Limerick Tunnel Closed

air

In practice people not merging soon enough forces people in the correct lane to brake and / or stop which causes a ripple effect back along the line, reducing the throughput rate.
If everyone merged well before the bottleneck where cars are still well spaced there could be a continuous flow into the bottleneck.
Those studies actully support this and the quotes above are not representing their findings properly.
Direct quote from the first article "We want people to merge at the point we’re asking them to, so it’s not 'late,' per se."
What this means is people merging well back from the actual point of constriction which is fair - not right at the last possible point.

What actually happens - say on the dock road outbound, is that people motor on hundreds of metres beyond the first "merge" arrow and then barge in at the very end, forcing the whole queue to a standstill.

The only situation when both lanes should fill right to the merge would be in very heavy traffic, the 2 lanes provide a buffer to keep things moving further back (on the ShannonBridge roundabout) but that's totally irrelevant to a merge on a motorway.

Cartman78

osarusan wrote: »

How does zipper merging actually help cars travel faster through a bottleneck?

The efficiency mentioned in the links above is related to reducing the length of the tailback, (because instead of 1 lane with say 1000 cars in it, there are 2 lanes with 500 cars in each) which means junctions before the bottleneck are not congested and people can get off the road more easily - so there are few cars caught up in a tailback who actually want to get off the road before they would reach the tailback.

But it doesn't mean that the cars actually get through the bottleneck any more quickly, does it? It would only be more effective in that way if zipper merging actually increased the speed at which cars can travel through the bottleneck, but I didn't see that mentioned.

Not necessarily, but surely anyone can see that it is a much more logical and equitable way of doing things

Using zipper-merging would ensure a steady, albeit slow, flow of traffic in both lanes and ensure that pretty much everyone has the same waiting time.

Staying exclusively in one lane seems to be a uniquely Irish thing from my experience - have driven a good bit in a few other countries and never seen it anywhere else.

Anyway back on topic, great to see the tunnel re-opened this morning, would be interested to hear what charges (if any) are brought against the truck driver

grogi

osarusan wrote: »

How does zipper merging actually help cars travel faster through a bottleneck?

Having the speed aligned before merging reduces the ripple effects and improves the flow.

Cartman78 wrote: »

Staying exclusively in one lane seems to be a uniquely Irish thing from my experience - have driven a good bit in a few other countries and never seen it anywhere else.

I don't think it is solely Irish thing. All the nations that did not have proper motorway network get in this mode for a while...

air

I think the key to zipper merging is tto merge before the point at which the gaps in the open lane become so small that the person behind you has to brake.
Once you go beyond that point, you force someone to stop to let you in which slows the whole thing.

osarusan

Cartman78 wrote: »

Not necessarily, but surely anyone can see that it is a much more logical and equitable way of doing things

Using zipper-merging would ensure a steady, albeit slow, flow of traffic in both lanes and ensure that pretty much everyone has the same waiting time.

If I'd driving towards a bottleneck and there are 999 cars between me and the bottleneck, whether those cars zipper merge or merge early, I'll still be 1000th in the line.

And if you don't think it's necessarily any faster in terms of getting car number 1000 to and then through the bottleneck (I don't think any of the links mentioned this), then I honestly don't see what's more logical or equitable about it.

I see the benefit of it when a tailback could extend back to the point that roads/junctions before the bottleneck are getting congested, and cars that never intend to go through the bottleneck are having to wait to use those roads/junctions, but I don't see how it is more beneficial otherwise.

air

Im in full agreement with you grogi, the problem is that people use the above to justify going way beyond the point at which they should zip / merge.

grogi

air wrote: »

I think the key to zipper merging is tto merge before the point at which the gaps in the open lane become so small that the person behind you has to brake.
Once you go beyond that point, you force someone to stop to let you in which slows the whole thing.

Zipper merging takes two lanes to cooperate. Both lanes are travelling at the same speed, and the closer to the merge point, the gaps widen so both lanes can combine without need to any additional gap.

What is causing the problems are the "professors" that are not letting proper merging and disturbing the flow.

air

grogi wrote: »

Zipper merging takes two lanes to cooperate. Both lanes are travelling at the same speed, and the closer to the merge point, the gaps widen so both lanes can combine without need to any additional gap.

This is impossible unless the people in the left lane have left exactly [twice safe stopping distance + length of car in right hand lane] between them and the car in front.
Related to the reason why all the cars in a line at a red traffic light can't move simultaneously when a light goes from red to green.

Cartman78

osarusan wrote: »

If I'd driving towards a bottleneck and there are 999 cars between me and the bottleneck, whether those cars zipper merge or merge early, I'll still be 1000th in the line.

And if you don't think it's necessarily any faster in terms of getting car number 1000 to and then through the bottleneck (I don't think any of the links mentioned this), then I honestly don't see what's more logical or equitable about it.

I see the benefit of it when a tailback could extend back to the point that roads/junctions before the bottleneck are getting congested, and cars that never intend to go through the bottleneck are having to wait to use those roads/junctions, but I don't see how it is more beneficial otherwise.

Fair enough....but if there are 999 cars ahead of you and they're all in the left hand lane then why would anybody chose to pull in behind them when there's an empty lane beside it???

osarusan

Cartman78 wrote: »

Fair enough....but if there are 999 cars ahead of you and they're all in the left hand lane then why would anybody chose to pull in behind them when there's an empty lane beside it???

If I overtake some of those 999 cars and go from number 1000 to number 500, is that 'equitable' like you mentioned just a few minutes ago?

air

The priority should be getting everyone through as fast as possible - which comes about by the earliest possible merging.
To take it to an extreme, if everyone was told that the M7 for 10km before the merge was 1 lane only for the duration and had an 80km/h speed limit, penalty points for anyone in the right hand lane at any time, then the traffic would move through the merge at 80km/h - assuming the single lane was fully navigable at 80km/h.

Cookiemunster

osarusan wrote: »

If I overtake some of those 999 cars and go from number 1000 to number 500, is that 'equitable' like you mentioned just a few minutes ago?

If there are 999 cars in front of you, then you're at least 5km from the merge point. You'd be an idiot to sit in a traffic queue 5km from the merge point.

osarusan

Cookiemunster wrote: »

If there are 999 cars in front of you, then you're at least 5km from the merge point. You'd be an idiot to sit in a traffic queue 5km from the merge point.

I should just overtake and merge later and get there faster myself and who cares about the others?

Cartman78

osarusan wrote: »

If I overtake some of those 999 cars and go from number 1000 to number 500, is that 'equitable' like you mentioned just a few minutes ago?

Of course not

Not sure what point you're trying to make tbh....if people insist on staying in the left hand lane then that's their decision but the general flow of traffic would be improved if people used both lanes and a bit of common sense and a bit of courtesy.

Cookiemunster

osarusan wrote: »

I should just overtake and merge later and get there faster myself and who cares about the others?

If 50% of the drivers use each lane then the queue in the left lane is 50% shorter and the cars in the right lane end up queuing for the same length of time as those in the left lane. It's hardly rocket science.

Mc Love

Cookiemunster wrote: »

If 50% of the drivers use each lane then the queue in the left lane is 50% shorter and the cars in the right lane end up queuing for the same length of time as those in the left lane. It's hardly rocket science.

For some though unfortunately it is - I tried explaining the dock road merge lane to some co-workers and even the OH and they said I'm wrong

Cartman78

Cookiemunster wrote: »

If 50% of the drivers use each lane then the queue in the left lane is 50% shorter and the cars in the right lane end up queuing for the same length of time as those in the left lane. It's hardly rocket science.

EXACTLY!

I am genuinely baffled that people don't get this tbh

osarusan

Cookiemunster wrote: »

If 50% of the drivers use each lane then the queue in the left lane is 50% shorter and the cars in the right lane end up queuing for the same length of time as those in the left lane. It's hardly rocket science.

If they queue that way from the very start, with no overtaking, then yes, each line will be queueing for the same amount of time, but then my question then becomes - if I am car 1000 in line, does my car actually reach the point of the bottleneck any faster depending on whether it is a 1-lane or 2-lane line of cars?


On the other hand, it's fairly obvious that if there is a line of 500 cars in the left lane, and then I drive up the right lane and overtake 499 cars and I merge after the first car in the left lane and therefore become car number 2 to go through the bottleneck, my wait time is shorter, and if 499 cars drive up behind me and then we all zipper merge, cars in the right lane will get through more quickly, but that comes at the expense of people in the left lane. It's not equitable at all.

Mc Love

osarusan wrote: »

If they queue that way from the very start, with no overtaking, then yes, each line will be queueing for the same amount of time, but then my question then becomes - if I am car 1000 in line, does my car actually reach the point of the bottleneck any faster depending on whether it is a 1-lane or 2-lane line of cars?


On the other hand, it's fairly obvious that if there is a line of 500 cars in the left lane, and then I drive up the right lane and overtake 499 cars and I merge after the first car in the left lane and therefore become car number 2 to go through the bottleneck, my wait time is shorter, and if 499 cars drive up behind me and then we all zipper merge, cars in the right lane will get through more quickly, but that comes at the expense of people in the left lane. It's not equitable at all.

If it was done properly there wouldnt be 499 cars in the LHL - but yeah thats their perogative if they are happy to sit and wait in a queue instead of joining the RHL and use it as intended.

Have a feeling this could be cut and moved to the Motors/Roads forum!

Or closed

yop

Mc Love wrote: »

If it was done properly there wouldnt be 499 cars in the LHL - but yeah thats their perogative if they are happy to sit and wait in a queue instead of joining the RHL and use it as intended.

Have a feeling this could be cut and moved to the Motors/Roads forum!

Or closed

Yip.

Is the tunnel fully opened since last night?

Mc Love

As fair as I am aware it is

Tefral

Yeah i drove through it around 11

Cartman78

yop wrote: »

Yip.

Is the tunnel fully opened since last night?

Yes - tunnel fully opened this morning.......there was even cars driving in the Sacred Right Lane

Irish_rat

It causes a ripple effect. Traffic moves well until you have about 5 or 6 at the end trying to merge which causes the left lane to halt.

martingriff

Mc Love wrote: »

Cookiemunster wrote: »

If 50% of the drivers use each lane then the queue in the left lane is 50% shorter and the cars in the right lane end up queuing for the same length of time as those in the left lane. It's hardly rocket science.

For some though unfortunately it is - I tried explaining the dock road merge lane to some co-workers and even the OH and they said I'm wrong

What i hate in the dock road are the ones in the outside is they expect they can just force there way in

Jofspring

martingriff wrote: »

What i hate in the dock road are the ones in the outside is they expect they can just force there way in

Well by the rules of the road they have to merge in. It's not them being entitled, it's the rule. If people don't allow them in then they are blocking the person merging and following the rules of the road.

The only annoying people on the dock road are the people that overshoot the end of the merge lane by 20 or 30 yards and end up being in the lane that is actually to turn right just before the lights. All for the sake of maybe skipping an extra couple of cars.

Insect Overlord

Irish_rat wrote: »

It causes a ripple effect. Traffic moves well until you have about 5 or 6 at the end trying to merge which causes the left lane to halt.

Would you rather those cars just join the back of the queue and have no way for vehicles to exit Topaz, An Post/the storage units, St Alphonsus Street, etc?

phill106

Would love to see this implemented

fryup

^^^^^^^^^^^^^^^^

that would frighten the sh!t out of me, seeing that for the first time

grogi

fryup wrote: »

^^^^^^^^^^^^^^^^

that would frighten the sh!t out of me, seeing that for the first time

The beauty of it is even if you don't break on time, the only thing that happens is you get wet...