The A12 is the main road through deepest Essex, providing access from London to Suffolk and the key ports of Harwich, Felixstowe and Lowestoft. This is one of the few major long-distance routes that was never considered for a blue line - no motorway was ever planned here. Instead, the original Roman Road has been widened where it's in the open and bypassed where it isn't. On a map the A12 looks quite odd, a perfectly straight line that repeatedly suffers bumps of varying sizes where it swerves around towns and villages.
Between the M25 and Chelmsford, the road was meant to be replaced by a shiny new M12 as recently as the early 1990s. The proposal was simply meant to be a cheaper alternative to widening the existing road.
The A12's motorway never got off the ground and widening was attempted instead - but that too faltered. The Brentwood bypass was never widened, and north of there it's three lanes wide to Chelmsford, with the exception of one mile of the Ingatestone bypass, which inexplicably remains just two lanes wide. Recently the three-lane section northbound from Brentwood was reduced to two lanes to alleviate queuing at the point the road narrowed at Ingatestone.
Various other M12 proposals have been floated, but surprisingly none of them were really meant to relieve a substantial part of the A12. The proposals made until the 1980s were only to relieve the section of road within the M25 and not beyond.
You're not looking at the whole A12
This page is about the parts of the A12 that are designated a motorway or that have motorway characteristics. Other sections of this road will not be featured here and will not count towards the length of the road as shown below.