A new safety system at the Dartford Crossing will turn around vehicles considered too unsafe to travel through the tunnel.
A traffic light and barrier system will stop traffic before it gets to the tunnel entrance.
It will come into force next month.
It will also enable dangerous goods vehicles to be safely escorted through the tunnels and stop vehicles entering the tunnels in the event of an incident.
"Since Dart Charge launched in November it has already significantly improved journeys at the Dartford Crossing. This new safety system is vital for the safe operation of the tunnels and will enable us to remove the old payment barriers for good. It will mean a significant change to the road layout, so I advise drivers to take extra care and pay extra attention to all signs and signals, especially for the first few times they use the crossing following the change."
Tunnel closures will be required overnight during the go-live weekend to introduce the system. To minimise the disruption, one tunnel will remain open at all times.