A382 Traffic Management Planning Part 2: from modelling to delivery

Building on the initial A382 traffic management (TM) planning work, Immense worked in close partnership with Core Highways and M Group on behalf of Devon County Council to take the scheme through a deeper, evidence-led phase of decision making.

The collaboration brought together complementary expertise to compare traffic management options, validate choices against real-world data, and directly shape the scheme’s carbon ambitions – turning collaborative insight into measurable impact. With the Immense platform remaining available throughout delivery, the partnership is embedded across the full project lifecycle, ready to support and enhance the programme as it progresses.

The background

The A382 near Newton Abbot is one of the most ambitious local highway schemes in the UK, with a goal to become the country’s first carbon negative highway. Delivering construction works on a live, busy route serving a market town of 27,000 people, with key connections to Exeter, Torbay and Plymouth, presented a significant traffic management challenge.

Core Highways needed to quickly assess whether full road closures could deliver a shorter programme with less disruption than conventional signal-controlled working. The question wasn’t just operational: a shorter programme meant less carbon, lower costs and reduced impact on road users. But the evidence needed to support that decision had to be credible, fast and affordable to produce.

Traditional transport modelling would have taken months and significant specialist resource. Immense provided cloud-based simulation platform capable of testing multiple scenarios simultaneously – delivering the evidence needed within the ECI process, before construction began.

The mission

The assessment needed to answer five core questions:

• Should sections be managed with temporary signals or full closures – and which produced less overall disruption?
• Which diversion routes were viable and how would they perform as traffic levels changed?
• How much difference would traveller awareness and proactive information make to delay impacts?
• Which stakeholders – businesses, schools, residents – would be most affected, and by how much?
• Could the evidence support a shorter overall programme, and what would that mean for carbon?

The solution

Immense built, calibrated and validated a dynamic 24-hour base model simulating a typical ‘day in the life’ of the network around Newton Abbot. Drawing on national travel behaviour data, local signal configurations, traffic counts and independent journey time data, the model was validated against real-world conditions before any scenarios were tested.

Five TM configurations were assessed, covering different combinations of closures and signal-controlled working at Trago Roundabout, Staplehill Road, Jetty Marsh, Stover and Ringslade. Each was modelled at two levels of driver awareness to understand the role of traveller information in reducing impacts.

The results were clear. Most scenarios produced critical delay impacts when driver awareness was low but those impacts reduced substantially once even modest levels of proactive information were introduced. Equally important: full road closures, despite appearing more disruptive on paper, were frequently less impactful than shuttle running under signals, particularly once traveller information was factored in. Closures also allowed larger, more efficient working areas, reduced the public-construction interface and shortened the overall programme.

Diversion management and hotspot mitigation

A dynamic diversion strategy

Rather than directing all traffic to a single diversion route, Core Highways used the Immense model outputs to design a two-route dynamic system. Portable VMS signs at key decision points displayed both journey times and recommended routes, switching between the A38 northbound and A380 options based on real-time conditions, with switch timings informed directly by the
modelling.

Without that evidence, designing an effective VMS strategy would have been guesswork. The modelling showed clearly that concentrating all diverted traffic on one route would quickly overwhelm capacity – a risk realised in early scenarios before information measures were introduced.

Hotspots identified and fixed

The model surfaced secondary issues that would not have been visible without simulation. At Clay Lane on the A38 diversion, increased flows caused queuing at a priority junction. Temporary signals proved insufficient. Immense modelling of an alternative – a temporary mini roundabout – showed it would reduce peak-hour queue lengths from 186 m to effectively zero. The mini roundabout was installed.

Other interventions followed: signal re-phasing at the A38 junction, speed limit management on the diversion, and targeted access signing for Trago Mills, Stover School and the local holiday park – all identified through the model.

The results

The modelling produced a clear, evidence-based recommendation: full closures with dynamic diversion management and proactive traveller information. This approach was validated when model predictions for the Jetty Marsh closure phase were compared against actual observed journey times – the model’s outputs closely matched real average journey times across all diversion route legs.

Programme and cost savings

• Full closure enabled up to one year to be saved from the overall project programme
• Larger, more efficient working areas reduced plant movements and preliminary costs
• Reduced public–construction interface improved site safety throughout
• VMS strategy delivered by Core Highways used directly from model-informed timings

Carbon benefits

• One year off programme = significant reduction in construction plant emissions and preliminary carbon
• HVO fuel used in site vehicles to further reduce operational carbon
• Solar-powered portable traffic signals eliminated generator fuel use
• Intellitag monitoring system reduced unnecessary sign-check vehicle journeys