Project Update - A303 Trunk Road Service Area

In 2023 we began providing Transport and Drainage input to a Detailed planning application for a new Trunk Road Service Area (TRSA) located off the A303 at Downhead in South Somerset. The site lies along the section currently being upgraded to dual carriageway by National Highways (NH) between Ilchester and Sparkford. The development will comprise a new farm shop and restaurant, 60-bed hotel, EV charging centre and petrol filling station, truck stop area with EV charging and a new solar farm. 

In highways terms, any facility proving the travelling public with an opportunity to take a break from their journey has the potential to generate highway safety benefits on the wider road network as drivers are less tired and more alert to road conditions. In addition, as their purpose is to serve the needs of those already making a journey rather than creating a destination in their own right, the generation of new trips to service stations is actually relatively low. Our Transport Assessment to support the planning application therefore focussed on these positive aspects of the nature of the development, as well as providing the evidence necessary to demonstrate that the localised diversion of existing traffic onto the Downhead junction slip roads and the local road network to access the service area, would not result in any road capacity or safety issues. 

We engaged in extensive consultation with NH to ensure that the development proposals would seamlessly connect into their dualling scheme, whilst ensuring that it would not have an adverse impact on the new junction at Downhead from which the site would be accessed. We also demonstrated that the overall masterplan for the proposed development would not conflict with any of the existing NMU proposals. This included the provision of a new Pegasus Crossing on the access road into the TRSA, and incorporating existing and proposed pedestrian routes into the designs. 

On the drainage side, owing to the mixed-use nature of the site and local topography, each ‘parcel’ within the site required a different approach for the management of surface water. We also needed to ensure that any Sustainable urban Drainage Systems (SuDS) would mitigate impacts on water quality from development, as well as providing the necessary attenuation. A bespoke solution was found for each parcel of the development, with a combination of proprietary treatment, above ground, and below ground SuDS features designed to provide treatment and amenity. We also provided input into the efficacy of the different SuDS ‘treatment trains’ in removing phosphorus from surface water runoff. This is an important aspect for development in parts of Somerset and an emerging area of expertise for AWP. By utilising data from CIRIA guidance, we were able to demonstrate that the proposed treatment trains would reduce total phosphorus runoff by up to 80%. 

The new A303 eastbound carriageway and Downhead junction was opened in January 2024, with the rest of the project expected to be completed towards the end of 2024 / early 2025. If planning permission is granted for the new service area in due course, the development will provide an important benefit in terms of increasing the available rest areas on the Strategic Road Network, and will represent a high-quality stopping point for motorists on the A303 “Highway to the Sun”.

Images prepared by BPL Architecture