TRAIL DESIGN FUNDAMENTALS GUIDE

INTRODUCTION

Trail design is both an art and a science. This guide provides comprehensive information on fundamental principles that create sustainable, enjoyable, and environmentally sound mountain bike trails. Whether you're planning a single trail or an entire network, these principles will help ensure your trails stand the test of time while providing exceptional riding experiences.

CORE DESIGN PRINCIPLES

1. The Half Rule

Principle:

A trail's grade shouldn't exceed half the grade of the hillside it traverses.

Application:

  • If you're building on a 20% slope, keep your trail grade at 10% or less
  • This prevents water from flowing down the trail instead of across it
  • Exceptions can be made for short distances with proper drainage features

Common Issues:

  • Trails that break this rule become water channels during rain
  • Erosion quickly damages trail surface and creates maintenance problems
  • Rider experience suffers from excessive braking and poor flow

2. The 10% Average Grade

Principle:

Maintain an average grade of 10% or less for the entire trail.

Application:

  • Calculate the total elevation change divided by the trail length
  • Short sections can exceed 10% when necessary
  • Balance steeper sections with more gradual grades

Benefits:

  • Sustainable trails require less maintenance
  • Accessible to a wider range of skill levels
  • Prevents excessive soil erosion and rutting

3. Maximum Sustainable Grade

Principle:

Short sections can exceed 10%, but rarely more than 20%.

Factors Affecting Maximum Grade:

  • Soil type (clay, loam, sand)
  • Rainfall/climate conditions
  • Expected user types and traffic volume
  • Available maintenance resources
  • Desired difficulty level

Implementation:

  • Reserve maximum grades for short, exciting features
  • Always follow steep sections with grade reversals
  • Consider armoring (rock reinforcement) for grades over 15%
  • Factor in soil moisture conditions during different seasons

4. Grade Reversals

Principle:

Incorporate frequent grade changes to shed water naturally.

Design Guidelines:

  • Include a grade reversal every 20-50 feet depending on terrain
  • Even minimal (1-2 foot) elevation changes effectively divert water
  • Natural dips and terrain features can serve as grade reversals
  • Essential after steep sections to prevent water channeling

Advantages:

  • Self-maintaining drainage that doesn't rely on artificial structures
  • Creates rhythm and playfulness in the trail experience
  • Prevents long fall-line sections that capture water flow
  • Works even when drains and culverts become clogged

5. Outslope

Principle:

Build trail surface with a 5% outward tilt to shed water.

Implementation Techniques:

  • Maintain consistent outslope during initial construction
  • Check outslope with clinometer or level during building
  • Re-establish during maintenance as trails naturally compact
  • Ensure berms and turns have proper drainage outlets

Maintenance Considerations:

  • User traffic tends to flatten outslope over time
  • Schedule regular maintenance to re-establish proper outslope
  • Pay special attention to inside edges of turns where debris collects

FLOW TRAIL DESIGN ELEMENTS

Rhythm Sections

Rhythm sections are series of rollers or jumps that create a "pumping" sensation and maintain flow:

  • Spacing: Generally 15-25 feet between features depending on speed
  • Height: Typically 1-3 feet tall with rounded profiles
  • Progression: Design for increasing or consistent rhythm
  • Landing Zones: Ensure adequate transition areas for safety

Berms and Turns

Well-designed turns maintain speed and create an engaging riding experience:

  • Radius: Match to expected entry speed (faster speeds = larger radius)
  • Banking: Increase inslope for higher-speed turns (up to 60%)
  • Entry/Exit: Gradually transition into and out of berms
  • Support: Build adequate material on outside of turns to prevent collapse
  • Drainage: Create exit points for water at the bottom of each berm

Rolling Grade Dips

These essential features combine trail flow with effective drainage:

  • Placement: Every 20-50 feet, especially before turns and steep sections
  • Design: Gradual approach, clear drainage outlet, smooth exit
  • Depth: 6-12 inches below trail grade
  • Maintenance: Keep outlets clear and re-establish as needed

TECHNICAL TRAIL FEATURES

Rock Gardens

  • Selection: Choose stable, durable rock material
  • Placement: Set rocks with 1/3 buried for stability
  • Flow: Maintain a clear "line" through technical features
  • Alternative Lines: Consider providing B-lines for progression

Drops and Features

  • Landing Zones: Always provide adequate, clear landing areas
  • Visibility: Ensure features are visible with appropriate signage
  • Construction: Build solid, immovable features that won't shift
  • Progression: Create features of varying difficulty within the same trail

TRAIL CORRIDOR DEVELOPMENT

Clearing Width and Height

  • Standard Singletrack: 4-6 feet wide clearing, 8-10 feet high
  • Technical Trails: Typically narrower but context-specific
  • Flow Trails: Often wider to accommodate higher speeds and movement
  • Maintenance Buffer: Clear additional width for future growth

Sight Lines and Speed Control

  • Corners: Ensure adequate visibility through turns
  • Technical Features: Provide clear sight lines to features and obstacles
  • Speed Control: Use natural terrain and features to maintain appropriate speeds
  • User Conflict Areas: Maximize visibility at intersections and multi-use sections

SOIL AND SURFACE CONSIDERATIONS

Understanding Soil Types

Different soils require different approaches:

  • Clay Soils: Drain poorly but form solid surfaces; control water aggressively
  • Sandy Soils: Drain well but lack cohesion; may require stabilization
  • Loam Soils: Ideal for trails but still require proper drainage
  • Rocky Terrain: Offers natural armoring but presents building challenges

Surface Materials

  • Native Soil: Often sufficient with proper design and drainage
  • Imported Materials: Consider for problem areas or high-traffic sections
  • Hardening Techniques: Rock armoring, geotextiles, natural cement
  • Maintenance Needs: Plan for regular surface refreshing in high-use areas

TRAIL NETWORK PLANNING

Stacked Loop Systems

  • Progression: Shorter, easier loops near trailheads; longer, more difficult loops further out
  • Connections: Strategic intersection points allow for multiple route options
  • Difficulty Management: Clear signage and consistent difficulty within loops
  • User Experience: Design for varying ride lengths and experiences

Directional Trails

  • Speed Management: Directional trails allow for flow-optimized designs
  • User Conflicts: Reduces confrontations between riders
  • Signage: Requires clear, consistent directional indicators
  • Emergency Access: Plan for maintenance and emergency vehicle access points

ENVIRONMENTAL CONSIDERATIONS

Sensitive Areas

  • Wetlands: Avoid when possible; use elevated structures when necessary
  • Habitat Protection: Identify and route around critical wildlife areas
  • Seasonal Closures: Consider temporary closures during spawning or nesting
  • Invasive Species: Develop plans to prevent spread during construction

Erosion Control During Construction

  • Minimize Disturbance: Work in small sections to limit exposed soil
  • Temporary Measures: Use silt fencing, straw wattles during construction
  • Revegetation: Plant native species on disturbed areas after construction
  • Phased Building: Complete and stabilize sections before moving forward

DOCUMENTATION AND ASSESSMENT

Trail Assessment

  • Pre-Construction: Document existing conditions, sensitive areas
  • During Construction: Track modifications, materials used
  • Post-Construction: Evaluate effectiveness of drainage, stability
  • Ongoing Monitoring: Regular assessment of wear patterns and issues

Maintenance Planning

  • Scheduled Maintenance: Calendar for regular clearing and assessment
  • Seasonal Work: Heavy maintenance after winter/rainy seasons
  • Volunteer Programs: Organize regular maintenance events
  • Documentation: Keep records of all work performed for future reference

CONCLUSION

Trail design is an ongoing process of learning, adaptation, and refinement. By following these fundamental principles, you'll create sustainable trails that provide exceptional riding experiences while protecting the natural environment. Remember that local conditions, user expectations, and environmental factors will all influence your specific design decisions.

FURTHER RESOURCES

  • International Mountain Bicycling Association (IMBA) Trail Building Books
  • Trail Solutions: IMBA's Guide to Building Sweet Singletrack
  • Managing Mountain Biking: IMBA's Guide to Providing Great Riding
  • Local trail organization workshops and training opportunities
  • Professional trail builder consultations for complex projects

This guide was developed by Trail Craft Pro to assist mountain bike trail designers, builders, and volunteers in creating sustainable, enjoyable trails.