The A12 will be extended to three lanes all the way from London to Colchester under a £15 billion plan to upgrade roads across the country.
The details of the project also reveal today (December 1) that the busy carriageway will also be upgraded with dedicated left-turn lanes and extra CCTV cameras.
Transport Secretary Patrick McLoughlin and Chief Secretary to the Treasury Danny Alexander will make a speech on the subject in parliament today.
Mr McLoughlin said: "Today I am setting out the biggest, boldest and most far-reaching roads programme for decades.
"It will dramatically improve our road network and unlock Britain's economic potential.
"Roads are key to our nation's prosperity. For too long they have suffered from under-investment.
"This government has a long term plan to secure the country's future and this £15 billion roads programme is demonstration of that.
"Better roads allow us to travel freely, creating jobs and opportunities, benefiting hardworking families across the country."
The news comes after repeated calls from Essex County Council highways boss Rodney Bass, Chelmsford MP Simon Burns and Witham MP Priti Patel to upgrade the A12 to motorway size.
Simon Burns MP for Chelmsford said: "I have been campaigning for some time to turn the A12 in Essex, in effect, into a motorway. I have been lobbying the Secretary of State for Transport for just over a year on this issue.
"I am delighted that both the Secretary of State for Transport and the Chancellor of the Exchequer have listened and that it has been announced today in the House of Commons that the A12 from the M25 to Chelmsford and from Junction 25 in North Chelmsford to Colchester will be turned into a 3 lane road. When done this will significantly improve the congestion problems on the A12.
"I am also pleased that at the same time the A12 from the M25 to Ipswich will have significant traffic management technology improvements along the whole route including CCTV cameras and various message signs to allow better information to drivers and enhance the Active Traffic Management of traffic on the route.
"This, too, will help improve the flow of traffic and deal with traffic congestion and enhance road safety.
"I am thrilled that following my campaign the Government has listened to ensure improvements to this main feeder road into the East of England."
The A12 is currently a mix between a two-lane and three-lane road.
The government, which includes the news in its 2015 Autumn Statement, says it will start spending on the various projects by the end of the decade.