Dartford free-flow crossing work begins
Work is due to begin later on signs on the approaches to the Dartford crossing in preparation for a new system of collecting toll charges.
A free-flow charging system is due to come into operation at the crossing between Kent and Essex in October.
Drivers will be able to pay online, by SMS text message or by phone.
Signs giving drivers information on the new toll system will be installed overnight on the A282, M25, A13 and M20, the Highways Agency said.
Nigel Gray, the Highways Agency project director, said: "Work to date has been progressing well behind the scenes. Now we are ready to start on the road."
The signs will be installed overnight from Tuesday evening. The Highways Agency said most of them will be covered up until the new payment system comes into force.
Lights and barriers will be used on the northbound approach to the tunnels to control traffic volumes when the free-flow tolls are introduced in the autumn.
Vehicles will be recorded via number plate recognition cameras.
Payments will be accepted in advance and up to midnight on the day after crossing, a Highways Agency spokeswoman said.