Contents

  • Cover
  • Front matter
  • Preface
  • Scope, purpose and use
  • 1. Terminology, economic analysis, risk management
    • 1.1 Terminology
    • 1.2 Economic analysis
    • 1.3 Understanding risk
  • 2. Regulations, consents and approvals
    • 2.1 National Environmental Standards for Plantation Forestry (NES-PF)
    • 2.2 Heritage New Zealand Pouhere Taonga
    • 2.3 The Health and Safety at Work Act
    • 2.4 NZ Transport Agency approval for access onto state highways
    • 2.5 District council approval for access onto council roads
  • 3. Planning for roads
    • 3.1 Road classes
    • 3.2 Arterial roads
    • 3.3 Secondary roads
    • 3.4 Spur roads
    • 3.5 Establishment tracks
    • 3.6 Spatial information
    • 3.7 Initial field work
    • 3.8 Manual design method: Stepping out a roadline on a topo
    • 3.9 Running a grade line in the field
    • 3.10 Full road design
    • 3.11 Working with road survey data
    • 3.12 Geometric road design
    • 3.13 Curve widening
    • 3.14 Horizontal alignment
    • 3.15 Vertical alignment
    • 3.16 Calculating the safe stopping distance
    • 3.17 Setting out the roadline
  • 4. Planning for landings
    • 4.1 Common landing layouts
    • 4.2 Landing planning considerations
  • 5. Road and landing construction
    • 5.1 Soil and rock properties
    • 5.2 Managing adverse environmental effects
    • 5.3 Marking clearing widths
    • 5.4 Roadline salvage
    • 5.5 Daylighting
    • 5.6 Road formation
    • 5.7 Drainage control during earthwork construction
    • 5.8 Earthwork machinery
    • 5.9 Estimating machinery production
    • 5.10 Stabilising cut and fill slopes during construction
  • 6. Pavement design, subgrade preparation, pavement construction
    • 6.1 Traffic loading
    • 6.2 Evaluating subgrade properties
    • 6.3 Determining pavement depth
    • 6.4 Pavement material properties
    • 6.5 Compaction of subgrade and pavement
    • 6.6 Compaction equipment
    • 6.7 Pavement construction
    • 6.8 Weak subgrades
    • 6.9 Chemical stabilisation of pavement or subgrade
  • 7. Erosion, sediment and slash control structures
    • 7.1 Ditches
    • 7.2 Cut-outs
    • 7.3 Berms
    • 7.4 Drainage culverts
    • 7.5 Flumes
    • 7.6 Sediment traps and soak holes
    • 7.7 Silt fences
    • 7.8 Sediment retention ponds
    • 7.9 Debris traps
  • 8. River crossings
    • 8.1 Fish passage
    • 8.2 Selecting the location and crossing type
    • 8.3 Fords
    • 8.4 Temporary river crossings
    • 8.5 Single culvert river crossings
    • 8.6 Battery culvert river crossings
    • 8.7 Drift deck river crossings
    • 8.8 Single span bridge river crossings
    • 8.9 Prediction of flood flows, and sizing culverts
  • 9. Road maintenance, repairs and upgrades
    • 9.1 Maintenance programme
    • 9.2 Economic evaluation of road maintenance projects
    • 9.3 Managing maintenance requirements
    • 9.4 Commonly used maintenance machinery
    • 9.5 Road surface maintenance
    • 9.6 Road foundation maintenance
    • 9.7 Landing rehabilitation and decommissioning
    • 9.8 Roadside vegetation maintenance
    • 9.9 Erosion and sediment control structure maintenance
    • 9.10 River crossing maintenance
  • Forest road engineering terminology
  • References
  • Websites, resources, databases

NZ Forest Road Engineering Manual

  1.  ›
  2. 3. Planning for roads ›
  3. 3.13 Curve widening
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3.13 Curve widening

Curve wideningCurve widening is required on both sides of the curve (FAO Watershed Management Field Manual, www.fao.org)

Off-tracking on a curveTrailer off-tracking on a curve. The magnitude of off-tracking depends on vehicle configuration, speed, corner radius and central angle (corner length)Additional widening at curves may be required to cater for trailer off-tracking. Curve widening is necessary to provide for the passage of loaded trailer axles outside of the truck wheel path and prevent them from tracking into the ditch. Curve widening is especially important when truck configurations with long drawbars and long trailers are intended to use the road.

The amount of curve widening needed varies significantly depending on the truck configuration, corner radius and central angle (corner length). Since vehicles travel in both directions, half of the required curve widening should be added to the inside and half to the outside of the curve. A tapered road section should be provided to allow a transition both into and out of the corner.

Curve widening for truck/trailer combinationCurve widening for a typical truck/trailer configuration as a function of curve radius and central angle (www.fao.org)Curve widening for logging truck (pole trailer)Curve widening for a typical pole trailer configuration as a function of curve radius and central angle (www.fao.org)Some existing roads designed for 44 tonne and standard 4 axle trailer units may no longer be appropriate for 50t Max and HPMV configurations. Additional curve widening may be required to accommodate these.

The charts on this provide curve widening for two common vehicle configurations – a truck-trailer combination and a stinger-type logging truck. The charts are valid for the specified vehicle dimensions and configurations only. Equations enabling calculation of curve widening for other truck configurations can be found in Chapter 3 of the FAO Watershed Management Field Manual (FAO, 1990).

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