(2) what guidance applies to the width of roads on which Trief kerbs are installed.
The Highways Agency's requirements for Road Safety Audits on trunk road schemes are set out in HD19/03 of the Design Manual for Roads and Bridges. This document prescribes the requirements for undertaking safety assessments for scheme inception, design development, construction, opening to traffic and monitoring. The safety implications of road restraint systems would form part of this assessment.
There is no centrally determined requirement on English local authorities to conduct safety assessments prior to the installation of Trief kerbs on the roads they manage. This is a matter for individual authorities. There is no centrally produced guidance on the width of roads on which Trief kerbs are installed.