Three sites put forward for new River Thames crossing
Three locations have been put forward as possible sites for a new River Thames crossing between Kent and Essex.
The government said a new Lower Thames road crossing, costing up to £5bn, was necessary to tackle congestion.
Option A is the site of the existing Dartford to Thurrock crossing, option B would connect the A2 with the A1089, while option C would join the M2 in Kent with the A13 and M25 in Essex.
Protect Kent said plans for a new Lower Thames crossing were premature.
Roads minister Stephen Hammond said motorists were currently plagued by daily congestion, with traffic levels expected to increase by a fifth over the next 30 years.
"It is vital we take action now on the future of a new Lower Thames crossing to make sure that our road network is able to meet future economic needs," he said.
"There are some tough decisions to be made, but this is the first step in making sure that the residents, businesses and motorists who rely on the crossing receive the service they expect and deserve in the years to come."
The existing Dartford to Thurrock crossing, which consists of the QEII Bridge and a tunnel, is used by 140,000 vehicles a day.
Option C, the most expensive, would pass through undeveloped green belt land including Kent Downs Area of Outstanding Natural Beauty, ancient woodland and the Thames Marshes.
The other options would cost between £1.2 bn and £2.2 bn.
Planning watchdog Protect Kent said a new crossing was unsustainable and claimed that road traffic had fallen recently.
It said it believed traffic bottlenecks caused by toll booths would ease when high speed tolls were fully operational in 2014.
"The impact of this should be investigated before any decisions are made as to whether there is a need for any new lower Thames crossing," it said.
It also said the new London Gateway port being built in Essex would make greater use of sea transport and ensure that in future cargo for London and the Midlands would be landed without needed to cross the River Thames.
A public consultation on the three options will run until 16 July with the results announced in the autumn.
Six public information events are being held in Kent and Essex in June.
The RAC Foundation said the big question was how the new crossing would be funded.
Director Professor Stephen Glaister said: "As with the existing crossing the suspicion will be that drivers will pay for any extra capacity through charges - charges which will remain in place long after the project is paid for."
The Freight Transport Association said there was no doubt it was necessary to improve capacity and ease congestion at Dartford, but the best option had to be selected.