The Highways Agency said that the full benefit of the changes will only be felt when the toll booths are removed.
Dart Charge Project Director Nigel Gray said: "We will get underway on this work at the same time that the new payment arrangements begin. It's complicated work - especially on the northbound carriageway, where we need to protect the tunnels - one of which was built in the 1960s and has a lower height restriction - from over-height vehicles.
"We’ll be completely redesigning the approach to the tunnels to detect and turn around these vehicles and other vehicles not suitable for the tunnels, using a system of signals, barriers and extra lanes, while keeping all other traffic flowing as much as possible.”
The Highways Agency has released images of how the Dartford Crossing will look when the toll booths are removed.
The current 27-lane system will be removed by four open lanes in each direction.
Work to remove the toll booths will coincide with Dart Charge - a remote charging system - going live in late November. The scheme is expected to be complete by next spring.
The introduction of new "cashless" payment arrangements at one of Britain's busiest road crossings has been delayed.
The Highways Agency had intended to scrap toll booths and introduce a "free-flow" traffic system at the Dartford River Crossing across the Thames east of London around mid-October. But the agency said that the new system will come into effect during late November.
Highways Agency project leader Nigel Gray said it was only right that the system be thoroughly tested before it was introduced.
It's a route used by more than a hundred thousand drivers a day. The Dartford Crossing is one of the biggest pinch-points for the south-east road network. Today the Government said it will do a detailed study of two final options for a new crossing over the Thames.
But some debate whether it's needed. David Johns reports, speaking to Roads Minister Robert Goodwill and Thurrock Council leader John Kent (Lab).
Part of the Dartford Crossing will be closed tonight from 10pm until 2am. Both northbound tunnels from Kent into Essex will be shut for an emergency exercise involving the Highways Agency and Kent Fire and Rescue Service. The bridge will remain open to southbound traffic.
New technology that will replace the country's most notorious toll booths, at Dartford, has been exclusively revealed to ITV News. The company who will operate the scheme insist traffic jams will be cut but critics say the tolls are a waste of money. See our full report by Mike Pearse.
Video. Work has started on a new layout for the Dartford Crossing.
The company running it says it will be similar to a scheme on the M50 in Dublin where cameras read number plates and automatically charge drivers.
We spoke to Simon McBeth, Sanef Director of Communications.
Work on a new layout for the Dartford Crossing begins today.
Barriers are being removed as a new payment system will be introduced in October 2014.
Drivers will pay online, by phone, text or at one of numerous retail outlets instead of stopping at the barriers.
The new payment method will ease congestion and traffic at the Crossing.
Signs will also be installed to help drivers understand the new system.
Nigel Gray, Highways Agency Project Director said, "This advance work has been carefully planned to minimise disruption to road users and so will largely be carried out overnight when traffic flows are lowest."
Newer technology and a change to the road layout should help reduce traffic congestion along the Dartford-Thurrock River Crossing. The scheme will be launched during October 2014 and the following changes are planned: you'll be paying remotely rather than at the barrier as you cross.
You'll be able to pay in advance of crossing or before midnight the day after crossing. It'll be cheaper for those to have an account and crossing between 10pm and 6am will still be free.
This spring, the Highways Agency will be doing some advance construction work to prepare for the new remote paying system in October. After that, the crossing road layout will change and work is due to complete in the spring of 2015.
A discount scheme which lets residents make unlimited trips across the Dartford Crossing comes into force today. People already registered in the Local Residents' Discount Scheme will be able to make unlimited trips over the crossing for £20 a year.
Meanwhile free-flow tolls will be operating at the crossing in October. It's hoped the new barrier-less system will help ease congestion for commuters.