To think that 40 in a 60 is too slow

[TwittyMcTwitterson]

Ok, so you're driving on a country road. The speed limit is 60. It has officially been deemed as safe to drive at 60. So why do so many people tootle along at 40 or less??? That's 2/3rds of the safe speed for that road and the limit safe for a lot of residential areas. If you do my feel safe driving at that speed then don't use the road! I'm fed up of getting caught behind Sunday drivers!!!

My car takes an AGE to get up to 60. I press my foot down and the speed climbs slowly and it REALLY does my head in when people overtake me the SECOND the road moves into a 60 limit.

I don't stop in the middle. When I stop to the side where the products are (and where people are normally stationary anyway) I apologise if I get in anyone's way. I know you can't really do that in a car as such. It's not rocket science.

Ha cumbercookie, do you also have a Picasso? Mine has the acceleration of my grandma

Err Bartman you fail at physics, it's indeed the addition of the two speeds.

Thanks backinthering.

It's an interesting mistake that bartman makes though.

I will finesse my position (and assume Bartman will agree with this part of my argument at least) to note more precisely that 2 cars hitting head on at 60mph is the same as one car hitting a stationary vehicle at 120mph.

I concede that this is the same thing as one car at 60mph hitting an infinitely heavy stationery object head on whilst the road moves at 60mph relative to the stationary object and a 60mph storm is blowing. That doesn't ever happen though in the real world.

Bartman it may clarify your thoughts to imagine the scenario (also impossible but a thought experiment) to the 2 vehicles being freely moving in space at 120mph relative to one another. When they hit, the combined speed of impact is 120mph. Nobody can say whether one is going at 120mph and the other at 0mph, or whether each is doing 60mph towards the other relative to some third object as speed is relative. It is however clear that the speed of one relative to the other is 120mph (again we are talking speeds well below that of light where relativity would kick in), and that this is going to result in very different forces on impact to the situation where there relative speeds are 60mph. In fact, as energy is directly proportional to the square of velocity, there will be a four times the energy to dissipate at impact.

Oooo, a physics argument, goodie!

ProfPlum, you are sort of correct (with certain assumptions, e.g. equal energy dissipated in both the vehicles at collision, inelastic collision, same mass of vehicles etc), but bartman is completely correct about a head on collision with something completely immovable is the same as a head on collision with a car travelling at the same speed.

There is certainly not 4 times the energy to dissipate at impact. If both cars are travelling at 60mph it is twice the energy to dissipate, but two cars for it to be dissipated by. For the 120mph car hitting a stationary car, there is twice the energy as the head on at 60mph scenario, but they would still be moving afterwards (at 60mph) so it is still the same amount of energy dissipated in the collision.

So:

• Two cars head on at 60mph is the same as:
• One car at 120mph hitting a stationary car, which is the same as:
• One car at 60mph hitting something immovable.

In reality it will never be exactly like that because they won't be the same weight, they will spin etc.

Oooh perhaps we can start a mechanics thread? ;-)
whatsthat you say:

"So:

• Two cars head on at 60mph is the same as:
• One car at 120mph hitting a stationary car, which is the same as:
• One car at 60mph hitting something immovable."

Spot on, and what I was trying to say (but you have put it more clearly). The "something immovable" in the above though, needs to be something infinitely heavy for the maths to be the same (any mass less than infinite will move a little).

you also say

"There is certainly not 4 times the energy to dissipate at impact."

Hmmm... 2 cars at 60mph head on will though have 4 times the energy to dissipate at impact as 2 cars head on at 30mph (just applying 0.5mv^2), although I agree with you that it is dissipated across two mangled cars and KSI drivers rather than just those in the one car.

I worry that Bartman has half understood and believes that hitting another car head on at 60mph is no worse than hitting a stationery car at 60mph and drives accordingly (tbf that is not what she said, but there was, I think, the implication).

.

Of course most head on collision result from inappropriate overtaking of

...... someone driving much slower than the road allows.

If you want to drive slowly please pull over to let others past.

At your estimate of taking 5 mins extra per 20 miles, that's 37 mins less family time every day for my wife caused by slow drivers not pulling over.

*Of course most head on collision result from inappropriate overtaking of

...... someone driving much slower than the road allows.*

Really? Is there some evidence to back this claim up at all please? I'd have thought a fair few head ons are achieved by risking-taking idiots, no matter what the non-defined 'much slower' means. At the moment your comment sounds like a driver getting to blame someone else for their really poor driving.

Got wires crossed Prof. I though you were talking about the 120 mph scenario for the kinetic energy. I think bartman did say something about it being immovable in their first post. So we're all agreed? How disappointing...

I once drove home and when about 12 miles from home I overtook a car doing about 35 max, and much slower on bends (safely, I waited until a good, clear stretch came along). I carried on, stopped off for some shopping spending about 10 mins max in Tescos, and as I drove out of their carpark, I watched that same car drive slowly past.

With a massive queue of cars behind him. I could see the frustration on the faces of many of the drivers.

See Fry I quite admire that driver's chutpah in not being hurried by the drivers behind. There's far too much rushing around these days.

"If you want to drive slowly please pull over to let others past...Really? Is there some evidence to back this claim up at all please?"

When we drove up to the Scottish Highlands for a holiday several years ago there were signs every few miles on the A9 asking slow drivers to pull over to allow faster drivers to overtake safely.

I think the wording was something like "Frustration kills, slower drivers please pull over to allow overtaking" or something like that. I don't know if these signs are still there.

Driving slower than you necessarily have to on a country road isn't dangerous but inconvenient. (Driving too dlowly on motorways or trunk road would be though). Being inconcevienced is not an excuse to drive dangerously.

You're wrong to assume NSL means someone has deemed it safe to drive at 60. It often means it hasn't been assessed at all. I learned this on the advanced driver course work sent me on.

There's a NSL road near me you'd be bonkers to do more than 25-30 on - single track, sudden bends, you don't see the car coming in the other direction until you're practically on top of them and even at 30mph there are some interesting moments...

Well there we have it. Unequivocal evidence.

It's like for anyone on the road - you only overtake when safe to do so. If you can't accept that then you should not be driving a car.

of course bikes would come into this category as well. Overtake when it's safe. It isn't rocket salad.

When we drove in Ireland I did like the road from Rosslare to Dublin, we had a huge clunky people carrier and could pull in to let others pass. I tend to drive at a max 45 (unless its straight) on an unfamiliar road. If I know the road well and someone is driving around 40 -45 I don't get impatient. I plan my journeys well and chill out.

The signs on the A9 have been there for years, but are really aimed at the lorries.

The A9 is a good case in point, tbh. There are dual carriageway bits, wide sweeping trunk road bits, and second-gear hairpins. Nearly all with glorious views.

To be honest I wish people knew what NSL was. The bypass of our nearest town is lovely dual carriageway, two wide lanes each way, good visibility, etc. But there's always some twat doing fifty because... actually I have NFI why, but people assume it's 50 (why?! it's never 50 unless you can see a sign reading 50) or 60 but they're doing below.

I know this because the 56mph-in-lane-two pootlers slam their brakes on as they go through the speed cameras. Fortunately I leave sensible stopping distance, but many drivers don't.

Some people need to read their Highway Code, I think. I believe not knowing what the speed limit is for the road you're driving on counts as "driving without due care and attention" and I wish more people were done for it. Driving on a 60 road at 50 knowing it's 60 and therefore other drivers may well be doing 60 or indeed more is safer than doing 50 and believing everyone else will too.

Once on the M6 we went into horrendous summer storms - mid-August, dusty road suddenly drenched, ground too hard to absorb water, flash floods, aquaplaning, etc. Visibility went down under fifty yards and most drivers, including DH, put fog lights on and slowed to 20-30mph. M6, remember. Some complete idiots were still hooning along without lights in lane three at 70 or more. Death wish?

I know this because the 56mph-in-lane-two pootlers slam their brakes on as they go through the speed cameras. Fortunately I leave sensible stopping distance, but many drivers don't.

It's your (collective your) responsibility to ensure sensible stopping distance. Those who drive too close are all stupid as those who slam on their breaks at speed camera.

UnderYourCommand Wed 19-Feb-14 18:06:43
See Fry I quite admire that driver's chutpah in not being hurried by the drivers behind. There's far too much rushing around these days.

That particular road has a lot of bends and very few clear stretches where it's safe to overtake. I was lucky, but would estimate that less than a handful of the drivers who'd been behind him would have managed to overtake. He should have taken the time to pull over and let the queue of traffic go by. I counted 34 cars before I got bored.

I didn't really have time to read your replies in detail but i will later. My point is this: take 3 identical cars, drive one into a concrete block at 60mph then crash the other 2 head on each travelling at 60mph and you should have 3 cars all with virtually identical damage. Now take a 4th identical car and crash it into the concrete block at 120mph. The damage will be far more severe than the other 3 cars - 4 times the energy will have been dissipated. So two cars head on each at 60mph is absolutely not the same as 1 car into an immovable block at 120mph. This can be proven experimentally.

I've had similar on motorways. Some people really do push their luck. Even with a big safe car and brand new tyres, driving fast in the rain isn't worth it. Sometimes a puddle is deeper than it looks and aquaplaning is no fun.

I agree about driving too close. I really don't see the point. The person is so unlikely to speed up and you're just putting everyone in danger.

I will finesse my position (and assume Bartman will agree with this part of my argument at least) to note more precisely that 2 cars hitting head on at 60mph is the same as one car hitting a stationary vehicle at 120mph

Absolutely agree. Not sure why exactly we are arguing.