Sowton Interchange

The Sowton Interchange, junction 29 of the M5, is the first of two junctions between the M5 and A30 (the other being Pearce's Hill). Between the two junctions, the A30 multiplexes with the M5. It also connects to the old A30, now A3015, which leads into Exeter city centre.

Between here and junction 30, the M5 is D4M, with a dedicated lane between the two junctions.

Evolution of the 1970's interchange design

• 

  (a) Early proposal from 1969

• 

  (b) First stage of intended full layout of current junction prior to dualling of A30

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  (c) Initial proposal for A30 dualling

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  (d) A30 motorway Scheme A

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  (e) A30 motorway Scheme B

(a) The earliest known layout for the junction is from 1969 when a roundabout interchange was planned. At the same time the favoured location for Exeter Services was on the southwest corner of the junction.

(b) By the middle of 1970 plans were made to dual the A30 between the M5 and Honiton. This called for a redesign of the junction to allow uninterrupted movements between the M5 and A30 east. Two loops would be provided on the western side of the junction allowing traffic on the northbound carriageway to get on and off. Collector/Distributor lanes were planned to link the loops together, to prevent weaving.

(c) The original proposal for the A30 dualling was for the an all-purpose road with an additional junction just to the east at Blackhorse. Sowton Interchange would remain essentially the same as in the original plans.

(d) By 1972 consideration was given to constructing the A30 as a motorway. This would mean prohibited traffic being unable to use the new road so alternative arrangements had to be made to enable this traffic to travel between Blackhorse and Exeter. This scheme allows that traffic to travel through the middle of the junction by means of the former A30. However, it does mean through A30 traffic has to use Blackhorse Interchange to continue into Exeter.

(e) This option for the motorway scheme overcomes the main shortcoming of Scheme A in that through A30 traffic can access Exeter and the M5 without having to use Blackhorse Interchange. A separate local access road is provided to the south of the junction allowing prohibited traffic to travel between Blackhorse and Exeter. This scheme performed the highest and was therefore the recommended option and borehole records taken at the time correspond with this junction layout.

Despite all this, the A30 improvement was not constructed and the only part of this design that was built was the northbound offslip and the southbound onslip, giving freeflowing movements between the A30 and M5 south. The links to the M5 north were not built, even though all the evidence suggests the second loop would be built as part of the first stage.

Changes since opening

Plans to dual the A30 re-emerged in the Roads For Prosperity white paper of 1989. This differed from the 1970s proposals by running to the south of the existing road and there was emphasis on providing full access at the junction to allow movements between the M5 and Exeter, which was never seen as important in the 1970s. The amended layout was opened in 1999, almost completely signalising the junction and ending the completely freeflowing conditions which had existed for the previous 24 years. Two right turns were added - S/b to W/b and W/b to N/B - as well as all three remaining left turns; the N/b to W/b left turn was accomplished by using the offslip loop to turn 180 degrees and doing a (third) right turn. One movement, the E/b to S/b right turn, was not included at all, so traffic leaving Exeter wanting to join the M5 South would still have to join at junction 30 instead. Other than the M5 main carriageway, the A30 W/b to M5 S/b left-turn movement became the only freeflowing movement at the junction.

More recently, around 2011 to 2013, the layout was altered again, adding a fifth arm to the junction for access to the Exeter Science Park and other nearby developments, as well as finally adding the E/b to S/b movement so that traffic leaving Exeter for M5 South no longer had to make what had by now become a very slow crawl through the Sowton industrial estates; the junction was at last made properly full access, though at the cost of interrupting that one remaining freeflow turn, A30 W/b to M5 S/b, with traffic signals, as well as making it a very strange layout. With this new layout, E/b to S/b traffic now uses a kind of hook turn, peeling off the left of the A30 to turn right into the exit of the science park access road, to then do what feels like a U-turn onto the A30 W/b, before turning left to finally reach the M5 S/b. The entire movement requires driving over 4 stop lines - 5 if you also count the pedestrian crossing at the end!

Routes

Route	To	Notes
M5	The MIDLANDS, Taunton, Bristol
M5	The SOUTH WEST, Plymouth, Torquay, Okehampton
A30	Honiton	Formerly signed to London (via A303 and M3)
A3015	Exeter City Centre	Former A30

Links

• SABRE Forum Discussion

legislation.gov.uk

• The M5 Motorway (Junction 29 and the A30 Trunk Road Honiton to Exeter Improvement) (Slip Roads Special Roads) Scheme 1994

• The M5 Motorway (Junction 29 Connecting Road) Scheme 2010 - This scheme provides for the widening of the M5 Motorway southbound exit slip road at Junction 29.