ed_m wrote:
i've often wondered why if zip merging is preferred they still insist on closing a specific lane..... much more ambiguous surely to put the hatching / cones to create a single lane between the original two, such that neither lane has an obvious 'right' of way ?
It is a good point, it does appear to a little contradictory.
I think an issue here could be the natural tendency to occupy the other lane in its entirety lane when changing lanes when seeing temporary cones. I doubt it is as much of a problem when the road is properly engineered for merging (road markings help).
If both lanes are halved and merged, I think a driver seeing the approaching cones in their lane would naturally want to change into the other lane. Those who do will of course be met with another set of cones, the latter set coming into view with less or no warning; this isn't really a problem when crawling but could be difficult at speed. Other factors aggravate the problems of free-flow merging nearing the start of the merge, such as the inevitable differential speeds as well as the obligatory selfish last-second, non-zipping lungers, so I’m tending towards believing one lane having the priority (with warnings for it) is the best method for merging free-flow traffic.
In the case I've shown, it is much better to use both lanes when queued, otherwise there is a massively increased chance of stationary traffic impacting the traffic coming from Lane -1 (from the M25 turn off onto the M3), that resulting with additional congestion and increased risk of collision (as well as the needless turbulence from not merge in turning).
Whilst not perfect, I reckon what we have today is the least of evils, or at least it would be if drivers abided by the signs leading to the bottleneck.
Freeflow or queuing, selfish behaviour will still have a detrimental effect when merge in turning and is certainly not the best policy.