The A1158 consists of two parallel roads through the Prittlewell area of Southend-on-Sea, each road carrying one-way traffic.
The northbound road starts at traffic lights on the A13 opposite Chalkwell Park in Westcliffe. It heads north along Southborne Grove, crossing a stream before crossing the unclassified D2 Prittlewell Chase at traffic lights. From this point on the road is two-way. After about the same distance again the road reaches a T-junction on the original line of the A127 (now part of the A1158). Traffic is advised to turn left, which soon reaches traffic lights on the current A127, where traffic must turn left towards London; eastbound A127 traffic may also turn right onto the A1158.
If, instead of turning left in the last sentence, we turned right instead, we would soon reach a bend to the right, with a road coming in on the left marked with a no-entry sign. This is the westbound offslip from the A127, although it is not signposted. Immediately after this we join the one-way Westbourne Grove, which is the southbound A1158. This follows the same route as the northbound road above, albeit in reverse, although this road is one-way for its entire length. At the far end the road ends at a signalised crossroads back on the A13, two blocks east of the start of the northbound road.