Natl_Design_Parameters.pdf

Design Parameters

Design Parameters are technical guidelines for the survey, design, construction, maintenance, and assessment of National Forest System trails, based on their Designed Use and Trail Class and consistent with their management intent1. Local deviations from any Design Parameter may be established based on trail-specific conditions, topography, or other factors, provided that the deviations are consistent with the general intent of the applicable Trail Class.

Designed Use HIKER/PEDESTRIAN Trail Class 1 Trail Class 2 Trail Class 3 2 Trail Class 4 2 Trail Class 5 2 Design Tread Width

Wilderness (Single Lane)

0” – 12” 6” – 18” 12” – 24” Exception: may be 36” – 48” at steep side slopes

18” – 24” Exception: may be 36” – 48” at steep side slopes

Not applicable

Non-Wilderness (Single Lane)

0” – 12” 6” – 18” 18” – 36”

24” – 60”

36” – 72”

Non-Wilderness (Double Lane)

36” 36” 36” – 60” 48” – 72” 72” – 120”

Structures (Minimum Width)

18” 18” 18” 36” 36”

Design Surface3

Type Native, ungraded

May be continuously rough

Native, limited grading rough

Native with some onsite borrow or imported material where needed for stabilization, occasional grading

Intermittently rough

Native with improved sections of borrow or imported material, routine grading

Minor roughness

Likely imported material, Uniform, firm, and stable

Protrusions ≤ 24” Likely common and continuous

≤ 6” May be common and continuous

≤ 3” May be common, not continuous

≤ 3 ” Uncommon, not continuous

No protrusions

Obstacles (Maximum Height)

24”

14”

10”

8”

No obstacles

Design Grade 3

Target Grade 5% – 25%

5% – 18% 3% – 12% 2% – 10% 2% – 5%

Short Pitch Maximum

40% 35% 25% 15% 5%

FSTAG: 5% – 12%2

Maximum Pitch Density 20% – 40% of trail

20% – 30% of trail

10% – 20% of trail

5% – 20% of trail

0% – 5% of trail

10/16/2008

Designed Use HIKER/PEDESTRIAN Trail Class 1 Trail Class 2 Trail Class 3 2 Trail Class 4 2 Trail Class 5 2 Design Cross Slope

Target Cross Slope Natural side slope

5% – 20% 5% – 10% 3% – 7% 2% – 3% (or crowned)

Maximum Cross Slope Natural side slope

25% 15% 10% 3%

Clearing

Height 6’

6’ – 7’ 7’ – 8’ 8’ – 10’ 8’ – 10’

Width ≥ 24” Some vegetation may encroach into clearing area

24” – 48” Some light vegetation may encroach into clearing area

36” – 60”

48” – 72”

60” – 72”

Shoulder Clearance 3” – 6”

6” – 12” 12” – 18” 12” – 18” 12” – 24”

Turn

Radius No minimum 2’ – 3’ 3’ – 6’ 4’ – 8’ 6’ – 8’

1 For definitions of Design Parameter attributes (e.g., Design Tread Width and Short Pitch Maximum) see FSH 2309.18, section 05.

2 Trail Classes 3, 4, and 5, in particular, have the potential to provide accessible passage. If assessing or designing trails for accessibility, refer to the Forest Service

Trail Accessibility Guidelines (FSTAG) for more specific technical provisions and tolerances (FSM 2350).

3 The determination of trail-specific design grades, design surface, and other Design Parameters should be based upon soils, hydrological conditions, use levels, erosion potential, and other factors contributing to surface stability and overall sustainability of the trail.

Design Parameters are technical guidelines for the survey, design, construction, maintenance, and assessment of National Forest System trails, based on their Designed Use and Trail Class and consistent with their management intent1. Local deviations from any Design Parameter may be established based on trail-specific conditions, topography, or other factors, provided that the deviations are consistent with the general intent of the applicable Trail Class.

Designed Use BICYCLE Trail Class 1 Trail Class 2 Trail Class 3 Trail Class 4 Trail Class 5 Design Tread Width

Single Lane 6” – 12”

12” – 24” 18” – 36” 24” – 48” 36” – 60”

Double Lane 36” – 48”

36” – 48” 36” – 48” 48” – 84” 72” – 120”

Structures (Minimum Width)

18” 18” 36” 48” 60”

Design Surface2

Type Native, un-graded

May be continuously rough

Sections of soft or unstable tread on grades < 5% may be common and continuous

Native, limited grading rough

Sections of soft or unstable tread on grades < 5% may be common

Native with some onsite borrow or imported material where needed for stabilization, occasional grading

Intermittently rough

Sections of soft or unstable tread on grades < 5% may be present, but not common

Native, routine grading with improved sections of borrow or imported materials

Stable with minor roughness

Likely imported material, Uniform, firm, and stable

Protrusions ≤ 24” Likely common and continuous

≤ 6” May be common and continuous

≤ 3” May be common, not continuous

≤ 3” Uncommon, not continuous

No protrusions

Obstacles (Maximum Height)

24”

12” 10” 8” No obstacles

Grade 2

Target Grade 5% – 20%

5% – 12% 3% – 10% 2% – 8% 2% – 5%

30% 50% on downhill-only segments

25% 35% on downhill-only segments

15% 10% 8%

Maximum Pitch Density 20% – 30% of trail

10% – 30% of trail 10% – 20% of trail 5% – 10% of trail 0% – 5% of trail

BICYCLE Trail Class 1 Trail Class 2 Trail Class 3 Trail Class 4 Trail Class 5 Design Cross

Target Cross Slope 5% – 10%

5% – 8% 3% – 8% 3% – 5% 2% – 3%

Maximum Cross Slope 10%

10% 8% 5% 5%

Clearing

Height 6’

6’ – 8’ 8’ 8’ - 9’ 8’ - 9’

Width 24” – 36” Some vegetation may encroach into clearing area

36” – 48” Some light vegetation may encroach into clearing area

60” – 72”

72” – 96”

72” – 96”

Shoulder Clearance 0’ – 12”

6” – 12” 6” – 12” 6” – 18” 12” – 18”

Radius 2’ – 3’

3’ – 6’

4’ – 8’

8’ – 10’ 8’ - 12’

1 For definitions of Design Parameter attributes (e.g., Design Tread Width and Short Pitch Maximum) see FSH 2309.18, section 05.

2 The determination of trail-specific design grades, design surface, and other Design Parameters should be based upon soils, hydrological conditions, use levels, erosion potential, and other factors contributing to surface stability and overall sustainability of the trail.

Design Parameters are technical guidelines for the survey, design, construction, maintenance, and assessment of National Forest System trails, based on their Designed Use and Trail Class and consistent with their management intent1. Local deviations from any Design Parameter may be established based on trail-specific conditions, topography, or other factors, provided that the deviations are consistent with the general intent of the applicable Trail Class.

CROSS-COUNTRY SKI Trail Class 1 Trail Class 2 Trail Class 3 Trail Class 4 Trail Class 5 Design Groomed Width

Single Lane

Typically not designed or actively managed for cross-country skiing

2’ – 4’ Typically not groomed

6’ – 8’ (or width of grooming equipment)

8’– 10” (or width of grooming equipment)

Typically not designed or actively managed for cross-country skiing

Double Lane 6’ – 8’

8’ – 12’ 12’ – 16’

Structures (Minimum Width)

36” 36” 36”

Design Grooming and Surface2

Type Generally no machine grooming

May receive occasional machine grooming for snow compaction and track setting

Regular machine grooming for snow compaction and track setting

Protrusions No protrusions

No protrusions No protrusions

Obstacles (Maximum Height)

12” Uncommon

8” Uncommon (no obstacles if machine groomed)

No obstacles

Grade 2

Target Grade 5% – 15%

2% – 10% 0% – 8%

25% 20% 12%

Maximum Pitch Density 10% – 20% of trail

5% – 15% of trail 0% – 10% of trail

Cross

Target Cross Slope 0% – 10%

0% – 5% 0% – 5%

Maximum Cross Slope (For up to 50’)

20% 15% 10%

CROSS-COUNTRY SKI Trail Class 1 Trail Class 2 Trail Class 3 Trail Class 4 Trail Class 5

Design Clearing

Height (Above normal maximum snow level)

6’ – 8’

8’ (or height of grooming machinery)

8’ – 10’

Width 24” – 60” Light vegetation may encroach into clearing area

72” – 20”’ Light vegetation may encroach into clearing area

96”’ – 168” Widen clearing at turns or if increased sight distance needed

Shoulder Clearance 0” – 6”

0” - 12” 0” – 24”

Radius 8’ – 10’

15’ – 20’ (or to accommodate grooming equipment)

≥ 25’

1 For definitions of Design Parameter attributes (e.g., Design Tread Width and Short Pitch Maximum) see FSH 2309.18, section 05.

2 The determination of trail-specific grades, surface, and other Design Parameters should be based upon soils, hydrological conditions, use levels, erosion potential and other factors contributing to surface stability and overall sustainability of the trail.