The following answer is based on the Link team’s collective experience, which includes involvement in hundreds of projects of varying scales from inception through to construction on site, across the UK over the past 15 years.

Design Manual for Roads and Bridges (DMRB) itself provides a guidance on this matter.

A Departure from standard is where a designer is not following the requirements given in the design standards. Departures from the standard guidance may be considered in an exceptional circumstance when it can be justified for various reasons. The DMRB acknowledges that it may not always be practical or possible to adhere to all of its standards, and therefore, it allows for departures in certain cases. These departures are typically subject to a formal approval process and should be well-documented and justified.

Departures may be appropriate in a variety of situations. A few of them are as follows:

• Site Constraints
• Development/updating of design Standards do not keep pace with emerging technology, exploration of new materials, methods of construction etc. and it might make advantageous to deviate from the Standards
• Standards cannot be reliably written to cover every situation
• Disproportionate costs and/or delays
• Trials and pilots
• Innovation
• An “elastic” solution
• Departures provide a useful source of ideas for updating standards

The specific conditions under which departures from DMRB standards may be considered and the approval process for such departures can vary depending on the specific project, the local authorities, and the nature of the deviation. Typically, a formal request or application for a departure should be made, and it would need to demonstrate why the departure is necessary and provide appropriate engineering justifications.

It’s important to work closely with the relevant authorities, such as the Highways Agency or local highway authorities, when considering departures from DMRB standards to ensure that the necessary permissions and approvals are obtained and that safety and design integrity are not compromised.

For specific details on when and how to request departures from DMRB standards for a particular project, it is essential to consult the most recent version of the DMRB and to work with the relevant authorities and agencies involved in the project.