FTVG 2022/23: The XT Junction Concept

Layout of XT Junction

Modelling team promotes the eXTra benefits of innovative junction design

In our second feature article about this year’s FTVG projects, we discuss the work done to research the benefits that could be generated by a different signalised junction configuration, known as the XT Junction.

The XT Junction team is formed of Omar M, a transport engineer for MDS Traffic Planners & Consultants, Elena Soboleva, a senior transport planner at Jacobs, plus Gautam Godavarthi and special adviser Steve Jones from Mott MacDonald.

Together with support from Emily Pittaway from Mott MacDonald on social outcomes, and Lior Steinberg from Humankind on urban planning, the project aimed to assess the potential benefits and drawbacks of the XT junction.

What is an XT Junction?

The XT Junction is a type of displaced right turn junction that has seen some limited use in the UK and USA.  It reduces the number of conflicts at t-junctions by introducing a second set of traffic signals on one approach of the junction that enables drivers to get into position for making or completing right-hand turns.

Originally designed to improve traffic flows, the team wanted to examine how the junction provides a more holistic and equitable range of improvements for all road users.

Omar defined the project’s goal as; “To advance the modern transport agenda in terms of sustainable and inclusive transport infrastructure for the future and support the UK’s aspiration of achieving net zero carbon emissions by 2050.”

Modelling benefits

FTVG provided funding support and access to expertise to contribute throughout the project. This support enabled the group to make wider connections and pursue research into the potential of the XT junction design.

The team modelled a range of hypothetical XT junction layouts varying in size and configuration using LinSig, Vissim, Sidra, and Infraworks software.

“We tested multiple scenarios using LinSig to benchmark the capacity savings and signal cycle time optimisation of the XT junction design compared to a standard T junction, with varying degrees of active travel provision”, said Gautam.

The team worked collaboratively across the UK, The Netherlands and Turkey to work through their ideas and consult with traffic engineering experts to ensure that their research was rigorous and informed.  The team explored where their junction design could deliver benefits to other road users to meet some of the challenges raised during the consultation phase.

Lior came into the project with these concerns front-of-mind; “My initial reaction to the XT junction was ‘wow this is cool,’ but on second thoughts, I realised it could create more complexity and confusion, particularly for vulnerable users”  he said, “But I came to see the potential of this innovation in reducing the need for wider roads and freeing up resources for active travel options. In the end, what may seem like a simple trick can lead to more sustainable solutions for all.”

The team found that the XT junction has the potential to increase capacity by up to 33% compared to a standard T junction, which can be used to benefit traffic flow, reduce congestion or improve crossing times for active travel modes.

The design can also potentially reduce operational carbon dioxide (CO2) emissions by up to 35%, which could help highway authorities and councils aiming to contribute towards the UK’s goal of net zero carbon emissions by 2050.

Commenting on the outputs, Elena said, “Our hope is that this inspires people to find innovative solutions to traffic problems without resorting to significant physical junction upgrades.”

The XT junction solution allows for more efficient use of the available space at a T-junction, creating additional capacity for both vehicular traffic and active travel modes without the need for major physical upgrades.

Real-world applications

The team want to restart the debate about the use of XT Junctions in the UK as a way to deliver on Net Zero ambitions and cater to the needs of more sustainable modes.

“We realised that the XT concept, while similar to some existing junction designs, was different in how it could deliver improvements holistically across a range of user groups – not just motorised vehicles”, reflected Steve upon completing the project.

His colleague Emily added; “All social benefits we’ve found in the design would be very minor if we only delivered it at one or two locations.  XT junctions would have to be rolled out on a larger scale for a tangible beneficial social impact to be realised, and these would to all need to incorporate pedestrian and cycling infrastructure to maximise the impact.”

The team’s next steps therefore are to promote the benefits of the junction to a wider audience and ensure the benefits they’ve calculated can be fully realised.

Reflecting on the road ahead, Omar concluded; “The outputs of the project could be used by transport planners and policymakers as part of their toolkit for improving the performance of t-junctions.  The project’s results should encourage transport planners to consider alternative designs that provide holistic benefits to active travel users and vehicular drivers while reducing environmental impact.”

The team will be presenting their findings at this year’s Transport Practitioners Meeting in Greenwich, June 28th – 29th.

Links to their papers and explanatory videos can be found here:

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