Blackbrook Roundabout is probably the most important junction in Taunton. It is the link between the M5, on which it is Junction 25, with the A358, which leads to the A38 and the centre of Taunton in one direction, and Yeovil and the A303 in the other. There is also a minor road to a large commercial area, part of which was also once part of the A358.
The junction is now partially signalised, with the two M5 offslips being controlled. The other three arms, however, are still standard roundabout entrances. The A358 towards the A303 and Yeovil now frequently jams, causing the whole junction to jam at busy times.
As with most of the M5 junctions in Somerset, this junction spent a small amount of time as a temporary terminus of the motorway.