On Fri, 2 Aug 2019 22:44:25 +0100, Steve Walker
wrote:

On 02/08/2019 18:07, Harry Bloomfield wrote:
NY has brought this to us :
Any fool can make zip merging safe, but it takes *skill* to make it
work without imposing a very severe bottleneck on traffic flow, when
with a bit of advance warning, everyone can get into one lane without
having to slow down much and then the single stream can keep moving
through the roadworks.

That just moves the merge point further back and reduces the capacity of
the road to store waiting vehicles. Merging just in time allows more
vehicles to be in the queue, when a queue forms.

Except that you can merge when there is a gap, with little adjustment of
speed and so not slow everything down, whereas merging at the
pinch-point often means cutting into a small gap, causing those behind
to brake and the ripple effect

‘backward traveling wave’ ;-)

to bring the whole road to a halt or
slowing to a stop yourself and holding up the traffic behind.

Bingo. It's as if Harry has never actually driven! ;-)

Cheers, T i m