The A12 was formed in 1922 as part of the Great Britain road numbering scheme, and initially the route went from Stratford to Gallows Corner along the present A118 road before continuing to Great Yarmouth. This section in London was rerouted to run on Eastern Avenue by the mid-1940s, and extended to follow the current route from Blackwall Tunnel along the East Cross Route, (previously the A102(M) & A106), the M11 link road in 1999.
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. The route was altered slightly by the Romans who created a paved road from London to Colchester, which was part of Inter V on the Antonine Itinerary, and parts of this were used by a turnpike road, the Great Essex Road. 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. A map from 1766 shows a route from London to Great Yarmouth which follows much of the current A12.
The "Ipswich to South Town and Bungay Turnpike Trust" was established in 1785, operating between Ipswich and Great Yarmouth. The trust was wound up in 1872 following the arrival of the East Suffolk Line which was fully operational between the two towns in 1859. Following the demise of the Turnpike trust, responsibility reverted to parish responsibility until the new county councils took over in 1889.
A new section of the A12, known as the "M11 link road" or "A12 Hackney-M11 Link Road", was built in the early 1990s in the face of the major M11 link road protest and finally opened in October 1999. The section of road had originally been proposed in 1903 in a Royal Commission on London Traffic. A public inquiry had been held in September 1961 and a further three public inquiries, a Parliamentary Bill and a High Court challenge had been required before the work started.
Initiated in 2000, the London to Ipswich Multi-modal study reported its conclusions late in 2002.
In 2008 improvements were made to the junction between the A12 and the M25 to increase slip-road capacity, in particular for clockwise M25 traffic turning north onto the A12, and to ease congestion on the Brook Street Roundabout (serving the M25, A12 and local Brentwood traffic as the A1023).
The bascule bridge in Lowestoft, built in 1972, was refurbished in spring 2008.
Essex County Council carried out its own inquiry into the road in 2008 (see below for details).
Work on a £12.4m scheme for the a new junction on the A12 at Cuckoo Farm, Colchester adjacent to the Colchester Community Stadium started in December 2009. It was promoted by Essex County Council who prepared plans in 2001. and received funding from the Community Infrastructure Fund. It opened on 16 December 2010.
The Eastern Avenue was built in the 1920s as a bypass for the section between Romford and Ilford, meeting what was the A11 at Leytonstone. It was numbered A106 until the 1930s when it became part of the A12.
The 5-mile (8.0 km) long Brentwood bypass was opened in November 1965.
A bypass for Chelmsford was first included in the roads programme in 1968. Draft orders for the southern bypass were published in 1974, however the public inquiry in 1975 suggested that the government should re-examine the appropriateness of a 'central route' and the government delayed the road. In 1979 the government announced that it would proceed with the southern dual two lane route which opened in 1986.
Ipswich's 'Southern by-pass' via the Orwell Bridge being opened in 1982. This section was later designated as part of the A14.
The Martlesham bypass (previously known as the Kesgrave and Martlesham Bypass) was completed in 1987/1988 as was the Saxmundham bypass.
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 to section from Saxmundham to Lowestoft and from Wickham Market to Farnham to dual 2 lanes. It also included a 'new route from the M25 to Chelmsford' as a dual two lane road following the proposed route of the M12 motorway.
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.
A public inquiry in the 'Saxmundham to Wickham Market bypass' was held in 1995 but this road has not been built.
During the 1960s there were plans for an M12 motorway (also known as the South Woodford – Chelmsford Motorway) which would have run from the North Circular at the base of the current M11 motorway joining the A12 south of Chelmsford or at Brentwood. The North Circular was to be upgraded to motorway-standard as part of Ringway 2 and be designated as the M15 motorway. The M11 was to have provided a motorway standard road into central London past Ringway 1 terminating at the Angel, Islington. The M12 motorway was never built, although the junction of the M11 with the north circular was designed to accommodate it.
Plans for the M12 motorway were withdrawn in March 1994 following a review of the trunk roads programme.
The A12 starts just north of the Blackwall Tunnel at a junction with the A102 and the A13. From here to past Ipswich (including the entire section through London) the road is a dual carriageway. North of the junction, the A12 heads northwards as a 2/3 lane dual carriageway mostly at street level. This stretch of road is known as the Blackwall Tunnel Northern Approach. This stretch ends at the triple-layer interchange with the A11 at Bow Road where it becomes the East Cross Route. This is mainly a 3/4 lane dual carriageway built mainly on flyovers and underpasses and was built in the late 1960s, previously called the A102(M). The road turns North Eastwards at the unfinished Hackney Wick Interchange where the carriageways split and the northbound carriageway has a right hand entrance. 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. The A12 heads to Lea. The section from the Lea Interchange to Leytonstone, also known as the M11 Link road, was built in the 1990s in the face of a major road protest. During this work the old section as far as Wanstead was rebuilt as a dual carriageway. Prior to that, the A12 started at the Green Man Roundabout at Leytonstone, and was single carriageway west of Wanstead tube station. It now has an underpass at that roundabout, which again is a junction with the old A11. East of Wanstead, the A12 runs roughly due east. It is known as Eastern Avenue, then Eastern Avenue West and Eastern Avenue East, built in the 1920s as a bypass for the section of the Roman road from Colchester to London running through Ilford and Romford (today's A118). The eastern end of the Eastern Avenue is Gallows Corner in the London Borough of Havering, just east of Romford. The junction also marks the start-point of the A127 Southend Arterial Road, also 1920s vintage. At the roundabout, an extemporised two-lane flyover still provides priority for A12 eastbound to A127 traffic (and vice versa). However, the A12 now veers roughly north-eastward, because it starts to follow the course of the Roman road; the Romans started building this road from Colchester, their original capital for the province. 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 M25 junction is number 28; it also marks where the A12 crosses the boundary from London to Essex.
Originally, the A12 followed the route of the Roman road closely and so was fairly straight, but there are now several town bypasses, so the road through Essex now has several meanders. 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 close to motorway standard for its whole length in Essex. Now, the A12 is behind the suburb of Chelmer Village.
It is this stretch of the A12, particularly between Chelmsford and Colchester, which has led to the poor reputation for surface quality of the A12. This is mainly for its bumpy or potholed surface, mostly due to worn concrete surfaces. In an ongoing process these sections are being relaid with tarmac, however some sections including the Kelvedon bypass, between Hatfield Peverel and Witham, and between Copford and Stanway have yet to be resurfaced.
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. The old bypass is still in existence – the western half now forms part of the A1124 and the eastern half part of the A133.
The Suffolk stretch of the A12 starts with the Capel St Mary by-pass. Originally the route from the Northern end of this bypass ran through the villages of Washbrook and Copdock and into Ipswich. 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 old dual carriageway through Washbrook and Copdock is blocked off at White's Corner and was renumbered to be the C475. A footpath still exists which enables passage underneath the A14.
The old route through Ipswich was renumbered as the A1214 following construction of the Ipswich Southern By-pass. The old route is more locally known by the road names, notably "London Road" to the Town Centre and Woodbridge Road out the other side. 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. As the A14 the road passes over the large Orwell Bridge with total length of 1,287 metres. This has a summit at 43 metres above the river giving a humped feel with reduced visibility for traffic. There are at-grade roundabout junctions past BT Adastral Park at Martlesham and around the Woodbridge bypass.
For most of its remaining length through Suffolk the A12 is a mostly single carriageway road and in many places its speed limit is less than the national limit, for example as it passes through towns and villages. During 2003/2004 some of these speed restrictions were further reduced from 40 miles per hour (64 km/h) to 30 miles per hour (48 km/h). There are, though, a few stretches of dual carriageway between the Woodbridge bypass and Lowestoft (at Wickham Market, Saxmundham, Wangford and Kessingland). This section of the A12 was detrunked in 2001 as part of the Highways Agency's streamlining of its Trunk Road Network. Control was therefore passed to the local authorities. Just south of Blythburgh, the old milestone shows it is 100 miles (160 km) to London.
The A12 ran through Lowestoft for about 5 miles (8.0 km) on urban 30 miles per hour (48 km/h) limited roads. 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 original A12 at Lowestoft bascule bridge. A further impediment is the harbour bridge, which has three lanes, the centre lane operating as a one-way addition to whichever direction of flow is deemed greater according to time of day. The presence of these bridge choke points can cause serious disruption to north-south trunk traffic, especially when local traffic is added during rush hours. An adequate bypass for Lowestoft would need to be well to the west, even to the west of Oulton Broad (the body of water), and its route would have to consider the great areas of marshland in that area. For that reason an often discussed compromise is a third bridge, crossing Lake Lothing, linking the sections of urban spine-road that run approximately along the western edge of Lowestoft.
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 now follows the route originally used by the railway line from Lowestoft to its terminus north of Breydon Bridge at Vauxhall Roundabout where the A47 also terminates.
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. Work is due to start in 2011/12.
A bypass for various villages was proposed in 1986 as part of the government's 1989 Roads for Prosperity white paper which detailed many road schemes across the country. Suffolk county council considered a bypass for the villages of Farnham, Stratford St Andrew, Glemham and Marlesford for the 2006 Local Transport Plan. The scheme will not be implemented until after 2016. Essex county council has put forwards plans for a bypass of Chelmsford connecting Junction 19 of the A12 to the A131. Plans to upgrade additional sections of the A120 into a dual 2 lane carriageway were scrapped in 2009.
In response to this increasing congestion Essex County Council announced it would hold an A12 inquiry which was tasked with deciding how to improve the A12 and prevent the congestion. The inquiry was headed by Sir David Rowlands, KCB, a former Permanent Secretary at the Department for Transport, with Professor Stephen Glaister, Dr David Quarmby and Lord Whitty, all with significant knowledge of the transport sector.
The inquiry began taking submissions in April 2008. 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. Comments were also received from over two hundred members of the public and through a petition organised by the Essex Chronicle newspaper. The commissions finding were published in July 2008 and its outline recommendations are:the A12 as far as Ipswich should be brought up to modern dual 2-lane standards (where not already dual-3), with urgent priority given to the Hatfield Peverel – Marks Tey section
substandard lay-bys should be replaced; one or more locations off but near the A12 should be identified for secure HGV parking, and an HGV overtaking ban should be trialled
a wide range of short term practical measures should be introduced to improve safety and reduce driver stress, such as selective speed limits and better information for drivers, and to improve the recovery from incidents and closures
a New Route Management Strategy should be drawn up by the Highways Agency, in collaboration with local stakeholders, and an ‘A12 Alliance’ should be formed to consolidate and sustain the momentum for improvement