Road Safety Audit Requirements for Speed Reduction Measures
Installing speed reduction measures on a public highway without a Road Safety Audit is contrary to best practice and may breach duty under the Highways Act. This guide explains when Road Safety Audits are required and how they affect speed reduction schemes.
What Is a Road Safety Audit?
A Road Safety Audit (RSA) is a formal safety performance examination of a highway scheme by an independent, qualified auditing team. The DfT's Road Safety Audit Standard (GG 119) requires audits at four stages: Stage 1 (preliminary design), Stage 2 (detailed design), Stage 3 (pre-opening), and Stage 3+ (post-opening monitoring).
When Is an RSA Required?
- New road humps on public roads (always required under Highways Act 1980)
- Speed cushion schemes
- Raised junctions and road tables
- Traffic calming as part of a 20mph zone scheme
- Narrowings and chicanes with physical installations
Minor schemes or private land installations do not require a formal RSA, but a design review is good practice.
Common RSA Issues with Speed Reduction Measures
- Signing and marking deficiencies: Missing advance warning signs, inadequate hatching on hump profiles
- Drainage: Water pooling on the flat top of table-top humps
- Cyclist safety: Hump profiles causing discomfort or hazard for cyclists
- Night visibility: Inadequate retroreflective markings or missing delineator posts
- Emergency vehicle delay: Hump spacing that forces ambulances to slow significantly — may require speed cushion substitution
20mph Zone Requirements
- TRO confirmed by the local highway authority
- Zone entry/exit signs (Diagram 674.1)
- Physical calming features (minimum one per 100m in most guidance)
- RSA at detailed design stage
- Consultation with emergency services
Private Land: No RSA Required
Rubber speed bumps in car parks or industrial estates, wheel stops, parking posts, and private road speed humps do not require an RSA (though a design review is recommended). Browse our speed bump and traffic calming range.