T0695 Diverging Diamond Interchanges - update to DMRB standard CD 122

National Highways (the Client) is seeking the provision of services to undertake research into Diverging Diamond Interchanges (DDI). STAGE 1 SCOPE: Overall, the aims of this task are to: 1. Measure the safety performance of DDIs to clearly understand how or if they are safer than existing junction types; 2. Examine potential risks and hazards such as Wrong Way Driving; 3. Review international standards and determine relevance to UK; and 4. Review the DMRB to understand how requirements and advice would need to change to encompass Diverging Diamond Interchanges.

The award of this work package is initially for Stage 1 only (see background).

Subject to further funding, a STAGE 2 FEASIBILITY task would be undertaken in the next financial year:

- Identify a location where the layout can be retrofitted and modelled to existing infrastructure such as at an existing dumbbell roundabout at a grade separated junction and then examine scalability across the network; - Investigate how any new risks such as Wrong Way Driving or failure of traffic signals can be reduced or removed; - Measure the environmental and economic benefits such as land take reduction and carbon saving; and - Provide recommendations for requirements, advice and drawings to update the DMRB and update the standards CD 122 and CD 123. This is anticipated to be a report and not an update to the standards in case the findings do not support changing the DMRB.