M4 Bus Lane

You are here: Home » In Depth » M4 Bus Lane

It might have been the most misunderstood piece of traffic engineering ever created in this country. In the years it existed, the M4 Bus Lane was something whose mere mention caused a thousand motorists' blood to boil. Introduced by Labour's then-Transport Minister, John Prescott, a change of government led to Conservative minister Philip Hammond ordering its removal in 2010. It is now open to all traffic, but will be closed again for a time to be used as an Olympics express lane before complete removal in late 2012.

But have all the complaints about it have missed the point? The bus lane may be, dare I say, a display of sheer genius by some lateral-thinking planner at the Highways Agency. Don't believe me? No, I didn't think so. Let me explain.

Signage approaching the M4 Bus Lane
Approaching the M4 Bus Lane

The History

The M4 heading into London is a victim of a lack of joined up planning. It approaches the city from the M25 and Heathrow Airport as a standard three-lane motorway. But from an arbitrary point between junctions 2 and 3, it narrows to two lanes each way and loses its hard shoulder, where it mounts a forty year old elevated viaduct. Essentially, there is a drop in available roadspace of 50% just as the road is getting to its busiest point.

The situation before the bus lane
The situation before the bus lane

It's virtually impossible (or unpopular with the locals and very, very expensive, which is the same thing in government terms) to widen the viaduct - it passes through a very built up area and across some enormous cantilevered steel structures to clear buildings. So the problem was left to remain, with an increase in capacity ruled out and funding unavailable to do anything else about the problem, and that is how the M4 still looked by the mid 1990s.

The Plan

Clearly the biggest problem on this section of road was the bottleneck where three lanes of busy M4 had to merge into two lanes. The astoundingly simple solution to this was to move the point where the road was reduced to two lanes further back - in this case, to junction 3, where a large amount of traffic left already. The transition to the raised viaduct ceased to be a problem because there was a consistent number of lanes across the whole section.

Before and after
Before and after

This plan works as long as there are two lanes eastbound from junction 3. It would be perfectly possible to simply paint white stripes across the redundant lane for the three or four miles that it was no longer needed.

Instead, the lane was kept open. The bottleneck would be prevented as long as there was a minimal amount of traffic using the 'closed' lane. Therefore it was restricted to buses - and why not.

It is possible to assume that from here, the plan was jumped on by the government's PR machine as a shining example of 'integrated transport', bus improvements, and so on. The scheme received an inordinate amount of publicity, all of it heralding the new motorway bus lane and none of it making mention of the way it got rid of that bottleneck.

Traffic flows
Traffic flows

A Highways Agency study in the years after it opened found that the bus lane was a success - not because it moved buses faster but because it resulted in more reliable journey times on the M4 for all road users, and because it removed one of the worst bottlenecks on the route. Some have disputed this, questioning whether the 'before' data was sufficient to allow a comparison with the masses of 'after' data.

It doesn't matter so much now: it's gone. Whether it went for solid engineering reasons or for entirely political ones, we may never know. Time will tell whether the traffic gets better or worse as a result.

Right to reply

Peter Edwardson writes:

Two points worth adding are that the lane was later opened to motorcycles, following extensive lobbying, and that the speed limit was initially cut to 50 mph, but later raised to 60. The motorway in the opposite direction remains at three lanes and NSL.

Alan Peryer has a conspiracy theory:

I think that the objections of private motorists are not as given - they know that they are approaching a two-lane section, and that little is lost by the early lane-drop. It is a little more subtle. In Moscow it was (and still is, for all I know) the custom for main roads to have reserved lanes down the centre reserved for the "Zil" limos of high party members. In the egalitarian West this was seen as the proof of the corruption of the Communist oligarchy. Who now uses the M4 bus lane? Blair, Brown, Prescott and the others as their motorcades speed from their dachas, or Heathrow, into central London. Of course, this is excused on the grounds of "Security". We know that Blair is a target for a bullet (mostly from his fellow countrymen, but he would be far less visible in an ordinary black cab than in the limo with police outriders which he gets now. The M4 bus lane is a VIP lane, but it has to masquerade under another name to have a vestige of acceptability.

In any case, what is the justification for its use by cabs? If you are going to work in central London as a bus driver, you can't use it. If you are going to work as a cabbie, you can, as long as you are in your cab. You don't have to have a fare. High occupancy lanes make sense, the M4 "bus" lane doesn't.

With thanks to Jacqui Thacker for photography on this page.