As part of the ongoing process of rewriting the Manual of Contract Documents for Highway Works (MCHW), everything related to design of a structure will be removed and hosted instead within the DMRB.
Speaking at the Institute of Highway Engineers Traffic Signs Conference Michael Lewis of National Highways confirmed that the MCHW will also include ‘Instructions for Specifiers’ and ‘Constructor requirements’.
The MCHW was announced at the beginning of the current (2020-25) Roads Period and is due to be complete by March.
Mr Lewis said the changes would be ‘quite a shock to the industry’.
A new version of the DMRB was launched in 2020 but it is now set to be rewritten again, in light of the reformed MCHW.
National Highways will also shortly issue new guidance to facilitate the use of socketed foundations on minor structures such as road signs and radar masts.
Such quick-change structures do not currently comply with the recently revised CD 354 Design of Minor Structures document within the Design Manual for Roads and Bridges (DMRB), and so are designed as an ‘alternative type’ of foundation.
Mr Lewis said that although there are potential issues with the design of retention sockets, it was a misconception that their exclusion from CD 354 means that National Highways has ‘banned’ them.
In fact, reflecting the ‘conundrum’ posed by the popularity of retention sockets, the company has been working with consultancy firm WSP to create a design guide for their use.
This will include an introduction to retention sockets; design standards and approvals; design principles; inspection and maintenance considerations and example calculations for engineers.
Mr Lewis said: ‘Any good design guide has to have a couple of example calculations. So we decided to pick three structures that would be used on the network – traffic signals, stopped vehicle detection and a traffic sign and we designed the foundation.’
The document will also examine the uses of foundation sockets, including for lighting columns, traffic signs and signals and hosting masts for stopped vehicle detection radar devices.
It will look at benefits such as cost, sustainability and reliability; construction programme benefits; orientation flexibility; and the potential for temporary removal, as well as risks including loose connection, corrosion from dissimilar metals and potential trip hazards when removed.
The guidance will also provide an overview of the different standards for ‘a broad church’ of structure uses and include guidance on wind action and issues of wind funnelling and wind induced vibration and resonance.
It will also cover the Construction (Design and Management) Regulations, whole life asset management of socket foundations and provide an overview of the design of supporting posts.
