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Grants & Regulations

Operations Note 25

Forest roads and tracks 

Table of Contents 

1 Purpose ............................................................................................ 4

1.1 Introduction .......................................................................................4

2 Background ...................................................................................... 4

2.1 Appraisal process ................................................................................4

2.2 Planning and design.............................................................................5

2.3 Construction and maintenance ..............................................................5

3 Route selection ................................................................................. 5

3.1 Initial scoping .....................................................................................5

3.2 Field survey........................................................................................6

3.3 Identifying the route ............................................................................8

3.4 Appearance in the landscape.................................................................8

3.5 Maps and drawings ..............................................................................8

4 Legislative issues and best practice.................................................. 8

4.1 Local planning system..........................................................................8

4.1.1 Highways / Roads authority .................................................................................... 9

4.2 Water management and protection ........................................................9

4.3 Environmental Impact Assessment (Forestry) Regulations....................... 10

4.4 Tree felling ....................................................................................... 10

4.5 Habitat Regulations ........................................................................... 11

4.6 Best practice .................................................................................... 11

5 Design and layout of access............................................................ 11

5.1 Design criteria .................................................................................. 12

5.2 What do we mean by a track? ............................................................. 12

5.3 Drainage .......................................................................................... 14

5.4 Soils & geology ................................................................................. 14

5.5 Using the right machinery .................................................................. 15

5.5.1 Choice of operator................................................................................................16

6 Construction and materials............................................................. 16
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6.1 Clearing the route line ....................................................................... 17

6.1.1 Felling trees and removing stumps .........................................................................17

6.1.2 Working on side slopes .........................................................................................18

6.2 Formation (Sub Grade) – the track base ............................................... 18

6.2.1 Soil management .................................................................................................18

6.2.2 Creating the track Formation .................................................................................20

6.2.3 Roadside drainage ditch ........................................................................................20

6.2.4 Batters and spills .................................................................................................21

6.2.5 Pavement (Capping layer) .....................................................................................22

6.3 Water crossings ................................................................................ 23

6.3.1 Culverts and Cross Drains .....................................................................................23

6.3.2 The Talbot formula ...............................................................................................24

6.3.3 Spacing of ditch relief culverts ...............................................................................25

6.3.4 Types of pipe for culverts ......................................................................................26

6.3.5 Culvert installation ...............................................................................................26

6.3.6 Head and tail walls ...............................................................................................30

6.3.7 Bridges, fords and causeways ................................................................................30

6.4 To stone or not to stone a track .......................................................... 30

6.4.1 Tracks and roads on thick clay ...............................................................................31

6.4.2 Tracks and roads over deep peat............................................................................31

6.4.3 Timber haulage roads ...........................................................................................32

6.4.4 Surfacing forest roads ..........................................................................................32

6.4.5 Depth of stone needed for surfacing .......................................................................33

6.5 Roadside harvesting facilities .............................................................. 34

6.5.1 Turn-rounds ........................................................................................................34

6.5.2 Passing Bay ........................................................................................................35

6.5.3 Loading and stacking areas ...................................................................................35

6.5.4 Sky-line and hi-lead timber landing areas ................................................................35

6.5.5 Ramps and tracks ................................................................................................35

6.6 Access to the public highway .............................................................. 36

6.6.1 Bituminous macadam surfacing..............................................................................37

6.6.2 Bituminous surface dressing ..................................................................................37

6.6.3 Road planing .......................................................................................................38

7 Contract specification ..................................................................... 38

8 Maintenance and aftercare ............................................................. 38

8.1.1 Road maintenance ...............................................................................................38

8.1.2 Road repair .........................................................................................................39

8.1.3 Ditch and culvert maintenance ...............................................................................40

8.1.4 Weather effects ...................................................................................................40

9 Useful references............................................................................ 41

Appendix 1: Economic appraisal.................................................................. 42

Appendix 2: Soil strength, Formation width and Pavement thickness................ 44

Appendix 3: Gradients, alignments and curves .............................................. 46

Appendix 4: Diagrams for a T Shaped turn-round .......................................... 49

Appendix 5: Diagram for a passing bay ........................................................ 51
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Appendix 6: Diagram for access to the public highway ................................... 52

Appendix 7: Cross section diagrams of track profile on slopes ......................... 54

Revision History 

Date Version Comments 

19.08.11 1.0 First issue 
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1 Purpose 

Without suitable access, many woodlands can not be managed economically. This 

guidance note provides an introduction to the planning and construction of access tracks 

and surfaced haulage roads in woodland, and aims to define the minimum appropriate 

standards for their construction, repair and maintenance, in England. 

1.1 Introduction 

The guidance has been drawn together in consultation with Forestry Commission civil 

engineers who have provided the specifications and practical advice. However, it is not a 

comprehensive forest engineering guide. 

The guidance details standards that are considered to be reasonable and are based upon 

good practice. The diagrams within this guidance show how tracks and roads should and 

should not be constructed. However, in certain circumstances it might be neither possible 

nor realistic to achieve them. The figures and tables give information that will help with 

decision making and work specifications. They are not available in other publications. 

This guidance note forms part of a suite of information to be utilised woodland owners, 

managers and contractors creating access infrastructure, and by applicants and 

administrators of the England Woodland Grant Scheme when handling applications for 

Woodfuel WIG. 

2 Background 

Apart from the initial investment in woodland establishment or a woodland purchase, 

access infrastructure represents the single greatest capital expense by the owner, with 

surfaced roads costing in the order of five times that of extraction tracks. It is therefore 

essential to establish the need for, and timing of access infrastructure. 

To avoid being reactive to situations a sound, up to date management plan for the 

woodland should already be in place. Through this plan, it will be possible to properly 

consider all relevant factors affecting the woodland, including identification of 

inadequately accessed areas and the timing of timber production, and therefore, provide 

an opportunity to reduce costs when planning access infrastructure needs. 

2.1 Appraisal process 

The aspiration in any woodland should be to implement the most effective and economic 

combination of surfaced and unsurfaced tracks to ensure sustainable forest management. 

An appraisal process will assist in determining an appropriate balance of track types, but 

as a guide, the minimum roading requirement should only be that which; 

 Is sufficient to facilitate safe access and egress to and from the public highway; 

 Has appropriate timber stacking, loading and turning provision; 

 Has the appropriate track based infrastructure required to be used for timber 

extraction. 
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2.2 Planning and design 

As part of the appraisal process, consideration must be given to the woodland 

environment (habitats, topography, soil type, tree species etc), harvesting systems 

(forwarder, harvester, motor manual, skidding etc), nature conservation, recreational use 

and landscape, as these will all have a material bearing on where access infrastructure is 

located, and on the type and timing of construction. 

The management plan will have much of this information contained within it, so route 

planning for access infrastructure should be able to be well planned, and well timed, 

achieving an optimum road and track density at a minimum cost. 

An Economic Appraisal may also be used in an attempt to minimise the costs of extraction 

from stump to the public highway, whilst providing the optimum road and track 

infrastructure to serve a particular woodland site. See Appendix 1. 

2.3 Construction and maintenance 

Woodland access infrastructure should generally be planned as a permanent facility for 

the management of woodland, and so it’s construction should be looked at as a long term 

investment covering several silvicultural interventions, if not a whole rotation. 

Construction is normally planned to fit in with the timing of the timber harvesting 

programme and will be undertaken when local seasonal conditions provide the best 

working conditions, i.e. avoid very wet conditions. 

Remember: Poor design or construction can result in inadequate access being created, 

cause significant environmental damage, and result in high repair and maintenance costs, 

or even legal problems. 

Well planned and properly constructed tracks will have minimal impact on the 

environment but will still need to be maintained in order to sustain the productivity of the 

woodland and maximise the life span of the investment. 

Whole Life Costing is a methodology that justifies an extra initial expenditure on key 

elements of the access specification in order to sustain a longer lifespan. 

3 Route selection 

Route selection is an essential part of your planning process and must follow a logical 

sequence in order to minimise time, effort and expense in survey, design and 

construction. 

The final route selected will be a compromise of a variety of conflicting constraints and 

restrictions but ultimately will also need to balance the management needs of the 

woodland versus the cost of the investment. 

Spending extra time and care at the route selection stage should reduce future harvesting 

and operating costs, and create less environmental damage. 

3.1 Initial scoping 

Undertake a map based desk study, utilising local site knowledge and information in your 

management plan about what work you propose to undertake in the woodland, and where 

there are constraints that have to be worked around or incorporated. 
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Possible restrictions could be: 

 The woodland type being managed, and the management systems being used. 

 Access off the public highway. 

 Agreements with third parties to cross their land. 

 Restraints imposed or consents required by Regulatory bodies. 

 Environmental, such as slope, water courses and service way-leaves. 

 Landscape implications of the route line. 

 Sites important for archaeology and nature conservation. 

 Public access, public rights of way, or public views. 

Through the desk study, these restrictions will give rise to a route corridor that can be 

broadly plotted on the map, within which the access route is best located, and which is 

most worthy of more detailed study. 

3.2 Field survey 

Now you need to get to know the woodland and the terrain in those optimum areas 

identified during scoping, by walking the route thoroughly. Keep an open mind about 

what you find and look for opportunities to keep access infrastructure simple. Remember, 

it may be more cost effective to go around an issue rather than through it. 

The reconnaissance should be carried out to gain information on: 

 terrain conditions and topography that could give rise to unstable road sections; 

 indications of sub-grade (soil) material, rock outcrops, marshy ground and soft soil, 

and potential sources of rock or other suitable construction materials; 

 areas for disposal of surplus material, either adjacent to the survey line, or in tips 

off –site; 

 the location water courses and other wet areas; 

 important features such as old walls or buildings, veteran trees etc.; 

 landscape issues that might arise as a result of the preferred route; 

 the location of important areas of wildlife habitat. 

Figure 1 shows some of the key considerations at the field survey stage. 

Points to consider: 

 The track should reach the areas of woodland most in need of access, but avoid 

unnecessary travel up and down slopes, and should avoid hairpin bends, especially 

on steep slopes. 

 The track should avoid wet areas, and be planned in accordance with the current 

Forest and Water Guidelines (4th Edition). 

 The track should seek a safe place to connect to the public highway, reducing the 

potential for conflict with the Planning Authority. 

 Avoid siting your track along existing paths and rides simply because they are 

there. They may be suitable for timber extraction and modern machinery, but you 
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may be removing significant biodiversity from the ride. Going through the 

woodland is generally more environmentally sustainable. 

 When planning the direction and felled width of the road line, an East – West 

alignment will be good for wildlife and conservation values but will have a problem 

with lack of sunshine and wind to keep it dry, unlike North – South alignments. 

Figure 1: View of a sloping woodland where the ground is not freely drained 
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3.3 Identifying the route 

The information gathered from the desk study and the field survey will allow a more 

detailed route selection to be formed. The depth of study needed will differ from site to 

site depending on the scale of the work proposed, and the complexity of the site. 

Once all the information available is reviewed you will be able to identify the actual route 

to be cleared, and be able to demark it on the ground. From the route selection process 

the detailed survey undertaken will have also identified: 

 what permissions and consents will be required, and who from; 

 which sections of track are to be surfaced for vehicular use, and which will be for 

timber extraction purposes; 

 the locations of access facilities such as turning and loading points, harvesting 

ramps, main culverts and other water crossings. 

3.4 Appearance in the landscape 

Try to avoid positioning tracks on prominent un-wooded slopes. Follow the land form and 

avoid long straight routes, especially along external boundaries. The ability to work to 

both sides of the road is obviously more efficient and would require less roading. 

Consider additional planting to conceal tracks across open ground in sensitive areas, and 

where they work across open land to provide access to woodlands. 

In exposed woodlands with unstable crops, cutting a track line will increase the risk of 

windblow. If a crop is too unstable to thin, avoid cutting a track through it. 

3.5 Maps and drawings 

Maps should be produced to an appropriate scale to detail where the route line will run. 

Maps must also indicate clearly where the route will be surfaced for vehicles or a track for 

forestry equipment and show where culverts will be sited. 

Cross sectional drawings should be undertaken showing gradients and crossfalls. For 

intricate sites, or sites containing bridges or access off public roads, it will be necessary to 

produce larger scale drawings. The scale should be sufficient to show clearly the 

necessary detail and measurements. 

Examples of technical drawings are located at the end of this guidance note. 

4 Legislative issues and best practice 

Once the requirement for access infrastructure has been established, there will normally 

be a need to consult various authorities, and obtain permissions or consents. 

4.1 Local planning system 

(Town and Country Planning (General Permitted Development) Order 1995) 

The Town and Country Planning legislation considers the formation, alteration and 

maintenance of a private way (road or track), for the purposes of forestry, to be 
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'permitted development'. Therefore, these operations, including obtaining minerals 

locally, are not normally subject to full planning consultation. 

However, in England and Wales, before any such work starts, the developer must apply to 

the local planning authority for a determination as to whether the work is in fact 

permitted development. You must submit a description of the work involved, including the 

materials to be used, a plan of route of the track, together with a fee to your local 

authority. 

Many Local Authorities do have standard ‘determination’ proforma, usually available via a 

link from their website. The authority must respond within 28 days, and where they 

approve the work they will often grant a “General Development Order”. 

NB: There may be regional variations between councils and planning authorities. 

However, if the track joins or runs within 25 metres of a classified public highway, or if 

the site is particularly sensitive, such as in a national park or an Area of Outstanding 

Natural Beauty (AONB), the development is not 'permitted' and a full planning 

consultation will be required. If a full planning consultation is required, allow a minimum 

of a further 8 weeks for the Planning Authority to come to a decision. 

It is sensible to submit your proposals to the local authority early. 

4.1.1 Highways / Roads authority 

Consultation is always required with the highway / roads authority when an access is 

constructed off a classified public highway. It is always advantageous to consult early, as 

the highway authority will need time to research and advise on the optimum positioning 

of the junction, and ensure that the location is safe in terms of visibility for other highway 

users. 

Prospective developers need to submit a description of the work involved, including the 

type of materials to be used, with a plan showing the route of the track, to the local 

authority, together with a fee. 

4.2 Water management and protection 

Consultation with the Environment Agency (England and Wales) is necessary where there 

is likely to be interference with a watercourse during construction, use or maintenance of 

a forest track or road. 

Water Resources Act 1991 – Any works in, over or under a main river require the prior 

consent of the Environment Agency under the Section 109 of the Water Resources Act 

1991. In the context of forest tracks, construction or replacement of both bridges and 

culverts will require formal consent (a Main River is defined as a watercourse shown as 

such on a main river map). 

Land Drainage Act 1991 – The installation of a culvert or alteration affecting the flow of 

an ordinary watercourse requires the prior consent of the Environment Agency under 

Section 23 of the Land Drainage Act 1991. In the context of forest tracks only culverts 

will require formal consent. Clear span bridges do not fall under the legislation. (An 

ordinary watercourse is any watercourse not defined as Main River. There is no de 

minimus to this definition). 
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Where a proposed forestry track or road crosses a number of minor watercourses, 

requiring a single assessment of flood risk, then a single consent application and fee 

should be submitted, and single consent issued covering a number of similar structures. 

This process will be the same as any other consent application and will be determined 

within 2 months. 

4.3 Environmental Impact Assessment (Forestry) Regulations 

(Environmental Impact Assessment (Forestry) (England and Wales) Regulations 1999) 

The Forestry Commission (FC) is responsible for administering the EIA regulations in 

respect of forest roads and quarries. The Regulations apply equally to both grant aided 

and non-grant aided projects. Applications for grant funding are automatically assessed 

by the FC, and there is a ‘Determination Form’ for those developers who do not seek 

grant support. There is no fee for an EIA opinion. 

Applicants must always seek an opinion from the FC on new forest roads and quarry 

projects. It is up to FC to determine if the work is a relevant project under the 

Regulations, or not. If a relevant project is identified, the FC then decides whether 

consent is required. Developers may be asked to provide additional information in order 

for the FC to make a decision. 

Existing tracks should only form part of the EIA process if there is to be significant surface 

vegetation removed as part of restoration, and where an existing track formation is being 

stoned as part of the process. 

If the FC decision is that no consent is required, the decision lasts for 5 years. However, 

when construction starts on a new road or track, any deviation in the route, for example, 

due to unexpected ground conditions, will require a further EIA opinion. 

If the FC decides that proposals will have a significant effect on the environment then, 

under these Regulations, the proposer must obtain the FC’s consent for the work. This will 

include submitting an Environmental Statement as part of the application for consent. 

4.4 Tree felling 

(Forestry Act 1967 as amended) 

Subsection 9(4) of the Forestry Act says that the requirement for a felling licence does 

not apply to any felling that is immediately required for the purpose of carrying out 

development authorised by planning permission or deemed to be granted (permitted 

development). 

However, for all other tree felling, Forestry Commission approval must be granted. It is 

an offence to fell trees without a licence if an exemption does not apply. The Forestry 

Commission will issue a Felling Licence where it is satisfied that the proposals meet 

forestry standards. 

If you propose to carry out felling or thinning as part of a grant scheme application, then 

you will get a Felling Licence Certificate with your approved contract. After any felling you 

must comply with the restocking conditions of the licence. 
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4.5 Habitat Regulations 

Since 1994 it has been an offence, under the Habitats Regulations, to deliberately kill or 

cause significant disturbance to a protected species, or to deliberately destroy their eggs. 

It has also been an offence to ‘damage or destroy a breeding site or resting place’ used 

by them (such as a bat roost in a tree or a dormouse nest on the woodland floor). 

Recently a number of changes were made to Habitats Regulations that increase the legal 

protection given to protected species in England. These changes are intended to reinforce 

implementation of the European Habitats Directive across the UK. 

There are several species covered by the regulations that are found in woodland, and the 

amendment therefore has implications for how woodlands are managed and forestry 

operations carried out. 

Woodland managers need to consider the presence of protected species and follow good 

practice guidance to avoid committing an offence. Management practices may need to be 

modified or rescheduled to a less sensitive time of year, and where this is not possible or 

adequate, operators may need to apply for a licence to comply with the law. 

A suite of guidance has been developed to support woodland owners and managers in 

England. 

4.6 Best practice 

There are many other areas of legislation and regulation that may need to be considered 

when undertaking civil engineering operations within woodlands, but which are equally 

relevant for wider sustainable forest management. 

Bio-security is particularly important at this time, as the forest industry deals with a 

number of plant health issues. Civil engineering operations, involving the movement of 

soil and use of heavy machines and lorries within woodland, could lead to the movement 

of tree pests and diseases around the country. Woodland managers and contractors need 

to be aware of what Bio-security measures need to be in place where they are working, 

and adhere to best practice guidelines. 

There is a wealth of Best Practice guidance published by the Forestry Commission and 

other organisations on all manner of topics to support and advise woodland owners and 

managers, for example, the FC Guidelines on Soil, Water, Archaeology, Landscape, 

Conservation and Heathland. 

5 Design and layout of access 

The design and layout of the access to be created, and its technical specification, will be 

greatly influenced by the immediate site characteristics on the route that you select and 

by the use of the access you propose. In general terms: 

 Surfaced forest roads need to be designed to a more detailed specification than 

tracks in order to be safe and effective for use by lorries travelling at low speed (15 

mph), and they should therefore be designed by a civil engineer. 

 It is also recommend an engineer be used for designing the construction of timber 

transfer and turning points, large culverts and any other major watercourse 

crossing. 
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 Harvesting tracks will require less surfacing materials and a lower specification of 

finish, but must still have a sound Formation, compacted and freely draining, in 

order to survive a series of harvesting operations. 

Key to establishing long standing and sustainable access will be: 

 understanding site drainage needs and management of water; 

 knowing the soils and geology on the site; 

 using the appropriate construction methods and construction plant; 

 creating consistent curves and gradients along which to operate. 

5.1 Design criteria 

At design stage, the main points which could influence the final geometry of a new track 

are set out below. Safety during construction and in subsequent use must always be 

considered. 

Terrain restrictions will influence: 

 The vertical and horizontal alignments and corner radiuses of the track. 

 The felling widths required to allow the track to be engineered. 

 Excavation and fill slopes, soil and rock side slopes, and therefore measures to 

maintain stability and mitigate bank erosion. 

 The availability of borrow pits or roadside side slope excavation for construction 

materials. 

 The carriageway pavement design – camber or crossfall. 

 The drainage and ditch provision. 

 The culvert and cross drain positions and approaches. 

 The location of bridges – if required. 

Harvesting methods and requirements will dictate: 

 The need for, and future usage of a track. 

 The volume and intensity of traffic to use the track. 

 The timing of use - all year, or use restricted by season and / or climate. 

 Harvesting facilities, such as access ramps and loading facilities. 

Timber stacking areas should be designed into the route line at the outset, as they will 

have a localised impact on both the track surface (vehicles loading / unloading and 

turning), and on drainage and water quality during harvesting operations. 

5.2 What do we mean by a track? 

Different specifications of access route and infrastructure can be used and the choice (or 

combination of choices) will be dependant on the intended purpose of the access. Table 1

below describes the most relevant categories for woodlands. 
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Table 1: Description of tracks 

Type of 

route 

Purpose Type of site Notes 

Light tracks Provide access to 

ATVs or horses 

On very sensitive sites 

or where only very small 

volumes of timber are 

being harvested. 

Widths vary but generally quite 

narrow (c.2.0 – 2.5 metres 

wide). Horse routes need to 

avoid uphill extraction. 

Tractor / 

Skidder 

Track

Allow working access 

for tractors and 

skidders, or light 4x4 

vehicles 

Small woodlands, or 

steeper sites where 

skidding or static 

winching are the most 

cost effective method of 

harvesting.

Sturdy track, wide enough for a 

tractor or light vehicle. Width of 

3.0m – 3.5m, widening to 4.0m 

on bends with a minimum 

radius of 6.0m. Max. gradient 

20%, but usually 10–15 %, with 

a cross fall of 5%, and lower 

gradients on bends. 

Forwarder 

Tracks 

Extracting large 

volumes of processed 

timber using purpose 

built forwarders or 

forestry tractors with 

timber trailers 

Larger woodlands on 

terrain suitable for 

short-wood harvesting 

systems. 

Heavier duty and wider than 

tractor tracks, with gentler 

bends. Running width of 4.0m. 

Bends, min. radius 8.0m with 

5.0m running width. Max. 

gradient 20%, but usually 10–

15%, with a cross fall of 5% and 

lower gradients on bends. 

Forest 

Roads 

Usually designed to 

carry 44 Tonne 

articulated lorries. 

Large commercial 

woodland where it is 

more economic to bring 

lorries into the woodland 

than to extract timber to 

existing lorry roads. 

Detailed specification to ensure 

good drainage and safe use. 

Stone is used to provide 

strength. Gradient not to exceed 

10%. Running width 3.2m, 

wider on bends. Geometry and 

specification are critical. 

Turning / 

stacking 

areas 

To turn large vehicles 

within woodland, and 

may also be designed 

for timber stacking. 

Essential for most small 

woodland. Could be 

positioned on the 

woodland edge. 

Can be round or ‘T’ shaped 

depending upon the gradient, 

and should be built to the same 

standard as the track or road. 

Transfer 

Points 

A lay-by beside the 

public road. Timber 

stacked for collection 

by lorry. Avoids mud 

on public road. 

Smaller woodlands or 

where it is not cost 

effective to bring lorries 

into the woodland. Steep 

sites are difficult. 

These need to allow a lorry to 

park off the highway safely and 

should be long enough to 

provide enough space for timber 

to be stacked. 
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5.3 Drainage 

Good drainage is fundamental to the strength of any across route, as a wet road or track 

will be weak, and will not provide a lasting solution to access needs. Therefore, all tracks 

and roads need to be designed to: 

 prevent water collecting on the surface; 

 keep water away from the running surface and prevent erosion by run-off. 

Roads and tracks generally do this in different ways, and these are illustrated in Figure 2. 

Figure 2: Road and Track profiles 

 

 Road profile Track profile 

Both Camber and Crossfall, if properly formed and compacted, provide a track profile that 

will allow water to run off the running surface and into a drain network. Side slopes are 

usually the best place to build roads and tracks, as it is much easier to channel the water 

away using the slope, and the ground is much drier and firmer than on flatter areas. 

5.4 Soils & geology 

In addition to land form, the underlying geology will have a greatly influence the way in 

which a track needs to be built, and the overall strength it will have. The local geology will 

dictate whether local stone and aggregate material is available and can be obtained used 

for construction, or whether aggregates and / or recycled construction materials will have 

to be imported. 

Freely draining slopes, such as shale banks, are often the driest and easiest places to 

construct tracks. However, on less well drained ground with poorer soils, construction will 

be more difficult, and some soils such as peat or clay will need particular techniques to be 

applied when creating tracks. 

Simply adding more stone on top of a wet route is no substitute for drainage and can be 

an expensive mistake! 
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5.5 Using the right machinery 

It is important to use a machine that can cope with the site conditions safely and produce 

a track cost-effectively. Table 2 indicates the suitability of the main different types of 

machinery. 

Table 2: Choice of machinery 

Type of 

machine 

Specification Advantages Disadvantages Comments 

Wheeled 

excavator: 

JCB type 

machine for 

use in 

restricted 

access. 

2.1m wide, 

front bucket 1.2 

m3 Backacter 

with 180° 

degree rotation 

and variety of 

buckets. 

Widely available, 

easy to transport, 

hourly rate low. 

Unsuitable for soft 

ground. Unstable on

slopes. Low power, 

therefore slow and 

unable to cope with 

larger stumps. No 

360° rotation limits 

ability to lay culverts. 

Only really 

suitable tracks on 

flat easy ground 

such as shale or 

sand, where the 

stumps are small 

and culverts are 

not needed. 

Tracked 

excavator: 

Small 3–6

Tonne 

excavators. 

1.5m wide. 

Fixed front 

blade. Backacter with 360° 

rotation. Variety 

of buckets as 

for JCB. 

Narrower, more 

precise than a JCB. 

Able to build 

narrow access 

routes on softer 

ground. More 

stable on slopes 

Needs transported to 

site on a trailer. 

Similar outputs and 

power to JCB. 

Struggles with larger 

stumps. 

For use in 

restricted access. 

An ideal machine 

for light tracks 

and paths. 

6–12 

tonne 

360° 

excavator 

2.1m wide. 

Fixed front 

blade. Backacter with 360° 

rotation. Variety 

of buckets sizes 

Greater power, 

higher outputs. 

Copes with large 

stumps. Stable on 

steep slopes and 

on wet ground. 

Less available than 

JCB. Hourly rate more 

expensive. Needs 

transported by low 

loader. 

Ideal machine for 

making tractor 

and forwarder 

tracks. Efficient 

and cost effective. 

Larger 

excavator 

2.7m wide. 

360° Backacter 

only. Variety of 

bucket sizes. 

Powerful and fast. 

Ideal for cutting 

forest roads. Easily 

copes with large 

stumps and harder 

rock. 

Boom may be too big 

for cutting forwarder 

tracks. High hourly 

rate. Transport by low 

loader. Expensive for 

small jobs. 

Widely available. 

Ideal for cutting 

forest roads but 

too large for 

working on tracks. 

Bulldozer

Various 

sizes 

Front blade only Ideal for formation 

work on very large 

roads and cuttings. 

No Backacter means 

unable to lay culverts 

or grade batters. Push 

only. Action is clumsy 

leading to wide tracks. 

Unsuitable for 

constructing 

tracks in 

woodlands. 

Note: Breakers can be fitted to all of these machines (except bulldozers) for cutting 

through rock larger machines can cut harder rock. 
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The most common machine used for creation of woodland access is a 360° tracked 

excavator. 

However, do not choose a machine solely on the basis of availability and low hourly costs, 

as a small machine may not be able to build a track to the right specification on your site 

conditions. Both the construction operation and the future use of the track may be 

unsafe. Furthermore, low outputs from smaller machines can result in slow progress and 

a higher overall cost than hiring an appropriate machine. 

5.5.1 Choice of operator 

All operators for the machines listed in Table 5 should be suitably qualified to use the 

machine, and have experience working on forest tracks. The current “industry standard” 

qualification is a CITB/CPCS licence. Checks should be made as to the competency of 

contractors and operators. 

The building of forest roads and tracks is a very small part of the construction industry, 

and operators are not taught about working in woodlands when working towards their 

licences. Contractors unfamiliar with working in forestry may not be aware of the 

specification of forestry tracks, and may not know how they will be used for timber 

extraction. 

Site conditions in woodlands are very different to construction sites, and even agricultural 

land drainage schemes. Woodlands present many unfamiliar problems and hazards to 

machine operators. Tree felling and extraction may need to take place during construction 

requiring co-operation and understanding between contractors. Tree stumps can 

destabilize machines, and operators need to know how to dig them up and incorporate 

them into the fill. 

All these things point to using contractors with experience in forestry. If you are in doubt 

about a contractor's suitability for the job, ask to see an example of a woodland track that 

they have constructed. 

6 Construction and materials 

Methods of construction will vary according to the type of ground being worked. However, 

the requirements of the Construction (Design and Management) (CDM) Regulations apply 

to all but the smallest projects. 

Construction in summer is usually easier, quicker and of better quality than winter 

working, but adequate time should be allowed for construction, particularly on peat. 

However, regardless of the site and underlying soil type, one should never be afraid to 

stop work if the weather gets really bad. 

Guidance is given within this document for; 

 Brown earth and shale 

 Working on side slopes 

 Thick clays 

 Deep peat 

However, there are many other soil types and situations to consider. 
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6.1 Clearing the route line 

The first operation on site is usually to fell all trees and substantive vegetation within the 

width of the route line. 

For new tracks, it is recommended that a cleared track line of 9m – 15m wide be created. 

Surfaced forest roads for timber haulage, and stacking and loading areas may need up to 

25m width. Existing extraction tracks or roads being upgraded to cater for modern 

forestry equipment will also need to be widened to these dimensions. 

The felled width is important for two reasons; 

 To provide sufficient unhindered room in which to create the grade of track or road 

required, and its associated drainage; 

 To allow the surface of the track, once constructed, direct sunlight and wind to 

encourage rapid drying of the running surface, and to assist melting snow and ice. 

6.1.1 Felling trees and removing stumps 

If the ground does not allow for felled timber within the track line to be extracted prior to 

access construction, then often the best method is for trees to be felled either up or down 

the slope, and for the branches to be sned out. 

This allows the machine operator to move lop and top and logs far enough from the track 

line with the bucket to allow construction of the track formation to start. Timber 

extraction can then take place when the track is complete. For larger trees this may not 

be possible, and co-operation is needed between the harvesting contractor and the 

machine operator. 

Avoid wiggling the route line around individual trees as this will make the track twisty. 

Trees retained within the route line are unlikely to survive if left close to excavations, as 

root damage is most certain to occur when creating the track Formation and drain, and 

compaction of the soil will adversely affect hydrology around the roots. See Figure 3. 

As a rule of thumb, a minimum clearance of 2 metres should be left between the edge of 

the route line excavation, and the edge of the woodland, and ideally, no excavation 

should take place under the canopy of adjacent trees. 

Additionally, root growth and overhanging branches from trees retained within the felled 

width will cause future problems for drains, and by overshadowing the running surface. 

This will allow water to persist on the running surface, causing damage, and branches 

may grow sufficiently to obstruct vehicles during future harvesting operations. 

Additional areas may have to be felled where locations have been identified for borrow 

pits or small quarries. 

The machine operator should not leave cut tree stumps in the ground along the track line 

as they will tend to poke up and, as stone settles, cause a hazard to future use of the 

track. Stumps should be dug out and cast side or upturned and placed back into the route 

line, and compacted down. See Figure 3. 

Remember, once the running surface has been constructed, the edges can be landscaped 

with the stored top soil, and the remainder of the felled width will naturally infill, or can 

be planted to provide varied habitat. Scallops and glades at irregular intervals can provide 

variety and shaded areas for wildlife. 
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However, care must be taken to ensure that the vegetation does not become a cause of 

instability or landslips, or restrict sight distances. Any vegetation growing in this zone will 

need to be managed to maintain the sunlight and wind access and soil stability. 

6.1.2 Working on side slopes 

The excavating machine needs to establish a level platform to work on. The Formation cut 

should be done with a small bucket to help identify poor material and suitable materials 

for the Formation. 

Loose, poor quality material, such as top soil should be pushed to one side. Good material 

from the cut should be used to fill under the running surface. Tree stumps must be dug 

out and inverted, making a hole for them if necessary, and the batter should also be cut 

at this stage but roughly. 

Looking at Figure 3, in places where the topsoil is deeper you can move the track towards 

to bank in order to access more shale or cut the track a little deeper. Alternatively you 

may be able to “win” stone from other sections of track in order to metal sections where 

there is less. 

6.2 Formation (Sub Grade) – the track base 

The Formation or Sub Grade is the part of a track or road structure on which the running 

surface and associated drainage is established. The Formation specification applies to 

tracks, forest roads, passing bays, entrance points and loading and stacking bays. Getting 

the Formation right will greatly benefit the final track structure. 

The minimum Formation width and depth will depend upon the composition and strength 

of the underlying soil material, the ground slope on which the road line lies, and the 

proposed track width – normally 3.4m. 

Soil strength decreases as moisture content rises, with different soils having different 

strengths when wet. 

For haulage roads, it is particularly important to assess the quality and quantity of 

Formation material available at an early stage to ensure you can construct a safe road, 

and inform if you need to import material. 

For more information on the strength of different soils, and how this directly affects the 

width of the Formation needed to carry an effective running surface, see Appendix 2. The 

running width will be somewhat narrower than the Formation width. See Figure 4. 

6.2.1 Soil management 

Organic surface material and topsoil is not a good Formation material. It is usually better 

to remove topsoil, which is a valuable commodity, and store it onsite for landscaping 

later, after the construction is complete. 

Remember, the structure of top soil is easily damaged, and it is important to handle and 

store top soil correctly so that it can be reused at a later date. 
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Figure 3: Cross sections of track built on a 30% cross slope 

Technical diagrams showing cross sections of track profile on a range of slopes are shown 

in Appendix 7. 
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6.2.2 Creating the track Formation 

Figure 3 shows good and bad practice for a track being cut on through brown earth 

overlying shale which is good enough to be used to make the running surface, and how to 

handle trees and stumps within the felling width. 

Wherever possible, the track should be founded on natural ground rather than on fill. By 

cutting further into the bank you increase the amount of Formation material available, 

and reduce the area to be filled. However, it may still be necessary to import additional 

stone to reinforce the Formation or to act as a Capping layer (see section 6.2.4). 

Ideally, the Formation should be shaped to mirror the final running surface, as this will 

require less metalling. The profile of the Formation also provides a linear drain to catch 

water from the running surface. See Figure 4. 

For a good quality Formation, compaction is essential. This will seal and strengthen the 

Formation, and help shed any water into the track side ditch. Rolling of the Formation is 

not always feasible, but movement of heavy construction machines can still achieve a 

certain amount of compaction. 

A poorly constructed Formation will not provide the strength on which to place a running 

surface, or the drainage, and the track will quickly break up and fail. 

Figure 4: Formation – the track base 

6.2.3 Roadside drainage ditch 

The prime function of the roadside drainage ditch is to carry away the surface water. See 

Figure 4. Ditches should be in place early in the construction process to ensure that the 
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Formation does not act as a drainage channel. Ideally, this will be undertaken during the 

excavation of the sub grade and the creation of the track Formation. 

A ‘V’ shaped linear ditch should be constructed on the up-slope side of the track. Ditch 

side slopes should be at a stable angle. ‘U’ shaped ditches should be avoided because of 

the tendency of the sides to slump or erode. 

The ditch should be positioned as not to undermine the edge of the track. 

Following compaction and sealing of the Formation, any surface water coming off the 

camber or crossfall and into the ditch, and any intercepted sub-surface water coming off 

the uphill side of the road, should be diverted away from the Formation to the nearest 

culvert. 

To be effective in keeping the ground water level low, the ditch must be at least 150mm 

below the formation level. This may also help to lower the ground water level to below 

the formation. 

 Ditch gradients should be greater than 2% to ensure water flows, avoid siltation 

and minimise maintenance. 

 Gradients of 2% - 6 % work well on all types of soil, but the distance between 

culverts may be a consideration on some soils on steeper slopes. 

 Gradients steeper than 6% may need stone protection on some soils to minimise 

erosion. 

In order to minimise pollution, a ditch should not lead directly into a significant 

watercourse. Instead, silt traps and ditch relief culverts should be installed (see section

6.3.1). 

Care must be taken to ensure that the ditch creates neither an unacceptable safety 

hazard (to road vehicles, users, maintenance teams or forest workers), nor a major 

hindrance to harvesting operations. 

Temporary drainage may occasionally be needed if there is a risk of inundation of the 

work area. Temporary measures will help to avoid damaging either the environment or 

the road structure in the short term, but must no become permanent solutions. 

6.2.4 Batters and spills 

In addition to creating a camber etc, on side slopes you need to design the angle of 

batters according to the strength of the underlying soil and sub soil material. Weaker 

ground needs to be graded to a gentler angle in order to provide a stable bank. 

Batters that are too steep, or on poor or soft ground, will crumble or slip onto the running 

surface, making the track narrower and blocking the drainage. Figure 5 shows the 

appropriate angles for batters on different materials. 

Once the formation cut has been made, a 2 metre wide bucket should be used to finish 

off the batters and spill to leave smooth slopes which will consolidate more quickly and 

tidily than rough faces. See Figure 5. 
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Figure 5: Angle of batters and spills 

Rain water runs to the side of the running surface, which forms a shallow V 

shaped, self cleaning drain and flows along to the next culvert.

Figure 5 also illustrates that regardless of the base material, the gradient of the spill on 

the lower side should not exceed 1 in 2. This is in order to provide maximum stability to 

the lower side of the track and to allow access for timber extraction. Spill slopes and 

batters cut at a gentle angle will also vegetate more easily than steep faces which can 

remain as scars in the landscape for many years. 

The cleared corridor will naturally infill with regeneration or through seeding and planting 

in time. Care must be taken to ensure that future vegetation does not become a cause of 

instability or landslips, block drains and ditches, or restrict sight distances. Any vegetation 

growing in this zone will need to be managed to maintain the sunlight and wind access. 

6.2.5 Pavement (Capping layer) 

Adding a Capping layer of crushed stone or recycled material on top of the Formation, for 

the full width of the running surface, will help protect the Formation from wear. See 

Figure 4. 

The depth of the Capping layer can be regulated to meet the needs of the underlying soil 

type, and to ensure that camber or crossfall meet appropriate gradients, and that 

longitudinal gradients can be kept even. 

On many track projects it is normal to construct the pavement in a single process, using, 

where possible, locally obtained material. Construction in a single layer protects the 
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Formation from possible damage caused by construction traffic running back and forth. 

However, a single layer construction does not allow for full compaction of the pavement 

by a vibrating roller where the pavement material is laid excessively deep. 

If the pavement layer can be constructed in compacted layers of less than 250mm, 

without damage to the formation, a stronger road will result, for the same depth of 

material. 

The pavement must be structurally sound over the total running width. By using a camber 

profile, it may be possible to reduce the depth of road stone needed on centreline, an 

area which is not normally subject to traffic, and therefore save on the quantity of 

material needed. 

The ideal pavement is made from a 75 or 100 mm well-graded granular material. Sharp, 

angular material is better than rounded gravel, and will compact well, but poor quality 

materials are difficult to compact. 

Saturated materials are impossible to compact properly. Strength will increase as the 

material drains and consolidates. 

6.3 Water crossings 

The definition of watercourse includes all channels for the passage of water, whether 

natural or man-made, including channels which would normally be dry, such as many 

forest drains. 

Every effort should be made not to pollute watercourses with alien material, and where 

possible, any works should be carried out during the “dry” season, and not during the 

spawning season from October to March. 

Available methods for crossing waterways are: 

 Culvert - can be disruptive to aquatic life; high embankments a possibility 

 Bridge - the preferred choice at most major stream and river crossings

 Vented causeway - overtopping may cause pollution problems and are liable to 

blockage

 Ford - high risk of pollution; probability of erosion if unpaved.

The Forestry Commissions Forests and Water Guidelines (4th Edition) should be consulted 

for information and guidance. 

6.3.1 Culverts and Cross Drains 

Roadside drains should not intercept large volumes of water from the ground above the 

running surface. Any watercourse or spring, however small, which is intercepted by a 

track or road line, should be culverted or bridged at that point. 

Culverts for such drainage should be of a sufficient size and spacing to avoid overloading, 

blocking or washout, and should follow the original line of the watercourse. Tables 4 and 

5 give guidance on pipe size and frequency of use. 

It is essential to minimize the amount of water diverted along the track side ditch to 

prevent the volume of water building up in the ditch and damaging the running surface. A 

cut off culvert can be used to relieve build up of water in the ditch. 
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Always take care when siting additional culverts to avoid discharging water where it may 

cause problems downhill for you, your neighbours, or on a highway, as you will be liable! 

Ditches on the upper side of the running surface should use cut off culverts to direct 

water to the lower side of the track a short distance before stream crossings, so as to 

prevent direct discharge. See Figure 6. 

Roadside drains likely to carry high sediment loads must not be allowed to discharge 

directly into, and pollute a watercourse. Where appreciable sediment movement is 

unavoidable, water must instead be discharged into a buffer area of adequate size, or into 

a silt trap or catch pit that have been constructed to allow sediment to settle. Provision 

must be made for cleaning out and maintaining silt traps and catch pits. 

Figure 6: A cut off culvert 

Roadside drains should discharge to a buffer area so that any suspended sediment can be 

filtered out before the water reaches a steam. 

Discharging water from a track side ditch directly into a standing crop of trees can lead to 

water-logging of the roots of trees. This could result in unstable soil conditions and 

potentially windblow of standing trees. It is important to judge where the water is 

discharged as much as where it is collected from. 

As well as being effectively located, a culvert needs to be of the correct size (diameter) to 

cope with storm flows. The size will depend on the nature of the site as well as the area of 

land that the culvert will drain. A detailed map showing contours is needed to identify and 

measure the catchment area. 

6.3.2 The Talbot formula 

The Talbot formula, shown in Table 3, is a useful starting point for calculating the 

diameter of culverts needed. However, it is important to understand that this is only a 

guide, and that local factors and knowledge will have a big effect on decision making. 
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It is now common for the Environment Agency to expect culverts to have a much greater 

safety margin as a result of changes in weather patterns, due to climate change. 

Table 3: Talbot values 

 

Catchment 

Area in ha 1.0 1.7 3.7 4.7 6.6 11.0 16.0 20.0 24.0 33.0 43.0 47.0 

Pipe Dia. 

in mm 

300 450 500 600 700 800 900 1000 1200 1300 1400 1500

Note: Culverts of 600mm and over need to have cut off culverts installed to the discharge 

ditch, as shown in Figure 6 above. Further guidance should be obtained from the 

Environment Agency or a qualified Civil or Agricultural Engineer. 

This is especially important in mountainous areas, on steep or recently felled areas, or 

areas where thin or saturated soil overlies impermeable bedrock, such as granite, and 

where water will be able to shed very quickly. Springs and drains may exist which can 

greatly increase the volume of water at wet times of the year, and may even bring in 

water from outside the catchment area. 

If in doubt, specify a larger diameter of pipe as the extra cost is minimal compared to 

rebuilding a washed out culvert and track. Also, remember that small pipes tend to block 

up more easily with debris, so it is better to have one large pipe than 2 smaller ones. 

6.3.3 Spacing of ditch relief culverts 

Culverts should be provided at all the low points along road and track sections, and at 

sufficient frequency to relieve the trackside ditch of excessive water. If a significant 

amount of water is allowed to remain in the track side ditch, it will begin to saturate the 

Formation, weakening the running surface and resulting in expensive repairs. 

Table 4 should serve as a guide to the maximum spacing between culverts: 

Table 4: Culvert spacing 

Ditch Gradient Culvert Spacing (m) 

% Normal conditions. Cross slope of 

the ground < 15% 

Very wet or steep conditions. Cross 

slope of the ground > 15 % 

<4 200 100 

5 160 80 

6 130 65 

7 115 55 

8 100 45 

9 90 40 

10 80 35 

11 70 30 

12 65 25 
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6.3.4 Types of pipe for culverts 

In addition to the size and number of culverts needed, you will also need to decide what 

type of pipe to use. Table 3 sets out the relative merits of the most commonly used pipes 

in forest and woodland settings. 

Table 5: Pipes types for culverts 

Type of pipe Advantages Disadvantages Comments 

Corrugated steel, 

galvanised, 

“Helcor/Armco” 

pipes 

Cheap and strong. 

Sections can be bolted 

together to form longer 

lengths by using collars 

Must order correct length. 

If pipes are cut the ends 

rust. 

Pipes liable to corrode, 

especially if laid poorly, 

especially in acidic water 

Cost effective, and 

durable if correctly 

installed. 

Do not use in acid 

rock areas. 

Twin wall plastic Light and easy to carry 

and simple to join 

together. 

Easily cut to length as 

required. 

Will not corrode in acidic 

water. 

A bit more expensive 

than galvanised pipes at 

larger diameters. 

Not quite as strong. 

Easiest pipe to work 

with. 

Ideal for most 

forestry use, 

especially in smaller 

sizes. 

Concrete pipe Very cheap and strong Very heavy. 

Only comes in 1m 

lengths. 

Push fit joints will come 

apart easily. 

Installation is difficult. 

Pipes over 60cm dia. 

must be concreted in. 

Not recommended 

for forestry use 

Perforated plastic 

land drainage pipe 

Spare lengths often 

found left over from land 

drainage jobs. 

Weak. 

Too floppy to lay at 

correct angle. Bends tend 

to trap debris 

Not suitable for 

culverts. 

Do not be tempted 

to use this type of 

pipe. 

6.3.5 Culvert installation 

Having planned the location, size and type of pipe that is to be used, you then need to 

install the culvert or cross drain pipe properly. 

For pipes to work efficiently, and to last - to cope effectively with storm flows and the 

weight of forestry operations crossing them, they must be installed in line with the 

manufactures recommendations. 

The installation of pipes for culverts and cross drains is set out in Figures 7 and 8. 
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Figure 7: Installation of a culvert, cross sectional view 

Figure 7 shows the difference between a pipe badly installed and correctly installed. 
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The trench the culvert pipe is to be laid into should be excavated perpendicular to the 

road line. For an existing watercourse, it may be necessary to divert water flow to enable 

the pipe to be installed well, as it is easier to install a pipe in dry conditions that in wet. In 

such circumstances, this may allow some straightening of existing watercourses. 

The trench should be of sufficient depth to accommodate the pipe and to allow a 

minimum compacted depth of backfill over the pipe, as specified by the manufacturer. 

The larger the pipe diameter becomes, the greater the depth of backfill that will be 

required. 

Catchpits should be provided at the pipe inlet to intercept suspended material. These 

must be at least 300mm below the pipe inlet invert, and large enough to contain the 

expected amount of material. The size will need to be reviewed with experience. 

The bed of the trench should be flat and smooth, and excavated on natural ground, not 

on fill as this could lead to serious scouring and soil erosion. There must be a gentle 

gradient to let water flow through the pipe to the lower side. 

A layer of selected stone material, which is free from sharp stones that might damage the 

pipe, should be compacted on the base of the trench before laying the pipe, and can be 

regulated to ensure the required gradient is achieved. 

The width of the trench should be kept as narrow as possible for the diameter of pipe 

being laid, but you should have at least 300 mm clearance on wither side to allow for 

compacting of backfill material. For larger pipe diameters, it will be necessary to reinforce 

the trench sides to prevent them from collapsing. 

Backfill material should be free from sharp stones that could damage the pipe. Backfill is 

laid in 150 mm layers on both sides at the same time, and thoroughly compacted, taking 

care not to float the pipe. 

Thin walled flexible pipes rely upon well-compacted backfill for their strength, and larger 

diameter pipes should be braced during installation to ensure the final shape is as 

designed. 
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Figure 8: Construction of a cross-drain culvert, longitudinal section

The above sketches are indicative of good and bad methods of installing a pipe; however 

in a larger watercourse, culvert location should be chosen so as not to impede the 

passage of fish. In certain cases a bridge may be required. 

NB: The example given for correct construction would not be applicable where 

passage is required for fish, in this instance the culvert pipe must be laid flush 

with the riverbed. 

Remember: Sub-standard or poorly located culverts are the most common cause for 

tracks to wash out. Culverts should therefore be designed by an engineer and installed by 

experienced operators. 
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6.3.6 Head and tail walls 

All culvert pipes will need protecting around the inlet and outlet, where the pipe goes 

under the track. A number of simple techniques can be applied, depending on the culvert 

diameter. 

 Construction of a sandbag collar, placed around the neck of the pipe and up to 

track level. 

 Construction of a masonry collar, where larger stones are placed around the neck 

of the pipe; 

 Construction of masonry headwall, where larger stones or blocks are cemented 

together to form a wall around the neck of the pipe 

For larger diameter pipes, it may be necessary to also construct ‘wing walls’ around the 

catch pit, or to retain the upper slope. In these cases it is likely that the walls constructed 

will need to be supported by concrete footings (foundations) of at least 200mm thick. 

6.3.7 Bridges, fords and causeways 

A bridge should almost certainly be the preferred option where the span over a 

watercourse is greater than 2 metres. Occasionally, it may be worth considering for spans 

as low as 1.2 m, as bespoke bridge construction could be a more cost effective or long 

term solution to crossing streams and rivers. 

Bridge design should includes full schematic / engineering drawings and be fully costed 

before agreeing then. 

Vented causeways (also known as Irish bridges) and fords are not to be recommended for 

forestry use. Although cheap, they are liable to be a source of pollution, both during 

construction and when in use, and can be dangerous in time of flood. They can also be 

the cause of scouring downstream.

6.4 To stone or not to stone a track 

The Formation and Capping layer will normally be enough to allow harvesting operations 

to take place, and for timber to be extracted from the woodland to a loading point. The 

main reasons for applying additional layers of stone material are; 

 To improve the strength of the track Formation in particular locations; 

 To aid repair of damaged areas in an existing track Formation; 

 To improve the quality of the surface, and thereby increase the variety uses the 

track can be subjected to. 

Adding layers of road surfacing will only usually be undertaken for those sections of track 

where haulage lorries or other such heavy vehicles require access. The route selection 

process will have identified how much of the track needs to be of sufficient specification to 

carry heavy haulage vehicles. 

However, the quality of the surfacing material used will define the running quality of the 

road surface, and ultimately determine the type of use it gets. Choice and treatment of 

surfacing material is therefore very important. 

If access is needed throughout the year for heavy machinery, you may need to put on 

extra stone to help form a strong running surface. However, this adds greatly to the cost 
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of the track, and can normally only be justified where access for machinery is essential all 

year round, or where the ground conditions are very poor. 

Where you are widening or reinstating an existing track, you will be able to reincorporate 

existing stone materials from the previous track structure as part of the Formation. This 

may help strengthen the formation and result in less stone having to be supplied for 

capping and or surfacing layers. 

Bringing in stone is very expensive, and different types and sizes of stone have different 

structural properties. If you think that you need to import stone, consult an engineer, as 

costly mistakes can be made by bringing in the wrong material. 

An awareness of the environmental implications of importing stone is also needed. For 

example, using an acidic stone in a sensitive base-rich area may adversely affect the 

native vegetation. 

6.4.1 Tracks and roads on thick clay 

Thick clay is one of the most difficult types of ground on which to construct access routes. 

Never use wheeled machinery for formation work on clay as it may sink and create huge 

ruts. A tracked excavator is essential, but only the minimum of cutting should take place, 

(but you must still remove stumps). Remember that you are not expecting to win stone 

from lower down as with shale. Instead, once the formation cut is made, you will need to 

bring in high quality stone to make the Formation and the running surface strong, and 

prevent the rain penetrating to the clay underneath. 

Stone needs to be carefully specified and laid in layers. The first needs to be fine to 

"blind" the clay, before larger material is added to build strength. A finer top layer is then 

needed to seal the surface well. ''Blinding" the clay will prevent larger stones penetrating 

into the clay which would weaken the road and lead to rutting. Consider the use of a geofabric as a separation layer. 

6.4.2 Tracks and roads over deep peat 

Deep peat is usually level and therefore a track should be built in a similar way to a forest 

road, with a crown that drains water both ways. This will make the track more stable. 

Utilizing vegetation and brash will help to reduce the amount of stone needed (see table 

4). Sitka Spruce brash is ideal for this, particularly if long tops are laid across the track in 

what is often called "corduroy" style. Large amounts of fresh, springy brash are needed in 

order to establish a thick mat as it will compress down to a remarkably thin layer. For 

example: A 2 metre pile of fresh, loose brash will compress to form a mat as thin as 

30cm thick. 

If cutting a new road line through a crop, incorporate all the brash from the trees felled to 

make the formation cut, as well as the upturned root plates of trees. 

Figure 9 shows how a road or track over peat needs to sit on top of the peat like a stable 

raft. 
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Figure 9 - Track over deep peat 

Consult with an engineer for best designs for tracks over peat. 

6.4.3 Timber haulage roads 

Forest roads are very well built sections of forest track, with several layers of well 

compacted surfacing applied to give a safe and consistent running surface for timber 

lorries. For issues that need considering when constructing forest roads, see Appendix 3

It should also be remembered that forest roads are very different to the public highway. 

Not only is the forest road normally single lane, but edges and verges are often soft and 

may not be safe for large or heavy vehicles. 

Traction on forest roads can often be much less than on public roads, particularly in wet 

conditions, and they are subject to more irregularities than many public roads, such as 

potholes, ruts, sharp stones and general roughness. 

Manoeuvring for large vehicles on forest roads can also be very awkward, but design 

standards take this into account. The design criteria are based on slow moving timber 

haulage traffic. 15mph should be regarded as the maximum safe speed. 

Therefore, the width of the Formation, and the running surface laid on top are critical to 

safe use of the road by hauliers. On straight sections, the normal running width should be 

around 3.4 m. A greater running width is required on forest road corners. Appendix 3

gives information on running surface widths required. 

Where possible, the design of the forest road and track network should encourage 

harvesting machines and harvesting activities to be kept off the surfaced carriageway. 

The harvesting infrastructure required, such as timber stacking and loading points, ramps 

etc, should be constructed at the same time as the road, as this will reduce overall costs. 

6.4.4 Surfacing forest roads 

Surfacing material is, at least to some extent, a sacrificial material in the sense that it will 

be lost (worn away) over the years. This should be considered when choosing the 

surfacing materials and designing the road thickness. 

Despite the knowledge that it will need to be replaced, the surfacing material should be 

durable and of a quality that will enable it to be shaped and properly compacted. 
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The ideal material is MOT Type 1, well-graded, granular material. There should be 

sufficient silt to clay fraction to facilitate sealing. When laid on top of the Capping layer 

and compacted, the initial surfacing thickness should be at least 100 mm. 

However, depending on the underlying soil type and the strength of the Formation, you 

may need to consider greater depths of surfacing materials. See Appendix 2. 

Importing material for surfacing is expensive. However, this cost is almost always 

worthwhile compared to using an unsatisfactory, locally worked material when all the 

attendant costs, including increased maintenance, are considered. 

6.4.5 Depth of stone needed for surfacing 

Table 6 gives some guidance about the depth of stone that might be needed for year 

round access on different types of ground. 

Table 6: Depth of stone needed 

Type of ground Recommended depth of stone 

(for running surface) 

Useful tips 

Firm Shale No need to bring in stone, self 

metalling. 

Shale can wash out easily so 

avoid steep gradients and 

bends. 

Brown earth, and 

weaker shales 

Up to 300mm stone. About 

200mm if a geo-fabric is used. 

If good stone can be dug on 

site, compare the cost of 

digging it to buying it in. 

Thick Clay Up to 450 mm of good quality 

stone is essential in order to 

make a strong running surface. 

About 250mm if a geo-fabric is 

used 

After formation, “Blind” clay 

with fine stone before adding 

coarser stone to build 

strength. 

Deep Peat 

Specialist 

construction 

techniques required. 

Consult an engineer. 

If lying directly on peat, you 

may need 600-1000mm of 

stone. 

Reduce the depth of stone 

needed to 300 – 500mm by 

laying slate waste, (100mm 

size), or geogrid on top of 

vegetation and/or brash mat. 

Commonly used grades of road stone are: 

 MOT type 1 37mm diameter down to dust 

 MOT type 2 18mm diameter down to dust 

Membrane – the use of a Geogrid material is preferred on peat, is recommended on 

heavy clay soils, and may be used in other localised situations where appropriate – for 

example, where there is water logging or site sensitivity. 

The membrane is rolled out over the full width of the running surface prior to pavement 

materials being added and compacted. The manufacturer’s guidelines should be followed 

to ensure that the correct sized stone used, preventing the membrane from being 

punctured or torn. 
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Great care should be taken when considering using material from old mine workings, as 

these can be very toxic and result in pollution of the local vegetation and watercourses. 

In sensitive landscapes, avoid importing types of stone that will look out of place, such as 

white limestone. 

6.5 Roadside harvesting facilities 

For forest roads to function satisfactorily, they must be supported by facilities such as 

turning points, passing points, timber stacking and loading areas, timber landing areas, 

ramps and of course, access to the public highway. 

6.5.1 Turn-rounds 

Turn-rounds need to be provided at or very near the end of the part of the track 

accessible by haulage lorries, optimising the distance that extracted timber has to travel 

between stump and public highway. 

For small woodlands, given the expense associated with surfaced forest roads, this will 

normally be just inside the woodland entrance, with a cheaper extraction track network 

bringing timber from stump to that location. 

However, on long lengths of forest road where there are no junctions or other turning 

facilities, additional turn-rounds are useful at about 1km intervals. 

Where possible, turn-rounds should be situated on level ground, for example, at the top 

or bottom of slopes. It is preferable to reverse turn into the bank side of the road, and 

not over the (weaker) edge, and preferable to reverse turn onto the driver’s side to avoid 

blind spots. 

Where possible, the turn-round should be positioned to be used empty – only for turning, 

as this function can be compromised by stacking timber next to it. 

However, by designing the turn-around to cater for harvesting equipment working off the 

road line, it will permit timber to be stacked next to the turn-round ready for loading. This 

can be achieved by increasing the felled width of the route line next to where turn-rounds 

will be located, but needs a larger area of flat ground in the process. 

However, for large volumes of timber, using a turn-round for stacking timber is not 

recommended as the effectiveness of the turn-round for its prime purpose will be limited. 

The normal turn-round configurations are: 

 ‘T’ shaped (see Figure 4.4 at the end of this section) 

 20m ‘U’ turn 

 Circular turn-rounds are possible down to 11m radius, but 25m transitions are 

required both in and out. There is a tendency for this type of turn-round to get 

clogged with mud and brash during harvesting operations. 

Turn-rounds need to be built to the same specifications as that for surfaced roads, using 

the same materials. However, dimensions for turn-rounds are greater than that for forest 

roads. 

See Appendix 4 for diagrams of styles of turn around. 
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6.5.2 Passing Bay 

Normal width forest roads do not permit vehicles to pass on the carriageway, so where a 

significant length of forest road is to be constructed, consideration should be given to 

providing passing bays, where deemed necessary. 

Because it is difficult for articulated lorries or lorries with trailers to reverse any distance, 

passing places should be situated where the last and next appropriate passing bay can 

still be seen. This will prevent drivers meeting between passing locations. 

Passing bays need to be built to the same specifications as that for surfaced roads, using 

the same materials. 

6.5.3 Loading and stacking areas 

Careful planning allows stacking areas to be off the road line and away from turn-rounds, 

so do not interfere with vehicle movements. However, lack of space often results in the 

timber stacks projecting into the carriageway, with obvious safety implications. 

Well-planned facilities can keep harvesting machines and timber conversion operations off 

the carriageway, limiting damage to the road surface, and minimise, if not avoid, the 

necessity for repairs. 

Lack of facilities may lead to conversion on the carriageway, resulting in the deposition of 

brash and chippings on the surface, and interruption of traffic. NB: Conversion and 

stacking bays are often the most neglected feature associated with timber extraction and 

roads adjacent to these areas are the most likely to require emergency repairs. 

Stacking bays can often be created on the down - side of the road using surplus 

excavated material from the road construction. However, care will need to be taken to 

ensure that the bay is capable of taking vehicle loading. 

Double width bays are useful in certain circumstances for both stacking and loading. 

Stacking areas should be located where the road gradient is not too steep, as fully laden 

lorries can have difficulty moving off. 

6.5.4 Sky-line and hi-lead timber landing areas 

Space is a major design criterion for landing cable extracted timber. The felled width of 

the track should be designed and planned to allow sufficient space for landing, conversion 

and stacking (as required). 

Wherever possible, skyline landings should be located off the track line itself, as the site 

can become very congested with timber. The design of the landing area should allow 

room for timber collection by forwarder or lorry, and therefore attempt to ensure that the 

forest track can be kept clean and clear, permitting the uninterrupted passage of vehicles. 

6.5.5 Ramps and tracks 

Mineral ramps are often necessary to allow harvesting machines access to and from 

extraction tracks or roadside facilities such as timber stacking areas. Heavy harvesting 

machinery should avoid travelling on surfaced forest roads whenever possible to prevent 

unnecessary damage. 
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Ramps and tracks should join the track or road at an acute angle to avoid severe 

manoeuvres scouring and eroding the surface. 

Other points to note are: 

 Ditch crossings must be constructed in a manner that limits the possibility of 

becoming blocked. Pipes should not be less than 300 mm in diameter 

 Care must be taken with ramps coming down onto the track or forest road, to 

minimise any flow of water and material such as soil onto the road. Cut-off grips 

across the ramp can be used to reduce the water (and mud) flow. Additionally, 

they often need silt traps to avoid pollution and contamination of the roadside ditch 

or other watercourses 

 It is sometimes useful to have a shakedown zone adjacent to the road. Stoning the 

first 25m of track with clean stone, in the range 100 – 200 mm, may help to shake 

off the soil and mud and avoid detrimental contamination of the road surface 

 Grips and shakedown zones require maintenance! 

 Log ramps over ditches are not recommended. Water flow is restricted and soil is 

easily stopped between the logs, causing water to be held up 

 Ditch crossings at track and road summits have least effect on the roadside 

drainage. 

6.6 Access to the public highway 

The junction of the forest road or track and the public highway will be the most trafficked 

part of the access infrastructure for the woodland. 

The junction has to provide safe entry and exit to the woodland entrance for heavy and 

slow timber lorries, and so it is no surprise that the local planning authority have a 

regulatory role in approving its placement and aspects of the construction specification. 

See section 4.1. 

The apron of the junction has to be constructed to a high standard in order to provide the 

stability needed by fully laden lorries turning. 

Most local highways/roads authorities will require some bituminous material to be laid in 

the immediate vicinity of a public road. Such work should be carried out to their required 

specification. 

Particular care will be required with visibility splays from the forest road onto the public 

road. Many local highways / roads authorities will specify the minimum requirements that 

have to be met. The maintenance of such splays should be of importance in order to 

protect those using the woodland entrance and the public highway. 

On a busy public road, it is undesirable for a lorry turning left (whether into or out of the 

access) to have to cross the public road centreline. Infilling the turning corner will help 

the lorry turn into or out of the junction. A possible layout for a 90 junction with a 

‘major’ public road is shown in Appendix 6. 

One-way skewed accesses can be used to reduce earthworks or to divert traffic in a 

chosen direction. An example is shown at Figure 4.7 at the end of this section. 
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6.6.1 Bituminous macadam surfacing 

Bituminous macadam surfacing is an expensive alternative to mineral surfacing of a forest 

road. As with mineral surfacing, it would be used when wanting to increase the pavement 

strength and provide a running surface for haulage lorries. 

In most situations, it will be cheaper to increase the depth of metalling need to 

strengthen the pavement, and therefore blacktop normally overlooked for the majority of 

forest roads. 

Compared to water bound materials, maintenance of and repairs to bituminous materials 

are both more difficult and more expensive. However, over any given period of time, a 

well-constructed bituminous road should require less maintenance than a water bound 

road. 

There are some instances where blacktop has justifiable uses: 

 to increase the pavement strength; 

 unavoidably steep gradients where it is necessary to increase the traction for 

lorries; 

 areas where dust suppression is required, for example, adjacent to property; 

 where ice and snow is cleared by mechanical means or salt application ; 

 at the junction with the public road. As required by the local highways/roads 

authority. 

If Bituminous macadam is to be used in a forestry setting, advice should be sought from a 

qualified civil engineer to ensure that the correct system or specification is used. 

Care should be taken to ensure that the underlying Formation material is: 

 non - frost susceptible to a depth of 450mm; 

 of adequate strength and in good condition; 

 correctly shaped and fully compacted. 

6.6.2 Bituminous surface dressing 

Using Bitumin as a surface dressing will not add to the pavement strength as it is simply a 

thin layer applied to the surface of an existing pavement. The main reasons for its use 

would be to: 

 increase the traction; 

 reduce water ingress into the pavement; 

 dust suppression. 

Bitumin surface dressing on water bound roads can easily fail in frosty weather. 

Vibrating rollers should not be used on surface dressing as the chippings may be pushed 

in 

Again, advice should be sought from a qualified civil engineer to ensure that the correct 

system or specification is used. Correct advice will help to minimise this risk. 
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6.6.3 Road planing 

Road planing can be a useful and cheap surfacing material where available, but does not 

add to the pavement strength. 

The main use for the material is as dust suppression and for avoiding the migration of 

other surface materials. They can be used thickly at bridges to stiffen approaches and to 

reduce potholes. 

On sensitive sites it is undesirable because it has the potential to leach toxins into the 

surrounding soils, damage vegetation and pollute watercourses. 

Road planing is viewed by some authorities as controlled waste, regardless of the fact 

that an end use is planned. Advice may be necessary from the local Environment Agency 

or planning authority on storage (if required) and conditions of use. 

7 Contract specification 

Understanding what is required to construct a sustainable track within woodland is key to 

being able to draw up a specification the contractor should follow. 

A typical specification should detail: 

 Is the track is to be constructed from new / upgraded from existing 

 What is the route line the track is to follow 

 Consents required / obtained, and where they apply 

 Felled width required for clearing the route line 

 Width and depth of the Formation – basic / stoned etc 

 The use (Tractor/Forwarder/Haulage), and therefore, the type of running surface 

 Width of the running surface and radius of corners 

 Gradient (between 2% and 20%) and crossfall (between 4.5% and 8%) 

 Stone type and depth 

 Using a Geotextile membrane, with alternative stone type and depth 

 Number of cross drains, their construction, location and diameter and placement. 

8 Maintenance and aftercare 

8.1.1 Road maintenance 

All waterbound tracks lose material over time due to attrition. This loss happens because 

of weathering as well by the harvesting and haulage of timber. 

The correct profile on a track made of good material will shed water efficiently and 

vehicles will experience a smooth ride. However, sudden changes in camber, adverse 

camber on bends, differential settlement of the wheel-tracks, deep potholes and ruts are 

all hazards that may emerge and need to be repaired. 

Recarpetting will be necessary from time to time to replace lost material and ensure a 

smooth running surface. 
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Maintenance should be carefully planned and programmed in order to maximise 

effectiveness. The frequency of routine road maintenance should be determined by need 

and not necessarily by time span. 

Take care to limit the loss of expensive pavement stone during maintenance operations. 

Herbicide spraying is an effective means of keeping down grasses and non-established 

woody growth, but it must be undertaken with care and adherence to safety precautions. 

Flail mowing can be effective for grasses and small diameter woody growth. A heavyduty flail mounted on a tractor can clear the vegetation off the carriageway. Given 

suitable access conditions, this combination can also control vegetation in the ditch and 

(to a certain extent) on the batter slope. 

The limitations on maintenance of harvesting tracks mean that they may well suffer from 

vegetation growth and water damage. This should not be allowed to progress to the point 

that the road is in danger of being lost. 

8.1.2 Road repair 

Routine road maintenance is not always sufficient to keep a road in the condition 

necessary for the required use. Other repairs are commonly needed because of: 

 harvesting damage; 

 pavement failure; 

 surface failure; 

 loss of material. 

Harvesting damage can often be minimised or even avoided by good planning and use of 

the site. However, where damage does occur, for any reason, often the only effective 

solution will involve additional stone. 

Pavement failure is often deep-seated, and may be due to failure in the foundation or 

structure of the road. This is often associated with excess water causing saturation of the 

material which has failed. Excavation of the poor material is likely to be the only longterm solution. 

In such cases, improvement of the drainage may well be sufficient to reduce the moisture 

content of the various levels. Reshaping and sealing the Pavement will then prevent the 

further ingress of water. However, new material may also be required. 

Surface failure can be the result of soft material or the breakdown of the surfacing 

material under repeated load – heavy vehicles travelling back and forth. It is associated 

with shallow rutting, potholing and an increase in surface fines. There is also some 

evidence to show that super-single tyres can increase the stresses in the surface layers 

leading to an increase in surface failure. 

In such cases, grading and rolling can easily bring back the track surface profile, but new 

material may also be required. 
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8.1.3 Ditch and culvert maintenance 

The purpose of ditch maintenance is not so much to have a clean ditch, but to ensure that 

there is a reasonably free flow of water. In some instances, a clean ditch can increase 

water velocity to the extent that damage ensues. 

Much ditch maintenance is carried out by excavator or by hand, although, on sections of 

forest road it can be possible to use the grader when road maintenance is occurring. 

Where the ditch abuts a forest road, care must be taken to ensure that no damage is 

done to the road structure during ditch maintenance. 

During ditch maintenance, it is essential that the culverts are: 

 not damaged by ditch maintenance operations; 

 examined to ensure that they are sound and free flowing; 

 cleaned out if required (particularly the entrance point); 

 that the associated sump is also cleared out. 

Although much of the necessary work can be done with the excavator bucket, there is 

often a need for some manual work. This is obviously true of the cleaning out of culverts. 

Care must be taken to ensure that culverts are examined to ensure work is carried out 

adequately to allow water flow. 

The sump to any culvert should be sized to accord with the maintenance regime and the 

capacity of the local soils and track material to erode. Any excavated material should 

either be removed or placed in a stable position away from the ditch. 

Where a culvert has been damaged and water flow through it is restricted, it must be 

replaced. This will involve excavating a trench to remove the existing culvert pipe and 

replace with a new one, as per Section 6.3.5. 

The removed pipe should be disposed of as per manufacturer’s guidance, and excess 

minerals either reused, if suitable, or cast aside and spread locally. 

8.1.4 Weather effects 

Although frost, snow, ice and rain are often the most commonly considered weather 

effects, dust control can also be very important. 

Water damage is common. It should be dealt with as early as possible to try to prevent 

serious damage ensuing. 

Frost, snow and ice must be treated with extreme care. Reduced traction will mean 

increased hazard. 

Salt should not be used in an effort to remove snow or ice. Not only will rapid thawing 

render the surface loose, saturated and weak, but salt is deliquescent to some extent and 

will continue to attract moisture from the atmosphere. Drying out of the track thus 

becomes a very slow process. Salt will also damage adjacent vegetation. 

Coarse grit should be used to improve traction. It will bed into snow and ice, and when 

the weather improves will be removed by traffic. 

In warmer, drier weather, dust control can be a problem with water-bound road surfacing 

materials. As the surface dries out, fine material ceases to be bound in and can be 
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removed by the effect of wind or the passage of a vehicle. Loss of fines not only affects 

the integrity of the road in that the surface may become loose due to lack of binding, but 

may represent a nuisance or even a health risk. This will depend on the situation. 

9 Useful references 

 Forest and Water Guidelines (4th Edition) 

 Forest Research TCB Technical Note 27/98 – Access track construction in small 

woodlands 
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Appendix 1: Economic appraisal 

Economic appraisal is a scientific equation used to minimise the total costs of extraction 

of timber from stump to the public road, and to provide an optimum road / track 

configuration for a particular woodland. In theory, the minimum infrastructure cost occurs 

when the total roading cost approximately equals the extraction cost. See Figure 10. 

The relevant equations for optimum road density and optimum spacing that result from 

this principle are: 

 _____ _______ 

Road density, x = / k.h.V m/ha spacing, S = /2.R.ni.wf km 

  R  h.V.ei 

Where, 

ei = extraction inefficiency, taken as 

1.30 for extraction using wheeled vehicles 

1.10 for extraction using cable crane 

h = extraction costs pence / m3 / 100m 

k = (0.25 . ni . ei) / wf 

ni = network inefficiency due to junctions, terrain limitations etc., taken as 

1.35 in flat terrain 

1.40 in hilly terrain capable of being worked by wheeled vehicles 

R = combined cost of initial construction and the capitalised cost of annual 

maintenance expressed as £ / m 

V = discounted vol. m3 / ha (i.e. average volume discounted back to time of 

first thinning) 

wf = working factor relating to the use of the road, taken as 

1.0 for extracting from one side of the road only 

2.0 for extracting from both sides of road 

The ability to work to both sides of the road is obviously more efficient and would require 

less roading. 

Although there is a theoretical optimum road density and minimum cost, a balance has to 

be struck in any particular location. More road length increases the roading cost but 

reduces the extraction cost by cutting down the distance from stump to roadside. 

Good forest roads cost more than tracks, but they should be usable throughout a greater 

part of the year. 

The choice of harvesting system could have a limiting effect upon the spacing of roads. 

The appraisal is usually taken over a complete crop rotation, and normally assumes the 

road to have no residual value. 
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Figure 10 

The positioning of a road can also be appraised to some extent. In steep terrain, uphill 

extraction will obviously be more expensive than downhill. A reasonable approximation 

might be to site the road so that the ratio of extraction distance uphill to downhill is the 

same as the ratio of extraction costs downhill to uphill. For example, in a simple 

situation, this means that for a rectangular plantation with boundaries and road 

perpendicular to the slope 

Dup = Vup = hdown

 Ddown Vdown hup 

where 'D' = distance, and 'V' and 'h' are as defined in the table above. 

A further appraisal may be required to ascertain the optimum timing of the provision of 

facilities in relation to the timing of harvesting. Computer appraisal programmes, such 

as FIAP, can be used to optimise timing of activities. 

. fgkl;sdgtkol;erotpertpoertporetpo 

`+--TIO 
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Appendix 2: Soil strength, Formation width and Pavement thickness 

The California bearing ratio (CBR) is a penetration test for evaluation of the mechanical 

strength of road subgrades and base courses. The CBR test is fully described in BS 1377: 

Soils for civil engineering purposes: Part 4, Compaction related tests. 

The CBR rating was developed for measuring the load-bearing capacity of soils used for 

building roads. The harder the surface material, the higher the CBR rating, but moisture 

in the soil can have a significant effect on soil strength. 

The following table which follows gives an indication of the variations of CBR which are 

possible at different moisture contents: 

Table 7 - CBR 

CBR (California bearing ratio) 

Position of Water Table 

Soil Type >600mm below formation <600mm below formation

Heavy clay 2 – 3 1 – 2 

Silty clay 5 3 

Sandy clay 6 – 7 4 – 5 

Silt 2 1 

Sand (poorly graded) 20 10 

Sand (well graded) 40 15 

Well graded sandy 

gravel 60 20 

Formation width and Pavement thickness are a function of many factors including: 

 sub-grade strength 

 variation expected in moisture content 

 pavement and surface material quality 

 number of axle loadings, and their intensity 

The Pavement width must be structurally sound over the total running width. By having a 

designed thickness of Pavement, it allows material quantities (locally won and imported) 

to be assessed and costed, and a Bill of Quantities to be formed. 

The final use of the running surface will dictate what materials are actually applied on the 

ground. NB - harvesting track will have a more robust surface than a haulage road, but 

they should be constructed to the same thickness of Pavement in order to have the right 

strength. 

The following table gives an indication of the total thickness of pavement that will be 

required for the various CBR values. 
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Table 8 

Typical material 

(but see previous 

table) 

CBR 

(%) 

Minimum Formation 

Width (mm) 

Pavement 

Thickness (mm) 

Peat, silt <2 6000 >850 

(consider excavation) 

Silty clay 2 5500 700 

Heavy clay 3 5400 550 

Sandy clay 4 5400 475 

Saturated sand 7 5400 325 

Fine sand 10 5400 250 

Graded sandy gravel 20 5400 150 

Rock 250+ 5400 Min. 100 to allow 

grading of surface 

Notes to Table 

 The minimum Formation width has been calculated based on a running width of 

3400mm, plus 1.5 times the Pavement thickness on each side, with an overriding 

minimum of 5400mm. 

 The minimum Formation width will need to be increased to allow for a topside ditch 

on sloping ground, an embankment, or for safety reasons e.g. to keep the traffic 

away from a large drop down an embankment or into a ditch. 

 Sub-grade strength often varies extensively under the Formation of a new road. 

Subsequent drying out of the sub-grade and pavement often increases the 

strength. 

 It may be impracticable to drain fibrous material (peat) and some clay soils 

successfully. 

 Pavement thickness can often only be assessed by using site based, competent 

judgement. 

 The minimum depth of construction to obtain the desired strength should be used. 

 The Pavement material needs to be of appropriate strength for the depth below 

surface. Lower layers can often be constructed using a low quality locally won 

material. 

 The top 100mm of pavement must be of a durable stone that will not readily break 

down under the wheel loading. It must also be suitable for grading and rolling. 

 Surfacing may need a binder / sealer of fines or cohesive material. 
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Appendix 3: Gradients, alignments and curves 

Measuring Gradient 

Forest roads are normally constructed of water-bound macadam. This form of 

construction has limitations for traction, particularly under wet or frozen conditions. 

 Where possible, gradients should be maintained within the range of 3-7% to avoid 

both flat gradient effects (e.g. potholing) and steep climbs. Given the normal 

methods of setting out a forest road, an accuracy tolerance of 0.5% is considered 

reasonable. 

 The nominal maximum gradient should be 10% on straights or horizontal curves 

that do not require road widening. 

Gradient should be measured between tangent points (TP) as shown schematically below. 

Method of Measuring Gradient 

Experience has shown that short lengths (< 200m) of steeper gradient (≤ 12.5%) within 

an overall gradient of 10%, can be accommodated on water-bound surfaces in good 

conditions. However, this relaxation must be used with caution, and only where it can be 

safely accommodated within the prevailing geometry. 

1 unit 

high 

TP 

Normal minimum = 10 units 

long 

TP NB not to scale 

It is difficult for lorries to move off from rest on a steep gradient. Where possible, 

stacking bay and turn-round locations should be planned for points where the gradient is 

no steeper than 5%, or where the gradient can be slackened over a short length to ease 

loading, increase stability when manoeuvring and aid traction. 

A bituminous surface will allow lorries to negotiate much steeper gradients (~ 16%), but 

such a surfacing is expensive both to construct and to maintain. However, in some 

circumstances this could save considerable road building costs. 

To facilitate ease of movement from rest, wherever possible, the approach gradients to 

junctions should be limited to 5%. 
 Operations Note 25 

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Version 1.0 issued 19.08.11 | Operations Note 25 | 47 

Vertical alignment – minimum gradient 

Water-bound macadam gives rise to problems of surface water disposal. 

Standing water on the surface rapidly leads to saturation, a reduction in Pavement 

strength, and the formation of potholes. 

Roads constructed with a longitudinal gradient will always shed water better than roads 

that are essentially level. This is especially important in the bottom of sag curves. Such 

lengths should be kept to a minimum. 

The recommended minimum longitudinal gradient is 2%. 

Horizontal alignment 

NB: The following recommendations are based upon the normal 16.5m length articulated 

vehicle permitted under the Road Vehicle (Construction and Use) Regulations 1986. 

In general, a rigid vehicle (even with drawbar trailer) will perform most manoeuvres 

within the space required by a large articulated vehicle. 

The design width for new construction and upgrading will be 3.4m on a straight 

carriageway. 

This width will have a tolerance of 0.2m resulting in an actual minimum width of 3.2m. 

 The tolerance quoted above has been introduced to take account of the normal 

construction methods used for forest roads. Every effort should be made to 

achieve the nominal design width. 

 The widths quoted above refer to running surface. This width does not include any 

berm, safety margin or side slope of any description. 

Horizontal curves 

Circular curves will normally be used for horizontal bends. The recommendations which 

follow are based upon the outside radius, this being the line normally followed by the 

outside front wheel of an articulated vehicle. 

To allow for trailer wheel cut-in, bends will normally be widened on the inside, as shown 

in Figure 11 below. Because of the assumed low vehicle speed, transition curves will not 

normally be provided. 

Straight transition lengths are normally used to gain the additional width. See Figure 1. If 

widening on the outside of the bend is unavoidable, these transition lengths should be 

increased by 10m. 

Table 9 below shows the recommended widths and gradients for horizontal curves. 

Intermediate values for distance, gradient and radius can be obtained from by 

interpolation. 

There is no need to widen curves of radius 90m or greater, or where the deflection angle 

is less than 15. 

It must be noted that bends below 45m radius cannot be safely negotiated at 15mph (25 

km/hr) by articulated vehicles. 
 Operations Note 25 

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Version 1.0 issued 19.08.11 | Operations Note 25 | 48 

Table 9: Horizontal curve recommended widths and gradients 

Deflection of circle. 

From chord of 

length for setting 

out (m) 

Outside 

Radius

Minimum widths for 

maximum Angle 

of deflection ( o ) 

Transition 

Straight 

Length 

Maximum 

desirable 

gradient on 

outside radius 

15m 20m 30m 15 45 90 180 ** ** 

Running surface width 

m m m m m m m m m % 

0.3 0.6 1.3 90 3.4 3.4 3.4 3.4 - 10 

0.5 0.8 1.9 60 3.4 3.8 4.0 4.0 20 8 

0.6 1.1 2.6 45 3.4 4.0 4.5 4.5 20 7 

1.0 1.7 4.0 30* 3.4 4.4 5.0 5.1 25 6.5 

1.2 2.1 5.0 25 4.6 5.1 5.3 30 5 

1.5 2.7 6.8 20 4.9 5.6 5.9 30 4.5 

2.0 3.8 15 6.3 7.0 40 4 

10*** 10.0 40 5 on diagonal 

* Preferred minimum radius 

** Figures based on experience 

*** Absolute minimum hairpin 

Figure 11 

Deflection Angle

Bend

W idth

Transition Length

3.4 m

B en d

R a d iu s

Bend

Width

Transition Length

3.4 m

Deflection of circumference

from chord for setting out
 Operations Note 25 

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Version 1.0 issued 19.08.11 | Operations Note 25 | 49 

Appendix 4: Diagrams for a T Shaped turn-round 25 m 10 m 5 m 5 m 5 m 5 m

1 m

20 m

The turn around is symmetrical about the spur leg.

It can be difficult to construct on steep cross-falls.

Drivers prefer to reverse onto their side,

i.e. with spur on RHS on approach, as shown.

The widening opposite the leg of the 'T' is optional,

but this allows more room for manoeuvring.

The leg can be lengthened to further ease manoeuvring.

There is no allowance for stacking or harvesting.

The leg can be lengthened and / or widened to provide

extra working space.

Figure 4.4(a) T - Shaped Turn Around

3.5 m

5 m

7 m

5.8 m

3.7 m

4.4 m

3.5 m

5 m

4 m

3.4 m

T Shaped turn-round 

The turn around is symmetrical about the spur leg. 

It can be difficult to construct on steep cross-falls. 

Drivers prefer to reverse onto their side, i.e. with 

spur on RHS on approach, as shown. The widening 

opposite the leg of the 'T' is optional, but this allows 

more room for manoeuvring. 

The leg can be lengthened to further ease 

manoeuvring. 

There is no allowance for stacking or harvesting. 

The leg can be lengthened and / or widened to 

provide extra working space. 
 Operations Note 25 

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Version 1.0 issued 19.08.11 | Operations Note 25 | 50 

Alternative diagram: T Shaped turn-round. 

25 m transition

transition

6.1 m

25 m transition

6.1 m

22.5 m

4 m

11 m radius

11 m radius

3.4 m

T Shaped turn-round
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Appendix 5: Diagram for a passing bay 

3.4 m

4 m

15 m 5 m

3.7 m

5 m 5 m 10 m

4.8 m

6 m

40 m

Figure 4.5 Lorry Passing Bay

The lorry passing bay is symmetrical 

about the centre line

10 m 5 m

7.2 m

6 m

4.8 m

Centre Line 

Passing bay for heavy vehicles 
 Operations Note 25 

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Version 1.0 issued 19.08.11 | Operations Note 25 | 52 

Appendix 6: Diagram for access to the public highway 

5 m

A junction with a classified public road will need consultation 

with the Highway / Roads Authority and local Planning Authority.

A junction with an unclassified public road will need consultation

with the Highways / Roads Authority.

Public road distances are measured from the centreline of the forest road.

Forest road distances are measured from the edge of public road.

This design caters for left hand turns (both into and out of the forest) - 

there is no need for the lorry to cross the public road centreline.

Gates need to be at least 18m back from public road.

Visibilty splays will need to be maintained.

Public Road

5 m

1.4 m

0.8 m

15 m 5 m

5.5 m 5.5 m

0.8 m

2.7m

10 m 10 m

3.65 m5 m

3.65 m 5 m

2.4m 3.6 m

2.7m 2.0m

11 m radius

5 m 5 m

1.8m 2.2 m

3.5 m

10 m

Forest Road3.4m

10 m

Junction with a major public road 
 Operations Note 25 

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Version 1.0 issued 19.08.11 | Operations Note 25 | 53 

Alternative diagram: Access to the public highway. 

Figure 4.7 Skewed Minor Public Road Junction

Consultation is required with the Highway / Roads Authority (and local Planning 

Authority if road classified).

Reducing the junction angle reduces the earthworks, but increases the interface,

(hence possible increase in surface treatment and longer ditch piping).

Increasing junction angle reduces the need for carriageway support.

Set forest road gate 18m back from edge of public highway.

Keep gradient to 5% on approach to forest road gate.

Visibility splays will need to be maintained.

Min. radius (to stop U-turns)

3.4m

Skewed junction for a minor public road 

Public highway 
 Operations Note 25 

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Version 1.0 issued 19.08.11 | Operations Note 25 | 54 

Appendix 7: Cross section diagrams of track profile on slopes Typical Road Cross - Sectional Details Carriageway See Fig. 5.6 250 mm minimum camber over half formationFigure 5.1 Cutting in Soil or Rock Drain on both sides of cutting. Minimum 150mm below formation level. SOIL 2 m min. Cut - off ditch if required 2 m Lip to be rounded 1.5 m 3.4 m Ledges on cut to assist vegetation growth. ROCK 2 m min. 1.5 m Excavated material to be side cast away from cutting and landscaped, used in construction or carted away. Do not obstruct harvesting routes. 25 m minimum preferred 75mm mimium camber over half width For side slopes see Section 5.6
 Operations Note 25 

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Version 1.0 issued 19.08.11 | Operations Note 25 | 55 25 m minimum preferred

Figure 5.2 Embankment on Good Foundation

Typical Road Cross - Sectional Details

Rock Fill

 3.4 m carriageway

Ditch if required

No need to remove stumps,if below formation level

Soil Fill

2m

Ditch if required

The embankment width will dependon height, safety etc..For side slopes see Section 5.6.

2m

75mm minimum camberover half width.

250mm minimum camber overhalf formation width.

See Fig. 5.6
 Operations Note 25 

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Version 1.0 issued 19.08.11 | Operations Note 25 | 56 Typical Road Cross - Sectional Details

Figure 5.3 Cross Fall up to 10 Degrees

25 m minimum preferred

250mm camber overhalf formation width

Ditch if required

Lip to be rounded

varies

Excavated material to be side cast

varies

away from the cutting, landscaped,used in construction or carted away.Do not obstruct harvesting routes.

3.4m carriageway See Fig 5.6

75mm minimum camberover half width.

For side slopessee Section 5.6

As far as possible,formation to be onundisturbed suitablematerial.
 Operations Note 25 

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Version 1.0 issued 19.08.11 | Operations Note 25 | 57 25 m minimum preferred

Pavement founded on undisturbed suitable material.Formation to have 250mm minimum crossfall inward.100mm minimum metalling to allow grading and rolling.

Figure 5.5 Rock Ledge Cut into Steep Cross Fall

 Typical Road Cross - Sectional Details

 3.4m carriageway

Rock cutting as steep as practical.For side slopes see Section 5.6.Small ledges on cut will assist vegetation growth.

Lip to be rounded.

2m minimum

1.5m

Berm if required assafety barrier or tohide road.

Excavated material to be side castaway from the cutting, landscaped,used in construction or carted away.Do not obstruct harvesting routes.Brash to be placed at the bottom ofthe slope for short term stability and as a safety barrier.

Cut-off ditchif required

75mm minimum camberover half width.

See Fig. 5.6

Initial bench required ifstability a problem.
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