A team from the UK, Turkey and the Netherlands has joined forces to investigate an innovative new approach to junction design. Taking inspiration and design principles from a junction type commonly used in the United States – the Diverging Diamond Interchange (DDI) – the team is testing a new T-junction layout called the “XT Junction”. The team hopes this new design can achieve capacity improvements, reduce delay, and lessen environmental impacts compared to more traditional engineering and signalling solutions.
The team is formed of Omar Mohsen, a transport engineer with MDS Traffic Planners & Consultants, Lior Steinberg, an urban designer and co-founder of Humankind, plus Steve Jones, Elena Soboleva and Gautam Godavarthi, transport specialists and modellers from Mott MacDonald.
The group came together through a combination of LinkedIn posts and meeting at conferences;
“I first met Steve at a conference in 2020 when he was presenting on the potential for the DDI junction design to be used in the UK”, said Omar, “I recognised some similarities between the DDI and XT idea and got in contact with Steve to see if he and his team could support taking this further.”
Steve added, “When Omar told me about his ideas, I was immediately interested and could see parallels with my earlier research work on the DDI. I was therefore only too happy to support the team to develop and test the concept further.”
Through producing a series of video-casts – Omar was able to enlist the support of Elena and Gautam from the Mott MacDonald modelling team, and Lior to offer people-centric and active travel expertise to the group.
“I was inspired by the DDI’s creative design and the people who were committed to confronting conventional thinking to achieve its realisation”, says Omar, “I’m passionate about seeking innovative ways to improve social and environmental outcomes through improving road conditions.”
The group are currently progressing with a literature review to illustrate how the DDI crossover idea has emerged.
Drawing from the features of the DDI, the XT design switches minor road traffic to the opposite side of the carriageway before entering the junction. This combines both movements to and from the minor road into a single conflict-free movement, reducing the number of traffic signal phases and improving safety. The layout can be accommodated within the current footprint of the junction and can even reduce the amount of carriageway required in the layout, releasing space for improved landscaping and active modes.
Once the group have demonstrated a proof-of-concept for the layout using theoretical examples, they will proceed with modelling the impacts of the junction design on real-life congested junctions.
FTVG is funding both the theoretical and practical tests of the junction layout.
Elena said, “We’ve been spending the past few weeks sketching the designs in InfraWorks and ensuring they meet UK standards, now we’re starting to simulate these in traffic signal modelling tools such as LinSIG and eventually on microsimulation platforms such as VISSIM.”
Gautam added, “What’s exciting at the moment is that we’ve started conversations with National Highways in the UK to provide us with traffic data and forecasts for a real-life case study. Using this data, we hope to replicate current congested conditions in our models and then illustrate how the XT Junction layout can address these”
The team have begun to test the new layout in VISSIM, which is already starting to yield some encouraging results.
The outputs from the traffic models will help to quantify the benefits of the new layout in terms of travel times and reduced congestion, applied to a specific case study.
It is hoped that with the design outputs and modelling results, the team can make a convincing case for change for implementing the new layout in practice.
By the end of the project, the team will produce a paper outlining how the XT Junction will:
“The profession of traffic engineers has been busy for decades with building bigger and wider roads to move more cars. It’s refreshing to have professionals who try to rethink from scratch the way we arrange the built environment” said Lior, “FTVG has connected like-minded people with a desire to deliver improved social outcomes through innovative and creative thinking.”
The initiative has provided a valuable platform for incubating idea, which the group hopes will deliver innovation in traffic engineering infrastructure, as well as professional development through being able to promote their ideas to the wider traffic engineering and transport planning community.