The report was commissioned by Essex County Council
A dual carriageway A12 with three lanes through Essex and into Suffolk is impossible while the government refuses to reclassify the road, a report said.
Essex County Council has published a report of its inquiry into the A12.
The report makes 28 recommendations to improve the A12's performance and to speed up recovery from accidents.
Despite witnesses wanting a three-lane road this is not included as the A12 is "regional" not "national" - the status that could bring it government cash.
Commission chairman Sir David Rowlands said: "The A12 is a real problem. Many people who use it will be disappointed we have not recommended widening the road throughout Essex to three lanes.
"But it is not going to happen as long as the Department for Transport classifies it as of only regional significance."
The commission recommended an urgent need for improvements on the Hatfield Peverel - Marks Tey section and replacement of substandard lay-bys.
One or more locations should be found off, but near, the A12 for secure HGV parking, and a heavy lorry overtaking ban should be tested.
Measures were recommended to improve safety and reduce driver stress. These include selective speed limits and better information for drivers.
The report said a new route management strategy should be drawn up by the Highways Agency, in collaboration with users, residents and others.
It also recommended the formation of an A12 Alliance to campaign for improvement.
The inquiry, commissioned by Essex County Council in February, was conducted over April, May and June chaired by Sir David Rowlands, former Permanent Secretary at the Department for Transport, together with Professor Stephen Glaister, Dr David Quarmby and Lord Whitty.
It was the first ever inquiry into a major trunk road sponsored by a local authority and heard from 24 organisations and 36 witnesses.
These included the Department for Transport and Highways Agency officials, MPs, local and regional agencies, the emergency services, business and motoring groups.
Comments were also received from more than 200 members of the public.
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