The Misunderstood M4 Bus Lane
Those of you who are not transport geeks may have missed the news that the M4 bus lane is to be removed.
The M4 bus lane has suffered from poor publicity for years. It is not a sign of the oppression of the motorist, but a symptom of the expense required to widen the Chiswick flyover to 3 lanes.
The main issue on the M4 Eastbound in this area is that the motorway narrows from 3 to 2 lanes between junction 3 and junction 2, and it is this narrowing that actually limits the London-bound traffic that can use the M4.
From a traffic flow perspective the main purpose of the bus lane is not in fact to speed buses and taxis up, but to move the bottleneck for the Chiswick flyover from where it was first built between junction 3 and 2 to at junction 3. The main benefit of this is that as the equivalent of a full lane of traffic leaves the motorway at junction 3, the lane drop from three to two lanes is much smoother than it would be if three full lanes of traffic continued until it becomes necessary to narrow to two lanes, with the delays and risk associated with merging two lanes of motorway traffic together.
The only way in which the bus lane could be removed without having this impact would be to just leave this stretch as a two lane motorway. This however removes the benefit of being able to improve bus journey times without having a noticeable detrimental effect on cars.
Also, it enables the Imperial College Ski Club to get back from Wednesday training in a minibus quicker!
The M4 bus lane has suffered from poor publicity for years. It is not a sign of the oppression of the motorist, but a symptom of the expense required to widen the Chiswick flyover to 3 lanes.
The main issue on the M4 Eastbound in this area is that the motorway narrows from 3 to 2 lanes between junction 3 and junction 2, and it is this narrowing that actually limits the London-bound traffic that can use the M4.
From a traffic flow perspective the main purpose of the bus lane is not in fact to speed buses and taxis up, but to move the bottleneck for the Chiswick flyover from where it was first built between junction 3 and 2 to at junction 3. The main benefit of this is that as the equivalent of a full lane of traffic leaves the motorway at junction 3, the lane drop from three to two lanes is much smoother than it would be if three full lanes of traffic continued until it becomes necessary to narrow to two lanes, with the delays and risk associated with merging two lanes of motorway traffic together.
The only way in which the bus lane could be removed without having this impact would be to just leave this stretch as a two lane motorway. This however removes the benefit of being able to improve bus journey times without having a noticeable detrimental effect on cars.
Also, it enables the Imperial College Ski Club to get back from Wednesday training in a minibus quicker!