A406 in Ilford A127 in Romford M25 near Brentwood A414 in Margaretting A130 near Chelmsford A120 near Marks Tey A14 near Ipswich The A12 is a major road in Eastern England.

It runs north-east/south-west between London and the coastal town of Lowestoft in the north-eastern corner of Suffolk, following a similar route to the Great Eastern Main Line until Ipswich.

[4] It was named as Britain's worst road because of "potholes and regular closures due to roadworks" in a 2007 survey by Cornhill Insurance.

[10][11][12] The route from London to Essex has long been important, with Old Ford being the location of an ancient Celtic crossing of the River Lea.

[15] The crossing of the Lea moved to its current location at Bow around 1110 when Matilda, wife of Henry I, ordered a distinctively bow-shaped, three-arched bridge to be built over the river.

[34] A white paper, Roads for Prosperity, published in 1989, proposed to widen the Chelmsford Bypass and the section from Hatfield Peverel to Witham to dual 3 lane; it also proposed widening the section from Saxmundham to Lowestoft and from Wickham Market to Farnham to dual 2 lanes.

[35] The Department for Transport published Trunk roads, England, into the 1990s in May 1990 which included ten proposed developments for the A12 between the M25 and Lowestoft including the M12 motorway between M25 and the Chelmsford bypass, Chelmsford bypass widening and improvements on the sections from Hatfield Peverel to Marks Tey, Four Sisters to Stratford St. Mary, Martlesham to Wickham Market, Wickham Market to Saxmundham, the bypass around Saxmundham, Saxmundham to south of Wrentham, South of Wrentham to Kessingland and the Lowestoft relief road.

In 2006, the 1.5 mile Tom Crisp Way "Southern Relief Road" opened, diverting the A12 away from the cliffs and built up Kirkely.

[38] 2015 saw Millennium Way extended to connect to the A47 at Corton [39] and 2024 saw a new third river crossing built, the Gull Wing Bridge, which linked the northern and southern relief roads and completes the A12 bypass in Lowestoft.

The entire bypass consists of single carriageway roads with modern cycle and pedestrian facilities and a mostly 40 MPH speed limit.

The M11 was to have provided a motorway standard road into central London past Ringway 1, terminating at the Angel in Islington.

When the London Ringways plan was being proposed, a motorway (North Cross Route) was to end here and the M11 was meant to extend from its current terminus on the A406 through this junction and to Angel.

Prior to that, the A12 started at the Green Man Roundabout at Leytonstone, and was single carriageway west of Wanstead Underground station.

However, the 2.5-mile (4.0 km) stretch from Gallows Corner to the junction with the M25 motorway, called Colchester Road, is still perfectly straight.

The A12 formerly went through Brentwood, Mountnessing, Ingatestone, Margaretting, Chelmsford, Boreham, Hatfield Peverel, Witham, Kelvedon, Copford, Stanway and Colchester, but these are all now bypassed, and the A12 is a dual carriageway with mostly grade-separated junctions for its whole length in Essex.

Built in 1982, the A12 Colchester bypass provides an uninterrupted dual carriageway where the national speed limit of 70 mph applies.

Before 1982, the A12 took a route much closer to Colchester itself, and although still a bypass it consisted of urban single carriageways with roundabouts and pedestrian crossings.

When Ipswich's Southern by-pass was built in the early 1980s, the route picked up from the northern Capel St Mary junction (now numbered 32b), to pass to the West of the original line – this allowed the relevant ground works and interchanges to be completed with minimal traffic disruption.

The Ipswich Southern By-pass allows the A12 to overlap the A14 to Seven Hills Interchange, 7 miles (11 km) from the Copdock junction, where the A12 reappears and heads North.

There are, though, a few stretches of dual carriageway between the Woodbridge bypass and Lowestoft (at Wickham Market, Saxmundham, Wangford and Kessingland).

However, as of June 2006, the A12 now follows the course of the new single carriageway 40 miles per hour (64 km/h) Southern Relief Road that joins the A47 at Lowestoft Bascule Bridge.

Before February 2017, From a point just south west of the mouth of the River Yare, northwards to the point where it crosses the River Yare in Great Yarmouth, the A12 followed the route originally used by the railway line from Lowestoft to its terminus north of Breydon Bridge[46] at Vauxhall Roundabout where the A47 previously terminated.

[47] In November 2008 the government announced a £60 million technology package including variable message signs, CCTV, Automatic Number Plate Recognition cameras and automatic incident detection sensors embedded in the road surface to improve journey reliability, reduce delays and give better information to drivers.

Suffolk county council considered a bypass for the villages of Farnham, Stratford St Andrew, Glemham and Marlesford for the 2006 Local Transport Plan.

[56] The Inquiry, the first ever local council sponsored inquiry into a major trunk road, heard from 24 organisations and 36 witnesses over three days including Department for Transport and Highways Agency officials, MPs, local and regional agencies and authorities, the emergency services, business and motoring groups.