The A1240 is a short A-road in east London. Originally part of the A1112 it gained its current number in the 1970s when that road was moved eastwards onto its current route.
The road starts at traffic lights on the A124 Wood Lane. As that road starts to turn westwards the A1240 continues its southerly course as it runs along the residential Heathway. The road is dead-straight and lined with houses, although there is the occasional set of traffic lights to relieve the monotony.
Presently the road reaches the Heathway shops and what passes for Dagenham town centre. There is a bridge over the District Line by Dagenham Heathway station. After passing Dagenham Library the road becomes residential once again, still on the dead-straight Heathway. The road eventually ends at traffic lights on the A1306 (former A13) by an out-of-town retail park.