ROAD GEOMETRY 

(CURVE RADII, GRADIENT AND SUPERELEVATION)

Curve Radii

Changes in the direction of streets may disorientate pedestrians and increase walking distances between destinations.

The scope for changes in the alignment of Strategic Routes is limited, as these routes will generally need to be straight in order to efficiently link destinations.

There is scope to use changes in horizontal alignment on Local streets to calm traffic and promote place (where curvilinear or more organic grid networks are proposed) to do so changes in horizontal alignment should be combined with contextual measures and reductions in forward visibility.

The Manual for Streets 2 contains a set of standards for curve radii that are four steps below the desirable minimum contained with the UK DMRB. These standards have been adopted for use in DMUS.

Gradient

A maximum of 5% is desirable where pedestrian are active. In hilly terrain, steeper gradients may be required but regard must be had to the maximum gradient for wheelchair users of 8.3%.

This also needs to be considered at the network level and as a response to place making.

The inclusion of streets that exceed these gradients may not be significant within a network where there are many routes that can be taken between destinations and may in fact have place making benefits.

Superelevation

Superelevation, where one side of the road is designed to be higher than the other in order to resist the centrifugal effect of turning a corner, is designed to assist drivers to maintain higher speeds around curves

Its use is inappropriate in urban areas where the design is intended to achieve a moderate or low speed environment. It is also difficult to implement in urban areas with frequent junctions and points of access.