It is also desirable that the structure is cost-effective and low-maintenance, while at the same time fulfilling the requirements for load-bearing capacity and durability [23]. Manual [9] presents suggested structural materials suitable for different levels of trail development (such as concrete, steel, timber and fibreglass), indicating that concrete is not preferable for use in low development, while fibreglass is not suggested for bridges in high trail development. Regardless of the material used, bridges must be robust enough to support the weight of horses and riders without swaying and preferably without unnecessary noise or echo [12,20].

The bridge should be sited where it will least disturb the natural and cultural values and care should be taken to ensure that the structure does not alter or obstruct the watercourse, taking into account reasonable flood events and possible future changes in flow [23].

Bridges spanning an obstacle at right angles are the shortest and usually the most cost-effective solution, but in this case the access routes should be adapted to avoid sharp bends in the immediate approaches to the bridges, as bends impair visibility. Adapting the route is usually more cost-effective than building a bridge inclined towards the obstacle [9].

Bridge approaches should be designed to encourage users to use the bridge to overcome the obstacle. It should be noted that crossing bridges, especially high bridges or bridges that cross busy roads or railway lines, can be very challenging for horses and riders. Falls from bridges or trails are much more frightening from the horse’s perspective than from the ground [20] (see Figure 1). A hesitant horse can lunge sideways and endanger itself and the rider if the bridge does not have a safe access [21]. Unprotected bridge approaches can tempt users to descend to the obstacle, i.e., not to cross the bridge [22].

It is recommended to build protected, widened areas at the bridge approaches, especially if the sides are steep. Widened, protected bridge approaches help nervous horses. The protection can take the form of wing walls, approach walls or railings. Widened approaches are built outside the bridge limits. The railings of the widening should be connected to the bridge railing to prevent stirrups from slipping or other avoidable accidents [12,22].

If the bridge or deck structure appears unsafe, horses are often reluctant to proceed. The use of familiar materials in the construction of the bridge helps to relax the horses. The colour, grip and texture of the bridge should ideally resemble the course of the trail. Steps are not desirable on bridges for horses or on their approaches [11].

The transition from the trail to the bridge should be as smooth as possible. Approaching ramps from the trail to the bridge (if necessary) should not be steeper than any part of the trail [23].

If an existing or historic bridge is to be integrated into a trail, the bridge must be adapted to the needs of equestrian traffic and its load-bearing capacity checked [23].

3.2. Clearances on Bridges

The clearances on the bridge are defined by the clear width (clear horizontal space above the bridge deck between the parapets) and the clear height (clear vertical space between the bridge deck and the underside of superstructure elements such as stay cables, roof structures, etc., if applicable) as shown in Figure 2. The clear height is also referred to as headroom. All obstacles (mounting blocks, traffic signs, vegetation, etc.) must not reduce the required clearances.

The clear width of equestrian bridges depends on many parameters, such as the level of infrastructure development (low, moderate or high), the type of route crossing the bridge, the length of the bridge (spanning distance), the height of the bridge deck above the obstacle, the type of obstacle and the type of users (single use, shared use, equestrian experience, etc.).

The dependence of clear bridge width on parameters mentioned above are listed in

Table 4. Clear width on bridges according to [2,17,18].

Route Type		Deck Height	Span Length	Clear Width
Over Watercourses	Equestrian trail	<1 m	<3 m	2 m
	Restricted Byway, Byway	<1 m	<3 m	3 m
	All Routes	<1 m	3–8 m	3 m
	All Routes	<1 m	>8 m	3 m with parapet 4 m no parapet
	All Routes	>1 m	<8 m	3 m
	All Routes	>1 m	>8 m	4 m
Any route over road		Any	Any	Min. 3 m
Any route over railway		Any	Any	Min. 3 m

and

Table 5. Clear width on bridges according to [9,13,20,21,22,23].

Manual	Clear Width	Note
[20]	Min. 1.5 m	up to 3 m span
	Min. 2 m	up to 8 m span
	Min. 4 m	for wider river or road crossings
[9]	Min. 1.5 m	areas with low level of development
	1.5 m–2.4 m	areas with moderate level of development
	3.6 m (preferable)	areas with high level of development
[23]	Min. 1.5	low-used trails
	1.8 m–2.5 m	moderate-used trails
	3.6 m–4 m	areas with high levels of development long or high bridges
[21]	Min. 2.4 m	single or limited-use trail bridges spanning very short distances with good visibility
	3.6 m–4.6 m	multi-use trails
[13]	Min 3.5 *	combined use by pedestrians and equestrians
[22]	3.5 **	preferred for all bridges used by equestrians

* If a large number of horses are expected to cross the bridge at the same time (e.g., if the bridge is adjacent to a riding school or stable), a greater width may be required. ** unless a smaller width is chosen in individual cases in consultation with the horse owners

.

It can be seen that minimum clear width of 1.5 m is specified in manuals [9,20,23] for areas with low level of development/low-used trails/very short spans.

For bridges in areas with moderate level of development, the clear width is often between 1.5 m and 2.5 m, whereby a width of 2.5 m is sufficient for most carriages [9,23]. The San Diego County Design and Construction Guidelines [21] specify a minimum width of 2.4 m for single or limited-use trail bridges spanning very short distances with good visibility. This is consistent with the Scottish factsheets [20], which recommends a minimum width of 2 m for bridges spanning up to 8 m, and the manuals published for England, Wales and Northern Ireland [2,17,18], which recommend a width of 2 m for equestrian bridges and 3 m for byway bridges less than 3 m in length and less than 1 m high.

Bridges that cross wider rivers, roads, and railways should have clear width greater than 3 m [2,17,18]. Manuals [13,22] define unique minimum value of 3.5 m in case of combined use by pedestrians and equestrians [13] and for all bridges used by equestrians [22].

In areas with a high level of development, and for long and high bridges, the clear width is usually defined as between 3.6 and 4.6 m [9,19,20,23]. On long bridges or bridges with restricted visibility that are narrower than 3 m, a waiting area is recommended. The preferred length and width of the waiting area is 4 m (acceptable minimum is 3 m) [2,17]. The area should be increased with the potential waiting time as horses can become restless, especially in a threatening environment [2,17].

The general adjustment of the clear bridge width presented in [9] is to add 0.6 m to the width of the trail crossing the bridge to ensure a minimum distance to the parapet and to provide space for manoeuvring when users pass each other. This is similar to [16], where a buffer zone of at least 0.3 m on each side of the trail is recommended.

The clear heights listed in analysed manuals are represented in

Table 6. Clear heights on bridges according to [2,13,17,18,20,22].

Manual	Clear Height for Ridden Horses		Clear Height for Horses to be Led
	to the Permanent Obstacle	to the Overgrown Vegetation
[2]	3.7 (3.4) * m	3 m
[13]	3.7 m		2.7 m
[17]	3.7 (3.4) * m	3.7 (3.4) * m
[18]	3.7 (3.4) * m	3 m
[20]		3.7 (3.4) * m
[22]		3.7 (3.4) * m

* acceptable.

. The clear height on bridges used by equestrians given in [2,13,17,18] should be at least 3.7 m, although, according to [2,17,18], a lower value of 3.4 m is also acceptable.

If a bridge or part of it is overgrown laterally by vegetation, the overhanging branches should ideally be cleared to a height of 3.7 m [17,20,22], although a reduction to 3.4 m [19] is permissible. In some manuals [2,18], a clear height of only 3 m is permitted for overhanging vegetation.

In exceptional cases, a lower clear height may be acceptable for the horse being led if there are mounting blocks [2,17]; a clear height of at least 2.7 m is recommended for use by dismounted riders [13]. If riders have to dismount and lead their horses across the bridge, warning signs must be placed at both ends of the bridge [13].

3.3. Slopes

Bridges with a slight incline or a curved deck drain water better than flat bridges. In addition, arched bridges are aesthetically pleasing. However, the slope of bridges and access ramps must ensure the safety of horses and prevent them from slipping and falling.

In general, the longitudinal slope on inclined or curved parts of the bridge deck should not be greater than on the trail itself. In general, a longitudinal slope of 8.33% (1:12) is the ideal maximum for use by horses [17,20]. If possible, the slope on the bridge deck should not exceed 5% (1:20) to prevent horses from slipping [9,21,23].

The access ramps to the bridge should have a maximum longitudinal slope of 8.33% (1:12), which is ideal for use by horses and can also be used by people with wheelchairs or similar vehicles, although lower ramps are preferable for the latter [2].

Cross slopes for bridges are not defined in any the of analysed manuals.

3.4. Steps

As already mentioned, it is not advisable to build steps on bridges or their approaches, especially if there are no steps on the equestrian trail.

If the construction of steps on bridge or their approaches cannot be avoided, the following recommendations should be followed:

• The width of the steps should ideally correspond to the width of the bridge deck; 2 m or more are recommended, but at least 1.5 m [2,18];
• The optimum length of the steps is between 2 m [2,18] and 2.9 m [17];
• The optimum riser height is 15 cm [2,17,18]. If there is insufficient space, the riser height can be increased as follows [2,18]:

  ○

  Up to 20 cm if there are no more than three consecutive risers;

  ○

  Up to 30 cm if there are no more than two consecutive risers;

  ○

  Up to 45 cm in remote areas and only if the tread length under the riser is at least 2 m.

3.5. Surfacing on Birdges

The surface of the bridge deck should be durable, non-slip, non-echoing and all-weather and should not have any gaps through which the river, road or railway to be crossed can be seen or through which a hoof can get caught [13,20,21,22,23].

Ideally, the surface of the bridge deck and the approaches to the bridge should not differ from the surface of the trail [12]. In this way, the horses remain calm when approaching and crossing the bridge. Unfortunately, in many cases this is not possible, especially when the trail is made of materials best suited for equestrian use, such as sand, wood chips, grassed gravel [24], as the bridges and their decks are usually made of reinforced concrete, metal (steel, aluminium) or wood, which are not particularly suitable for equestrian use.

The concrete decking should not have a top layer or can be covered with asphalt. Asphalt and concrete are slippery and do not absorb noise well [22]. The same problems occur with metal decking. Wood decking is natural and causes fewer noise problems, it becomes slippery when wet [2,23].

Surfaces with grooves, spraying or mats provide additional traction and low noise [22,23]. Grooves and a heavy broom finish roughen the concrete surface and ensure better adhesion [2,21]. Asphalt surfaces can be treated with grit (quartzite) during the construction phase or afterwards, whereby dry, uncoated grit are rolled into the asphalt surface to make it slip-resistant. Metal and wooden decking coated with epoxy resin or sprayed with grit-based surface (e.g., bauxite grit) [2,20,22] provides grip and dampens noise. Grit-based surfaces are also available in the form of strips or sheets [2]. The use of rubber mats for equestrian use dampens noise and provides a non-slip surface [22].

For short and low bridges, the deck can be designed as a box filled with sand or another material similar to the trail, so that a non-slip and noise-reduced crossing is achieved [23]. A quick and cheap solution for flat wooden surfaces is to spread a generous amount of sand, which needs to be topped up regularly [2].

3.6. Paraptes, Infills and Kickboards

Parapets on the bridge deck prevent users from falling off the bridge. According to [25], all pedestrian, cycle and equestrian bridges over roads or railway lines must have a parapet. In some cases, short and low bridges over watercourses do not require parapets [17,20,22], especially if they are wide enough [2,17,18]. An exception is bridges over marshes, which should have a parapet because if a horse falls off the bridge, it can get stuck in the marsh, which is more dangerous than falling into the water [17].

The recommended values for parapet heights on equestrian bridges are between 1.2 and 1.8 m [2,9,17,18,20,21,22,25] as shown in

Table 7. Heights of parapet, infill and kickboard according to [2,9,17,18,20,21,22,25].

Manual(s)	Type of Obstacle	Type of Route/Users	Deck Height	Deck Length	Parapet Height	Infill Height	Kickboard Height
[2,17,18]	Watercourse	All routes	<1 m	<8 m	1.2 m	0.6 m	0.25 m
	Watercourse	All routes	<1 m	>8 m	1.2–1.8 m	0.6 m	0.25 m
	Watercourse	All routes	>1 m	Any	1.8 m	0.6 m	0.25 m
	Road	All routes	Any	Any	1.8 m	1.0 m
	Railway	All routes	Any	Any	1.8 m	1.8 m
[9]					137.2 cm
[20]		All bridges used by horses			1.8 m (possible reduction up to 1.5 m *)	0.6 m **	0.25 m
[21]		All bridges on multi-use trails			1.52 m ***
[22]	All bridges near or over highways				1.8 m	1.8 m	0.25 m
[25]	railway				1.8 m	1.8 m ****
	not over railway				1.8 m	0.6 m

* depending on drop below bridge deck. ** over main roads. *** depending upon the location and length of the bridge, higher railing may be required. **** or to parapet full height.

.

According to [2,17,18,22,25], all bridges over or near roads or railway lines must have at least a 1.8 m high parapet. The same value is considered optimal for all bridges used by horses [20].

Depending on drop below bridge deck, the minimum height of the parapet can be reduced from 1.8 to 1.5 m according to [20]. The value of 1.52 m parapet height is also given in [21] as the minimum value for all bridges on multi-use trails. The minimum parapet height of 137.2 cm, which applies to all bridges regardless of deck height, bridge length, or the obstacle to be crossed, is specified in [9].

The most detailed guidance on determining parapet height for equestrian bridges can be found in the BHS publications [2,17,18], where heights between 1.2 and 1.8 m depend on the type of obstacle, deck height, and deck length (Table 7).

Although heights of less than 1.8 m are acceptable for low bridges with a bridge deck less than 1 m above the watercourse [2,17,18], manual [17] recommends choosing higher parapets.

Horses can be spooked by traffic or fast flowing or turbulent water passing under the bridge. To obstruct the view from the bridge, solid infills are required at the bottom of the railing parapet [17,18,25]. The height of the infill in manuals [2,17,18] depends on the obstacle to be bridged (watercourses, roads, railway lines), as shown in Table 7. A similar recommendation can be found in other manuals, according to which bridges over railways must have a solid infill to the full height of the parapet (at least 1.8 m) [25], and at least 0.6 m for bridges that do not cross railways [20,25]. Manual [22] recommend height of infill of at least 1.8 m for bridges over or near highways and for specific type of horse (e.g., young racehorses).

Parapets or infills may not be suitable for low spans over watercourses, as debris could accumulate during flooding and increase the load on the bridge. For bridges over watercourses, the infill can be replaced by a kickboard (raised edge of the deck) to prevent hooves from slipping off the deck. The preferred height of the kickboard is 25 cm [2,17,18,20,22].

According to [22], a parapet is not required for wide bridges with good visibility and a deck height of less than 60 cm above the obstacle. A similar recommendation can be found in [20], according to which a parapet is not required if the deck height is less than 1 m above the obstacle, and in [2,17,18], where in addition to a deck height of less than 1 m, the deck width must be at least 4 m for a parapet not to be required.

For bridges without a parapet, the bridge deck must have raised sides or kerbs at least 20 cm high to provide a visual guide for the horse to stay on the centre line of the bridge and to protect the hoof from slipping off a bridge [23].

The infill/kickboard/kerb must be raised at least 25 mm above the bridge deck to allow water to drain away [2,17,18,20,22] if water drainage is not ensured by other means (e.g., a bridge drainage system or a longitudinal slope).

3.7. Loads

Many manuals for the design of bridges intended for equestrian or multiple use lack a definition of equine loading. The mass of horses ranges from 200 to 1000 kg, while riding horses generally weigh between 350 and 700 kg, with an average of 500 kg [2,9,20]. Manuals [2,9,20] provide information about horse weight distribution when standing, trotting/cantering, or in full gallop (

Table 8. Weight distribution for a 500 kg horse, according to [2,9,20].

Type of Movement	Each Foreleg		Each Rear Leg
	Times Horse Weight	[kg]	Times Horse Weight	[kg]
standing	0.3	150	0.20	100
walking	0.5	250	1/3	167 *
trotting/cantering	1	500	2/3	333 *
full gallop	2.5	1250	5/3	833 *

* rounded to the nearest whole number.

).

There are only two of analysed manuals [14,17] that prescribe loads due to equestrian use to be included in bridge analysis as static actions. Non-factorised load values are displayed in

Table 9. Loads due to equestrians according to [14,17].

Manual	Uniform Load	Peak Force Loading
		Point Load	Patch Load
[14]	5 kN/m2	8.12 kN
[17]	4.3 kN/m2 (1.00 kips)		453.6 kg * (90 psf)

* to be applied over a 10 cm (4 in) square area.

.

Advice on Specifications and Standards recommended for equestrian routes in England and Wales [17] specify a uniform load and a point load to be applied to the bridge deck as live loads. The uniform load is only applied in the unfavourable parts of the influence surface.

LRFD [14] defines, in addition to a uniform live load patterned to produce the maximum load effect, a patch load to be applied to decks intended for equestrian use to check the punching shear capacity of the bridge deck. The patch loading was derived from hoof pressure measurement.

4. Underpass Design Parameters

As previously mentioned, grade-separated crossings in the form of overpasses and underpasses minimise the number of potential conflicts and offer maximum safety for equestrians at road or rail crossings. Underpasses are favoured by riders over overpasses at grade-separated crossings [20,23,24].

Although equestrian underpasses are mentioned in the manuals [2,12,17,18,20,22,23,24], there are very few guidelines for their design, which will be presented below.

4.1. General on Underpass Design

When planning the underpass at the equestrian trail, the location and access routes should be carefully selected to ensure adequate sight lines. The shortest and most cost-effective solution is an underpass that runs at right angles to the obstacle (road, railway, etc.). The approaches should be kept clear of overhanging vegetation to facilitate sightlines and access [22].

Good drainage must be ensured in the underpass so that water does not accumulate in it [23].

It is desirable for the underpass to have the same dimensions as the rest of the trail corridor. Underpasses with a constant cross-sectional height ensure sufficient vertical clearance over the entire clear width, in contrast to arched cross-sections, where the vertical clearance required for equestrians is only present in the centre part of the cross-section, which limits the possibility of passing [23].

4.2. Clearances on Underpasses

As with bridges, a clear height of 3.7 m is prescribed for equestrian use [2,17,19,20,22,24], with a minimum of 3.4 m [2,17] or an absolute minimum of 3 m [2,23]. Greater values are preferable, as prescribed in [12], where the height must be at least 4 m, while [2] recommends 5 m as the preferable clear height (

Table 10. Underpass clearances according to [2,12,17,19,22,23,24].

Manual	Clear Width	Clear Height— Ridden Use	Clear Height— Horse to Be Led
[2]	Min. 3 m 5 m (desirable)	3.7 m (min 3.4 m) 5 m (preferable) 3 m (absolute minimum)	Min. 2 m
[17]	3 m 5 m (desirable)	3.7 m (min 3.4 m)
[19]	5 m (desirable)	3.7 m
[20]	3 m	3.7 m
[22]	4 m	3.7 m
[23]		Min. 3 m
[12]		Min. 4 m	Min. 2 m
[24]	Min. 3 m	Min. 3.7 m	Min. 2.7 m

).

Underpasses with a clear height less than that prescribed in Table 10 are permitted if it is not possible to increase the height. In these cases, riders must dismount from their horse and lead it [3,12]. The height of 2.7 m is defined in [24] as the minimum clear height and the value of 2 m as the absolute minimum clear height [2,12] when the horse is being led. In the event that dismounting is necessary, mounting blocks and warning sings should be provided at both ends of the underpass [2,19,23,24].

According to Table 10, a minimum clear width of 3 m is recommended for an underpass on a two-way trail or a share-used trail suitable for equestrians [2,17,20,24]; a minimum of 3.6 m is recommended for carriage driving [17]. The preferred clear width according to [22] is greater than 4 m, while [2,17,19] define a width of 5 m as desirable.

4.3. Surfacing on Underpasses

Ideally, the same trail surface continues in the underpass to maintain the horse’s confidence [12,22]. This recommendation is much easier to achieve than with bridges.

Filter drains are not suitable for equestrian underpasses as they can be problematic for horses [24]. It is extremely important that manholes and other devices installed in the underpass are flush with the walls and floor to prevent horses or riders from tripping over or getting caught in them, i.e., to avoid possible injuries [22]. Drainage system gates and covers can be slippery, so care should be taken with their placement [24]. The longitudinal slope of the underpass should be no less than 0.7% to allow the drainage [24].

4.4. Lithening

When planning an underpass, attention should be paid to good lighting. There must be sufficient natural light or artificial lighting must be provided [22].

Horses’ eyes do not adapt quickly to changes in light, which can cause them to hesitate. On longer underpasses, lighting should be installed so that riders can see and react to approaching trail users. According to [19], lighting during the day should be twice as strong as during the hours of darkness, but if an underpass is part of an unlit route, this may be excessive.

The lighting must not restrict the clearances in the underpass.

5. Discussion

In countries with a well-developed equine industry, the horse industry and related tourism are significant contributors to both local and national economies. For example, the economic value of the UK equine industry is estimated at around GBP 5 million per year [2,6], while in Spain, it exceeds EUR 7 million per year (about 0.6% of GDP) [26]. In the autonomous community of Andalusia, Spain, income related to the equestrian industry is more than EUR 2.1 million per year [26]. It is estimated that, in the UK, an average of GBP 6887 per horse per year goes into the local economy [6].

When riding, equestrians may use public rights of way (including roads) and open spaces, but routes free from motorised traffic, such as equestrian trails or shared-use trails suitable for equestrians, are preferable for safety and freedom from noise and pollution. Areas with good networks of traffic-free routes attract more riders, including tourists, and therefore boost the local economy [4].

Any development can create opportunities to extend access for equestrians. New development plans can significantly increase opportunities for equestrian access when equestrians are considered early in the planning process for new trails or upgrades to existing ones. This also applies to new road and railway projects that cross existing equestrian trails, where development plans must include provision for equestrian crossings, bridges, or underpasses.

As there is no comprehensive standardised manual for defining provisions for equestrian bridges or underpasses, the evaluation of design parameters found in existing manuals can assist planners and developers in the planning process.

5.1. Discussion on Bridge Design Parameters

As bridges are the most expensive single item in the construction costs of an equestrian trail, their design must be carefully planned to ensure their robustness, resistance, durability, cost-effectiveness and minimum maintenance, taking into account the parameters that ensure safe use of the bridge by equestrians.

This can be achieved considering general recommendation as follows:

• Place the bridge in an optimal position (usually crossing the obstacle at a right angle) that does not significantly impact the environment;
• Ensure easy access to the bridge with good sight lines, preferably without steps;
• Design clearances that ensure safe and comfortable crossing and, if necessary, allow horses and riders to pass, overtake or ride in pairs;
• Design slopes, parapets and surfaces that protect horses and riders from slipping or falling off the bridge;
• Ensure mounting blocks and warning signs are present at both ends of the bridge if riders must dismount and lead their horses over the bridge;
• Consider the loads to which the bridge may be subjected during its service life, including the loads caused by the horses, as well as possible exceptional environmental conditions, such as flooding;
• Select durable material for the bridge construction.

The following text summarises and compares the specific recommendations for the design of equestrian bridges and provides critical comments on them.

All basic rules for bridge design (material selection and its protection, limit states verification, etc.) in a particular country should also be applied to equestrian bridges. For example, manual CD 353 [13] which applies to pedestrian bridges in the UK defines the following: “Where a bridge is designated for equestrian use, it shall be designed in accordance with the relevant parts of the Eurocodes as implemented by DMRB CD 350”.

The live load on equestrian bridges considered in the analysis of bridge load-bearing capacity is defined in only two of the manuals reviewed, namely as a uniform load on the bridge and as an additional force or patch load caused by a single horse trotting/cantering. The uniform load is used for global verifications, while the force or patch load should be applied for local verification of the bridge deck’s punching shear capacity. If local verification of the bridge deck is not performed, the deck may be locally punched by horse loading and the horse could fall through the bridge deck, as it can be seen in [27,28].

The non-factorised values of uniform and force or patch loads in [14,17] are not similar, as shown in Table 9. According to the Eurocode standards applied to the loads defined in [29], the multiplication factor (partial factor) for live loads is 1.5 for combinations of actions for persistent or transient design situations (fundamental combinations), while LRFD applies a load factor of 1.75 for live loads. The values of non-factorised uniform load of 5 kN/m² [17] and 4.3 kN/m² [14] are identical to those for pedestrian bridges [14,30]. The factorised values for the uniform live load on bridge decks according to [12,16] are almost identical.

The force load from a single horse is defined in [17] as the sum of the load on the front and rear limbs during trot/canter (8.12 kN). This is comparable to the value for trot/canter weight distribution for an average riding horse [2,17,18] shown in Table 8 where sum of weight on one front and one rare limb is 833 kg (8.17 kN). This force has to be factorised by partial factor of 1.5 [17]. In manual [14], the patch loading of 453.6 kg over a 10 cm square area represents the load transmitted to the bridge by the most heavily loaded limb during trot/canter of a typical horse and rider, with the loaded area corresponding to the size of a horse’s hoof [20]. A patch load of 453.6 kg corresponds to the lower end of the typical weight of a horse and rider [9]. A load factor of 1.75 must be applied to a patch load [14]. By comparing the factored loads resulting from the action of a single horse for local verifications, it can be determined that the load value according to [17] is approximately 50% higher than the value according to [14]. Although peak force loading is defined differently in manuals [14,17], selecting the loading caused by trot/canter is reasonable, as the horse is not expected to cross the bridge at a full gallop.

All the above-mentioned loads should be applied as static actions in the bridge analysis. To the best of the author’s knowledge, the influence of equestrian dynamic action on bridge structures is not addressed in analysed manuals or other literature. The best way to prevent dynamic problems, such as vibration and amplification, is to design the structure outside the equestrian frequency range, similar as is prescribed in case of pedestrian bridges under pedestrian action [31].

Manuals [2,9,20] provide information about horse weight and weight distribution when standing, trotting/cantering, or in full gallop, which is important for understanding the prescribed loads in [14,17] and can be used by designer in specific situations not covered by the loads presented in [14,17]. Values indicated in aforementioned manuals of horse weight and weight distribution are similar and are in line with literature sources [32,33].

Although there are no strict restrictions on the use of structural materials for the construction of equestrian bridges in analysed manuals, concrete, steel and timber structures are most commonly used as it can be seen in [9]. In recent decades, the use of aluminium and fibre-reinforced polymers (FRP) has increased for the construction of bridges for pedestrians, cyclists, and equestrians, as these materials provide durable, low-maintenance, and cost-effective structures that can be easily installed without heavy equipment [34,35]. Notable examples of aluminium and FRP equestrian bridges include the Blainville Equestrian Park footbridge in Blainville, Québec, Canada [34], and the 60′ FRP truss bridge for the Buncombe Horse Trail in the Francis Marion and Sumter National Forests in South Carolina, USA [36].

It is rare for the most suitable surfaces for equestrian traffic, such as sand, wood chips or grassed gravel, to be provided on bridges. Therefore, it is recommended that metal, wood, asphalt and concrete surfaces be made non-resonant and non-slip using commonly employed techniques such as grooving, spraying and rubber matting, as specified in the manuals [2,20,21,22,23]. All these techniques have proven effective on completed bridges as can be seen in [37,38,39,40]. However, new materials that prevent slipping, which are not listed in the manuals, have recently been developed, such as glass reinforced polyester (GRP) [41], and fibre-reinforced polymer (FRP) [42], which are well suited for equestrian use. Thus, for decking materials, designers should regularly update themselves on new products that may not yet be included in the design manuals.

Although noise is a challenging problem for equestrian concrete, metal, or wooden bridge decks, there is no specification for maximum sound pressure levels or reverberation time in the analysed manuals or other literature. According to investigations of noise levels and horse behaviour, levels below 65 dBA are recommended to avoid sudden or high-pitched sounds that can cause fear [43,44].

To prevent horses from slipping, in addition to selecting anti-slip decking material, the longitudinal slope on the bridge deck and approaches should ideally be limited to 5% (maximum 8.3%) according to all manuals analysed [9,17,20,21,23]. This is in good correlation with slopes recommended for pedestrian bridges where a slope of up to 6% meets the needs of persons with reduced mobility and wheelchair users [45]. Example of a well-designed arch pony-truss-style bridge is Aluminium Equestrian Bridge for Blainville Horse Park (Québec, Canada) with longitudinal slope of less than 5% [46]. Cross slopes are not defined in any of the manuals analysed, but the literature [45] states that cross slopes of at least 1% allow rain and snowmelt to run off the pavement, while 2% to 2.5% are defined as the maximum slope for pedestrian bridges or share-used bridges and ramps.

Although it is not advisable to build steps on bridges, recommendations for the design of steps can be found in manuals [2,17,18]. The recommended values for stair design are similar in these manuals. The width must correspond with the bridge width (at least 1.5 m) [2,18], which aligns well with step designs on pedestrian bridges presented in [46]. A step length between 2 m [2,18] and 2.9 m [17] allows a horse to stand on all fours on each step (the approximate length between front and rear limbs while standing is 1.5 m [9,12]). The optimum riser height of 15 cm, as recommended in the manuals [2,17,18], ensures universal accessibility for users on shared-use trails [45].

Avoiding sharp and blind curves on the immediate approaches to bridges is suggested by manual [9], as curves adversely affect sight distance; however, none of the analysed manuals address sightline design at bridges or their approaches. In the absence of specific rules for bridges, the visibility parameters for horse-riding routes presented in CD 143 [24] may be applied.

Although most bridges do not have height limitations (such as superstructure elements, roofs or overgrown vegetation over the deck), in cases of overhead obstructions, a clear height of 3.7 m to the underside of the obstruction is defined as ideal in all analysed manuals [2,13,17,18,20,22], while a value of 3.4 m is also acceptable in [2,17,18,20,22]. These values align with the recommendations for adjusting the clear bridge height in [9], where at least 0.5 m should be added to the height of the trail user. The average height of a mounted rider is about 2.5 m above the ground [9,17,20], while the height of tall riders on large horses can reach up to 3 m [9]. Some manuals allow a minimum clear height of 3 m for overgrown vegetation [2,18], which does not provide a sufficient buffer zone above the rider, especially for tall riders on large horses. A clear height of at least 2.7 m, when the bridge is used by dismounted riders, is prescribed only in [13] and ensures a sufficient buffer zone above the horse (the total height of a typical riding horse is about 2 m [12]).

The greatest differences in analysing the design parameters of equestrian bridges were found in determining the clear width, although by comparing the various parameters that influence this, the following can be established: the clear width on the bridge depends on the type of route crossing the bridge, the type of obstacle it crosses, the length of the bridge, the expected traffic on the bridge (levels of development), the need for overtaking or passing and the type of users (single use or shared use).

It should be noted that rider and horse span about 1.2 m at the widest point, seen from behind [9,23], not including the space for manoeuvring, so that the minimum clear width for riders is about 1.5 m [12]. An absolute minimum clear width of 1.5 m on the bridge leaves sufficient space for the individual rider to manoeuvre when crossing the bridge. This means that only bridges on less frequented trails in remote areas (low level of development) and very short span bridges (where visibility is not disturbed) can have a clear width of at least 1.5 m what is consistent with recommendation in [9,20,23].

As shown in Table 4 and Table 5, most of the manuals, in certain situations, provide for the possibility of a clear bridge width of less than 3 m [2,9,17,18,20,21,23]. Bridges narrower than 3 m are only suitable for riding single file. Equestrians generally avoid overtaking on bridges, but on bridges between 1.8 and 3 m, riders may be tempted to overtake or ride two abreast, which can lead to conflicts [9]. In addition, a width of less than 3 m may not be sufficient for a horse to turn on the bridge [2,17].

Thus, on long bridges or bridges with restricted visibility that are narrower than 3 m, a waiting area is recommended. The example of bridges with clear width between 1.5 and 3 m with good visibility and no waiting are truss bridge on Buncombe horse trail in South California with span of 18.23 m and width of 1.72 m [36] and Equestrian Bridge for the Town of Woodside California with span of 15.24 m and width of 1.82 m [47].

A minimum clear bridge width of at least 3 m, which allows riding in pairs, passing, and horse turning, is specified in all analysed manuals except [21]. In areas with a high level of development, and for long and high bridges, the clear width is usually defined as between 3.6 and 4.6 m [2,9,17,18,20,21,23]. A single minimum value of 3.5 m is defined in [13] for combined use by pedestrians and equestrians, and in [22] for all bridges used by equestrians, ensuring a comfort level consistent with bridges in high-developed areas. The clear bridge width of 3.5 m also allows for the turning of most carriages [2].

An example of bridge on share-used trail of more than 3.5 m is bridge along US route 6, near Channahon, Illinois [48].

The most detailed guidelines on bridge clear width are provided in manuals by the BHS for England, Wales, and Northern Ireland [2,17,18]. These manuals, except for very short and low bridges on equestrian trails, prescribe a clear bridge width of at least 3 m, which allows for passing and horse turning. Although manuals [2,17,18] are comprehensive, the recommended clear width values smaller than 3.5 m do not align with CD 353 [13], which applies to the design of pedestrian bridges for combined use by pedestrians and equestrians in England, Scotland, Wales, and Northern Ireland. A similar inconsistency is found in the manual by the British Horse Society Scotland [20].

Parapets on the bridge ensure the safety of equestrians, especially on narrow bridges.

The height of the parapet depends on the width of the bridge deck, the type of obstacle to be bridged, the length of the bridge, the traffic density and the height of the deck above the obstacle. In general, the narrower the bridge, the longer the bridge, the higher the deck above the obstacle, the higher the parapet.

Most of analysed manuals specify a minimum or optimum parapet height of 1.8 m [2,12,18,20,22,25]. A parapet height of 1.8 m reduces the likelihood of a horse jumping over it and increases the rider’s protection from falling off the bridge should he fall off the horse for any reason [17]. Manuals [22,25] are the strictest: all bridges for equestrian use should have parapets at least 1.8 m high. Manual [20] allows a reduction form 1.8 m to 1.5 m depending on the drop below the bridge, but does not provide any information on drop values, making it problematic to determine the criteria for possible reduction. Manuals by BHS [2,17,18] enables parapet heights of between 1.2 and 1.8 m for bridges over watercourses in case the deck height over obstacle is less than 1 m. In all other cases parapet must be at least 1.8 m height. These manuals are the most detailed among analysed manuals and, in author’s opinion, most suitable for determining the minimum parapet height. The minimum parapet height prescribed by manual [9] for all equestrian bridges is 1.372 m, which is not appropriate, and it only makes sense to apply it to low-decked bridges, as specified in [2,17,18].

The height of solid infill, in case of bridges over turbulent water or busy road or railway is defined in four of analysed manuals [2,17,18,25], while three of them, published by BHS [2,17,18] gives the same values between 0.6 m for watercourse crossings, 1.0 m for road and 1.8 m for railway crossings. In case of railway crossing the infill height of at least of 1.8 m is defined in [25] while for other crossing infill have to be 0.6 m in height. It can be concluded that manuals [2,17,18,25] only differ in defining the height of the infill at road crossings: 1.0 m [2,17,18] and 0.6 m [25]. An example of a bridge on an equestrian trail over a railway with full-height infill can be seen at [49], while in [50] the infill in the lower part of the parapet is visible.

All bridges without infill should have kickboards to prevent the risk of hooves slipping between the railing and decking. A height of 25 cm is specified in all analysed manuals addressing kickboard height [2,17,18,20,22].

Wide bridges with good visibility and a low deck height, according to manuals [2,17,18,20,22], do not require a parapet. The allowable deck height above an obstacle varies: 0.6 m [22] and 1 m [2,17,18,20]. Manuals [20,22] do not define the minimum width of a bridge without a parapet, which, in the author’s opinion, is a significant shortcoming, while manuals [2,17,18] specify a clear width of at least 4 m.

A high kerb should be installed on the sides of the deck without a parapet to prevent slipping and falling off the bridge, as occurred in [51]. The minimum height of the kerb is specified only in manual [23] as 20 cm. Examples of built bridges without parapets, equipped with kerbs, are: Stringer bridge for Eugene Parks, Oregon, USA; FRP I-beam stringer trail bridge for the Crater Lake National Park, Oregon USA; Cannan Valley I-Beam Stringer Bridge, West Virginia, USA [52].

Following previous discussions on specific design parameters for bridges on trails suitable for equestrian use, the best practices are highlighted:

• The absolute minimum clear width of the bridge is 1.5 m for single-line riding (preferable minimum 2 m), and 3 m for riding in pairs and passing. In areas with a high level of development, the desirable clear width ranges between 3.6 m and 4.6 m.
• The acceptable minimum clear height on the bridge for ridden horses is 3.7 m (allowable minimum is 3.4 m). The acceptable minimum clear height on the bridge when horses are led is 2.7 m.
• The ideal bridge slope is up to 5% (maximum 8.3%).
• The ideal bridge deck surface is rarely achievable; various techniques should be used to ensure a non-slip and non-echoing surface, as well as the use of new materials such as FRP and GRP.
• The ideal height of the equestrian parapet on bridges, which prevents a horse from jumping over and increases rider protection from falling, is 1.8 m (this can be reduced to 1.5 m when the bridge is short, low, and crosses a watercourse).
• A solid parapet infill of at least 1.8 m should be used on rail crossings, and at least 0.6 m at road and turbulent water crossings; in other cases, a kerb of at least 0.25 m should be installed on both sides of bridge deck.
• Only bridges wider than 4 m crossing a watercourse at a height of less than 1 m may have no parapets.
• All design procedures for pedestrian bridges should be applied when designing an equestrian bridge.
• Live uniform load should be applied as for pedestrian bridges; additionally, the bridge deck should be checked locally for peak force load from a single horse in trot/canter.

5.2. Discussion on Underpass Design Parameters

Manuals addressing the design of equestrian underpasses are much more limited than those for equestrian bridges (as can be seen from Table 2 and Table 3), although underpasses are favoured over bridges for grade-separated crossings of roads and railways. The following is a summary of general recommendations for the design of underpasses:

• Location and access routes should be carefully selected to ensure adequate sightlines and should be clear of overhanging vegetation;
• The best alignment of the subway to the obstacle is at right angles;
• The best cross-section of the underpass is box-shaped or square with a constant height to ensure sufficient vertical clearance across the full clear width of the underpass;
• The accumulation of water in the underpass should be prevented by good drainage;
• The mounting blocks and warning signs should be provided at both ends of the underpass if riders have to dismount and lead the horse through the underpass.

The specific recommendations for the design of subways for horses analysed in this paper include clearances, surfacing and lighting, and are summarised, compared and critically commented on below.

Most manuals define a vertical clearance for underpasses of 3.7 m or over [2,12,17,19,20,22,24], while some allow a reduction to 3.4 m [2,17,19,20,22] or even 3 m (as an absolute minimum) for riding horses. The greatest minimum height is prescribed in [12] as 4 m. According to manual [2], underpasses higher than 3 m provide additional clearance in case the horse spooks, jumps, or rears up. A clear height of 3 m provides a buffer zone of 0.5 m horse and rider height of 2.5 m, but this may be insufficient for tall riders on large horses [9]. Clearances greater than 3.7 m are desirable, not only to provide a buffer zone for all riders, but also because horses are reluctant to pass under low ceilings, especially in dark environments, as they have difficulty adjusting their vision from light to dark spaces [2]. If horses are led, the clear height can ideally be reduced to 2.7 m as defined in [24], which is in line with the clear height for led horses on bridges [13]. Although manuals [2,12] allow a height of only 2 m for led horses, the author believes that such a height should not be used because there is a significant risk of injury to horses, as the total height of a typical riding horse is about 2 m [12].

All manuals define a clear width of underpasses of 3 m or more [2,17,19,20,22,24], which allows two-way traffic and enough space for turning or driving in pairs. A minimum clear width of the underpass greater than 4 m [2], or a desirable width of 5 m [2,17,19], ensures comfortable passing, especially if the underpass is long.

The most detailed source regarding the definition of clearance for underpasses is manual [2], which prescribes different values for clear width and height (preferable, desirable, minimum, absolute minimum).

Forward visibility related to equestrian underpasses is not specified in any of the analysed manuals, but designers should note that at least 4 m should be provided at corners and changes in direction for pedestrians [24]. In the absence of prescribed visibility for equestrian underpasses, the recommendations for visibility at horse riding routes, junctions, and crossings defined in [24] may be applied.

Ideally, the same trail surface should continue into the underpass [12,22]. There are numerous examples of underpasses with surfaces identical to the trail, some of which are shown in [12,22]. Drainage should be provided with the minimum longitudinal slope defined in [24] as 0.7%, which is in line with the recommendation for a minimum longitudinal slope on bridges of 0.67%, to ensure adequate drainage [45].

There is no specific requirement for lighting of underpasses in the analysed manuals; only general remarks are given, which can be summarised as: sufficient natural or artificial lighting must be provided, especially if the underpasses are long and shallow. For additional information on underpass lighting, designers can refer to other literature such as BS 5489-1 [53], where details on underpass lighting are provided.

The best practices for specific design parameters of underpasses on trails suitable for equestrian use, as derived from the previous discussion, are outlined below:

• The acceptable minimum clear width is 3 m, which allows two-way traffic. Greater widths are desirable.
• The acceptable minimum clear height of an underpass for ridden horses is 3.7 m (the allowable minimum is 3.4 m). The acceptable minimum clear height when horses are led is 2.7 m.
• To ensure good drainage, the minimum longitudinal slope is 0.7%.
• Forward visibility must be ensured using the relevant domestic or international literature on underpass visibility.
• Sufficient natural or artificial lighting must be provided; the relevant domestic or international literature on underpass lighting is to be applied.

6. Conclusions

As mentioned in the introduction, the benefits of riding are numerous, but they can be summarised as improvements to social well-being, as well as mental and physical health. Areas with good networks of equestrian routes attract riders, contributing to the development of tourism in a region and boosting the local economy.

The most critical elements of equestrian routes are road, railway, and watercourse crossings. Bridges and underpasses at these crossings, suitable for equestrian use, must meet requirements that are not considered when planning bridges and underpasses not used by equestrians.

As presented in this paper, there is a lack of clear, standardised guidance for the design of equestrian bridges and underpasses, highlighting a current research gap. None of the analysed manuals provides a comprehensive guide to the main design parameters listed in Table 2 and Table 3, although it can be concluded that the most comprehensive manuals on the design of equestrian bridges are those published by the BHS, while for underpasses, the most comprehensive manual is the Horse Trail Infrastructure Guidelines for peri-urban precincts published by Horse SA, Australia.

This paper summarises, compares, and comments on the design parameters of equestrian bridges and underpasses that must be considered to achieve an optimal solution for horse and rider. It also provides an overview of general recommendations and best practices for specific design parameters.

In the absence of a manual providing comprehensive, standardised guidelines for the design of equestrian bridges and underpasses, this paper may assist policymakers, developers, and designers in creating a trail network suitable for equestrians.