Tuesday, 25 November 2008

Fault 3: No adequate super-elevation on the bend.

The carriageway was completed with a adverse camber on the bend rather than being super-elevated as originally planned and approved. Unfortunately this bodge was done after the gulleys for a super-elevated bend had been installed. As a result the carriageway now has an adverse camber on the bend with gulleys and drains for a super-elevated carriageway geometry.

Designing curves for safety: Cant, camber or super-elevation, is the difference in elevation of two road edges. Designers ensure that a curved road is sloped so it is higher on the outside of the curve. Super-elevation allows part of a vehicle’s weight to assist in maintaining a circular path. It reduces the required amount of side friction between the tyres and road surface when driving a circular path. This is important for the safety and comfort of all road users. The amount of super-elevation depends mainly on the operating speed of the curve and the curve radius, with more super-elevation applied on tighter curves. However, with the need to drain water off the road surface there is a minimum amount of super-elevation applied to all curves.

There are many factors limiting how much super-elevation to use, including:
  • stability of high laden commercial vehicles
  • stability of loads on trucks
  • tendency of the rear wheels of slow moving vehicles to track towards the centre of the turn
  • appearance, particularly in flat terrain and in urban areas
  • effect on out-of-control vehicles leaving the inside of the curve
  • tendency of vehicles to slide on the road surface in frost/icy conditions
Cheshire County Council's own Design Aid states that a Local Distributor road with a curve radius of less than 100metres shall have a super-elevation of 4.0%.

The curve radius on the bend in the vicinity of my property is about 60metres the super-elevation is practically none existent.

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