B4.5.1 Speed restraints

To ensure that the design speeds identified for each type of street are not exceeded, proposals must design speed restraint measures into the development, which are self-enforcing. They must be designed from the beginning of the process, and not introduced as an after thought. Applicants must justify proposed speed restraint measures within the Design and Access Statement (DAS). The type of speed restraint features and its frequency must be appropriate for the street context and align to the Street Hierarchy (List 3).

Proposals that indicate that an entrance ramp is to be utilised as a speed restraint must comply with the Street Hierarchy (List 3). Entrance ramps must be of an adoptable standard.

Design proposals must demonstrate how vehicles are to be prevented from overriding landscaped and amenity areas, areas of public realm, or impacting on trees, by providing information about the boundary treatments proposed under such circumstances.

Junction speed tables should be proposed on Local Streets. They should be constructed in materials that differ from the main carriageway, and wherever possible should be aligned with pedestrian desire lines to accommodate a pedestrian crossing area, to create a more ‘natural’ and logical feel to the traffic system. Where junction speed tables are proposed, upstands or abrupt changes in gradient should be avoided, to avoid creating a risk or discomfort to cyclists. The maximum height of a speed table should be to the top of the kerb, subject to a constructed maximum of 100mm, a maximum length of 6 metres, with a preferred ramp gradient:

• on Local Streets of 1 in 15 (6.7%)

• on a bus route of 1 in 18 (5.5%)

Street design should incorporate elements that influence drivers’ perception of the street environment to encourage lower speeds. These may include:

• visual narrowing through edge markings or carriageway design

• pedestrian presence cues, such as active frontages, crossing points, or features suggesting potential pedestrian activity

• carriageway framing using features like street trees or other vertical elements that provide partial visual screening

Wherever possible, these “natural” speed-reducing features should be integrated into the design so that they complement the built form and layout of the development.

Gateways can indicate visually to drivers that they are entering an area where reduced speeds are expected (such as on the entry to Local Residential, Shared Surface Streets, or Private Drives), and there is a greater likelihood of encountering vulnerable street users. Gateways should be used to clearly signal to drivers that they are entering a reduced-speed zone. Physical interventions should be enhanced by landscape elements, such as tree planting to visually narrow the carriageway (albeit trees cannot be located within visibility splays as per Code: C2.17), or the use of differing hard surface materials to reinforce a change in the environment.

Speed control bends may be appropriate on lower-order streets (such as Local Residential, Shared Surface or Private Drives), however they should not compromise the layout of the site (see Guidance G1.10 and G1.11 for more information). Speed control bends should be a specific and obvious speed restraint feature with the bend being tighter than the normal recommended minimum centreline radius for the street type, down to an absolute minimum centreline radius of 7.5 metres. The full forward visibility for the appropriate design speed should still be provided. The deflection angle should be greater than 60 degrees and some carriageway widening maybe desirable. Overrun areas should be used sparingly to allow the passage of larger vehicles whilst maintaining ‘tight’ carriageway dimensions.