Sustrans Design Manual Chapter 6 - Traffic free routes: detailed ...

1July 2014

Sustrans Design Manual Chapter 6

December 2014

Traffic free routes: detailed design (draft)Construction and ancillary details

Sustrans Design Manual • Chapter 6: Traffic free routes: detailed design (2014, draft)

2 December 2014

About SustransSustrans makes smarter travel choices possible, desirable and inevitable. We’re a leading UK charity enabling people to travel by foot, bike or public transport for more of the journeys we make every day. We work with families, communities, policy-makers and partner organisations so that people are able to choose healthier, cleaner and cheaper journeys, with better places and spaces to move through and live in.

It’s time we all began making smarter travel choices. Make your move and support Sustrans today. www.sustrans.org.uk

Head Office Sustrans 2 Cathedral Square College Green Bristol BS1 5DD

© Sustrans December 2014

Registered Charity No. 326550 (England and Wales) SC039263 (Scotland)

Photography: Sustrans or CTC Benchmarking unless noted otherwise

Issue level: 01

Owned by: NCN Director

Contact: [email protected]

ContentsThis chapter of the Sustrans Design Manual should be read in conjunction with Chapter 1 “Principles and processes for cycle friendly design.” That chapter includes key guidance on core design principles, whether to integrate with or segregate from motor traffic, the space required by cyclists and other road users as well as geometrical considerations. Readers are also directed towards the “Handbook for cycle-friendly design” which contains a concise illustrated compendium of the technical guidance contained in the Design Manual. This chapter has initially been issued as a draft and it is intended that it be reviewed during 2015; feedback on the content is invited and should be made by 31 May 2015 to [email protected]

1. Key principles

2. Introduction

3. Overview of path construction

4. Formation and sub base

Sub grade construction

Geotextiles

Sub base

5. Surfacing

Introduction

Sealed surfaces

Tar spray and chip surface dressing

Concrete surfaces and paviors

Unsealed surfaces

6. Path edges, verges, hedges and fencing

Kerbing and edges

Verges

Hedgerows

Fencing

7. Drainage

Surface drainage of path

Flooding

Ditches, filter drains, soakaways and culverts

8. References

Sustrans Design Manual • Chapter 6: Detailed design of traffic free routes (2014, draft)

3December 2014

1. Key principles

The following principles are key to effective construction and maintenance of traffic free routes:

• utility routes wholly in urban areas or within 5km of urban areas or 2km of a village environment should have a fully sealed surface. This should apply to main cycle corridors as well as feeder routes. Any route that has potential for school links or general utility use should be a sealed surface. Sealed surfaces are also required between villages, where school journeys are to be expected and will benefit

• sealed surfaces benefit a much wider range of user groups than just cyclists, opening up potential corridors for mobility impaired and parents with small children. Not only does this enable greater movement by these groups, but in many cases it leads to a better quality of life

• machine laid surfaces provide better comfort for cyclists and wheel chair users. Hand laying creates an uneven surface which can be subject to standing water and lead to greater maintenance requirements

• kerbs should be flush (maximum +/- 6mm upstand). Channel blocks laid flush are recommended and drainage must be adequate

• drainage provision should be adequately provided for lateral and longitudinal water movement. Slopes in excess of 1 in 20 (5%) will increase surface water run off. This is not appropriate for unsealed surfaces due to water erosion

• verges should be finished lower than the path edge. This allows for any surface water run off to collect away from the path

• construction and maintenance access can affect the construction specification; access points to some paths may require material to be moved several hundred metres along the path by construction or maintenance vehicles

• new boundary fences should be set back from the path edge, as a minimum 1.0m. Vegetation and new hedge lines should be set back by at least 1.0m, and always allow room for growth. The areas immediately adjacent to the path should be free from tall grasses and vegetation that can impact upon visibility or reduce the overall usable width of the path

• a pre-completion audit should be used to identify and address any construction deficiencies. Involving the design and construction teams in a ride-through audit can improve future scheme delivery

• prior to construction responsibilities and requirements regarding maintenance regimes should be defined, with a clear management plan put in place. Allow for regular visits and include inspections of access controls, lighting, signing, verges, fencing and litter. A well managed path will become an asset and be popular with the public


4 December 2014

2. Introduction2.1Traffic free routes should deliver high standards of all of the five user requirements: coherence, directness, safety, comfort and attractiveness. Adaptability should also be considered with regards to future growth in user numbers. This is vital for routes that involve new structures.

2.2Construction quality and quality of maintenance has a strong influence on cyclists speed and delay (directness). Infrastructure must be maintained to a high base level and remain fit for purpose.

2.3The attention to detail in the design process and the quality of materials and construction will have a direct impact upon the levels of use and the future maintenance costs incurred.

2.4Investment in infrastructure (design, construction and marketing) represents poor value for money if design details or deficient maintenance deter usage - even if other elements of the facility are exemplary. Common examples of construction features which undermine otherwise good routes include poor surfacing or drainage; upstands at dropped kerbs, or failure of the path surface after winter conditions.

2.5Successful traffic free routes require proper consideration of each element of the construction. These are:

• formation and sub-base

• surfaces

• edges and verges

• ecology

• drainage

• ancillary works, such as lighting, fencing, access controls and landscape features

2.6This chapter describes construction requirements for high quality traffic free walking and cycling routes. Chapter 5 provides guidance on best practice in the design of traffic free routes. Maintenance is also a key consideration, which is covered in Chapter 15.

2.7Ecological considerations may affect the timing and methods of construction used. Extra measures may be required to avoid impacting on wildlife and to reduce or compensate for the impact when unavoidable.

2.8Whilst machinery is on site it is easier to undertake habitat enhancements such as pond scrapes in the wider verges to make routes better for wildlife.


5December 2014

3.2Specification of the appropriate capping/subgrade, geotextile materials and sub base thickness will need to respond to the local ground conditions, i.e. the type, stability and moisture content of the soil or rock on which the path is constructed. Sub grade stabilisation, more robust geotextile materials and a thicker sub base may be required where ground conditions are poor.

3.3A sealed surface should be specified in all but exceptional circumstances. This comprises a base (binder) course plus an optional wearing course or surface dressing.

Wearing course (asphalt concrete) - typically 30-40mm thick, 6mm or 10mm stone (AC6 or AC10)

Base (binder) course - typically 60-80mm thick, 14, 20 or 28mm stone size (AC14 / AC20 / AC28) - 14mm or 20mm preferred stone size, depending upon whether wearing course is to be included

Sub base - typically 150-225mm thick layer of crushed stone to Dept for Transport specification. Crushed limestone with maximum stone size of 37mm is generally used and classed as DoT Type 1

Geotextile layer - can be a weed control membrane where underlying ground conditions are strong enough to support path construction. Poor ground may require geo-textile or geo-grid layer.

Capping/sub grade may be necessary where route encounters poor ground / contaminated material. Generally 300-600mm of clean inert material (clay based)

sub

gra

de

Pav

emen

t d

epth Fig 3.1 Typical path construction

2.9Disturbance to wildlife can be reduced by undertaking works at the correct time of year. This will vary depending upon the nature of the habitat and the species present or affected.

2.10For clarity, ‘path’ is used in this guidance to refer to traffic free routes used by pedestrians and cyclists, whether segregated or unsegregated, although technically many of these will have the legal status of a cycle track, albeit with a right of way on foot.

3. Overview of path construction3.1The layers of specified materials which make up a road or traffic free route are referred to as “depth of construction” or “pavement depth”. Figure 3.1 illustrates the typical construction layers that should be used in most circumstances to construct traffic free routes for cyclists and pedestrians. Equestrians may dislike a sealed wearing course, preferring a parallel earth route or user specified path surface.


6 December 2014

3.4The following options are appropriate to form the sealed surface:

• construction using two layers of surfacing (binder and wearing course). Use of a wearing course will provide a higher quality of finish

• single layer construction: a binder course using 14mm stone size (AC14) laid at a depth of 80mm will give a very good surface and can negate the need for a wearing course layer

• construction using 20mm stone size (AC20) for the binder course will require either a surface dressing or a wearing course. AC28 binder course on its own will be unacceptably “open textured”. Consider use of a surface dressing where equestrian use is to be expected

3.5Guidance on each construction layer is provided in the following chapters.

4. Formation and sub baseSub grade construction4.1The sub grade (also referred to as formation level) is the native ground material underneath a constructed road or path. It is commonly mechanically compacted and may need to be further stabilised by the addition of imported materials. The sub grade is the foundation of the ‘pavement’ structure, on which the sub base is laid.

4.2Path construction involves excavating to reach good quality strong ground that can form a stable sub grade. The strength of the subgrade must be sufficient to support the loadings of the intended users and any subsequent maintenance vehicles. The load-bearing strength of any underlying soils which comprise the sub grade is measured by California Bearing Ratio (CBR) test or other geotechnical tests.

4.3Loadings imposed by cycles and pedestrian use are much lower than motorised traffic, but use by maintenance vehicles should also be designed for. Lighting especially may require larger or heavier vehicles to install or maintain lanterns.

4.4Excavating a formation will create a flat U shape, called a formation tray, with vertical sides.

4.5In good ground conditions, excavating to reach strong sub grade material may only require removal of 50mm of top soils to create a suitable formation level. However, it is essential to remove all surface vegetation prior to construction because organic materials will decompose over time and this can lead to voids and settlement of the path.

Imported fill material to be inert and of consistent size. Material classed as DfT Type 6F1 or 6F2 is generally acceptable, Sheffield

Sub grade excavation to create a flat U or “formation tray”, Watton


7December 2014

4.6Excavating beyond a depth of 200mm will require a geotextile material to support the base of the path.

4.7Made ground is a very weak mix of materials with little structural integrity and removal is the most realistic solution.

4.8Excavated topsoil should be retained on site (along with any suitable made ground). Any excavated soils can be re-used around the path edges once the path construction is complete. Disposal of soils off site incurs transport costs and payment of landfill tax.

4.9Where paths are constructed over land that is contaminated, excavating should be avoided. Path levels should be raised if it is not possible to avoid the contaminated area.

4.10For routes constructed through ecologically sensitive woodland or around specimen trees a ‘no-dig’ construction method should be considered.

Geotextiles4.11Geotextile materials give added strength to poor sub grade ground conditions (typically soils with high clay levels) and can give added stability.

4.12Geotextiles are usually puncture resistant and have a nominal tensile strength that can help to spread the loads of construction and path users. Some types are also valuable as a weed-control barrier.

4.13Geotextiles come in several forms including:

• non-woven felts (Terram);

• woven polypropylenes (Autoway/LoTrak);

• more rigid grid systems in a plastic mesh (Netpave/Netlon/Tensar)

4.14Medium grade materials are capable of managing loadings generally associated with traffic free routes.

4.15Non-woven felt geo-textiles are also useful as a weed control barrier, and can be of great use on routes that have generally good or stable ground conditions.

4.16Woven polypropylene materials tend to be in 100m x 5m rolls. This is ideal for 3m wide paths, where the additional geotextile material on each side of the path is re-covered with as-dug materials. All rolls should overlap by 1m and all joints be taped together.

Access roads built on linear traffic free routes with material that is retained as a good quality base layer for path, Derry

Woven geotextile being rolled out along a path, with a secondary layer of geogrid laid on top, Maryport

Poor ground conditions require several layers of geogrid to be rolled out and filled with locally sourced shingle, Hastings

A strengthened footway alongside allotments can give added parking provision – keeping the main route clear for cyclists, Royston


8 December 2014

4.17Table 4.1 looks at the most common formation types, and lists geotextile options that may be appropriate. It is intended to assist designers to make an initial presumption, but all new paths will require CBR tests to determine the exact requirements.

Table 4.1 Geotextile requirements

Formation description

Test Likely CBR*

Geo-textile requirements Sub base depth

Railway path with ballast in-situ

Visual +10 Not required to stabilise subgrade, but a geomembrane may be desirable as a weed control barrier

Min 50mm

Railway path no ballast but ash/ clinker present

Visual +10 Not required to stabilise subgrade, but a geomembrane may be desirable as a weed control barrier

Min 150mm

Glacial till / free draining sands and gravels

No heel print, no standing water, little or no topsoils

6-10 Not required to stabilise subgrade, but a geomembrane may be desirable as a weed control barrier

Min 150mm

Firm well drained granular soils, parkland, agricultural fields

As above but topsoil may increase to 150mm

6-10 Not required to stabilise subgrade, but a geomembrane may be desirable as a weed control barrier

Min 150mm

Granular soils with high clay content, hard when dry, soft when wet

Medium – large heel marks depending on how wet soils are.

3-6 Yes Min 150mm – may need to increase to 225mm

Clay with minimal granular Material (Heavy Clay)

Large heel marks unless very dry. Test in wet conditions to avoid under estimating

1-3 Yes Min 225mm

Peats with minimal granular Materials, wetland areas

Visual; little or no supporting loads

1-2 Yes 300-500mm rock base with min 150mm sub base. Structural solution may be needed

The above table gives a simple guide to an initial assessment of ground conditions, but this should not inform final design.

Geotechnical investigations, and CBR testing, are required to enable an appropriate construction specification to be determined.

* Higher CBR values indicate greater bearing strength


9December 2014

Sub base4.18The sub base is the main load-bearing layer within the path construction and its role is to spread the load evenly over the sub grade.

4.19The thickness of sub base required depends on underlying ground conditions and the vehicle loading expected. Walking and cycling movements generate small loadings. However, all routes will require maintenance and construction specifications should allow for light vehicle use.

4.20A sub base thickness of 150 mm is typical for traffic free routes on many soils (Table 4.1). However, different ground conditions can require sub base thicknesses ranging from 50mm (on existing railway ballast) to 225mm or greater (on clay soils).

4.21Use of geogrids can reduce the thickness of sub base layers needed because the geogrid will increase the ability of the existing ground to support the weight of the construction.

4.22The quality of sub base is very important for the useful life of the path. A properly constructed sub base layer will aid drainage and prevent uneven settlement. Inadequate depth or quality of the sub base will have a detrimental effect on the ride comfort and longevity of the surface layer.

4.23The most common form of sub base is Department for Transport (DfT) Type 1 (a granular material to the DfT Specification of Highway Works). Limestone and Gritstone are popular choices.

4.24Material should be from a recognised source and comprise a mix of lumps (stone) and fines (dust). Stone size should be a maximum of 37.5mm.

4.25Minimum sub base layers should be at least twice the size of the largest particle. A 37.5mm stone requires a minimum sub base thickness of 75mm or greater. This ensures that no particle can contact top and bottom of each layer, which would reduce the interlocking nature of the stone and create potential weak points.

4.26A finished sub base layer should be within 10mm tolerance of the finished level and reflect the final paving layers.

4.27Sub base layers need compaction. A compacted layer of 150mm thick sub base requires an initial layer approximately 200mm thick. 1 Tonne of material will cover roughly 3.5m² at a compacted depth of 150mm.

Sub base with geogrid to give added strength and a minimal amount of excavation, Crewe

If kerbing is needed it should be installed before sub base is laid, Worcester

Paths can consist of a variety of solutions. This section of sub base stands in isolation – raised boardwalks continue the route across floodplain, Newport


10 December 2014

4.28Vibrating rollers will give better compaction than a hand operated ‘wacker plate’ or vibrating plate. There are certain situations where the use of a vibrating roller is not acceptable, immediately adjacent to or on bridge decks, canal towpaths, river side paths and other vulnerable locations, such as badger setts, properties or some embankment edges.

4.29Larger rollers will need to make fewer runs (passes) over the sub base to achieve maximum compaction. A roller between 2.3- 3.6T will need 5 passes to create a compacted 150mm layer.

4.30Different sub base materials have different pH values (acidity/alkalinity). Designers should check local soils, and ecological constraints, before specifying a particular material. This will prevent any changes to the natural pH of the soil that can occur through rainwater leaching through the sub base.

4.31In remote areas, or distant from path access points, construction access paths may be required for heavy vehicles. Suitable imported rock material used for construction access paths can be re-graded and used to form a substantial sub base layer for a new route.

4.32Disused road alignments can be incorporated into new path construction. Scraping back vegetation and punching through the disused road surfacing to provide drainage can give a good base layer. In some cases simply re-surfacing can be the appropriate option.

Although still a construction site, rolled sub base will enable cycles to be ridden rather than walked during an inspection prior to surfacing, Hamilton

Bridge access ramps require sub base to be laid and compacted, Omagh

Formwork installed for areas that require concrete surfacing, Maryport


11December 2014

Table 5.1 Path construction requirements, unsegregated shared use

Nature of route

Type of surface

Urban traffic free

Sealed surface imperative

Surface dressed top to bitumen base course may be appropriate

Urban fringe / semi rural traffic free

Sealed surface imperative


Rural traffic free

Sealed surface required on any route within 5km of urban area or 2km of village environment

Sealed surface required on routes linking villages where school traffic or other utility trips will benefit.


Use of unsealed surface requires a rigid maintenance plan

Use of unsealed surface not recommended on paths:

• with gradient steeper than 1 in 20

• shared with equestrians

• where significant run off expected

5. SurfacingIntroduction5.1Experience of maintaining sections of the National Cycle Network indicates that routes constructed with a sealed surface give better performance and reduced whole-life maintenance costs than an unsealed surface. Recommendations on surface requirements are shown in Table 5.1.

5.2Initial concerns about use of tarmac surfacing in the countryside, rarely continue to be an issue once a path is finished and open. If necessary paths can be surface dressed with appropriate materials, or different coloured tarmac can be used.


12 December 2014

Sealed surfaces5.3A sealed surface is an impermeable layer, or layers, primarily of bitumen-based tarmac or asphalt material.

5.4Machine-laid sealed surfaces provide better ride comfort than unsealed surfaces, with less unevenness and lower rolling resistance. The benefits are most marked in wet or winter conditions when unsealed surfaces can become soft, uneven and poorly drained. Sealed surfaces benefit pedestrian and mobility impaired users, as well as cyclists, and will tend to generate greater levels of use by all groups.

5.5Different options exist for constructing the wearing (surface) course for sealed surface paths:

• Two-layer surfacing comprising a binder course (60mm depth AC201) overlain by a finer surface course (a 20mm layer of AC62 or AC10, or alternatively surface dressing) See Figure 2. This provides a very smooth surface and may be local authority policy, or desirable for comfort and aesthetic purposes. However, two-layer construction incurs additional construction cost.

• Single-layer surfacing comprising a thicker base layer, up to 80mm thick, of AC14 (asphalt concrete with a 14mm stone size). This provides adequate ride comfort in most situations and reduces construction costs compared to two-layer construction. AC14 is now generally specified in preference to AC20 for the single layer surfacing construction because it provides a much tighter bound material and a smoother ride.

5.6All sealed surfaces should be machine laid as this gives a much more even surface with better ride comfort and better drainage than using a hand laid approach. It is nearly always possible to gain access for a paving machine, even for constrained working areas and sites with longitudinal constraints.

5.7Sealed surfaces are achievable in a variety of locations, which may initially provoke concerns, such as SSSIs, riverbanks and nature reserves.

5.8A sealed surface is often the better solution. Maintenance works are often less and a fully sealed surface from the outset results in less long term disturbance to the to the local environment. Always liaise with the relevant body, but starting with a sealed surface is often the best option.

1Asphalt Concrete with a 20mm stone size

2Asphalt Concrete with a 6mm stone size

Alongside the River Nene, Northampton

Edge of SSSI, Weymouth

Wooded area Local Nature Reserve, Norwich


13December 2014

0.3m

1.0m mown verge to

fence / building line

Machine laid 3.0m width sealed surface. Widen on

busy routes

Crossfall 1/40

Optional 300mm wide x 600mm deep stone filled trench

Finished soil levels to fall from path edge. Material to be locally dug. Nutrient poor soil will improve conditions for establishing wild flowers

20mm layer AC6 or AC10 surface course, machine laid(Optional - binder course can be surface dressed instead)

150mm Type 1 sub-base increased to 225mm where necessary

60mm minimum layer machine laid AC20 binder course

Geotextile for filter or strength purpose - to extend 500mm beyond edge of sub base

Fig 5.1 Path construction

37.5mm on 3m wide path

1/40 1/40

1/40 camber to be central, giving 37.5mm fall to each side of carriagewayAlternative option

with camber

Not to Scale

Verge planting must use species that maintain visibility and avoid root damage

Tar spray and chip surface dressing5.9Single layer surfacing dressed with tar spray and chip will soften the colour of a newly laid tarmac path, especially in sensitive areas where there is a desire to avoid “a black stripe”. Successful application of surface dressing can give added longevity, protection from water damage and provide added skid resistance compared to an unsealed surface using local stone.

5.10Achieving a quality solution requires contractors to adopt specific procedures, outined below, and the engineer should ensure that the contractor employed to undertake the works has a record of working with this solution. Successful application is limited to working at certain times of the year and in favourable weather conditions.

5.11Application on traffic free routes should ensure that the amount of chippings is not over-specified. On roads, vehicle movements help to embed the chippings, but on traffic free routes it may take several months to achieve the same result.

Natural vegetation will grow anywhere. Nettles, brambles and tall scrub has a value away from the immediate verges


14 December 2014

Criteria for successful application of surface dressing

• use a 6mm rounded stone

• Undertake works between May – July

• during favourable (warm and dry) weather conditions, works may be possible in April and August (late April working may not give optimum daylight or warmth, but work will benefit from summer months to help embed chippings, when path use may also be greater. Beyond mid-August both daylight and temperature are reducing, and will hinder the embedding process)

• moisture, both on the path surface and in the air, can affect how well the process works. Paths must be dry

• paths must be clear of any debris, vegetation and leaf fall

• the specified viscosity of the binder should not be changed to extend working conditions, or to try to compensate for the weather. Too much binder (to extend working conditions) can be problematic during summer months when chippings are more susceptible to loosening and wearing away

5.12The images below show the results of not implementing the surface dressing processes correctly. Surface dressing is beginning to wear away, resulting in a poor finish.

Path soon after application

Path after six months


15December 2014

Concrete surfaces and paviours5.13Concrete is very durable in a variety of environments and is an effective solution where traffic free routes are likely to be used or crossed by larger vehicles. Typical urban situations are service yards and maintenance paths, and in rural areas where a route is used by farm traffic.

5.14Provided precast slabs and joints are flush and in good condition, concrete can give adequate ride comfort, but surface markings tend not to be clearly visible because of low colour contrast.

5.15Avoid a tamped finish to concrete as this creates a very uneven and uncomfortable surface for cyclists. Brushed finishes are preferred.

Concrete track used by farm vehicles, Kenilworth Concrete at farm access crossing path, Caerleon

5.16Concrete block paving can be suitable for cycling, and use of different colour/size/orientation of the blocks can be used to mark a cycle route across a larger paved area without the use of a level difference. Edge restraint is needed to prevent separation of blocks.

5.17Concrete paving slabs/flags are not generally suitable as a cycling surface because of lower wet skid resistance and risks of trips and rocking.

Concrete block paving in traffic free area, Port Talbot

Concrete block paving across vehicular access, Bury Green


16 December 2014

Unsealed surfaces5.18Many traffic free routes have been constructed historically with unsealed surfaces because this involves lower construction costs than sealed surface construction and is considered less visually intrusive and more in keeping with rural environments. Unbound surfaces also tolerate some ground movement without cracking.

5.19However, there are overriding disadvantages to unbound surfaces which should preclude their use except as a measure of last resort. These disadvantages are:

• ride quality is poorer on unbound surfaces than sealed surfaces, particularly in wet weather. Skid resistance is reduced which increases sight stopping distance. The surfaces are dusty in dry weather and generate a mud spray when wet

• limestone, self-binding gravels and re-cycled materials are prone to erosion by general use, rainwater, horse traffic and motorcycles. Erosion is particularly common on gradients. Levels of maintenance required are greater which will require more frequent access by contractors’ vehicles and temporary path closure

• whole-life costs are greater than for a comparable sealed surface path

• paths built originally in limestone dust have required re-construction with a bitumen surface. This reduces funding available to develop new sections of network

5.20Sustrans, in conjunction with several local authorities, has trailed alternative surfaces such as “Toptrek”, “Finepath”, “Cedec” and “Consolid”. An update of Sustrans Technical Note 8 will be available for download in early 2015.

5.21Designers should fully explore all other funding, alignment and land issues before contemplating an unbound surface as a solution. Designers are requested to seek guidance from Sustrans Engineering team on the suitability for any new surface type before specification/construction.

Damage to unsealed path through horse use

Damage to unsealed path through longitudinal drainage run off


17December 2014

6. Path edges, verges, hedges and fencingKerbing and edges6.1In most situations, traffic free routes do not require kerbing or other edge restraint. Instead, the path is constructed so that the sub base extends around 300mm beyond the surface course on each side and finished soil levels fall away from the path edge to aid drainage. A stone trench can also be used along the path margins to further facilitate drainage.

6.2This form of construction without edge restraint is illustrated in Figure 5.1 and following photographs:

6.3Parapets to bridges and structural walls also form path edges. These are dealt with in Chapter 8.

6.4Many low flow/low speed rural roads also use verges without kerbing.

Country lane in Somerset Country lane in Cheshire (anti skid surface added to aid horses)

Newton Abbey Bury

Kenilworth


18 December 2014

6.5Any edge treatment will increase the overall construction cost. Pre-cast concrete kerbing approximately doubles the cost of a path, due to the need for concrete footings and installation as well as the kerbs.

6.6Table 6.1 identifies reasons why kerbs are used for highway construction but generally are not needed for traffic free routes.

Table 6.1 Reasons why kerbs are generally not needed for traffic free routes

Reason why kerbs are required for highway construction

Reasons for not installing kerbs on traffic free paths

To retain the carriageway edge and prevent structural failure

Path construction depth is less, speeds and loading generated by pedestrians and cycles are less. Damage to the path edge and structural failure is unlikely

As a demarcation barrier between vehicles and pedestrians.

Traffic free routes, by their name, are routes free from vehicles. Pedestrians and cyclists are encouraged to mix freely. The is no need for formal demarcation

To prevent vehicles from leaving the carriageway

Pedestrians are not going to fall off a traffic free path into an oncoming vehicle. Cycle speeds are significantly lower than vehicles

To enable surface water to be drained from the carriageway

Paths without formal kerb edges allow surface water to percolate into the verge and are less likely to create flooding / ponding

6.7Kerb edgings to paths can be appropriate under certain circumstances, such as through formal parks or where there is a need to link into the highway or formal public realm. Routes that run parallel to rivers and watercourses are prone to flooding, and in these situations kerb edges will prevent wash out of supporting material and extensive damage to a path.

St Columbs Park, Derry River Monnow, Monmouth


19December 2014

Verges6.8Constructing new paths commonly requires the forming of new side slopes, particularly on falling ground. To ensure stability, these should not exceed a 1 in 2 slope (batter). Planting these slopes with low maintenance vegetation can ensure stability as the root systems will help bind soils together. Thorny species such as gorses and tall scrubby vegetation should be avoided.

6.9Verges on a traffic free route provide the immediate environment through which users walk or cycle and are a key determinant of the visual interest and wildlife value of a traffic free corridor.

6.10Mown edges prevent the vegetation encroaching and reducing the effective width of the path. The remainder of the verge can be managed, more or less intensively, to create a variety of habitats appropriate to the location and the resources available.

6.11Mown edges which prevent vegetation encroaching on the path. Note that the continuous scrub undergrowth offers little variety or biodiversity.

6.12Sustrans Ecology Note 02 describes the management of the immediate mown path edge and the various options for the remainder of the verge width.

Mosaics of scrub, tall rank vegetation and grassland


20 December 2014

Hedgerows6.13Hedgerows can provide an attractive bounding feature for rural and semi-rural traffic free routes and can offer protection from wind.

6.14Existing hedgerows can be reinvigorated by removing dead wood, brambles and unwanted species to encourage new growth. Hedgerows that have become ‘gappy’ can be re-planted with a variety of non-thorny species. Hazel, elm, oak and field maple are ideal. Thorny species such as hawthorn, dog rose or gorse should generally be avoided and, if used, will require planting further back from the path edge.

6.15Refer to Sustrans Technical Information Note E 01 “Hedgerow Management” for further guidance.

A new field path set behind a hedge. Wide

verges allow for growth of the existing and new

hedges, Carlton le Moorland, Lincs

A new path may disturb an existing hedgeline. Tidying

and re-shaping can give added ecological

benefits, Northampton

Training volunteers to help maintain hedges and paths can ensure

that a route remains usable


21December 2014

FencingFunction6.16Fencing may be required along one or both sides of a traffic free route to ensure:

• Safety of path users

• Security of neighbours; and/or

• Livestock control

6.17Wherever possible, paths should be unfenced. This will provide a more open visual aspect, lessen concerns about personal security of path users, and reduce construction and maintenance costs.

Access points6.18Fencing also reduces accessibility to journey attractors along a route. Access points to the road network and connecting traffic free routes should be maximised and clearly signed, and wherever possible direct accesses into adjacent premises should be sought.

Fence line position6.19Fencing or building lines positioned directly along a path edge reduce the effective width of a path and creates an enclosed feel. Wherever possible, fence lines should be set back at least 1m from the path edge to minimise the tunnel-like appearance of a path. This is particularly important where fencing is required on both sides of a route. Verges will allow space for drainage and, if necessary, ducting for lighting. Increasing the set back to fencing or building lines can accommodate landscaping, which will contribute to visual interest and maximise the route’s value as a wildlife corridor.

6.20As a minimum, fencing should be set back 500mm from the path edge to avoid reducing the effective width of the path. Fencing positioned hard up against both sides of a path reduces the effective width of the path by 1m (or 0.5m for fencing on one side only)3. Where a new fence has to be installed with no clearance from a path margin, the path should be repositioned or widened by at least 500mm.

Type and height of fencing6.21Fencing should be as visually unobtrusive as possible. Under most circumstances 1.5m high fencing is adequate for users’ safety and to control stock. Adult cyclists and pedestrians will be able to see over 1.5m high fencing and the negative aesthetic impact and sense of enclosure with be minimised.

6.22Timber post-and-rail stock proof fencing is often preferred by landowners, but this can be more than is required for safety or livestock control. Post and wire provision is often all that is necessary.

6.23Security fencing can be unattractive and oppressive and traffic free routes through urban areas can quickly become enclosed for considerable distances. Where adjoining premises require security, weld mesh designs are a good alternative to palisade fencing. Weld mesh fencing is largely un-climbable and is widely used throughout the UK.

3 Vertical features greater than 600mm high reduce the effective width of a path by 500mm; upstands between 150mm and 600mm reduce effective width by 250mm; a kerb upstand of 150mm reduces the effective width by 200mm (Source: LTN 1/12)

Post and wire fencing separating path from farmland is set back from track edge, Glais, Clydach

Path alignment positioned away from adjacent embankment to remove the need for fencing along the embankment side, Cwm Ogwr, S Wales


22 December 2014

Corridor effect created by fence lines close to path, Huyton, Merseyside

Palisade fencing around industrial sites set back from path, Blyth, Northumberland

6.24Buildings and fence-lines can become prone to vandalism and graffiti. Swift repair as soon as the problem is reported will help to reduce negative safety and personal security perceptions and help to prevent reoccurrence.

6.25Fencing or guard rail can be used to channel people away from hazards, steep gradients, or to ensure that they use designated crossing points in urban areas. Fencing should be sensitive to the local environment, and only where essential should it cause people to deviate significantly from their desire lines.

6.26Security fencing can be unattractive and oppressive and traffic free routes through urban areas can quickly become enclosed for considerable distances. Where adjoining premises require security, weld mesh designs are a good alternative to palisade fencing. Weld mesh fencing is largely un-climbable and is widely used throughout the UK.

6.27Designs should avoid creating a path hemmed in between fence lines; it reduces the effective width for all users, creating conflict and is aesthetically poor. The redevelopment of adjacent land may necessitate temporary fencing adjacent to a path but the completed solution should then minimise fencing and set any fencing back at least 1m from the path.

6.28Fencing can also restrict the movement of wildlife in both urban and rural environments. Consideration should be given to including gaps under fencing to allow animals such as hedgehogs to move freely across the landscape.

Ottery St Mary, Devon Rugby


23December 2014

Fencing alongside rail network6.29Network Rail requires a minimum clearance of 4m from an operational railway line. In urban areas, palisade fencing is commonly used to prevent access to the railway, but examples exist of lower level fencing in urban areas (see Derby example below). In rural areas, less intrusive fencing designs (for example timber post and wire fencing), are common along railway corridors.

6.30Weldmesh fencing is largely un-climbable and has better aesthetics than palisade fencing. Treforest (left), Openshaw, Spen Valley Way (right).

Bermondsey - palisade fencing between a traffic free route and the railway. The lower level fencing used in Derby (right) is a more attractive solution

Derby – low level fencing separating cycle path from the railway improves views

Routes alongside rivers and canals6.31Routes alongside rivers and canals may need edge protection to safeguard users from falling into water. This may include fencing.

6.32The need for fencing will be determined by the speed of water, depth of watercourses, nature of ground, height differential and gradient of channel, path width and volume of users. Many paths alongside streams have operated successfully for many years without a requirement for fences.

6.33Protection is merited where water is fast flowing or deep or the channel is steep-sided or has a rock base. Some rivers, especially in urban areas were artificially dredged over many years of industrial use. This can create very fast flows, often within tidal sections of a river, and fencing is a necessity to prevent accidents by route users. These locations often have plenty of level public space that is already successfully operating as shared use space.

6.34To remove the need for fencing, the preferred options are:

• to widen or set the path back from the water’s edge; and / or

• where there is space, to grade banks alongside rivers to roughly 1 in 5 or shallower. It may also be appropriate to shelve the first metre of river bed. Planting with reeds will also help break a fall. In these situations consultation and approval of the Environment Agency may be necessary

Openshaw, North Yorks - Spen Valley Way


24 December 2014

6.35Fencing alongside rivers should be set back sufficiently from the path edge to maximise the usable width of the path. This can be difficult to achieve if a path alignment is close to the bank edge.

6.36Railings which curve upwards and away from the water are used in some locations to discourage people climbing over them, or for heritage or aesthetic reasons. However, this can reduce the effective path width by up to 500mm. Path widening, wherever possible, is required to mitigate this.

6.37Effective fencing requirements may only be for a timber ‘knee rail fence’. Visually this can be enough to act as a warning / reminder to users.

Leeds – fencing above steep bank

Newtonabbey, N Ireland – fence between narrow path and steep sided river

Birmingham - fencing between narrow path and steep sided canal

Worcester – curved railings reduce effective path width


25December 2014

South Wales – fence set back from path edge to maximise effective width

Newcastle upon Tyne – fence along wide shared use riverside promenade

Salisbury – path without edge protection alongside slow moving water course

River Dour, Dover - path without edge protection alongside slow moving water

River Weaver, Northwich – path without fencing alongside gently sloping bank

Southampton - widened path without edge protection alongside slow moving water

Grand Union Canal, Leicester – verge forms edge protection

Newtonabbey, N Ireland - path with wide verge forming edge protection


26 December 2014

7. DrainageSurface drainage of the path7.1 Standing and surface water run off can seriously damage a path surface, leading to a rapid decline in its usability. Sealed surfaces are less likely to suffer these effects and are re-usable immediately once flood water recedes. Moving water efficiently off and away from a path will increase its longevity, reduce maintenance requirements and encourage greater user numbers.

7.2Paths should be constructed with a cross fall or camber of at least 1:40 to shed water laterally. This approach minimises the depth and energy of flowing water, thereby minimising the potential for erosive scour. On short sections it may be preferable for paths to fall to either side of the centre. In some situations it may be appropriate to construct the lateral fall on the path to alternate the side to which water is shed along a route.

7.3Machine laid paths will shed water better than hand laid surfaces, which tend to give uneven surfaces, resulting in areas of standing water. Sealed surfaces are more resilient than an unbound surface material.

7.4The drainage system may need to extend beyond the immediate edges of a new path to be effective.

7.5A path should always fall from its outer edge to the inside on bends. This reduces the risk of a cyclist being affected by an adverse camber. Crossfalls should be no steeper than necessary to enable a path to drain freely. Beware of creating localised ponding adjacent to a path edge, as this may lead to flooding, ice and mud on a path surface. Where possible leave a wider verge area and introduce a shallow scrape in the ground to act as a storage area.

7.6Falls of 1:120 longitudinally are preferred. Long straight sections of route on gradients steeper than 1:50 can generate water movement along the path. In such cases water volume and energy build up along the path can increase the risk of damage.

7.7Designs should avoid creating a path that is lower than the adjacent ground on all sides, as water will tend to drain onto the path with no potential escape route. Excavated soils should not be deposited as a continuous bund alongside a path as this may also prevent paths from draining effectively.

7.8Drainage gullies on a sealed surface path should be set flush with the final surface. Gully grates need consideration; a slotted grate set at right angles to the cycle direction of travel will not catch cycle/buggy or mobility scooter tyres. Grid or pedestrian friendly style covers are also acceptable.


27December 2014

Flooding7.9Occasional flooding need not be a major problem, provided the path is constructed to withstand inundation. A path that floods 5 to 10 days a year is acceptable, and even 20 days a year may be preferable to no path at all. Suitable diversion routes need to be identified and coherently signed.

7.10The construction specification is crucial in determining the extent of any damage and the speed at which a path can be re-opened. Waterside paths that suffer flooding, or excessive run off are easily eroded if the specification is too light, or is of unsuitable material. Unbound paths are easily destroyed; tarmac ones are resilient.

7.11Constructing a path on a causeway can be beneficial in areas that are liable to flooding or have wet or damp ground conditions. Raising the path level by 150mm may be sufficient to ensure that the path remains dry for longer and, as flood waters recede, can be used again sooner.

7.12Where a path crosses a river or stream floodplain, raising the level of a path could impact on the drainage and flood storage capacity of the wider area. Proposals to raise the level of a path by even a small amount should be discussed with the Environment Agency (EA).

7.13Paths that traverse wetland or ecologically sensitive areas may not permit changes to existing water levels. This is because of the damage that could be inflicted on sensitive flora and fauna. Always seek advice to minimise damage in these areas.

7.14Ditches and drainage channels may not be appropriate solutions. Instead, building paths on causeways or constructing boardwalks may be necessary.

Ditches, filter drains, soakaways and culverts7.15The drainage design should consider where rainfall run-off can be discharged, to avoid creating localised flooding or exacerbating problems elsewhere.

7.16Designs should avoid increasing surface water flows across neighbouring land. Ditches and drainage channels are used to collect run-off from a path and channel it into an existing stream or watercourse. This is the simplest and most common approach. However, designs should avoid diverting and concentrating run-off into water courses where this may create problems downstream.

7.17Where possible, designs should aim to increase local water storage and reduce discharge rates. Soakaways help to reduce discharge rates by allowing water to percolate gradually directly into the sub strata.


28 December 2014

7.18If there is scope to create a wetland area, this can give added interest to a path, but designers should safeguard against leaching soils and changing local pH (acidity) values. It is advisable to talk to the wildlife experts within local authorities and the EA.

7.19Paths that traverse wetland, or ecologically sensitive areas may not permit changes to existing water levels as this may harm sensitive flora and fauna. Ditches and drainage channels should be avoided in these environments; instead building paths on causeways will be more appropriate.

7.20Ditches and filter drains are two alternative options to channel surface run-off into existing watercourses.

7.21Open ditches or drainage swales are more natural in appearance than filter drains. Ditches are easier to clean and maintain. Maintenance of ditches typically comprises removal of loose material monthly, plus removing larger material and checking sides are stable twice a year. Key design considerations are:

• a V-section with 45º sides 300-450mm deep is preferred, but U sections are accepted where space is at a premium. Smooth beds generate even and unimpeded water flows. Gently vegetated banks can be better for wildlife

• gradients need to be sufficient to cause water to flow at the rate needed to discharge the inflow, but not so steep as to generate scour (water erosion) of the banks; 1:50 to 1:30 is ideal. Steeper sections should be avoided, and where appropriate piped

• verges between ditch and path edge should be not less than 500mm

7.22Filter drains can be used to intercept surface water run-off or sub-surface drainage. When used to prevent surface water run-off from reaching and eroding the path, the stone fill should be level with the path edge. When used to intercept sub-surface water (i.e. springs or high water tables) it is possible to conceal the drain by turfing over the top level. Key design considerations are:

• a typical filter drain comprises a 150mm diameter UPVC semi perforated pipe laid in a rectangular section trench filled with clean stone. The trench is lined with a polypropylene geotextile to filter surface water before it reaches the pipe

• inspection / sediment pits located every 20m will provide access for maintenance to short sections of pipework. A drain that becomes blocked may require full excavation and re-laying, regular inspection pits will minimise the extent affected. Pipes should be cleaned every six months

• filter drains near to tree or shrub growth will eventually become blocked or damaged by root growth

• pipe gradients less than 1:50 are to be avoided. Gradients should not exceed 1:15

Fig 7.1 Ditch

Open ditch - generally ‘v’ section, or ‘U’ section if space is restricted

Filter drain is rectangular section with perforated pipe laid in clean stone. Line with geotextile to filter inflowing water

Figure 7.2 Filter drain


29December 2014

7.23Soakaways collect water from piped networks and allow it to percolate back into the sub strata at locations away from the path. A soakaway can be a pit filled with clean inert stone and rubble. A more formal alternative solution is to construct a soakaway using standard concrete manhole rings with perforated sides. Key design considerations are:

• they should be located far enough away and at sufficient depth to avoid water backing up and flooding the path. The level of a soakaway should be at least 1m above the natural water table

• they should not discharge into the sides of embankments or raised paths because this can undermine the earthworks structure

• where a traffic free route follows a disused railway corridor the condition of the original drainage system should be assessed as this may provide an existing viable drainage solution

• soakaways should not be located within 5.0m of any adjacent building or structure

7.24Where a traffic free route crosses a stream or watercourse, a culvert provides a simple and lower-cost alternative to constructing a bridge. A culvert usually comprises a pipe, or series of pipes, laid along the bed of the watercourse, overlain by fill material retained by stone or concrete ‘headwalls’ which are bedded into the stream banks.

7.25Culverts on watercourses can have a significant impact on the movement of some wildlife and the ecological implications will need to be fully assessed.

7.26Sizing of the pipes is critical; if they are too small, the culvert will partially dam the watercourse in high flow conditions. The following guidance addresses sizing of culverts:

• the flow capacity of the culvert should be the same as or slightly larger than any existing on the same watercourse

• pipes should never run full; with the worst case flow the pipe should be running at no more than two-thirds full

• deep, slow moving streams require a pipe size twice that of the stream depth

Fig 7.3 Soakaway at culvert outfall

Ditch or filter drain

CulvertRubble filled pit. Water percolates back into subsoil

Figure 7.4 Typical single pipe culvert

Build headwall at both ends to retain backfill and hide pipe

Firmly embed headwall stones into the stream or ditch bank

Position large flat stone as ‘splash plate’ to prevent erosion of stream bed


30 December 2014

Fig 7.5 Typical multiple pipe culvert

Headwall

Position stones to direct water into pipes so as not to wash out fines from pipe backfill

• it is advisable to visit the site of a proposed culvert during, and just after, heavy rainfall to assess the how stream levels respond. Where the “wetted area” – depth of water multiplied by the width of flowing water – in raining conditions can be estimated, pipe sizes should be designed to accommodate this plus 50%

• the minimum pipe size recommended is 300mm diameter. Pipes greater than 450mm diameter may encourage small children to explore inside, a series of parallel pipes may be a better solution

• if a stream is prone to flooding, the Environment Agency should be consulted about the proposals. The Agency’s knowledge of the drainage network will help ensure the proposed culvert does not inadvertently increase flood risk elsewhere. In some instances, this may identify the need for significant works. Conversely, the Environment Agency may have flood alleviation schemes planned that could help reduce the required capacity of the proposed culvert

• pipe gradients should be 1 in 40 or more, to ensure adequate flow rates and minimise the risk of silt deposits blocking the pipes

7.27Culverts can be installed in a variety of locations, and for a variety of reasons.


31December 2014

Path routed through a long and wet cutting set on a causeway to one side leaving the remainder wet as an interesting and varied wildlife area, Kilbirnie

2.5m minimum width, 3.0m track preferred width

1.0m verge

Path built on 1.0m high causeway

Fig 7.6 Causeway built in cutting to keep path clear of flooding

7.28On occasion it is desirable to set a traffic free path on a causeway, with the area either side left wet to encourage a wide diversity of plant life. In these instances the path should always be built slightly above the general level of the ground, maybe by as little as 100mm and should always be set dead level along the path length, with a central camber or crossfall. This is to ensure that as flood waters recede and the surrounding ground is generally wet and soggy, the path itself emerges above the water over the whole of its length.


32 December 2014

8. ReferencesLocal Transport Note 2/08, Cycle Infrastructure Design, DfT 2008

Local Transport Note 1/12, Shared Use Routes for Pedestrians and Cyclists, DfT 2012

The Merits of Segregated and Non-Segregated Traffic-Free Paths, Phil Jones Associates, Sustrans 2011

A Guide to Controlling Access on Paths, Sustrans 2012

Advice on Surfaces for Horses in England and Wales, The British Horse Society 2013

Sustrans Technical Information Notes;

TIN07: Aggregates for Path Construction, 2011

TIN08: Cycle Path Surface Options, 2012

TIN11: Trees, 2012

TIN28: Horses on the National Cycle Network, 2011

TIN29: Lighting of Cycle Paths, 2012

TIN30: Parapet Heights on Cycle Routes, 2012

Sustrans’ Ecology Notes

Ecology Note 01: Hedge Management

Ecology Note 02: Grass Verge Management

Ecology Note 03: Himalayan Balsam

Ecology Note 04: Japanese Knotweed

Ecology Note 05: Ragwort

Ecology Note 06: Ecology in the Planning System

Date post:	04-Jan-2017
Category:	Documents
Upload:	hahanh
View:	247 times
Download:	2 times

Sustrans Design Manual Chapter 6 - Traffic free routes: detailed ...

Documents