Lorries tailgating

[LSWR Cavalier]

For what it's worth I'm observing that the increase in motorway roadworks speed limits to 60mph pretty much gets rid of the issue, as cars can legally do 4mph faster than the lorries physically can (and in practice also get 10% + 2mph or so on top).

Really? Even when there is a lot of traffic?

What about in heavy rain and bad visibility? Doing 60 or 50 could far too fast in such conditions.

 

[Bletchleyite]

Really? Even when there is a lot of traffic?

Yes.

What about in heavy rain and bad visibility? Doing 60 or 50 could far too fast in such conditions.

It's a limit not a target.

 

[AM9]

Yes.



It's a limit not a target.

Well that's already true, so why do you think that raising it 10mph will make all drivers keeping at or below to the new maximum? So many don't respect the 70mph limit irrespective of driving conditions, so why won't they ignore any new limit?

 

[Bletchleyite]

Well that's already true, so why do you think that raising it 10mph will make all drivers keeping at or below to the new maximum? So many don't respect the 70mph limit irrespective of driving conditions, so why won't they ignore any new limit?

What is it about this Forum and people arguing that something is not viable that (a) the professionals have already decided is, and (b) has already been implemented?

The reason people respect the lower limits in roadworks is that they are covered in cameras. And the reason it improves safety is that due to their legally-required speed limiter, lorries cannot reach 60mph therefore are unable to tailgate cars.

 

[Factotum]

agreed - you could try the old break light dab Works with Audi drivers.

I used to fit a switch to the brake lights circuit so I could test them without a mirror. But it was also useful for tail gaters.

 

[Bikeman78]

What is it about this Forum and people arguing that something is not viable that (a) the professionals have already decided is, and (b) has already been implemented?

The reason people respect the lower limits in roadworks is that they are covered in cameras. And the reason it improves safety is that due to their legally-required speed limiter, lorries cannot reach 60mph therefore are unable to tailgate cars.

When I started this thread I was thinking of roadworks. As you say, most of the time cars can out run lorries so tailgating isn't a problem. It does happen when there is congestion but that's usually at lower speeds.

 

[AM9]

What is it about this Forum and people arguing that something is not viable that (a) the professionals have already decided is, and (b) has already been implemented?

The reason people respect the lower limits in roadworks is that they are covered in cameras. And the reason it improves safety is that due to their legally-required speed limiter, lorries cannot reach 60mph therefore are unable to tailgate cars.

The "professionals" in road design and operation decide and implement a lot of things, some of which clearly don't work as they intended, (aspects of smart motorways spring to mind here).
As a consequence, 'some' motorists patently don't obey the rules, even on roadworks with cameras, and at the same time a few truck drivers don't respect the safety of other rod users. If/when the speed limit through road works is raised in effect for light vehicles only, some car drivers will dart in and out of gaps in queues of trucks. That will tempt some truck drivers to block lanes (at limiter speeds) so there will be situations that create more hazards.
Also, as @Bikeman78 says above, things change when traffic density causes speeds drop below the magic 56mph.

 

[bramling]

The "professionals" in road design and operation decide and implement a lot of things, some of which clearly don't work as they intended, (aspects of smart motorways spring to mind here).
As a consequence, 'some' motorists patently don't obey the rules, even on roadworks with cameras, and at the same time a few truck drivers don't respect the safety of other rod users. If/when the speed limit through road works is raised in effect for light vehicles only, some car drivers will dart in and out of gaps in queues of trucks. That will tempt some truck drivers to block lanes (at limiter speeds) so there will be situations that create more hazards.

It wasn’t just a few truck drivers though, in my experience pretty much every one expected to drive through on the speed limiter, and in very many cases were prepared to bully others in order to achieve that.

You can’t blame car drivers for this one.

 

[ABB125]

You can’t blame car drivers for this one

You can always blame car drivers!

 

[ATW Alex 101]

Occasionally, I can be doing an indicated 60mph, and a nearby lorry will be doing exactly the same speed. On a single carriageway. Which demonstrates two things: the speedo in my car is ~4mph out, and the lorry is speeding by ~6mph.

For what it's worth I'm observing that the increase in motorway roadworks speed limits to 60mph pretty much gets rid of the issue, as cars can legally do 4mph faster than the lorries physically can (and in practice also get 10% + 2mph or so on top).

I have observed such too on 60 mph restricted sections (Such as the M1 roadworks ). In my van, I can overtake the majority of lorries with my speedo needle on exactly 60mph. In reality this is probably around 57-58 mph hence why lorries are often overtaken slowly when they are being driven flat-out at 56mph. I can even bring the speedo up to a displayed 62mph which will probably see me at an actual speed of 60mph. Bearing in mind the 10% + 2mph recommendation.

I agree that this makes driving through such restrictions slightly more bearable and less likely to be tailgated by a HGV. In a 50mph zone? No chance.

Then you throw in coaches which are limited to 62.5mph…. Even the lorries hate them.

But even if a car speedometer is reading 4mph high and the driver is travelling at a speed that they deem from their indicated speed to be travelling the legal maximum, that is no justification for an HGV driver following dangerously close.

Quite..

44+ tons has nowhere near the braking distance of a car…

Yes this should have happened ages ago.

50 mph through roadworks has been *extremely* dangerous and stressful as a result of the tailgating issue. Much as it shouldn’t happen, reality is this has been endemic.

Agree about 50mph sections. They are dangerous and I firmly believe that one of the biggest dangers is the way that HGV’s are driven.

 

[90019]

44+ tons has nowhere near the braking distance of a car…

You'd be surprised just how fast an HGV can stop, especially when fully laden.

 

[AM9]

You'd be surprised just how fast an HGV can stop, especially when fully laden.

They might make a lot of noise and some smoke, but still not stopping in anywhere near as short a distance as a modern car from the same speed! A fully laden truck weighs about twice as much as it's tare weight so double the inertia.

 

[Dai Corner]

They might make a lot of noise and some smoke, but still not stopping in anywhere near as short a distance as a modern car from the same speed! A fully laden truck weighs about twice as much as it's tare weight so double the inertia.

And four times the kinetic energy to dissipate as heat in the brakes. Theoretically, that means four times the breaking distance.

 

[AM9]

And four times the kinetic energy to dissipate as heat in the brakes. Theoretically, that means four times the breaking distance.

Precisely, - the idea that trucks can stop in a shorter or even the same distance as a passenger car is twaddle.

 

[Ediswan]

And four times the kinetic energy to dissipate as heat in the brakes. Theoretically, that means four times the breaking distance.

Twice the mass(weight) is twice the kinetic energy. It is the velocity(speed) term which is squared.

 

[Dai Corner]

Twice the mass(weight) is twice the kinetic energy. It is the velocity(speed) term which is squared.

Yes you're right.

 

[Bletchleyite]

Twice the mass(weight) is twice the energy. It is the velocity(speed) term which is squared.

Though it can of course have larger pads and discs and features like vanes to dissipate that energy more quickly than a car. Adhesion to the road is the more limiting factor. (Similarly the reason trains take a long time to stop is not purely because they are big and heavy).

 

[AM9]

Though it can of course have larger pads and discs and features like vanes to dissipate that energy more quickly than a car. Adhesion to the road is the more limiting factor. (Similarly the reason trains take a long time to stop is not purely because they are big and heavy).

But they still rely on rubber to road surface material contact, - and truck operators have for years lobbied the DfT to allow tyres to be chosen for long life (i.e. lower costs) rather than maximum adhesion. Thus the lower threshold of losing grip reduces the braking power. Truck have safety features at the lowest performance level permitted by law.

 

[Ediswan]

Though it can of course have larger pads and discs and features like vanes to dissipate that energy more quickly than a car.

In the case of an emergency stop, is there time for dissipation of energy (to the environment) to play a significant part ? My understanding is that vehicle brakes need to be massive enough to absorb all the energy, for subsequent dissipation, hence the large pads and disks. Effective cooling is more of an issue when there is sustained/repeated braking, such as descending a long steep hill. The 'runaway train' is the classic example.

 

[bramling]

But they still rely on rubber to road surface material contact, - and truck operators have for years lobbied the DfT to allow tyres to be chosen for long life (i.e. lower costs) rather than maximum adhesion. Thus the lower threshold of losing grip reduces the braking power. Truck have safety features at the lowest performance level permitted by law.

And you can probably add that people will generally under-estimate their reaction time in practice. Quite simply, HGVs shouldn’t be tailgating.

 

[Dent]

Adhesion to the road is the more limiting factor. (Similarly the reason trains take a long time to stop is not purely because they are big and heavy).

Actually the limit on on the stopping distance due to the limit of adhesion to the road is independent of mass. Trains take a long time to stop because there is not much grip between metal wheels and metal rails, nothing to do with how heavy they are.

 

[AM9]

And you can probably add that people will generally under-estimate their reaction time in practice. Quite simply, HGVs shouldn’t be tailgating.

Nobody should be tailgating. This does seem to be a one-sided threadf mainly to criticise HGV drivers and absolve car drivers of all blame. Car drivers tailgating and various other moving traffic bad habits can result in sudden moves that cause all sorts of problems for all other road users.

 

[bramling]

Nobody should be tailgating. This does seem to be a one-sided threadf mainly to criticise HGV drivers and absolve car drivers of all blame. Car drivers tailgating and various other moving traffic bad habits can result in sudden moves that cause all sorts of problems for all other road users.

Not disagreeing, however in the specific situation of 50 mph roadworks it is HGV drivers causing the issues described. I’d also regard it as being significantly elevated risk because of the inflated consequences of an HGV going into the back of someone compared to a smaller vehicle.

HGV tailgating is very difficult to mitigate against, especially in a 2-lane roadworks where there isn’t a third lane they’re prohibited from.

 

[Harold Hill]

Yep, one of the most dangerous is the 'convoy', two or more lorries, drivers known to each other, same company etc, heading in the same direction. Bonding / Rivalry kicks in. Avoid like the plague

 

[90019]

They might make a lot of noise and some smoke, but still not stopping in anywhere near as short a distance as a modern car from the same speed! A fully laden truck weighs about twice as much as it's tare weight so double the inertia.

I didn't say they'd stop in the same distance, but they aren't as far off as you might expect.