Usefulness of Crawler Lanes on D2+

[Nicola_Jayne]

there are 2 notable sections on the Lincoln Eastern bypass ( fitted for but not built with D2 alignments ) uphill from Washingborough to Branston which is well executed ( second lane there from the Roundabout at the bottom of the hill and the right hand lane drops once over the crest

the north of the river to Greetwell road section is less well executed ending at the roundabout , with very short tapers on the A15 northbound after the Roundabout ( despite fitted for but not with D2 alignments) and the start of the lane is a 'pick up' to the right, what lets it down is becasue of the short tapers norther of the Greetwell roundaobut traffic a lot of the Northbound traffic stays in Lane 1 regardless rather than Lane 1 being heavies and traffic wanting to go into Lincoln via Greetweel road ( the signed route to Lincoln Hospital's ED)

[Herned]

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?

Yes that makes sense, and I'm sure when it was built they didn't expect it to be 35 years before any more of the road was dualled

[darkcape]

I used to commute through the M6 4-3 section where there was the climbing lane southbound, worked fine in lighter traffic but during rush hour the volume of company cars blasting all the way to the end & then diving causes daily queues & was an accident hotspot, works far better in the current layout with the merge removed.

[trickstat]

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.

While it is a steep hill it is relatively short (compared with some of the long drags on motorways). I suspect HGVs are reluctant to use it for 2 reasons:

1. The worries about rejoining.
2. The relatively shortness of the hill means that drivers don't think they'll cause much congestion for other drivers by not using it.

There is something of a dichotomy with any crawler lane where slower vehicles have to merge, in that, if there is lots of traffic about, drivers of slower vehicles are torn between using it to help others and not using it because of the difficulty of merging back in.

[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.

While it is a steep hill it is relatively short (compared with some of the long drags on motorways). I suspect HGVs are reluctant to use it for 2 reasons:

1. The worries about rejoining.
2. The relatively shortness of the hill means that drivers don't think they'll cause much congestion for other drivers by not using it.

There is something of a dichotomy with any crawler lane where slower vehicles have to merge, in that, if there is lots of traffic about, drivers of slower vehicles are torn between using it to help others and not using it because of the difficulty of merging back in.

Agreed, which is why, as Bryn says, it's better that lane three is dropped at the end of the stretch with the climbing lane, rather than the climbing lane itself.

[AnOrdinarySABREUser]

Interesting stuff, everyone!

I’ve got the comment about crawler lanes being referred to as climbing lanes in contemporary documentation. I knew this and wanted to name the thread as such, but I thought that the former was more widespread in the UK.

What is the maximum gradient for dual carriageways without climbing lanes today? I’ve seen responses that indicate the maximum is higher in the continent than Britain. Likewise, what is the maximum gradient for dual carriageways with climbing lanes? I would assume that it’s around 1.5x the maximum gradient, so for example, 9 to 12% (4.05 to 5.40°).

I’ve noticed that the slopes I provided in my original example was calculated incorrectly (x / 45, not x / 90. I’ll be editing my OP shortly to reflect this.

[Bomag]

There has been may variations of lane gain and lane drops on D2. Some were specifically for when gradients when speeds would drop but there was greater potential differential - the third lane maintains capacity rather than overtaking opportunities. Then there was extra lanes on single carriageways for overtaking (2+1), the exact length needed to clear queues, but not waste road space can vary.

Based on a whole raft of data both lane gains and drops not at junctions should be offside except on the M25, where the traffic flows (in each lane) make no sense, where its nearside.

[solocle]

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

Is this the one? Because I used it as an unofficial climbing lane on my bike when I took this

[roadtester]

I believe the A417 Missing Link scheme is going to have an extra lane on the climbing side of Birdlip Hill.

It occurs to me that there’s also an example further south on the A417/A419 corridor at Blunsdon, where the old below-par section was upgraded/bypassed about fifteen years ago. The old road was quite steep, taking a straight run up the hill, but the replacement is a on bit of a loop, which eases the gradient, although it must still be one of the steeper bits of modern dual carriageway in the country. That’s also two lanes down and three lanes up, although again, I’m not sure whether lane one of the uphill side is explicitly signed as a crawler/climbing lane.

[Mark Hewitt]

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.

They are way too short to be useful however. They really need the same length again at the start and end, as it is they are too short to do anything much without going way in excess of the speed limit. I keep out of them myself.

[wallmeerkat]

NI didn't have D3M until relatively recently, and even at that they're extra capacity heading into/out of Belfast rather than long distance stretches.
One stretch with a 3 lane crawler lane was the M2 "hill" section, originally a lane gain on the left, then (still is) a lane drop to Sandyknowes junction.

A8(M) also has a 3 lane crawler lane to get up its hill - https://www.google.com/maps/@54.6800866 ... ?entry=ttu - lane 3 then ends and the carraigeway shifts right to open up a left hand turning lane before the roundabout.

M8 at Livingston has a crawler lane to get up a bit of a hill, it starts and ends on the left - https://www.google.com/maps/@55.9172672 ... ?entry=ttu - the signage was removed sometime between 2018 and 2021 - https://www.google.com/maps/@55.9169932 ... ?entry=ttu

[Peter Freeman]

They are still definitely needed. Although modern cars and vans are capable of effortlessly negotiating steep inclines, lorries can struggle. ...

They are definitely needed at some uphill locations, and are useful at many others - whether on D2, D2+, or S2.

They're quite closely related to simple overtaking lanes on S2, because the latter are (in Australia anyway) often placed at up-gradients. This is to maximise the number of slower vehicles that can be overtaken in a given length of overtaking lane.

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

In Australia, some, mainly older, ones are like this. Here too they are often not used, either for Bryn's reason or because the slow drivers are not sufficiently altruistic ('Can't be bothered'). In AU though, the faster driver could legally, but carefully, overtake the lorry by using the left lane.

The best design is arguably start on the left and end on the right.

Australian design seems to disagree with this. Lanes that end (overtaking lanes, climbing lanes, compressions due to lack of width, ending of an intersection flare, etc) always** end on the left. Before the end of a climbing or overtaking lane, there's a sign that reads "Left lane ends in (500) m". A sign that reads "Left lane ends, merge right" precedes the taper. A dashed line giving priority to lane 2 may or may not be present, so yes, you'll need to push-in from lane 1 to lane 2. This may sometimes be difficult, especially if you leave it too late. For an HGV it should be relatively easy: who in lane 2 is going to argue with a huge semi-trailer, right indicators flashing, and moving across in front of you?

The non-use problem is eliminated by growing the extra lane on the right instead of left: stay in-lane, and you find yourself in the climbing lane by default - whether you need it or not. Optionally then move right, if you're not slow.

I was converted to this left-lane-ends design by thinking about the hair-raising maneouvre of squeezing leftwards from lane 3 to lane 2, at high speed. What happens if you can't get in? Answer: you have a serious high speed crash. On the other hand, if a lane 1 vehicle really can't merge right, then it will stop - in a slow lane, without any high-speed consequence. Worst case, there's a low-speed accident.

The best design is arguably start on the left and end on the right.

A problem with this design is that it too might be shunned, because until you reach the top of the hill, you don't know whether it will end on the left or end on the right (unless you're already familiar with the particular road). So it still risks being unused.

My preference is start on the right and end on the left.

** My observations are based mainly in AU state Victoria, but I think they're reasonably country-wide. An exception is in Canberra, where flat three-lane carriageways compress to two-lanes after intersections. Lanes 2 and 3 simply lose their separator line, preceded by painted-on-road words "form one lane" and sometimes by curved 'kicker' arrows. This is fairly similar to the UK, which is not surprising since Canberra originally copied much UK practise.

[Keiji]

Since we're all giving opinions on this, I'll join in with mine: additional lanes should start on the right and end on the right, whether they are climbing a hill or not. This way, by default, you just continue in the lane you are in; if you're climbing a hill then the only potential downside to staying in lane is that you may need to slow down; if you want to go faster, you actively choose to move to the right and perform and complete an overtake in a safe manner.

Ending the left lane just causes everyone to get out of the left lane way too early (or not go into it at all, if they're familiar with it), which is about as useful for capacity as not having the lane at all. Especially because we suffer from a) a lot of stubborn road users that won't allow anyone to get in front of them, and b) a lot of road users that don't understand what a safe stopping distance is and therefore expect you to go in front when it's clearly unsafe, which then causes problems regardless of whether you go in there or not.

I was converted to this left-lane-ends design by thinking about the hair-raising maneouvre of squeezing leftwards from lane 3 to lane 2, at high speed. What happens if you can't get in? Answer: you have a serious high speed crash. On the other hand, if a lane 1 vehicle really can't merge right, then it will stop - in a slow lane, without any high-speed consequence. Worst case, there's a low-speed accident.

This argument doesn't hold water imo. Here's my counterargument:

Who do you expect to be in the leftmost lane? Vehicles which are hard to maneuver, and have to rely on others to get out of their way, such as big, heavy lorries.
Who do you expect to be in the rightmost lane? Vehicles which are easy to maneuver, that can easily nip in wherever they need to, such as motorbikes or decently powerful cars.
Why? Because you should only be going into an overtaking lane in the first place if you are confident that you can complete your overtake.

If you end the left lane, then the onus is on the drivers of hard-to-maneuver vehicles to merge, which causes a great nuisance for anyone else around them.
If you end the right lane, then the onus is on the drivers of easy-to-maneuver vehicles to merge, which causes minimal fuss all round.

Also, it's a fallacy to suggest that a vehicle stopping on the left is "safe" just because it's a slow lane. When you are approaching such a stopped vehicle from behind, in a faster lane, it's hard to actually tell straight away that the vehicle is stopped, and it's very common to panic: to try to move right or do anything else to evade the vehicle in case it suddenly pulls out. A vehicle stopped in a live lane on a fast, multi-lane road is not a safe situation. Every approaching driver has to handle the sudden realisation that there's a stopped vehicle, and the moment that just one of them handles it badly you risk a collision.

So, yes, in general, if there is a collision resulting from a lane ending, then the collision will be worse if it is at a higher speed. But, from the above, one can easily conclude that, if it's the right lane that ends instead of the left one, then 1) simply progressing along the road is less stressful for all drivers involved (since the right lane will generally have fewer vehicles in it, those vehicles will be more maneuverable, and their drivers will have actively chosen to be there) and 2) the likelihood of a collision in the first place would be lower.

Another argument against arrangements that start on the left and end on the right, or vice versa, is if the road starts with 2 or more lanes in the first place, then everyone has to shift over by one lane just to make progress. This is especially annoying when the length of additional lane is short. The A30 eastbound at M5 J29 does this (through traffic signals), and it's always a right pain no matter which lane you start in or aim to end in.

[jnty]

The right lane is also generally the most empty, so putting lane gains/drops there ensures that the minimum of manoeuvres are necessitated. If you end the crawler lane on the left having started it on the right, it means that at quieter times almost every vehicle has to perform (or accommodate) a lane change. Ending it on the right means that almost none do.

There's a more general problem with creating a norm that left lanes 'randomly' disappear - middle lane hogging. People bemoan the fact that lane 1 on ALR smart motorways is often underused, and blame it on some kind of fear in some motorists that they'll encounter a stranded vehicle which would otherwise be in the hard shoulder if it existed. But I think a lot of it is the fact that so many smart motorway junctions use a lane drop, and people get into the habit of avoiding it. This is inconsiderate but understandable, and worsening the problem by putting lane drops on the left when they could just as easily be on the right makes the problem worse.

[KeithW]

Since we're all giving opinions on this, I'll join in with mine: additional lanes should start on the right and end on the right, whether they are climbing a hill or not. This way, by default, you just continue in the lane you are in; if you're climbing a hill then the only potential downside to staying in lane is that you may need to slow down; if you want to go faster, you actively choose to move to the right and perform and complete an overtake in a safe manner.

Here is a classic example of a climbing lane heading up the A6 at Shap Fell.

It starts here
https://www.google.com/maps/@54.4429695 ... &entry=ttu

Here is where you are warned to merge left.
https://www.google.com/maps/@54.4446005 ... &entry=ttu

This is the actual merge. Note the arrows and double white lines.
https://www.google.com/maps/@54.4452061 ... &entry=ttu

After that there are markings to merge into the left lane before the right lane ends.
https://www.google.com/maps/@54.4490141 ... &entry=ttu

There used to be many more S3 sections, I recall a couple on the A5 but they seem to have been either marked down, this was one just north of Hockliffe.
https://www.google.com/maps/@51.9371527 ... &entry=ttu

Or south of Magna Park dualled, as I recall in the 1980's it was S3 but was later dualled.
https://www.google.com/maps/@52.438055, ... &entry=ttu

[Keiji]

Here is where you are warned to merge left.
https://www.google.com/maps/@54.4446005 ... &entry=ttu

This is the actual merge. Note the arrows and double white lines.
https://www.google.com/maps/@54.4452061 ... &entry=ttu

That's not a merge - that's a change from uphill traffic being allowed to use all three lanes, to only being allowed to use the left two.

[KeithW]

Here is where you are warned to merge left.
https://www.google.com/maps/@54.4446005 ... &entry=ttu

This is the actual merge. Note the arrows and double white lines.
https://www.google.com/maps/@54.4452061 ... &entry=ttu

That's not a merge - that's a change from uphill traffic being allowed to use all three lanes, to only being allowed to use the left two.

Spin around and guess what you see
https://www.google.com/maps/@54.4491581 ... &entry=ttu

Yup back to 2 lanes followed by the overtaking lane switching sides, now its a long time since I first drove that section (1968) but I am pretty sure it used to be S3, not least as there are some nice photos here.
viewtopic.php?t=13757

[Owain]

... now its a long time since I first drove that section (1968) but I am pretty sure it used to be S3, not least as there are some nice photos here.
viewtopic.php?t=13757

Good lord, cars all over the place jostling for position - looks like Italy!

[DB617]

... now its a long time since I first drove that section (1968) but I am pretty sure it used to be S3, not least as there are some nice photos here.
viewtopic.php?t=13757

Good lord, cars all over the place jostling for position - looks like Italy!

Okay, now in one picture I understand why S3 was discontinued. These things work in theory... rarely in practice!

[SteveA30]

More from that sequence on Shap and a few more of the fun and games in those days. Some drivers and passengers must have found it very exciting or very terrifying.......

Right click to magnify........

https://wheathill.wixsite.com/holiday-roads/about-7