• Capabilities: Engineering
  • Sectors: Highways and Intelligent Transport Systems

Modelling the impact of driverless cars on the Strategic Road Network

South East, UK - Highways England operate, manage, maintain and enhance more than 4,000 miles of Strategic Road Network (SRN) in England. The SRN connects major cities, ports and airports. Although the SRN is only a small proportion of the road network in England (2.4%), it carries a third of all motorised traffic. As the UK moves closer to the introduction of driverless vehicles, Arcadis, working as joint venture partner with WSP, undertook modelling work on behalf of Highways England to analyse what impact this might have on the SRN.


to test impact of CAV


in CAV on the SRN

The Department for Transport (DfT) recently undertook some initial exploratory analysis into how the introduction of Connected and Autonomous Vehicles (CAV) may impact supply and demand on our roads. This used existing transport models, with the results being presented in the DfT’s Road Traffic Forecasts (2018).

Arcadis, working with WSP, used these assumptions and, combined with other wider research, was able to model the impact of CAV specifically on the SRN using a new model we developed called the South East Regional Traffic Model (SERTM). 

SERTM covers the East of England, London and South East. It is currently being used to assess the impact of CAV on a number of new road schemes that are likely to be implemented in Highways England’s Road Improvement Strategy 2, which covers the period 2020-2025. 

These schemes are likely to provide new opportunities for economic growth and relieve congestion. Using SERTM, we could undertake a range of ‘what if’ scenario testing for the impact of CAV and how it would affect the operation of the SRN. This included making a number of assumptions around network capacity, driver behaviour and travel demand. The assumptions were categorised as:

Demand: How CAV uptake might vary. Are people more likely to switch travel modes, and how will this change the number or passengers in a vehicle?

Supply: CAV can communicate with each other, which means they can maintain a reduced gap between vehicles. This improves efficiency and increases capacity, because it means more vehicles can be on the road and travel closer together.  

Parameters: CAV are assumed to have lower operating costs. Also, the passenger car unit (PCU) – which is a metric used to assess the rate of traffic-flow on a highway and takes into account the impact that a vehicle has on variables like speed and density - is likely to be less for CAV compared to other vehicles, as CAV can travel closer to each other.

The modelling results show that, even with the introduction of CAV, the majority of traffic is still likely to use and rely on the SRN. In fact, with more capacity available following the introduction of CAV, there is likely to be a bigger shift away from local roads and towards the SRN, particularly as speeds are generally higher (40mph to 70mph), and therefore journey times will be quicker. 

For Highways England, this modelling work helped to provide certainty around upcoming investment. It ensures that investment is not only being concentrated in the right areas, but guarantees that any upcoming work on the road network is futureproofed for the long term.


“In developing SERTM, the project team were able to apply our core modelling skills to provide insights on the potential impact of CAV on network operations.”

Narasimha Rao, Associate Technical Director and Project Manager for this modelling study 

“SERTM is another great example of Arcadis using transport modelling to help shape Future Mobility policy; adding to other CAV modelling studies including OmniCAV in the UK and the CAV Impact Study for the Province of North Holland and Amsterdam Municipality in the Netherlands.”

Tim Strong, Transport Innovation Director and Chairman of Arcadis UK’s Future Mobility Board  




to test impact of CAV


in CAV on the SRN

Questions about this project

Narasimha Rao

Associate Technical Director +44 (0)1483 803083 Ask me a question

Tim Strong

Transport Innovation Director Ask me a question
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