A30 Temple to Higher Carblake five-year post-opening project evaluation (POPE)
A summary of our evaluation of this major road project against its objectives five years after opening.
For more details of our evaluation methods, please refer to the Major Enhancements evaluation approach.
For information on limitations, contextual factors and data constraints that may affect project performance assessment in POPES, see our POPE factsheet.
Glossary of terms used in POPE evaluations.
Evaluation summary
Five years after opening, the A30 Temple to Higher Carblake project has successfully removed a key bottleneck on a strategically important route. The project has improved safety, reliability, reduced congestion and improved traffic flow. While some benefits are lower than originally forecast, particularly journey time savings, the project continues to deliver high value for money. Some environmental features require ongoing maintenance to ensure long-term benefits are fully realised.
Overview of objectives
The project which was promoted, designed and constructed by Cornwall Council, was developed to meet a number of specific objectives. The table below assesses the extent to which these objectives have been achieved based on the evidence collected through the evaluation.
Overall, the evidence shows the project has achieved its core objectives and continues to deliver positive outcomes for road users.
| Objective | Result |
|---|---|
| Reduced congestion |
In neutral months 2 to 4 minutes reduction in journey times on A30 compared to before and counterfactual scenario (in both directions and all time periods). In summer months Weekend journeys are 16–26 minutes quicker than both the before project and counterfactual scenarios, while weekday journey times remain similar to before or slower by one minute. |
|
Improved journey time reliability |
In neutral months, journey time reliability on the A30 improved, with more consistent journey times in both directions.
|
Improved safety |
Safety has improved. The average number of personal injury collisions reduced from 3 before the project to 2 following project opening. The annual average number of KSIs also reduced, decreasing from 1 prior to the project to 0 post opening. |
| Improved network resilience |
The dual carriageway reduced the likelihood of full road closures and enabled faster incident response and clearance. |
| Support the economy | Improved customer journeys on the A30 during peak tourism periods, contributing positively to the Cornish economy. |
Project outcomes compared to forecasts
Appraisal forecasts set out the impacts anticipated during project development. The tables below compare these forecasts with observed outcomes to assess the extent to which expectations have been met.
The project has achieved its intended outcomes, however there are some differences between:
- what was expected at appraisal
- what has been observed five years after opening.
The tables below compare forecast and observed outcomes across each evaluation theme.
Customer journeys
| Sub-area | Performance vs forecast | Keynotes |
|---|---|---|
| Traffic growth | In line with forecast |
Some variation across time periods reflecting seasonal demand and tourism patterns. Similar to forecasts in neutral months, higher than forecast on summer weekdays. |
| Journey time | Mixed outcomes | Better than forecast in off-peak tourism periods, more variable in summer. |
|
Journey time reliability |
Better than forecast | Reduced variability in journeys with more consistent journey times for road users. |
Safety
| Sub-area | Performance vs forecast | Keynotes |
|---|---|---|
| Safety | In line with forecast | Fewer collisions and casualties. |
Environment
| Sub-area | Performance vs forecast | Keynotes |
|---|---|---|
| Noise | In line with forecast | Noise levels around the project reflect the predicted minor to moderate improvements for many nearby properties. |
| Air quality | In line with forecast | Observed traffic patterns indicate that air quality outcomes remain stable with no significant air quality impacts identified. |
| Greenhouse gases | Better than forecast | Lower than forecast traffic flows suggest the project may have resulted in a smaller increase in CO₂ emissions than expected. |
| Landscape | In line with forecast | As anticipated, the widening of the A30 and the new junction infrastructure has increased the roads’ presence in the landscape. However, mitigation planting and locally appropriate design measures are helping the project integrate into the surrounding landscape. |
| Historic environment | In line with forecast | The settings of listed buildings and historic features were affected broadly as predicted, with no direct impacts. |
| Biodiversity | Worse than forecast | The appraisal predicted that biodiversity impacts would primarily arise from habitat loss and fragmentation during construction, with mitigation reducing residual effects to slight adverse overall. However, more active maintenance is required to deliver this outcome. |
| Water environment | Worse than forecast | Drainage infrastructure was in place as intended. However, balancing ponds and drainage ditches had become overgrown, increasing the risk that their drainage performance and biodiversity benefits could reduce over time if maintenance is not improved. |
Value for money
| Sub-area | Performance vs forecast | Keynotes |
|---|---|---|
| Value for money | High value for money, but lower than the “very high” at appraisal | Lower traffic flows on some routes, reducing total user benefits. |
Why do some outcomes differ from the original forecasts?
Evaluation compares what actually happened with what was expected during appraisal. Several external factors influenced the outcomes, including:
- changes in travel demand following the COVID-19 pandemic
- slower long-term traffic growth than forecast
- strong seasonal tourism in Cornwall
- nearby roadworks affecting traffic patterns.
These factors help explain why some outcomes, particularly journey time savings, were lower or more variable than expected.
Continuing to maximise benefits
The project has achieved its intended outcomes and is delivering many of the environmental outcomes that were originally forecast. The environmental (landscape and ecology) aspects of the project are still being maintained and monitored by Cornwall Council pending handover to National Highways. While much of the mitigation implemented during construction has established, issues have been identified relating to the condition of some landscape plots and outstanding drainage features.
The evaluation highlights the need for continued maintenance to ensure that the anticipated long-term environmental benefits are fully realised.
Project overview
The A30 is a key strategic route linking Cornwall with the wider regional and national road network. It connects with the M5 at Exeter and provides access to London via the A303 and M3. The route is vital for local communities, businesses, freight, and tourism.
Before the project, the section between Temple and Higher Carblake was the last remaining single carriageway between Exeter and Truro. This created a significant bottleneck, causing congestion, delays and unreliable journey times, particularly during the summer tourist season.
The project upgraded this section to dual carriageway, improving connectivity and resilience across Cornwall.
- upgrade of 2.8 miles of single carriageway to dual carriageway.
- construction of three grade-separated junctions.
- introduction of local access roads to reduce direct accesses onto the A30.
The project opened to traffic in 2017 and was fully completed in 2018
Why the project was needed
Prior to the upgrade, this section of the A30 constrained movement across Cornwall. As the only single carriageway section on the route, it created:
- regular congestion and delays
- unreliable journey times, particularly in peak tourist periods
- reduced network resilience, with limited alternative routes
The project was designed to remove this constraint by providing continuous dual carriageway, improving traffic flow and supporting economic activity across the region.
