Three possible sites have been identified as the Government looks at options for a new road bridge across the River Thames to help reduce congestion.
The bridge would be in addition to the Dartford-Thurrock River Crossing on the M25 east of London.
The first site is at the existing crossing. The second would link the Swanscombe Peninsula in Kent with the A1089 and the third would be east of the port of Tilbury in Essex and cross to a point east of Gravesend in Kent.
The study, published by transport minister Lord Adonis, also said further work should be considered to identify short-term improvements at the existing crossing.
Lord Adonis said: "The Dartford-Thurrock river crossing is a vital transport link for both the national and south east England economies which has brought huge economic benefits and opportunities.
"However many more vehicles want to use the crossing than it can accommodate and congestion here is likely to get worse in the future unless something is done.
"Following the completion of the first phase of a Department for Transport-commissioned study, I am pleased to announce that further work is now to be carried out to look at improving journey time reliability and safety at the existing Dartford Crossing, alongside a more detailed analysis of potential options for a new crossing."
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