running red light-can I get a course instead of the 3 points

[SS2.]

Pete317 said:

Er, no.
While decelerating, your average speed is lower, which means you take more time to cover the same distance.
You'll find that your emergency stopping distance from 70 is roughly the same as the distance you'd cover in 3 seconds at 70, give or take.

If you anchor on at a constant rate (lets say -1G, although that's way beyond the capabilities of most vehicles and drivers), then the rate of deceleration would be about 9.8m/^2. That's a reduction of 32 ft per second per second, or a drop in speed of 22mph per second.

To go from 70mph to stationary at -1G would thus take 70mph / 22mph = 3.2 seconds plus ~1 second braking time = 4.2s.

Edited by SS2. on Monday 23 November 21:49

[vonhosen]

At 70mph in 3 seconds you'll travel a fraction under 94m.
At 70mph (with a deceleration rate of 8.5m/s^2 - very achievable in a modern car) your braking distance is 58m.

[Pete317]

SS2. said:

Pete317 said:

Er, no.
While decelerating, your average speed is lower, which means you take more time to cover the same distance.
You'll find that your emergency stopping distance from 70 is roughly the same as the distance you'd cover in 3 seconds at 70, give or take.

If you anchor on at a constant rate (lets say -1G, although that's way beyond the capabilities of most vehicles and drivers), then the rate of deceleration would be about 9.8m/^2. That's a reduction of 32 ft per second per second, or a drop in speed of 22mph per second.

To go from 70mph to stationary at -1G would thus take 70mph / 22mph = 3.2 seconds plus ~1 second braking time.

Edited by SS2. on Monday 23 November 21:43

At 70mph you cover 93.33 metres in 3 seconds.

At a deceleration of 0.8G, your braking distance from 70 is 61.7metres. Add a 1-second reaction time gives you a total stopping distance of 92.8 metres

Except that your average speed while stopping is less than 70mph, so you'll take around 5 seconds to cover the same distance. Doesn't matter though, you still stop in the required distance (just) but it just takes you longer to cover that distance.

[TwigtheWonderkid]

Are there any 70mph limit roads with traffic lights?? Doesn't the limit normally reduce before you get things like lights?

There may well be some, but I'm struggling to think of one.

[0000]

vonhosen said:

At 70mph in 3 seconds you'll travel a fraction under 94m.
At 70mph (with a deceleration rate of 8.5m/s^2 - very achievable in a modern car) your braking distance is 58m.

Been a while since I've used v = u +at, but if 70mph = 31.2928m/s ...

I reckon you'd stop in 3.7 seconds given the above, stopping before the line but not before it turns red.

[LoonR1]

TwigtheWonderkid said:

Are there any 70mph limit roads with traffic lights?? Doesn't the limit normally reduce before you get things like lights?

There may well be some, but I'm struggling to think of one.

I don't know. I asked if anyone lived near a set and I only picked 70 limits as it was worst case scenario if the Amber phase was fixed at 3 seconds.

I'm pretty certain that stopping from 30 won't be a problem.

[0000]

TwigtheWonderkid said:

Are there any 70mph limit roads with traffic lights?? Doesn't the limit normally reduce before you get things like lights?

There may well be some, but I'm struggling to think of one.

One here I think.

I did think this was one but it appears there is a 30 sign (at least on one side of the road) just before them.

[TwigtheWonderkid]

0000 said:

TwigtheWonderkid said:

Are there any 70mph limit roads with traffic lights?? Doesn't the limit normally reduce before you get things like lights?

There may well be some, but I'm struggling to think of one.

One here I think.

Street lights tent to suggest that's a 30.

[vonhosen]

TwigtheWonderkid said:

0000 said:

TwigtheWonderkid said:

Are there any 70mph limit roads with traffic lights?? Doesn't the limit normally reduce before you get things like lights?

There may well be some, but I'm struggling to think of one.

One here I think.

Street lights tent to suggest that's a 30.

Not when there is a NSL sign (look to left beneath tree)
https://www.google.co.uk/maps/@52.6734784,-2.13027...

[Flibble]

I live near one: https://www.google.co.uk/maps/@53.2496212,-2.48439...
I'll try to keep an eye out next time I'm there for the amber timing.

[SS2.]

Pete317 said:

At 70mph you cover 93.33 metres in 3 seconds.

At a deceleration of 0.8G, your braking distance from 70 is 61.7metres. Add a 1-second reaction time gives you a total stopping distance of 92.8 metres

Except that your average speed while stopping is less than 70mph, so you'll take around 5 seconds to cover the same distance. Doesn't matter though, you still stop in the required distance (just) but it just takes you longer to cover that distance.

It does matter - the original question was whether you could come to a complete stop from 70mph within the 3 second amber only phase which, as stated from the outset, isn't likely to be possible.

[SS2.]

Flibble said:

I live near one: https://www.google.co.uk/maps/@53.2496212,-2.48439...
I'll try to keep an eye out next time I'm there for the amber timing.

If it isn't 3 seconds (+/- 0.25s), then it won't be conforming.

[Pete317]

SS2. said:

Pete317 said:

At 70mph you cover 93.33 metres in 3 seconds.

At a deceleration of 0.8G, your braking distance from 70 is 61.7metres. Add a 1-second reaction time gives you a total stopping distance of 92.8 metres

Except that your average speed while stopping is less than 70mph, so you'll take around 5 seconds to cover the same distance. Doesn't matter though, you still stop in the required distance (just) but it just takes you longer to cover that distance.

It does matter - the original question was whether you could come to a complete stop from 70mph within the 3 second amber only phase which, as stated from the outset, isn't likely to be possible.

Of course it's going to take longer than 3 seconds to stop, and the lights will already have been red for around 2 seconds by the time you reach the line.
But you will stop before the line - only just though.

Putting it another way, 93 metres will take you 3 seconds at 70, but if you're decelerating then it will take longer than 3 seconds to cover that distance. But it doesn't alter the distance you cover, only the time it takes to do so.

The thing is, if you're around 93 metres from the line when the lights turn amber, nothing less than a full-on emergency stop is going to stop you from going through on the red, and if you're any closer, or a bit slower onto the brake, then you have no chance.

Edited by Pete317 on Tuesday 24th November 08:36

[TwigtheWonderkid]

vonhosen said:

TwigtheWonderkid said:

0000 said:

TwigtheWonderkid said:

Are there any 70mph limit roads with traffic lights?? Doesn't the limit normally reduce before you get things like lights?

There may well be some, but I'm struggling to think of one.

One here I think.

Street lights tent to suggest that's a 30.

Not when there is a NSL sign (look to left beneath tree)
https://www.google.co.uk/maps/@52.6734784,-2.13027...

Yes, see that now. So they do exist, but probably few and far between.

[Flibble]

SS2. said:

If it isn't 3 seconds (+/- 0.25s), then it won't be conforming.

A rough check this morning makes it around 3 seconds, so I think it is.

TwigtheWonderkid said:

Yes, see that now. So they do exist, but probably few and far between.

Not that few there are at least 4 I can think of within a mile or to of my house (granted all on the same road).

Edited by Flibble on Tuesday 24th November 12:45

[Pete317]

Flibble said:

SS2. said:

If it isn't 3 seconds (+/- 0.25s), then it won't be conforming.

A rough check this morning makes it around 3 seconds, so I think it is.

If that's the case then it would be much easier to get into trouble than to stay out of it, and it's probably sensible to slow down on the approach to the lights as a matter of course even if you don't have to, just in case.

ETA:If you're still doing 70 when you see the lights turn amber then you're very possibly already in a dodgy situation, unless you're still a long way off.

Edited by Pete317 on Tuesday 24th November 13:40

[Flibble]

Pete317 said:

If that's the case then it would be much easier to get into trouble than to stay out of it, and it's probably sensible to slow down on the approach to the lights as a matter of course even if you don't have to, just in case.

Edited by Pete317 on Tuesday 24th November 12:56

I generally do; I've done a few sharp stops at the 70 limit lights around here in the past so these days I tend to ease off a fair bit.