M4 J4B Thorney Interchange

Layout and signage

Watford (M1 Link)
Oxford (M40 Link)
(M3 Link)
Gatwick Airport
Heathrow Airport T4, 5 & Cargo
M25 Link
  M25
(M1)
(M40)
    M25
(M3)
(M23)
  (M3 Link)
Gatwick Airport
Heathrow Airport T4, 5 & Cargo
Watford (M1 Link)
Oxford (M40 Link)
M25 Link

Lane configuration

LanesLanesLanesLanesLanesLanesLanes

  • Lane 1 exits and returns after the junction.
  • Lane 2 exits and returns after the junction.
  • Lane 3 continues ahead.
  • Lane 4 continues ahead.
  • Lane 5 continues ahead.

LanesLanesLanesLanesLanesLanesLanes

  • Lane 1 exits and does not return.
  • Lane 2 exits and returns after the junction.
  • Lane 3 continues ahead.
  • Lane 4 continues ahead.
  • Lane 5 continues ahead.

Other events

  • Signs Variable Speed Limits apply
  • Signs Variable Speed Limits apply

In this section

What's new

The forever bottleneck, part 2

The second part of the story, where we learn why exactly the M4 gets narrower on the final approach to Europe’s biggest city.

The forever bottleneck, part 1

The M4 into London was one of the UK's earliest and most ambitious motorway projects. It was bold, pioneering... and almost instantly regretted.

Hello, here's my ridiculous side project

An introduction to what I write, and why I write it, and where my strange new road sign simulator fits in to all this.

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