GANTRIES are to begin going up over the M25 approach to the Dartford Crossing tolls booths.
The sructures will display signs for the free flow toll system, which will see barriers on the Kent side of the crossing scrapped.
It is thought all the works will be complete and the system fully operational by next Spring.
Motorists will then pay to use the crossing in advance of their journey either online, by text/phone or in some local shops.
In total five gantries will be put up near the tunnel entrance and on the Queen Elizabeth II Bridge to accommodate signs relating to the system and camera equipment to identify vehicles.
Work is being done overnight in the next two weeks when traffic flows are lowest.
Northbound work will take place on Wednesday 14 and Thursday May 15, between 8.30pm and 5.30am, on Friday 16 between 9pm and 6am and on Sunday, May 18 between 8.30pm and 5.30am. On these nights, one of the two tunnel bores will be closed.
Southbound work will take place for four nights from Monday, May 19 and on Tuesday 27 and Wednesday 28 May. On each of these nights, the bridge will be closed between 10pm and 5.30am, with traffic diverted through one of the tunnels.