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A30 / M5 Junction 31 Slip Road Improvement
The Project
The eastbound carriageway of the A30, which carries trunk road traffic from west Devon and Cornwall, meets the M5 at Junction 31 on the south west side of Exeter. The A38 from Plymouth and south east Cornwall also meets the M5 at this point.
During normal traffic conditions for most of the year, the slip road carries an average of 14750 vehicles per day. These join an M5 northbound flow of 34000 vehicles per day. However, on a summer weekend in August these figures can rise to 26000 and 59000 vehicles per day, respectively, with much of this being concentrated into the late morning, afternoon and early evening. This has resulted in traffic queuing for up to 14 km (9 miles), with occasional delays of over 60 minutes.
We carried out some alterations to the junction in 2005/2006 following a traffic modelling exercise which guided the design. Whilst the scheme was successful in improving the operation of the merge with the motorway, the anticipated queuing results were not achieved. We monitored traffic queues and behaviour following the works and listened to comments received from members of the public. As the result, it was decided to make more extensive modifications to the layout.
We carried out improvements to the junction in order to increase its ability to cope with peak traffic flows during holiday periods. The basic principle involved the provision of two lanes of traffic between the A30 (eastbound carriageway) and the M5 (northbound carriageway).
The work mainly consisted of new signing and road markings, but also involved some surfacing, installation of safety barriers, drainage, street lighting and some bank retention. A redundant sign gantry on the A30 was removed and replaced with four new structures.
The majority of the works were completed around Easter 2009, but the installation of the 4 large gantries took place in May and early June.
