Route
Junction number
None
Markerpost
28.5 km
Name
Black Cat Roundabout
Type
Roundabout
Terminus
Terminus at top of exit list
Other routes
A1
Authority
Restricted turns
Full access
Services
No services
A421 Black Cat Roundabout
60mph speed limit begins
National Speed Limit beginsWhat'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.
Have you seen...
British Roads FAQ
The most Frequently Asked Questions where British Roads are concerned, and the answers. A good place to start if you're new to the subject or you're looking for quick facts.
About this page
Published
Last updated
Published
Last updated
