On congestion and cutting in
Discussion
I see the end result of the following motorway scenario quite frequently. I do not often drive particularly long distances on motorways but do drive the busiest 10 mile stretch of the M25 twice every day. I'm interested in other views, especially any wagon drivers and resident BiBs.
Imagine a busy but free flowing motorway. A wagon in lane 1 is approaching the 1 mile marker to a junction, say a motorway interchange. He's on the limiter at 56mph. Somewhat timid driver in L2 behind, perhaps unsure of route, sees the 1 mile marker and decides to tuck in behind wagon. A little further back, there are a few cars in lane 2 at 70mph, who are also want that junction. They could go past car 1 and wagon but there's a middle lane resident ahead. So they too reduce speed and tuck in. Soon there's a dozen or so cars in single file behind the wagon and all at 56mph - and all bunched up. The wagon is still 3/4 mile from the junction.
A faster car coming up from behind in lane 2, having passed the 1 mile marker, sees the back of this convoy and thinks "uh-oh - that's a queue for my junction". Not wanting to jump the queue or risk missing his junction, he brakes heavily to join the back of the 'queue'. The heavy braking forces a ripple backwards and now the flow has been interrupted. Following cars in lane 1 are also forced to brake and the resulting drop in lane 1 speed forces wagons further back into lane 2. This of course means that two lanes of 70mph+ traffic are now forced into filtering past the wagon in lane 2 who is now passing lane 1 traffic forced to slow and bunch up because of the convoy further ahead.
Now, to traffic approaching the 1 mile marker from behind, the tail of the convoy really does look like a queue. So, inevitably, more people join it. Some drivers, perhaps with local knowledge, get past the wagons, see the tail off the convoy and decide to cruise on past in lane 2, and then slip into a space nearer the junction. Problem is, all the traffic is bunched up and the gaps to slip into look a bit on the small side. So they slow down, to make it easier to take advantage of a smaller gap. This slows down the traffic behind, that was starting to get back up to speed, having passed the wagons forced into lane 2 and so the lane 2 traffic now bunches up as well.
Now some cars, who were travelling much faster in lane 3, and were slowed to filter past the wagons in lane 2, start to get back up to speed. But wait, some of them want this junction and now they're approaching the half mile marker and the back of the convoy (still headed by the wagon on the limiter, who now has 1/2 mile of empty lane 1 ahead of him). And the gaps in the lane 2 traffic have all closed up so it's hard to get back into lane 2 now, never mind lane 1. A few of the bolder drivers (who also want this junction) actually accelerate, reasoning (correctly) that if they can get ahead of this congestion, there will be gaps further ahead. They sail past the head of the convoy, still 1/4 mile from the junction, congratulating themselves on their perspicacity.
Meanwhile the problems behind the convoy continue to build. Traffic has slowed in lanes 1 and 2 and gaps have closed up. Traffic which is trying to keep moving in lane 3 is passing the slower traffic in lanes 2 and 1 but the ones who want this junction are slowing down, increasingly anxious to find a gap to get into lane 2 and then into lane 1. There are still some bolder drivers who recognise the symptoms and press on in lane 3. Some of them make it comfortably but the later ones are now approaching the 300 yds marker. They have a problem getting into lane 2 and even more of a problem to get into lane 1, because that's full of slower traffic and other traffic which is also looking for gaps in lane 1.
These people become increasingly desperate. There are no gaps anywhere. They can't slow down because of traffic behind. Some maintain speed, hoping to find a gap where the slip road widens to two lanes. Some make it but others find their exit is cut off by slower traffic going straight on in lane 1 or by cars at the head of the convoy pulling out to overtake the lead wagon, now that the slip road has widened to two lanes. The gaps, of course, are still tiny. Meanwhile, at the head of the convoy, the wagon driver with open road stretching ahead of him is thinking "Why the f*** is nobody overtaking me?"
Not surprising, is it, that we have congestion around junctions and instances of cars 'cutting in'.
So what lessons can be learned? I suggest the following.
1. Leave decent gaps, especially around junctions. If another car wants to fill the gap, then let it. It's not slowing you down and may be avoiding congestion behind you.
2. Don't be a sheep. Before you tuck in at the back of a convoy, look ahead and consider whether you could comfortably get ahead of the convoy. It's not queue jumping and it will help to avoid congestion behind.
3. If somebody 'cuts in' to the gap ahead of you, consider whether the cutting in is actually because you didn't leave enough space for a comfortable merge.
4. The 'cutting in' driver, even the one who joins the slip road very late, may be acting selfishly or may have been unfortunately stranded when he was trying to keep things moving. You can't know what's in his mind so give him the benefit of the doubt.
Imagine a busy but free flowing motorway. A wagon in lane 1 is approaching the 1 mile marker to a junction, say a motorway interchange. He's on the limiter at 56mph. Somewhat timid driver in L2 behind, perhaps unsure of route, sees the 1 mile marker and decides to tuck in behind wagon. A little further back, there are a few cars in lane 2 at 70mph, who are also want that junction. They could go past car 1 and wagon but there's a middle lane resident ahead. So they too reduce speed and tuck in. Soon there's a dozen or so cars in single file behind the wagon and all at 56mph - and all bunched up. The wagon is still 3/4 mile from the junction.
A faster car coming up from behind in lane 2, having passed the 1 mile marker, sees the back of this convoy and thinks "uh-oh - that's a queue for my junction". Not wanting to jump the queue or risk missing his junction, he brakes heavily to join the back of the 'queue'. The heavy braking forces a ripple backwards and now the flow has been interrupted. Following cars in lane 1 are also forced to brake and the resulting drop in lane 1 speed forces wagons further back into lane 2. This of course means that two lanes of 70mph+ traffic are now forced into filtering past the wagon in lane 2 who is now passing lane 1 traffic forced to slow and bunch up because of the convoy further ahead.
Now, to traffic approaching the 1 mile marker from behind, the tail of the convoy really does look like a queue. So, inevitably, more people join it. Some drivers, perhaps with local knowledge, get past the wagons, see the tail off the convoy and decide to cruise on past in lane 2, and then slip into a space nearer the junction. Problem is, all the traffic is bunched up and the gaps to slip into look a bit on the small side. So they slow down, to make it easier to take advantage of a smaller gap. This slows down the traffic behind, that was starting to get back up to speed, having passed the wagons forced into lane 2 and so the lane 2 traffic now bunches up as well.
Now some cars, who were travelling much faster in lane 3, and were slowed to filter past the wagons in lane 2, start to get back up to speed. But wait, some of them want this junction and now they're approaching the half mile marker and the back of the convoy (still headed by the wagon on the limiter, who now has 1/2 mile of empty lane 1 ahead of him). And the gaps in the lane 2 traffic have all closed up so it's hard to get back into lane 2 now, never mind lane 1. A few of the bolder drivers (who also want this junction) actually accelerate, reasoning (correctly) that if they can get ahead of this congestion, there will be gaps further ahead. They sail past the head of the convoy, still 1/4 mile from the junction, congratulating themselves on their perspicacity.
Meanwhile the problems behind the convoy continue to build. Traffic has slowed in lanes 1 and 2 and gaps have closed up. Traffic which is trying to keep moving in lane 3 is passing the slower traffic in lanes 2 and 1 but the ones who want this junction are slowing down, increasingly anxious to find a gap to get into lane 2 and then into lane 1. There are still some bolder drivers who recognise the symptoms and press on in lane 3. Some of them make it comfortably but the later ones are now approaching the 300 yds marker. They have a problem getting into lane 2 and even more of a problem to get into lane 1, because that's full of slower traffic and other traffic which is also looking for gaps in lane 1.
These people become increasingly desperate. There are no gaps anywhere. They can't slow down because of traffic behind. Some maintain speed, hoping to find a gap where the slip road widens to two lanes. Some make it but others find their exit is cut off by slower traffic going straight on in lane 1 or by cars at the head of the convoy pulling out to overtake the lead wagon, now that the slip road has widened to two lanes. The gaps, of course, are still tiny. Meanwhile, at the head of the convoy, the wagon driver with open road stretching ahead of him is thinking "Why the f*** is nobody overtaking me?"
Not surprising, is it, that we have congestion around junctions and instances of cars 'cutting in'.
So what lessons can be learned? I suggest the following.
1. Leave decent gaps, especially around junctions. If another car wants to fill the gap, then let it. It's not slowing you down and may be avoiding congestion behind you.
2. Don't be a sheep. Before you tuck in at the back of a convoy, look ahead and consider whether you could comfortably get ahead of the convoy. It's not queue jumping and it will help to avoid congestion behind.
3. If somebody 'cuts in' to the gap ahead of you, consider whether the cutting in is actually because you didn't leave enough space for a comfortable merge.
4. The 'cutting in' driver, even the one who joins the slip road very late, may be acting selfishly or may have been unfortunately stranded when he was trying to keep things moving. You can't know what's in his mind so give him the benefit of the doubt.
I must confess I read this post whilst nodding in agreement. As a user of the M25 regularly (every day in fact, full circuit completed yesterday - again!), I am astonished at how poor people's driving habits are. I'll not digress from the point of your post though...
The situation you describe can be avoided by people being more willing to think rationally and more positively whilst they drive. It doesn't take any more than a couple of seconds thought to know that a truck travelling 56mph can be passed in about 3-4 seconds (travelling at 70mph). Many drivers however, are very reluctant to undertake the manoeuvre as they prefer to take the 'safe' (and might I say very British) option of tucking in so as not to take any risks.
It's not just with driving that you see this kind of attitude; it's endemic in everything the Brits do. Playing it safe (so we think) is a national institution. Go to Italy or France etc. and you don't see this kind of thing happen. Admittedly the rules of the road in Italy are a joke, but you will take the point.
The situation you describe can be avoided by people being more willing to think rationally and more positively whilst they drive. It doesn't take any more than a couple of seconds thought to know that a truck travelling 56mph can be passed in about 3-4 seconds (travelling at 70mph). Many drivers however, are very reluctant to undertake the manoeuvre as they prefer to take the 'safe' (and might I say very British) option of tucking in so as not to take any risks.
It's not just with driving that you see this kind of attitude; it's endemic in everything the Brits do. Playing it safe (so we think) is a national institution. Go to Italy or France etc. and you don't see this kind of thing happen. Admittedly the rules of the road in Italy are a joke, but you will take the point.
I see this same situation on my way to work each day, and agree with all that you say.
It's the middle lane dawdlers who make life hard - usually you can pass the wagon plus convoy, but find yourself computing the speed that the middle laner is passing the convoy to see if the gap is going to open in time. Of course the middle laner might have been influenced a few seconds earlier, by a cutter-in who has slowed the middle lane as well in the process.
Usually it sorts itself out. Twice I think, in about 5 years, I have got it so wrong that, rather than brake and cut in, I've had to go past the intended junction and go on the the next one to get to work (which doesn't really take very much longer in my case).
The worst, the absolute gits, are the ones who blast past the inside lane, in the middle lane and then, at the very last possible moment, move from lane 2 straight into the right hand lane on the slip road. I don't like them.
It's the middle lane dawdlers who make life hard - usually you can pass the wagon plus convoy, but find yourself computing the speed that the middle laner is passing the convoy to see if the gap is going to open in time. Of course the middle laner might have been influenced a few seconds earlier, by a cutter-in who has slowed the middle lane as well in the process.
Usually it sorts itself out. Twice I think, in about 5 years, I have got it so wrong that, rather than brake and cut in, I've had to go past the intended junction and go on the the next one to get to work (which doesn't really take very much longer in my case).
The worst, the absolute gits, are the ones who blast past the inside lane, in the middle lane and then, at the very last possible moment, move from lane 2 straight into the right hand lane on the slip road. I don't like them.
observer said:
4. The 'cutting in' driver, even the one who joins the slip road very late, may be acting selfishly or may have been unfortunately stranded when he was trying to keep things moving. You can't know what's in his mind so give him the benefit of the doubt.
But if you're seeing this on your commute, you can be reasonably sure most of the people doing this also drive this route often and they're just driving like to55ers. You can usually tell.
If the exit causes traffic to bunch up so much then perhaps it needs it's own lane for a short distance before the exit.
We should all be paying attention and if not on a familiar road we should be watching/reading the signs, preparing to exit and get in the left hand lane soon enough.
I see the to55er variety quite often on the M4, Westbound, exiting at J10 for Bracknell/Reading East. Fly up the outside lane and cut in front of everyone who is waiting patiently for the dawdler at the front to get past the exit.
targarama said:Spot on - I was going to mention M4 jc10 too. As I turn off to Reading I normally peel off from lane 1 in to the right hand slip lane. Often finding myself coming close to a colision with vehicles from lane 2.
I see the to55er variety quite often on the M4, Westbound, exiting at J10 for Bracknell/Reading East. Fly up the outside lane and cut in front of everyone who is waiting patiently for the dawdler at the front to get past the exit.
The solution? I leave my indicating to the last minute! Not great driving I know, but it creates enough hesitation with the
in his german car in lane 2 that he'll miss the exit!targarama said:
I see the to55er variety quite often on the M4, Westbound, exiting at J10 for Bracknell/Reading East. Fly up the outside lane and cut in front of everyone who is waiting patiently for the dawdler at the front to get past the exit.
I think you've missed the point then. If you can get past and onto your exit sliproad comfortably, don't "wait patiently for the dawdler". That's what causes the congestion.
parrot of doom said:
How about we increase the speed limiter on large vehicles from 56mph to 65mph, which seems to be about the speed most people in the middle lane travel (certainly up here).
Common sense, unfortunately it won't happen because common sense isn't needed in government nowadays. Back on topic, I am very happy to let people pull in front of my truck, but please peeps, can we do it sensibly? Obviously the stopping distance on a truck is greater, so we leave a bigger gap, it amazes me how many drivers will dive into it, then anchor up to make the sliproad
do they want to be hit up the arse by 44 tonnes?. IMHO, this is the sort of thing we need more trafpol for. There is an awful lot of bad driving going on, it's getting worse. Automated enforcement doesn't do anything to change it. We all NEED to look out for each other, if somebody is being a tw@, their day will come
For me, it's give and take.
Phil
targarama said:
4. The 'cutting in' driver, even the one who joins the slip road very late, may be acting selfishly or may have been unfortunately stranded when he was trying to keep things moving. You can't know what's in his mind so give him the benefit of the doubt.
But if you're seeing this on your commute, you can be reasonably sure most of the people doing this also drive this route often and they're just driving like to55ers. You can usually tell.
<snip>
I think there are a lot more occasional users of the M25 than you would think and if they don't know the road they will go for the option the original poster described.
The only other option
is to stop commuters coming onto the M25 during the busy periods. Think of the nightmare of that 
philthy said:
How about we increase the speed limiter on large vehicles from 56mph to 65mph, which seems to be about the speed most people in the middle lane travel (certainly up here).
Back on topic, I am very happy to let people pull in front of my truck, but please peeps, can we do it sensibly? Obviously the stopping distance on a truck is greater, so we leave a bigger gap, it amazes me how many drivers will dive into it, then anchor up to make the sliproad
IMHO, this is the sort of thing we need more trafpol for. There is an awful lot of bad driving going on, it's getting worse. Automated enforcement doesn't do anything to change it. We all NEED to look out for each other, if somebody is being a tw@, their day will come
For me, it's give and take.
Phil
What an absolutely splendid post. Thanks Phil, and I mean it.
Best wishes all,
Dave.
thepeoplespal said:
The only other option
That's a very fair point thepeoplespal, London apart from being the capital city also suffers from the accident of geography that it stands between the docks,ferries and tunnel links to Europe, and the rest of the country. Not many other Capital Cities around Europe do this.
Every city needs a fast ring road and the M25 serves this purpose, but it is also req'd to take heavy through traffic that doesn't wish to go anywhere near London never mind into it.
What London needs is a By-pass that will remain a by-pass with no local junctions (except in emergency) for through traffic only, thus making life easier for local people on the M25. The obvious route would be to the West of London. Anyone care to suggest it to those living there,
no, I know what you mean. Manchester has a similar problem with the M60 ring when it becomes the M62/M60 over the northern section through the aptly named "Death Valley". The problems described, happen here too and I'm sure are the cause of many motorway accidents elsewhere.
I once saw the result of one of these accidents though on a section the M6 motorway northbound at jct27 at Standish,(just north of Wigan) in a quite rural area. The result seemed to be that a lorry had hit a car which was trying to leave the M6, and peeled it open like a can. The cause here was heavy traffic, a steep gradient for the trucks leading up to the jct, and the exact conditions described by Obsever.
The start of the massive increase around the M25 can be traced back to the time when we joined the EU and left the Commonwealth. This shut down the Atlantic trade into Liverpool docks and switched it to Southern ports via Rotterdam. I don't think the then planners were expecting that and it is now overloaded and doing two jobs.
Since then British and foreign trucks have pounded the M25. It also explains the explosion of concrete and congestion over the last 25 yrs or so in the SE. And the loss of jobs in the NW as industry moved south creating a boom there. The SE is becoming: the new Liverpool. But, whereas Liverpool has several fast routes from the dock road to the surrounding countryside and beyond, London stands in the way of the SE ports. In my view, sooner or later the problem will have to be addressed or it will be gridlock.
>> Edited by 8Pack on Sunday 27th March 03:27
observer included the key words in his original post.
"Look Ahead"
Yes indeed lift vision and plan properly.
I'm one of the ones keeping going with a plan to get into lane 1 somewhere between 1/2 mile and 300yd marker.
Maybe I misunderstood the point but what is wrong with exiting lane 1 of the main carriageway straight onto lane 2 of the off slip?
"Look Ahead"
Yes indeed lift vision and plan properly.
I'm one of the ones keeping going with a plan to get into lane 1 somewhere between 1/2 mile and 300yd marker.
Maybe I misunderstood the point but what is wrong with exiting lane 1 of the main carriageway straight onto lane 2 of the off slip?
Gassing Station | Speed, Plod & the Law | Top of Page | What's New | My Stuff