Usefulness of Crawler Lanes on D2+

[AnOrdinarySABREUser]

Hi everyone,

The title says most of my question. With the performance of modern vehicles, are crawler lanes still useful on multi-lane dual carriageways, especially with the objective of separating slow-moving heavy goods vehicles from other vehicular traffic? Is their usefulness limited by the steepness of a slope, for example, the difference between a 3.15°(7%, 7 : 100) and 6.30°(14%, 7 : 50) slope? In general, would you say that they’re a necessity today?

Similar questions have been raised before, but the threads they were posted in are very old and I didn’t want to dig them up.

edit: x / 90 -> x / 45

[Truvelo]

They are still definitely needed. Although modern cars and vans are capable of effortlessly negotiating steep inclines, lorries can struggle. When I'm at 40+ tonnes I'm lucky to be doing 30mph up this hill. At the moment it's down to a single lane for building a HS2 bridge and the traffic soon builds up behind.

[Bryn666]

Crawler lanes work when they start on the right and end on the right so faster traffic can overtake.

If they start on the left and end on the left, HGVs won't use them as they don't get back out.

The best design is arguably start on the left and end on the right, I believe the A55 at Rhuallt does this with HGVs instructed to keep left.

The M65 has an oddity in that the westbound crawler lane from J4 starts on the right and the merge from J4 westbound is a normal taper - this is a terrible layout. On the eastbound it's a lane gain.

[swissferry]

Crawler lanes are still useful. I think they would work better if they were extended for a short distance beyond the top of the hill to allow slow vehicles to speed back up.

I partially agree with Bryn's observations but think starting and ending on right works best. The crawler lane between junction 3 and 4 on the M77 southbound started on left (lane gain) and ended on right but suffered from middle lane hoggers. It was changed last year so it is now starts and ends on left (lane gain / lane drop) which has improved traffic flow by reducing merge conflicts.

In the plans for the M80 the southbound section between Castlecary and Old Inns was described as having a crawler lane. When it was built it was marked as a mile long slip / lane drop. This produces two congested lanes and a free flowing slip. Changing the lane marking and using a bit of the hard shoulder beyond the diverge would reduce congestion.

[Rob590]

There are three on the A1(M) in County Durham, two northbound and one southbound, and they seem to work well. If nothing else they provide a chance on a lengthy D2 section of road for traffic to stretch out a bit, they certainly feel when you're driving on them that they make a difference not just because of a few slow lorries up the hills, but because they give a chance for clumps of traffic that can form on D2s to loosen.

[owen b]

The A505 westbound crawler lane on the Great Offley bypass is rarely used in my experience. Admittedly it's a road I rarely use at peak times. It's a conventional layout where lanes one and two carry straight on throughout with the crawler lane added to the left marked for "SLOW VEHS", and traffic generally doesn't move over from lane one to use it : https://www.google.co.uk/maps/@51.93431 ... ?entry=ttu

[JammyDodge]

The A34 between Didcot and Newbury could really do with them. Often end up sitting behind 2 lorries going up a big hill doing 40mph or less
Although the A34 could really do with being a D3 (or D4 in places) expressway, with climber lanes on this stretch

[Owain]

Something I dislike is when a D2 becomes an S2+1, as you can get into the mood for overtaking and easily forget that the change in road configuration means an often-unsigned drop in the speed limit... easy to forget when you're making progress!

[Gaz909909]

A30 at Camborne West is a good example of D2 -> S2+1. So true as you go from 70mph to 60 (and there is a cam there!)

Special mentions to the A30 Indian Queens eastbound lane gain, known locally as hamburger hill, as it is next to a McDonalds. Works well with a right hand gain, but ends just before the A39 junction. Also very similar is the M3 east of J9 - A34. One more: M27 Copnor east and westbound. The gain eastbound comes off the on slip, but actually it seems to work.

[MotorwayGuy]

This one on the A21 starts on the right and ends on the right just before the brow of the hill. It was added sometimes in the mid 2000s. The new section near Pembury could have done with one here but compared to the old S2 it replaced it's much better.

[Herned]

Why was the one on the A303 at Chicklade removed? It's quite a steep hill and seems as good a location to have one as anywhere

[Bryn666]

The A505 westbound crawler lane on the Great Offley bypass is rarely used in my experience. Admittedly it's a road I rarely use at peak times. It's a conventional layout where lanes one and two carry straight on throughout with the crawler lane added to the left marked for "SLOW VEHS", and traffic generally doesn't move over from lane one to use it : https://www.google.co.uk/maps/@51.93431 ... ?entry=ttu

This is the "bad" layout where the lane ends on the left meaning a slow HGV can't get back out.

[SouthWest Philip]

Why was the one on the A303 at Chicklade removed? It's quite a steep hill and seems as good a location to have one as anywhere

Almost certainly due to the road returning to single carriageway a short distance after, I would imagine. From one lane to two to three and back to two then one within about two miles wasn't ideal. Maybe the crawler lane will make a return if/when the A303 is fully dualled?

[owen b]

The A505 westbound crawler lane on the Great Offley bypass is rarely used in my experience. Admittedly it's a road I rarely use at peak times. It's a conventional layout where lanes one and two carry straight on throughout with the crawler lane added to the left marked for "SLOW VEHS", and traffic generally doesn't move over from lane one to use it : https://www.google.co.uk/maps/@51.93431 ... ?entry=ttu

This is the "bad" layout where the lane ends on the left meaning a slow HGV can't get back out.

Yes, that makes sense. The way it's configured at the moment makes it barely worth the trouble. It would be better if lane three dropped at the end rather than lane one.

I know this comment has been made on previous threads, but very few vehicles on dual carriageways crawl up hills at 10-20 mph these days. Calling them crawler lanes might have the effect of making drivers think that only ultra-slow vehicles should use them. I prefer the term "climbing lane".

[DB617]

I believe the A417 Missing Link scheme is going to have an extra lane on the climbing side of Birdlip Hill. There was some criticism of the initially proposed layout because the end of the lane interfered with the onslip at the top of the hill. Not sure what became of that since - as that was some years ago when a green bridge etc was still included.

[roadtester]

Is their usefulness limited by the steepness of a slope, for example, the difference between a 6.3°(7%, 7 : 100) and 12.6°(14%, 7 : 50) slope? In general, would you say that they’re a necessity today?

A good test of the ability of modern traffic to cope with these sorts of gradients this will be the Crickley Hill section of the A417 Missing Link, a modern new build dual carriageway but with an eight per cent gradient (reduced from the originally proposed ten per cent). I'm assuming this wouldn't have got through if it didn't pass the latest standards/thinking for the impact on traffic speeds with modern vehicles but I suspect some trucks are still going to be crawling. There seem to be three lanes going up-hill but I'm not sure if lane one is actually designated as a crawler lane.

I also wonder about the downhill direction - how many drivers will have the discipline/car control to stay within the limit on such a long and steep downhill section on a modern fast road.

PS - just as I was writing this DB617 got there first!

[Bryn666]

8% is the maximum gradient on most European motorways in hilly terrain - we used to cap at 6% I think, but obviously the A417 and A465 have been special cases.

I agree with Owen above that crawler lane is a deprecated term - certainly official documents refer to climbing lanes now.

[DB617]

Is their usefulness limited by the steepness of a slope, for example, the difference between a 6.3°(7%, 7 : 100) and 12.6°(14%, 7 : 50) slope? In general, would you say that they’re a necessity today?

A good test of the ability of modern traffic to cope with these sorts of gradients this will be the Crickley Hill section of the A417 Missing Link, a modern new build dual carriageway but with an eight per cent gradient (reduced from the originally proposed ten per cent). I'm assuming this wouldn't have got through if it didn't pass the latest standards/thinking for the impact on traffic speeds with modern vehicles but I suspect some trucks are still going to be crawling. There seem to be three lanes going up-hill but I'm not sure if lane one is actually designated as a crawler lane.

I also wonder about the downhill direction - how many drivers will have the discipline/car control to stay within the limit on such a long and steep downhill section on a modern fast road.

PS - just as I was writing this DB617 got there first!

Great minds!

Interesting question about the downhill. It would have made sense to have it SPECS enforced by design. With regenerative braking becoming more and more prominent, in my opinion there is no excuse. It has always been a problem with the S2+1 version of that road, too, but perhaps some people's sense of self-preservation prevented rampant speeding. But alas, this is most certainly off topic.

Adding an extra lane for uphills is helpful on any standard of road, assuming it is anywhere near capacity. The three-lane M5 southbound constantly gets strangled on the upper gradients of the Gordano hill pass when it's near capacity; the lower sections have an extra lane but at the top where the gradient is slightly less, but the construction cost per lane was much higher (due to the massive cuttings and viaducts) the lane was left out and that's where snarl ups happen. The usual traffic pattern up there is in waves, as each platoon of slow movers spreads out to cover all three lanes (something like, a heavy HGV in lane 1 doing 40, lighter HGVs and the constant procession of caravans doing 50, and then a Honda Jazz or something doing 55 in lane 3 ruins everything for all the holiday-goers).

I agree that the return to normal width should always happen once the gradient is passed, not near the top of it, which is what usually happens. The Batheaston Bypass irritatingly loses its extra lane about 300 yards short of the summit, but the traffic at Cold Ashton usually means that no gains would be made by overtakers anyway. I'd guess this happens a lot all over the country and I can't decide if in most cases it was dictated by constraints, or was something of an error in deciding the scheme boundaries i.e. the scheme took in the road to the point where the gradient ends, rather than say a few hundred yards downstream of the end of the climb.

[jackal]

Why was the one on the A303 at Chicklade removed? It's quite a steep hill and seems as good a location to have one as anywhere

Almost certainly due to the road returning to single carriageway a short distance after, I would imagine. From one lane to two to three and back to two then one within about two miles wasn't ideal. Maybe the crawler lane will make a return if/when the A303 is fully dualled?

It always struck me as overkill given the road is S2 either side. "You've not seen an overtaking lane for so long we thought we'd give you two, one of which is useless 90% of the time".

[SteveA30]

It was the original S2/1 which then became a D3 uphill, before being hatched down to D2. It may have been done at the same time as the S2/1 west of Chicklade, which is still there. Short but very steep and soon knocks the stuffing out of most lorries. Missing a gear then rolling backwards with front wheels locked and overturning was not unknown with older lorries in the 60's/70's.