Documenting Problems That Were Difficult To Find The Answer To

The Truth About the M4 London Bus Lane

For three years I commuted along the M4 past the bus lane that was so famously derided by Jeremy Clarkson and, eventually, removed in 2010. I’ve had experience driving with and without the bus lane.

The bus lane was a great idea and, correctly implemented, the right thing to do. There was one fly in the ointment, however, that everybody missed – and incorrectly blamed congestion on the bus lane. In fact nothing could be further than the truth and I will attempt to explain it here.

The Ultimate Goal

The Boston Manor viaduct from Junction 3 to Junction 2 is only 2 lanes wide. It is a 40 MPH stretch of road (although it is rare to see anybody do 40 MPH – more commonly drivers are doing 45-60 here even though it is obvious that nobody wants this stretch of road closed due to an accident as there is no emergency lane to pull over in – and breakdowns were a not-uncommon occurrence).

Traffic must be fed, as fairly as possible, into this 2-lane stretch of road. Without the bus lane 3 motorway lanes must be jammed into 2 – and the piece of road that does this, right before the viaduct, is ineffective. Nowadays, during congestion, one waits for quite some time to inch down that piece of road and then is forced to aggressively maintain their position to prevent many other drivers pushing in. It’s aggressive and frustrating. And needn’t have happened.

British M4 Drivers

Whether you like it or not one thing is true about British drivers on the M4. They push in. They will slam on their brakes at the last minute in the high-speed lane as they attempt to push into the stationary middle and slow lanes in an attempt to beat the queue onto the slip road.

It’s appalling and selfish behaviour but it is British. People who think British can queue have never been on a motorway. It’s a fanciful story sold to tourists so that locals can beat them to the front of queues. It is this selfish behaviour that contributes to unfairness during congested periods. And proper planning can minimise the opportunities for the opportunists to unfairly push in and delaying the remaining traffic disproportionately for the gain they may make.

Priority Queueing

The bus lane afforded, rightly, more efficient forms of public transport (buses) and, it can be debated, taxis, a priority over general traffic at the funnelling point to the viaduct. I always thought this was right – as one wants visitors to London to have a positive experience and not stuck in miles of general motorway traffic.

Without Congestion

The following figure is a basic diagram of the traffic flowing on from J4a (the “Heathrow Spur”) towards London and the way one of the lanes peels off as the slip road to J3.

Traffic flowing from J4a to J3 on the M4

Traffic flowing from J4a to J3 on the M4

See how 3 lanes of motorway traffic are effectively transformed into just 2 by using the natural weaving of traffic on and off the motorway as a transition mechanism. Even with congestion the behaviour at this intersection was no different to the others (traffic in the left lane is halted, traffic in the middle lane stops and starts as it tries to push into the left lane, and traffic in the right lane moves just above a snail’s pace as traffic from the right lane attempts to push into the middle lane).

The positive about this is that once you are through J4a on your way to London you are now part of 2 lanes of flowing traffic. And this is the end of it during uncongested periods. There is no further merging (apart from the occasional bus in the bus lane) to worry about as you approach the viaduct. This was an ideal plan.

During Congestion

The problem occurs during congested periods – specifically when traffic starts moving slowly around the Heston Services. Why? Because the Heston Services actually provide a shortcut for drivers trying to “beat the queue”. Although zipping off to the services and back onto the M4 is a longer route than normal – it does save significant time when cars are moving slowly on that section of the M4. However as many cars start doing this the remaining cars staying on the M4 have to stop and wait a disproportional time while cars from the back are pushing in at the front. The following diagram illustrates how this is done:

How Selfish Drivers Push In By Going Through the Heston Services

How Selfish Drivers Push In By Going Through the Heston Services

This is what caused people to blame the bus lane for problems. They’d be stuck beside the Heston Services as selfish drivers were pushing in ahead – and looking at the buses and taxis whizzing past in their dedicated lane. No wonder people were frustrated.

The Irony Of the Present Situation

Now, with the bus lane removed, the queues around the Heston Services are largely eliminated – because drivers use that 3rd lane moving the congestion point further up the road towards the viaduct entrance. This means that selfish drivers have no motivation to duck through the Heston Services.

But drivers have to queue for longer – and behave more aggressively – at the choke point – rather than being relatively naturally sorted out further back at J3 as they used to be.

The Right Solution

I call for the bus lane to be re-instated. But with a key difference. The shortcut by the Heston Services must be eliminated. This could easily be done by making the entrance to the services closer to London and the exit further away from London (make a left hand loop). Then the motivation to take a shortcut would be eliminated as, by entering the services, you guarantee you will come out further back than where you entered.

This would allow for fair and consistent 2-lane travel all the way from J3 to J1 without any other lanes of congested traffic fighting to merge.

Jeremy Clarkson – Knows Cars?

The sad thing is that Jeremy Clarkson – a champion for driving – was so wrong about this one. For somebody that loves driving I cannot, for the life of me, think why he thought the bus lane was a bad idea. It wasn’t. It was an incredibly good idea. For public transport and improving the flow of congested traffic onto and over the Boston Manor viaduct.

Jeremy Clarkson – and any road minister – should have realised the Heston Services entrance/exit mechanism was fouling up traffic senselessly.

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