trails manual section9

Crusher Fines Surface Trails

SECTION 3

Crusher Fines Surface Trail Specifications

CRUSHER FINES (crushed stone) TRAILS combine some of the rustic feeling of natural surface trails with a durable surface suitable for higher usage levels in more seasons. As a recreational resource, these paths should provide a good trails experience to residents and visitors alike in all seasons. As a transportation resource, these trails can serve a limited role as an alternative to motorized travel. For both recreation and transportation, it’s essential that the trails be well designed, well constructed, and properly maintained.

The Goals of the County for crusher fines trails are to:

Accommodate a moderate number of users safely, as well as a moderate variety of users.

Promote the feeling of being outdoors, the feeling of proximity to nature.

Provide not just multiple usages, but also multiple purposes. For example, recreation as well as commuting.

Link multiple activity centers/population hubs and a variety of destinations.

Provide a quality recreational experience regardless of the main purpose of each individual user (a user may be primarily commuting but should also enjoy the commute).

Connect to other trails of all types whenever possible.

Be accessible (or at least barrier-free) to the physically challenged whenever possible.

Be built to high-quality construction and aesthetic standards so that people will use, enjoy, and support the path.

Be consistent in design yet have enough spontaneity to avoid the “master-planned” feel.

Blend with the landscape so that the path seems as though it belongs there.

Be physically stable.

Be easy to maintain (less than 6% cost/year).

3-1 Trails Design and Management Planning Handbook


Usage and Site Parameters

Usage Parameters

Crusher fines (crushed stone) surface trails are moderate-use trails that can accommodate all foot traffic and limited wheeled traffic. Unlike hard surface trails, crusher fines cannot develop cracks or break up, and the naturalistic gravel-like surface feels more like a trail than a hard surface path and thus easily integrates with undeveloped sites. When properly constructed and drained, the trail surface is sufficiently stable to be usable in all seasons at almost all times. Crusher fines trails can be designed and constructed to be barrier free to the physically challenged but, due to the soft surface, cannot be considered fully accessible.

The flexibility of crusher fines usage makes it possible for these trails to serve many different purposes. Crusher fines can be used for bike paths, as an adjacent trail for a hard surface multiple use trail, and as a weather-resistant surface for some hiking, walking, and nature trails. The width of the trail can vary as needed.

These trails can be considered a part of an alternate transportation system, but the rougher surface makes these paths more difficult than a hard surface for all bicyclists. Generally, crusher fines are less suitable for road bikes than for mountain bikes.

Do not plow crusher fines trails in winter. Besides possibly disturbing the surface, the piled snow on each side will trap runoff during spring snowmelt and possibly cause large-scale washouts.

User Types

Unconditional usage

Crusher fines trails can easily accommodate:

Hikers Walkers Joggers Runners

Conditional use

Usage by each of the following should be determined on a case-by-case basis. Some design and construction restrictions apply where some of the following are permitted:

Equestrians Mountain bikes Road bikes Cross-country skiers may be able to use the trail in winter depending on snow

conditions. Grooming is optional.


Site Parameters

Trail WidthRefer to the Trail Widths based on Usage Level chart on page 1-4 for the proper width and add a side clearance of 3’ each side for safe and enjoyable use.

Critical issues for crusher fines trailsWater, drainage, and the types of usage are the primary considerations for designing and constructing crusher fines trails. Crusher fines are highly susceptible to washouts from running water. Also, depending on the fines material, the surface can become unstable if the fines are saturated with water (such as during spring snowmelt). The interrelated critical issues for crusher fines trails are:

1. the types of trail usage,2. the selection of the fines material,3. the grades and alignment of the trail, and4. the construction and maintenance of drainage features.

The Three types of Crusher Fines TrailsBecause the types of trail usage largely dictate trail design and construction, the County has standards for three types of crusher fines trails:

Type 1: Bike pathsType 2: Primarily pedestrian with bicycle and/or wheelchair accessType 3: Pedestrian only

The standards for each trail type include grades, drainage features, curves, sightlines, hazard zones, and clearances. For an introduction, see Overview of Crusher Fines Trail Types, p. 3-7. For details on a given trail type, see Crusher Fines Type 1: Bike Paths, p. 3-9, Crusher Fines Type 2: Primarily Pedestrian With Bicycle and/or Wheelchair Access, p. 3-14, and Crusher Fines Type 3: Pedestrian Only, p.3-19.

Selection of the fines materialCrusher fines are available in various stone types, colors, and screens (particle sizes). Not all crusher fines are suitable for trails. Moreover, a series of trade-off may need to be made between surface smoothness and erosion resistance, between colors and rock types, and between choice and availability. See Crusher Fines Characteristics, p. 3-4, for explanations of how crusher fines behave on trails and Specification and Testing of Crusher Fines, p. 3-6, for methods of testing various crusher fines mixes for suitability and for the criteria for selecting a mix.

Crusher fines surface construction methodsGuidelines for building crusher fines trails on various cross slopes are given in Crusher Fines Trails Cross Sections, p. 3-23. Various construction methods for crusher fines trails surfaces (depending on subgrade soils, site drainage, and motor vehicle traffic) are given in Crusher Fines Path Construction Methods, p. 3-42. Crusher fines trails can also be built as foundations or interim surfaces for later hard surface trails (see Crusher Fines Path Construction Methods).

Drainage features Drainage is critical to crusher fines. The trail surface must be protected from even small concentrated flows of running water, and efforts must be taken to prevent the fines from being saturated with water. If drainage is not handled correctly, the trail can wash out or form semi-permanent ruts from usage. See Crusher Fines Trail Drainage, p. 3-28, for complete guidelines to drainage features for crusher fines trails.

Access by the physically challengedMany crusher fines trails can be made barrier-free to the physically challenged. Whenever feasible, barrier-free construction should be used. See Crusher Fines for the Physically Challenged, p. 3-49.

Trails Design and Management Planning Handbook

MaintenanceIf the trail is properly constructed, maintenance of the trail surface should be minimal but must be timely. In general, maintenance will be needed more often but will be much less expensive than for hard surface trails. Maintenance consists largely of continual inspection of the surface for washouts, immediate repair of washouts and the source of those washouts, regrading of parts of the trail surface as needed, and occasional addition of crusher fines material to the surface when and where needed. See Crusher Fines Trail Maintenance, p.3-52.

Other featuresOther features of crusher fines trails not specified in this Section are to be done as specified for hard surface multiple use trails.

Crusher Fines Characteristics

What are crusher fines? Crusher fines are small particles of crushed rock. Sometimes there are leftovers from rock crushing operations in which large particles (gravel) are desired, other times rock is ground especially to make fines. Crusher fines should have a range of particles from a fine dust up to a specified maximum particle size. When the rock type, particle sizes, particle distribution, and installation are correct, a crusher fines trail surface is firm underfoot, usable when wet, and requires little maintenance.

Differences between crusher fines, gravel, and road base Crusher fines are not to be confused with gravel, road base, or other rock products.

Gravel is made from crushed stone but is screened to eliminate the dust and smaller particles so that all particles are within a narrow size range. Gravel is intended to have voids between particles that drain freely and do not compact, but this is undesirable on a trail surface because the surface always remains loose underfoot.

Road base is usually made from crushed pit run (river sediment of cobbles and silt) obtained from gravel pits. Unlike crusher fines, which are purely crushed stone, road base contains all the silts from the river sediments and becomes muddy when wet. Because of the silts, road base lacks the mechanical interlock


and natural cements that make crusher fines good for trails (see below). Intended only to be an inexpensive foundation for a hard surface above and not to be exposed to weather, road base is generally a poor choice for trail surfacing.

Trails for Collingwood should use crusher fines instead of gravel or road base unless crusher fines are unavailable or the alternate choice can be made to function as well as crusher fines (see explanations which follow).

Physical and chemical characteristics of crusher finesA combination of three simple physical and chemical characteristics makes crusher fines useful for trail surfaces:

1. The rock must be crushed into irregular and angular particles. These particles can then interlock and form a tight matrix. The more angular the particles, the better - rounded particles like pea gravel or decomposed granite never mechanically lock together.

2. The matrix is much tighter when the angular particles range in size from dust upward. The smaller particles evenly fill the spaces between the larger particles and greatly strengthen the interlocking matrix. Everything from the largest chunks down in size to the dust particles is mechanically interlocked.

3. The crushed rock must retain all of the original binders (natural cements) that bound the particles in the original rock to each other. Inside the tight matrix of interlocked and adjacent particles, the binders once again cement the particles together after the crusher fines are moistened, compacted, and allowed to dry.

When all of the above happens, the resulting trail surface is hard. The top 1/8-inch to 3/8-inch of the surface will often be loose from weathering and traffic, but below the immediate surface the crusher fines mass should be so hard that it is difficult to break it even with a pickax. The fines, when laid to a depth of 4 to 5 inches, should bind to each other in a consolidated slab that is porous yet, because of the binders and the nature of rock dust, resistant to water falling on its surface. Once it is thoroughly compacted, the fines do not settle or compact further (although some subsoil will absorb particles and/ or the subgrade could compact).

Strength of crusher fines binders Since the binders come from the original rock, it follows that the harder the original stone, the stronger the binders are likely to be in the crusher fines.

Conversely, crushed sandstone is just sand. The weak binders easily release individual particles, and even larger particles will break apart into sand when handled and compacted.

The binding strength of any crusher fines can be greatly increased by adding lime to the mix (this is most effectively done at the time the stone is crushed).

Particle size and particle size distributionParticle size is one of the main ways by which crusher fines are specified. The particles in a given mix have a maximum size based on the coarseness of a screen through which all the particles have passed. Hence a mix termed “3/8 minus” will have only particles which measure 3/8 inch or less (minus) in diameter. In practice, some particles will be larger than the specified screen, but not many and not by much.

Fines will also have varying distributions of particle sizes. For example, in a 3/8 minus mix, some percentage of the total will pass a 1/4” screen, another percentage a 3/16” screen, another a 1/8” screen, etc., and some percentage will be dust. The ideal particle size distribution is one where there are enough smaller particles to completely fill the voids between the larger ones. This distribution requires about half of the fines by weight to be smaller particles. See Specification of Crusher Fines, p. 3-6.


Relationship of particle size and traffic wear characteristics The more large particles the fines have, the coarser the trail surface will be. A coarse surface, however, is much more resistant to traffic and erosion than a finer surface. The larger particles on the surface form a wearing surface that helps protect the smaller ones from being worn loose by traffic, water, and wind. Coarse surfaces are desirable on parts of trails with heavy traffic or lateral surface stress (such as the lateral stress from a bike tire on a tight curve).

Finer surfaces are smoother for wheeled users but the smaller particles that form those surfaces sometimes lack the strong mechanical interlock critical to crusher fines consolidation. The lack of interlock (which can be partially compensated by strong binders) can cause the top of the surface to be excessively loose, even up to a depth of an inch or more. This looseness is a serious impediment to bicycles and especially wheelchairs. Nonetheless, the coarseness of the surface (the maximum particle size) is a choice that depends in part on the user and users of the trail.

Relationship of particle shape and interlockingThe crushing machinery and, more importantly, the type and grain of the original rock determine the shapes of particles. The best fines tend to have highly random and irregular angular shapes that can interlock in many ways. Fines in which particles tend to all be the same shape (such as small flat chips or rounded grains) should be used with care since mechanical interlocking is weak when the particles are too regular or too rounded (or too small).

ColourCrusher fines will have exactly the same color as the rock from which they are ground. Individual particles may have varying colors from color differences in the source rock, resulting in a richer appearance in the trail. The color is constant with time and is constant throughout the mix.

If crusher fines surfaces need to be patched in the future, the fines added for the patch should be from the same rock source or the color will likely not match.

Specification of Crusher Fines

See also Crusher Fines Characteristics, p. 3-4.

Order 3/8” minus crushed granite or other suitable hard stone. Look for a hard original stone - the harder the original stone, the stronger the binders will be in the crushed stone.

The crusher fines should have approximately the following composition by weight:

100% (by weight) passes 3/8” screen65% passes 1/4” screen50% passes 3/16” screen35% passes 1/8” screen25% passes 1/16” screen

The color should either match or complement the native stone and surroundings of the site, but color is of secondary importance to the structural characteristics of the fines.

Add lime if possible The binding strength of any crusher fines can be greatly increased by adding lime to the mix (this is most effectively done at the time the stone is crushed). Try to make arrangements to have lime added to the crusher fines before delivery. The amount of lime to add will vary with the crusher fines - use the advise from the crusher fines supplier to determine a suitable amount per ton for mixes.



Cost and Estimation of Quantity

Crusher fines are not expensive, but the cost of delivery can equal or exceed the cost of the material. Crusher fines weigh approximately a ton per cubic yard before compaction.

Fines are ordered by the ton. Using a ton per cubic yard for uncompacted fines, calculate the amount needed for the length, width, and depth of the surface and add approximately 20-30 percent to compensate for compaction. Lime is inexpensive, so adding lime should not add much to the cost.

Order and stockpile extra finesAfter initial construction, stockpile approximately 5 to 10 percent of the original amount of fines for future trail maintenance. It’s difficult or impossible to match the color and composition of fines from a different source, so stockpiling extra fines ensures there will be enough for future maintenance. The extra fines can be stockpiled on site or in any other convenient location.

Overview of Crusher Fines Trail Types


The basic design of crusher fines trails varies according to trail usage and drainage requirements. To best optimize crusher fines trails for intended uses, standards exist for three types of trails:

1. Bike paths2. Primarily pedestrian with bicycle and/or wheelchair access3. Pedestrian only

These trail types vary widely in both design and construction methods as well as in the trail experience of users. Pedestrian-only trails are the most naturalistic, while bike paths are the least.

The choice of which trail type to use should be driven by the intended use. If, however, topography and alignment limit the technical feasibility of a trail type, trail usage and type can be based on what trail type can feasibly be built.

Type 1: Bike Path

Intended as both recreation and transportation for bicycles and pedestrians, these are highly engineered paths with a minimum width of 8’, long sightlines, and minimum curve radii standards optimized for bicycles. Since the trail surface must be as smooth and unobstructed as possible for primary bicycle usage, trail surface drainage features must be unobtrusive and limited in frequency.

Only outslope, crowning, superelevation, side swales and culverts, and grade breaks can be used to drain the trail surface. This limitation on drainage methods, however, reduces the ability to effectively drain the surface and therefore limits trail grades and alignment. Overall trail grades should be 4% or less whenever possible and the upper limit for short grades is 8%. Long grades over 6% are infeasible without using a hard surface (concrete or asphalt) in at least parts of the trail. Grade breaks should be built into the alignment as a fail-safe drainage method to prevent potential large-scale washouts.

Because of the extensive engineering involved in side swales, culverts, wide superelevated (banked) curves, and long sightlines on a wide trail surface, this is the least naturalistic crusher fines trail type. Nonetheless, the overall effect is much more naturalistic than a hard surface.

For details, see diagram Crusher Fines Type 1: Bike Paths, p. 3-9.

Type 2: Primarily Pedestrian with Bicycle and /or Wheelchair Access

These are recreational trails of varying width designed for pedestrians and for either or both wheelchair and limited bicycle access. Usage by bicycles is intended to be occasional, not primary, and travel speeds are intended to be lower than for bike paths. For wheelchair users, the trail is designed to be barrier-free with limited grades and some safety features. (Full wheelchair accessibility cannot be claimed due to the soft surface.)

These paths can use outslope, crowning, side swales and culverts, drainage dips, and grade breaks to drain the trail surface. The frequent use of drainage dips can eliminate the need for side swales and culverts in many instances, therefore making this type of trail less expensive to construct and maintain than a full bike path.

The use of frequent drainage dips to increase trail drainage combines with less restrictive limits on sightlines and curve radii to create trails which can take advantage of site features and topography and be more naturalistic than bike paths.

For details, see diagram Crusher Fines Type 2: Primarily Pedestrian With Bicycle and/or Wheelchair Access, p.3-14.

Type 3: Pedestrian Only



Recreational crusher fines trails of varying width limited to pedestrians only can have the widest range of alignments, grades, and site conditions. All drainage techniques - outslope, crowning, side swales and culverts, drainage dips, grade breaks, and steps - can and should be used to create a very naturalistic, fun to use, physically stable, and easy to maintain trail. The use of steps effectively removes upper limits to trail grades and makes possible the widest variety of alignments.

Pedestrian-only trails are intended to create an intimate experience for trail users. The trail should dip and roll with the landscape, come close to trees and small-scale site features, vary widely in alignments and curve radii, and use steps as both a grade reduction method and as a trail design element. Small drainage crossings can be features along the trail, rocks and other natural features can sometimes extend into the trail where this makes sense, and a given trail can mold to its site by varying in width in logical response to site constraints. Because the trail is designed to be enjoyed at slow pedestrian speeds, the trail and its structures should be rich in detail and carefully designed and crafted to create a positive added experience.

Soft surface trails, which parallel hard surface multiple use paths, are usually this type of crusher fines trail, as well as interpretive trails through unique environments. This trail type is also potentially the most stable and maintenance-free crusher fines trail because so many trail drainage features can be combined with great flexibility to handle any grade and drainage situation.

For details, see diagram Crusher Fines Type 3: Pedestrian Only, p. 3-19.

Crusher Fines Type 1: Bike Paths


Grades for Bike Paths

In general, grades should be kept as minimal as possible. Grades of 3% or less are preferable with grades up to 5% acceptable. Grades above 5% should be used only where absolutely necessary. The maximum crusher fines grade is 8% - higher grades require a hard surface. See the table below for the relationship between trail grades and drainage specifications.

Whenever possible, trails should traverse slopes. To minimize the possibility of site and trail runoff following the trail, the trail grade should not exceed 30% of the cross slope at any given point. If the trail grade does exceed 30% of the cross slope, both sides of the trail should have swales (to drain water off the trail faster) and grade breaks should be located more frequently.

Grades long and steep enough to make it necessary for bicyclists to skid should either be hard surfaced, realigned, or have long sightlines.

Avoid steep grades on sharp curvesOn trails used by bicycles, minimize the need for higher speed bicycles to brake on curves. Avoid grades exceeding 4% on curves with a radius less than or equal to 50’. Where a path must curve on a grade, provide long sightlines and a transition zone at the top and bottom of the grade.

Signs for steeper grades Trail signs must warn users of a steep downgrade ahead at the tops of grades of 6% or more where the length of the grade is 100’ or more (or where the end of the grade is not visible). Provide a transition zone at the top and bottom of the grade.

Bike path drainage specifications by trail gradeUse this table to determine the use of side swales and grade breaks based on trail grade.

Grade Swab on uphill side

Swale on both sides

Minimum grade break spacing

Comments

0-1%If concentrated

water likely from above

If wet site with minimal cross slope

No grade breaks requiredWashouts along trail

length nearly impossible

2%If concentrated water possible

from aboveIf cross slope 5%

1200’ if cross slope 5%, otherwise none required

More frequent grade breaks preferred

3%If concentrated water possible

from aboveIf cross slope 7% 1200’ (700’ in wetter areas)

More frequent grade breaks preferred

4% Required If cross slope 8% 800’ (500’ in wetter areas)Maximum grade for

fines’ natural erosion resistance

5% Required If cross slope 8% 500’ (300’ in wetter areas)Maximum preferred

grade

6% Required If cross slope 8% 300’ (200’ in wetter areas)Possible erosion of

swales

7% Required If cross slope 8% 150’ (100’ in wetter areas)Consider hard

surface

8% Required If cross slope 8% 100’ (60’ in wetter areas)Suggest hard

surface

9% - - -Hard surface

required



Drainage Features for Bike Paths

In order to safely accommodate bicycle traffic, the only permissible drainage features on bike paths are:

Trail surface outslope/superelevationCrowningSide swales and culvertsGrade breaksSwale crossings

Outslope, superelevation, and crowningEvery part of the trail surface should pitch water at a 2% slope. Typically, the surface is pitched toward the downhill side (outslope). Where superelevation (curve banking) is required, this takes precedence over outslope (see “Superelevation”, following). Crowning is suggested for trails with grades exceeding 30% of the cross slope - see Crusher Fines Trail Drainage, p. 3-28.

Side swales and culverts Side swales and culverts prevent water from reaching the trail surface and give water on the trail surface a lower place to drain. Usage of these depends on the trail grade and width. See the table on previous page for the requirements for swale usage.

Grade breaksIn order to prevent possible washouts of long stretches of trail on grades, grade breaks should be designed into the alignment as a fail-safe drainage feature. Grade breaks can be smoothly and elegantly integrated into the trail alignment in several ways - see Crusher Fines Trail Drainage, p. 3-28, and the table on previous page.

The steeper the grade, the more often grade breaks are required - this further limits the overall running grade of the trail. A hard surface should be considered for trails (or parts of trails) that consistently require grades of 6% or higher.

Swale crossingsSwale crossings let surface water on the site flow across the trail surface. For minimal flows, the swale crossing can be made of crusher fines. For concentrated flows, concrete should be used in the crossing (see Crusher Fines Trail Drainage, p. 3-28). Culverts or other drainage crossing methods should be used to cross drainages that carry more than occasional storm runoff or which continue to flow after rainfall has ceased.

Curve Radii for Bike Paths

The loose surface of crusher fines can cause bicyclists to lose control on sharp curves at higher speeds. For this reason, curves of less than 50’ should be avoided whenever possible except at switchbacks, intersections and other slow zones. See the table below for curve radii for bicycles and equestrians.

Minimum curve radii

User Type Traveling Switchback Turning

Bicycle 50’ (@ 15 mph) 35’ (@15mph) 8’

Equestrian 12’ 10’


Sightlines for Bike Paths

Some mountain bikers can travel almost as fast on crusher fines as on a hard surface. To give bicyclists ample time to see ahead and slow down without skidding or losing control, design the sightlines of at least 120’ into crusher fines bike paths. See table below.

Avoid curves on gradesA hill combined with a curve is fun to ride downhill, but the speed combined with the curve may lead to accidents between fast and slow users. Where a path must curve on a grade, provide long sightlines.

Signs for exceptionsWhere these sightline guidelines cannot be followed, trail signs must warn users of the curve ahead. A “Slow” sign may also be needed for particularly blind curves.

Sightline distances In general, use the 15-mph figures.

Speed Sight Distance

20 mph 130 – 200’

15 mph 85 – 130’

10 mph 35 – 60’

Hazard Zones and Side Clearance for Bike Paths

Crusher fines bike paths have the same hazard zone and side clearance specifications as do hard surface multiple use trails. Use the specifications in Hazard Zones and Side Clearance, p. 2-9.

Vertical Clearance for Bike Paths

Bike paths require 10’ vertical clearance, and more may be necessary or desirable to accommodate construction or maintenance vehicles. Paths used for cross-country skiing may require additional clearance (up to 16’ depending on expected snow depth).

Superelevation for Bike Paths

Curves with a radius of 100’ or less should be banked, or superelevated, in high to moderate speed travel zones.

In the table below, “High speed, uncongested zone” refers to sections of path which are not commonly busy and where bicycle users are likely to be traveling fast.

This zone does not include any intersections.

"Moderate speed, mainline path” refers to trail sections that are in somewhat busy areas. This zone also includes mainline path sections with a straightforward low-use intersection on a curve such as a low-use spur trail which connects to a nearby open space access point - the mainline trail should be banked through the intersection.



Busy path sections, marked slow zones, busy intersections, and sections with heavy pedestrian traffic should not be superelevated.

The superelevations given in the table are to be the final pitch of the trail surface from side to side (as opposed to crowning).

Superelevation

Curve Radii High speed, uncongested zone

Moderate speed, mainline path

50-100’ 3/8” per ft. 5/16” per ft.

<50’ 1/2” per ft. 3/8” per ft.


Crusher Fines Type 2: Primarily Pedestrian With Bicycle and/or Wheelchair Access

This trail type is not meant to be a higher-speed bike path but instead merely barrier-free to wheeled users. Standards for this type of trail are not as restrictive as a bike path but are considerably more restrictive than a pedestrian-only path. Wheeled users can be bicycles, wheelchairs, or both. The width of the trail can vary as needed.

Grades for Primarily Pedestrian

Grades should be kept as minimal as possible. Grades of 3% or less are preferable with grades up to 5% acceptable. Grades above 5% should be used only where absolutely necessary. The maximum crusher fines grade is 8%. See the table below for the relationship between trail grades and drainage specifications.

Whenever possible, trails should traverse slopes. To minimize the possibility of site and trail runoff following the trail, the trail grade should not exceed 30% of the cross slope at any given point. If the trail grade does exceed 30% of the cross slope and the trail is more than 4’ wide, both sides of the trail should have swales (to drain water off the trail faster) and grade breaks and drainage dips should be located more frequently.

Steep gradesGrades long and steep enough to make it necessary for bicyclists to skid should be avoided or else given long sightlines. Provide a transition zone at the top and bottom of steep grades.

Limits on running gradesThe steeper the grade, the more often drainage dips and grade breaks are required - these further limit the overall running grade of the trail.



Avoid steep grades on sharp curvesOn trails used by bicycles, minimize the need for higher speed bicycles to brake on curves. Avoid grades exceeding 4% on curves with a radius less than or equal to 50’. Where a trail must curve on a grade, provide long sightlines and a transition zone at the top and bottom of the grade.

Drainage Features for Primarily Pedestrian

If the trails, or parts of the trail, are to be barrier-free for wheelchair users, the specifications given under Crusher Fines Trails for the Physically Challenged, p. 3-49, supersede the following for the applicable trail sections.

In order to safely accommodate wheeled (but slower-moving) traffic, the permissible drainage features for these trails are:

Trail surface outslopeCrowningSide swales and culvertsGrade breaksDrainage dipsSwale crossings

Outslope and crowningEvery part of the trail surface should pitch water at a 2% slope. Typically, the surface is pitched toward the downhill side (outslope). Crowning is suggested for trails with grades exceeding 30% of the cross slope - see Crusher Fines Trail Drainage, p. 3-28. Superelevation should not be done.

Side swales and culvertsSide swales and culverts prevent water from reaching the trail surface and give water on the trail surface a lower place to drain. Usage of these depends on the trail grade and width. See the table below.

Grade breaksIn order to prevent possible washouts of long stretches of trail on grades, grade breaks should be designed into the alignment as a fail-safe drainage feature. Grade breaks can be smoothly and elegantly integrated into the trail alignment in several ways - see Crusher Fines Trail Drainage, p. 3-28, and the table below.

Drainage dipsDrainage dips are small grade breaks - dips in the trail surface that catch water running down the trail and divert it off. These are easy to form in crusher fines trails but must be broad and shallow enough to avoid becoming trench-like obstacles for bicycles or wheelchairs. After outslope or crowning, drainage dips are one of the primary methods of draining the surface of this type of trail. See the table above for drainage dip usage.


Pedestrian and bike/wheelchair path drainage specifications by trail gradeUse this table to determine the use of grade breaks, side swales, crowning, and drainage dips based on trail grade.

Grade

Grade break

spacing*

Trail surface drainage options (use singly or combine) Comments

0-1% None requiredUphill swale if heavy drainage from above Washouts along trail length

nearly impossibleNone required Uphill swale if heavy drainage from above Minimal maintenance required

30% 1200’Drainage dips every 350’ (every 150’ if

cross slope 7%)Uphill swale if heavy drainage from above

More frequent grade breaks preferred over drainage dips,

minimal maintenance required

4% 800’

Drainage dips every 200’ (every 100’ if cross slope 8%)

Uphill swale if moderate to heavy drainage from above

Swale both sides and crown if cross slope 6%

Maximum grade for natural erosion resistance of crusher

fines, more frequent grade breaks preferred

5% 500’


Uphill swale if moderate drainage from above


Preferred maximum grade, grade breaks preferred over

drainage dips, minimal maintenance if correctly

designed

6% 400’




Difficult for wheelchair users without electric chairs or

assistance

7% 300’

Drainage dips every 50’Uphill swale required


Approaching practical limit for crusher fines grades, avoid turning drainage dips into

trenches

250’

Drainage dips every 40’Uphill swale required


Practical limit for crusher fines grades, wheelchair use almost

infeasible, upper limit for bicycle use

9% —--- Use Type 3 (ped only)

standards*If drainage dips are used correctly, grade breaks are technically unnecessary but still serve as a fail-safe drainage device. When topography is used to create grade breaks, user comfort and enjoyment is increased, as long grades are broken.

Swale crossingsSwale crossings let surface water on the site flow across the trail surface. For minimal flows, the swale crossing can be made of crusher fines. For concentrated flows, concrete should be used in the crossing (see Crusher Fines Trail Drainage, p. 3-28). Culverts or other drainage crossing methods should be used to cross drainages that carry more than occasional storm runoff or which continue to flow after rainfall has ceased.

Curve Radii for Primarily Pedestrian

For trails used by bicycles, curves can be as tight as a 35’ radius with an 8’ turning radius. For trails used by wheelchairs but not bicycles, no minimum radius is set.



Sightlines for Primarily Pedestrian

These trails are not intended to be high-speed paths, even for bicyclists. For trails used by bikes, design sightlines of at least 60'. Sightlines can drop to 35’ when necessary. No minimum sightlines are set for trails used by wheelchairs but not bicycles. See the table below.

Avoid curves on gradesAvoid curves on grades. A hill combined with a curve is fun to ride downhill, but the speed combined with the curve may lead to accidents between fast and slow users. Where a trail must curve on a grade, provide long sightlines.

Sightline distancesIn general, use the 15mph figures.

Speed Sightline distance

20 mph 130 - 200’

15 mph 85 - 130’

10 mph 35 - 60’

Hazard Zones for Primarily Pedestrian

Hazard zones are places where users can be expected to slow down or stop. Hazard zones include:

Unusually busy trail sections Busy intersections and intersections with directional signs Intersections at the bottom of or along a sustained grade Curves of less than 50’ radius and more than 15’ running length Blind or near-blind curves Beneath a bridge overpass Long or interesting bridges where users are likely to stop Boardwalks or other crossings over unusual or special terrain or ecosystems Places with scenic views* Places with low side clearance for 10 or more running feet (see below)

* On trails with high or very high use, these situations may be considered extreme hazard zones (see below). Other hazard zones may exist in addition to the above.

Extreme hazard zonesExtreme hazard zones are specific instances from the above list where trail usage is either very high or conditions are particularly adverse. These zones should be widened even more. See the table on next page for the increased trail widths in hazard zones.

Width change zoneUpon entering and leaving hazard zones, the changes in trail width should not be sudden or even noticeable by users. The width can change over any distance that makes sense at that location, typically this will be from 3 to 15 feet.

See table on next pageSee the “Hazard zones and low side clearance zones” table on the next page for hazard zone widths.

Side Clearance for Primarily Pedestrian


Path typeHazard zone†

Extreme hazard zone†

Low clearance

on one side*

Low clearance on both sides*

Length of width

change zone

Pedestrian with bike/wheelchair

+ 1-2’ + 2-4’ + 1’ + 2’ 3-15’

†See definition of hazard zone, above.* Applies only where clearance is restricted for 10 or more continuous feet.

Vertical Clearance for Primarily Pedestrian

Vertical clearance should be 10’ if equestrians are not permitted or 12’ if the trail is open to equestrians.Trails used for cross-country skiing may require additional clearance (up to 16’ depending on expected snow depth).

Crusher Fines Type 3: Pedestrian Only

Grades and Alignment for Pedestrian Only

Grades of up to 3% are the easiest to construct and maintain. On grades of 4% to 6%, steps are used to decrease crusher fines grades where washouts are more likely (i.e., when the trail alignment is close to the fall line for site drainage). For grades of 7% and higher, steps are required in order to reduce grades on crusher fines surfaces to 4% or preferably less. By using steps, upper limits on trail grades are limited only by practicality of step construction and by user comfort. See “Steps” under Crusher Fines Trail Drainage, p. 3-28. See the table on next page for the relationship between trail grades and drainage specifications.



Alignment on slopes Whenever possible, trails should traverse slopes. To minimize the possibility of site and trail runoff following the trail, the trail grade should not exceed 30% of the cross slope at any given point.If the trail grade does exceed 30% of the cross slope, steps are recommended at lower grades to reduce the possibility of washouts. Also, if the trail is more than 4’ wide at a grade exceeding 30% of the cross slope, both sides of the trail should have swales (to drain water off the trail faster) and grade breaks and drainage dips should be located more frequently.

Pedestrian path drainage specifications by trail gradeUse this table to determine the use of grade breaks, side swales, crowning, drainage dips, and steps based on trail grade.

Grade

Grade break

spacing

Trail surface drainage options (use singly or combine) Comments

0-1%None

requiredUphill swale if heavy drainage from above

Washouts along trail length nearly impossible

2% Uphill swale if heavy drainage from above Minimal maintenance required

3% 1200’Drainage dips every 350’ (every 150’ if

cross slope 7%)Uphill swale if heavy drainage from above

More frequent grade breaks preferred over drainage dips,

minimal maintenance required

4% 800’


Uphill swale if moderate to heavy drainage from above

Use steps and crown if cross slope 8% - see text

If cross slope 6%, use steps to reduce crusher fines grades to

3% or less

5% 500’




If cross slope 8%, use steps to reduce crusher fines grades to

3% or less

6% 400’




Use of steps in general suggested to reduce grade

Suggest aligning in such a way as to use steps occasionally to limit crusher fines grades to 4%

or preferably less

7% —

Use steps to reduce crusher fines grades to 4% or less

Raise steps above ground level if cross slope 10% - see text

Use of steps permits trail grades up to 80% for short distances


*If drainage dips are used correctly, grade breaks are technically unnecessary but still serve as a fail-safe drainage device. When topography is used to create grade breaks, user comfort and enjoyment is increased, as long grades are broken.

Drainage Features for Pedestrian Only

All drainage features can be used on pedestrian-only trails:

Trail surface outslope: Crowning Side swales and culverts Grade breaks Drainage dips Swale crossings Steps

Outslope and crowningEvery part of the trail surface should pitch water at a 2% slope. Typically, the surface is pitched toward the downhill side (outslope). Crowning is suggested for trails with grades exceeding 30% of the cross slope - see Crusher Fines Trail Drainage, p. 3-28. Superelevation should not be done.

Side swales and culvertsSide swales and culverts prevent water from reaching the trail surface and give water on the trail surface a lower place to drain. Usage of these depends on the trail grade and width. See the table above.

Grade breaks In order to prevent possible washouts of long stretches of trail on grades, grade breaks should be designed into the alignment as a fail-safe drainage feature. Grade breaks can be smoothly and elegantly integrated into the trail alignment in several ways - see Crusher Fines Trail Drainage, p. 3-28, and the table above. Frequent use of drainage dips, however, can replace grade breaks.

Drainage dipsDrainage dips are small grade breaks - dips in the trail surface that catch water running down the trail and divert it off. These are easy to form in crusher fines trails but should be broad and shallow to avoid becoming trench-like obstacles. After outslope or crowning, drainage dips are one of the primary methods of draining the surface of this type of trail. See the table above for drainage dip usage.

Swale crossingsSwale crossings let surface water on the site flow across the trail surface. For minimal flows, the swale crossing can be made of crusher fines. Minimal to occasionally moderate flows can be crossed with stone paving or other methods. For concentrated flows, concrete should be used in the crossing (see Crusher Fines Trail Drainage, p. 3-28). Culverts, bridges, causeways, or boardwalks should be used to cross drainage that carry more than occasional storm runoff or which continue to flow after rainfall has ceased.

StepsStone (preferably) or timber steps should be used to reduce grades on crusher fines surfaces. Care must be taken to ensure that water is periodically diverted off steps - this is done by adjusting the height and location of steps above ground level and by optionally crowning the crusher fines between steps.See the table above for guidelines on where to use steps and Crusher Fines Trail Drainage, p. 3-28, for step construction.

Curve Radii and Sightlines for Pedestrian Only

No restrictions are placed on curve radii and sightlines except that they vary along a given trail - a trail is much more interesting if both curves and sightlines range from tight and short to broad and long. Within what is logical on a given site, try to align the trail with a wide range of curves and sightlines.



Avoid long straight sectionsPedestrian-only trails should not have unbroken straight sections longer than 200’. Use curves, topography, hills, trees, and site features to create opportunities for curves, intermediate path goals (see Section 1, Part E), and varying sightlines.

Hazard Zones for Pedestrian Only

Hazard zones are places where users can be expected to slow down or stop. Hazard zones include: Unusually busy trail sections Busy intersections and intersections with directional signs Blind or near-blind curves* Beneath a bridge overpass* Long or interesting bridges where users are likely to stop Boardwalks or other crossings over unusual or special terrain or ecosystems Places with scenic views Places with low side clearance for 5 or more running feet (see below)

* On trails with high or very high use, these situations may be considered extreme hazard zones (see below). Other hazard zones may exist in addition to the above.

trails manual section9

Documents

types of crusher fines

crusher fines trails

crusher fines type

trail surface

hard surface trails

trails design

fines material

nature trails