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Dropped kerbs with flush surfaces and gentle gradients <1:20 towards the carriageway are necessary for accessibility at crossings and walking/wheeling and cycling access points.

1. 
   

   Gradients between 1:20 and 1:12 are ramps. Gradients above 1:12 (1:10 in very limited situations) are hazardous and not accessible.

2. Crossfall above the minimum gradient required for drainage (usually 1%) always reduces accessibility. Traversing ramps (gradients above 1:20) is hazardous and not accessible.

Best practice at crossings includes installation of carriageway raised tables to improve pedestrian safety and prioritisation. Raised tables help maximise footway and crossing accessibility, especially the safety and accessibility of crossing tactile paving areas.

Carriageway alterations at walking/wheeling and cycling carriageway access locations away from crossings are recommended to minimise associated footway accessibility reduction.

Steeper gradients up to 1:10 for no more than 1m length are appropriate at many driveway crossover points to maximise level footway width and reduce vehicle speeds.

Dropped kerbs on hills or sloping ground need to be designed and installed with great care to ensure accessible gradients are made on the dropped kerb and the surrounding area.

1.    Dropped kerb associated with 120mm high standard kerbs

With a 120mm kerb height, 2.4m of the footway width will have to slope towards the carriageway to retain an accessibly traversable gradient of <1:20:

Installing this dropped kerb will decrease accessibility of 2.4m of the total footway width. Most footways have less than 2.4m total width.

Note that the side tapers associated with this dropped kerb will often have much steeper gradients than the dropped kerb itself.

2.    Dropped kerb associated with 60mm high kerbs

With a 60mm kerb height, 1.2m of the footway width will have to slope towards the carriageway to retain an accessibly traversable gradient of <1:20. 60mm is the minimum reliably detectable kerb height for Blind and visually impaired people:

3.    Dropped kerb side tapers

Dropped kerb installation usually requires triangles of tapered slopes at the sides to match up the dropped kerb to the rest of the footway without creating steps.

Side tapers are always steeper than the adjacent dropped kerb. Side tapers associated with dropped kerbs steeper than 1:20 are likely to be hazardously steep.

4.    Guidance alignment to create good practice

Building Regulations approved document M vol 2 states that ramps with gradients above 1:20 need handrails on both sides, level landings, and must be made of slip-resistant materials that are similar to walk on to the material at the foot and top of the ramp.

BS8300-1:2018 recommends 1:20 gradients on dropped kerbs, but allows maximum 1:12. This is close to the same as fig 1 in Guidance on the Use of Tactile Paving Surfaces, which additionally states the side slopes can be 1:11 – above the usual permitted ramp gradient.

But a tactile-paved dropped kerb always has an uneven and often slippery surface which is unlike the surrounding surfaces, with no handrails and rarely with level landings.

Side tapers associated with 1:12 gradient dropped kerbs will tend to have slopes of 1:8.5 or steeper (depending on taper kerb length) – which will be very hazardous and inaccessible.

Dropped kerb gradients need to be <1:20 for adequate accessibility. To make continuous, accessible footways and crossings, we recommend using 60mm height kerbs and/or carriageway modifications, especially for dropped kerbs on sloping sites.