The inner lane at M25 junction 3 closes round the clock from 2 November to 18 December while 20-year-old traffic lights are replaced. Half the roundabout shuts tonight.
The inner lane of the Swanley Interchange roundabout will be closed 24 hours a day for seven weeks from Monday, while National Highways replaces its traffic lights.
The work at M25 junction 3, where the motorway meets the M20 and the A20, starts tonight with an overnight closure of half the roundabout. It runs in two phases until the spring. (National Highways, letter to residents, 27 October 2026)
National Highways said the signals had been in service for more than 20 years. Swanley Town Council, which met the contractor on Wednesday, was told the old system can no longer be repaired because the parts are no longer made. That, the council said, is why some of the lights on the roundabout have been out of action for a long time. (Swanley Town Council, 29 October 2026)
The dates
National Highways’ letter, dated 27 October, sets out this timetable:
- Saturday 31 October, 11pm to 6am: the northern half of the roundabout is closed, to install temporary traffic signals and traffic management.
- Sunday 1 November, 10.30pm to 5.30am: the southern half is closed for the same reason.
- Monday 2 November to Friday 18 December: the inner lane of the roundabout is closed 24 hours a day. The outer lane or lanes stay open around the clock.
- Christmas and New Year: the lane closure comes off by 18 December, so the roundabout is back to full capacity over the holidays.
- From January 2027: regular overnight closures from 10pm to 6am, limited to one quarter of the roundabout at a time.
The letter says the second phase runs from January to April 2027. National Highways’ own scheme page gives the end of the whole scheme as April 2027, but lists the overnight phase as January to March. It says further details will be added once they are confirmed. (National Highways, south east maintenance schemes)
Why the inner lane, and why for so long
National Highways said closing the inner ring for the first phase cuts down on frequent changes to the traffic management, overnight closures and diversions. Traffic can keep using the junction 24 hours a day.
The town council was told the static lane closure also makes room for a temporary pedestrian walkway. That keeps local access and lets every set of signals and every approach keep working while the new equipment goes in.
The work includes:
- digging to install the new signal equipment
- removing the old signals
- removing and replacing the existing cable
- slot cutting in the road surface
The new signals will be more energy-efficient and better able to manage traffic at the junction, National Highways said. It is also replacing the electrical equipment behind them to cut unplanned failures and repairs.
Diversions on the closure nights
During the overnight closures there will be signed diversions. Motorway traffic will go via the M25, the M20 and the A20.
The town council said non-motorway traffic would be sent via Wested Lane, Crockenhill Lane and Sparepenny Lane. National Highways has published separate diversion maps for the northern half closure on 31 October and the southern half closure on 1 November.
Extra signs will go up on the A20 eastbound telling non-motorway drivers to leave at the Swanley Interchange, which is also M20 junction 1.
What the town council asked for
Swanley Town Council said it asked for the work to be coordinated with Kent County Council and with the contractors building the new Lidl roundabout, to keep disruption for residents down. It also pressed for regular litter picks during the works and talked about new measures to stop litter building up on the roundabout.
The council said its information was correct when it was published but could change.
What it means for you
- Tonight and tomorrow night: if you use junction 3 late at night, check the diversion map for your route and allow extra time.
- For the next seven weeks: expect one fewer lane on the roundabout at every hour, including the morning and evening rush.
- After Christmas: the overnight closures return in the new year, a quarter of the roundabout at a time. Dates have not been published yet.
- Questions: the National Highways contact centre is on 0300 123 5000, 24 hours a day, or info@nationalhighways.co.uk.
National Highways’ order for a 24-hour 40mph limit at the interchange, made for this signalling work, has allowed the limit since 19 October and can last up to 18 months. Our Sevenoaks roadworks page carries that order and every other motorway and Kent County Council closure in the district, and our train times guide covers the rail alternatives.
Sources
- National Highways, “Traffic signal upgrades: M25 junction 3 Swanley Interchange, Kent”, letter to residents, 27 October 2026 (reference 613248, published by Swanley Town Council)
- National Highways, south east maintenance schemes: M25 junction 3 Swanley interchange traffic signal upgrades (read 31 October 2026)
- Swanley Town Council, “Swanley Town Council collaborates with Connect Plus on Junction 3 upgrades and litter prevention”, 29 October 2026
- National Highways notice: M20, M25 and A20 Swanley Interchange temporary traffic restrictions, order made, published 7 October 2026 (the 24-hour 40mph limit, reference NH/SE/2026/A20/80)
Image: The M20/M25 interchange, Swanley. Photo by David Howard, CC BY-SA 2.0, via Geograph
Have your say