M25 J15 Thorney Interchange

Layout and signage

The WEST
Slough
Reading
London (W)
Heathrow Airport (T1, 2 & 3)
M4 Link
  M4     M4   The WEST
Slough
Reading
London (W)
Heathrow Airport (T1, 2 & 3)
M4 Link

Lane configuration

LanesLanesLanesLanesLanesLanesLanesLanes

  • Lane 1 is gained from the entry sliproad.
  • Lane 2 is gained from the entry sliproad.
  • Lane 3 exits and returns after the junction.
  • Lane 4 continues ahead.
  • Lane 5 continues ahead.
  • Lane 6 continues ahead.

LanesLanesLanesLanesLanesLanesLanesLanes

  • Lane 1 exits and does not return.
  • Lane 2 exits and does not return.
  • Lane 3 exits and returns after the junction.
  • Lane 4 continues ahead.
  • Lane 5 continues ahead.
  • Lane 6 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.

Share this page

Have you seen...

A470 End to End

The road that connects Wales together, but which nobody really uses... All five hours of the A470, from Llandudno to Cardiff, are here.

About this page

Published

Last updated