Evaluating traffic and safety impacts of diverging diamond interchange replacing roundabouts: A microsimulation study

With increasing traffic volumes and worsening congestion, conventional interchanges are facing ever-growing challenges. These issues can potentially be mitigated by implementing suitable alternative designs, such as the Diverging Diamond Interchange (DDI). While simulation studies and real-world implementations have validated the DDI’s superiority over conventional interchanges, existing research primarily focuses on right-hand driving and has not considered roundabout layouts prevalent in the UK. This study employs the simulation of the UK Strategic Road Network (SRN) to address this gap. Four hypothetical scenarios are constructed, transitioning conventional junctions between J23 and J26 on the M1 Motorway of SRN to DDIs. By comparing a series of Key Performance Indicators (KPIs), the study quantitatively assesses the impact of DDI implementation on traffic flow, delay and safety. The simulation results reveal that replacing roundabouts to DDIs in a motorway corridor can lead to a 55% reduction in average delay and a 5.96% increase in average speed. However, upon evaluating traffic safety through the Surrogate Safety Assessment Model, a slight decline in the majority of safety performance measures is observed. This study provides evidence to support the adoption of DDIs in the UK, highlighting the trade-offs between improved traffic flow and potential safety concerns.