Speed Limit sign

[larmen]

Have you been watching my sister driving? Mind you 50 mph would be speeding for her.
What I hate the most of these type of drivers is them joining the motorway at 30 MPH.

I think I have seen her a couple of weeks ago, or someone like her.

Starting at about 40 mph but losing confidence when not seeing a gap and then slowing down to 30 before joining. Trying to join behind that car was scary, not sure what happens if a handful of cars all coming up the ramp behind a crawler like that.

 

[BiMGuy]

I thought this thread would promote some level of discussion.
It's funny how breaking the speed limit seems to be an acceptable breaking of the law. I really do my best not to break speed limits. In 30mph areas it's a definite no-no as they are often in areas where somebody could jump out at you at any moment. I have been flashed and had people on my bumper in 30mph limits, but that's an indication of the person behind me, and not me.
Even on motorways, I will tend to put my car at 70 and stick to it. I'll be honest, I get overtaken more than I overtake, but whilst my car can do well over the National Speed Limit in comfort, I am also aware that even 10mph over the limit feels a fair bit faster.
I often find as well that the more people are over the speed limit, the more aggressive their driving technique.
I do a fair bit of motorway driving, and I often wonder what happened to the much publicised clamping down on middle lane hoggers. Nothing seems to have happened on that and, IMHO, they do constitute a danger.

I think its all relative to the car, and just the way physics works.

So your car may stop from 100mph in a shorter distance than say, an E reg Sierra. But will still be doing 70 at point X relative to your starting point. Point X for the Sierra will be different.

What doesn't change is reaction times. They are fairly consistent.

 

[GreiginFife]

Always thought these figures were done on an average and a lot of the laws / rules are to protect people from the average

Like some cars can stop faster, some drivers can handle speed a lot better etc but for safety the law is this for people to cater for average

And therein lies the danger of averages. As it would follow that in order for that to be an average there would need to be an "opposite" end of the scale where someone is still doing 50 at 'x'. So therefore would not be safe even travelling at 70 in theory.

No, I think many of these braking figures are measurements from years gone by that, like speed limits themselves, are not reviewed much.

All opinion, of course as I do not work for or am I affiliated to the DFT.

 

[Jamesbrown]

I disagree , as national is different to different vehicle types .. so put up 70 and that's incorrect for those towing trailers .. lorries etc

I did a speed awareness course a few years ago and the bit that hit home was the 100mph stat

If traveling at 70 you will stop at point X

If traveling at 100 and you full brake you will still be traveling at 70 when you hit X

Just sent shivers

Ah, I forget about over vehicles limits. ?

 

[hairball_89]

Surely braking distance is not a constant but is driven by a number of factors. Size of brakes, size and number of pistons, distribution of force across the disc, temperature of disc and ability to dissipate said heat, control systems and distribution of braking relative to grip.

I'm pretty sure my car will stop from 80 in a shorter space than my neighbour's people carrier.

I'm not saying that to justify travelling at speed BTW but merely to highlight that its not a simple argument based purely on a "static" braking distance.

Oh absolutely. There are loads of holes in the statement. But as @pauljames87 said, it's about averages and making you think.

It must be true *enough* for them to use it. And yes, if you are a brand new Porsche doing a 100 behind an old Cortina doing 70 you're probably safe based on the porches brakes. whereas the Cortina doing 70 behind a porche doing 100 (extremes here, I know) the Cortina driver is toast.

It was explained to me as the same driver in the same car at point x and the stopping point from 70mph as point y. At 80 you're doing c. 30. At 100 it's c 70mph. Enough to make you think. Don't think too much though - you'll pick the holes out!

 

[ExRabbit]

https://www.justpark.com/creative/reaction-time-test/

Enjoy!

 

[Imurg]

https://www.justpark.com/creative/reaction-time-test/

Enjoy!

Woohoo I'm 33

 

[Robster59]

https://www.justpark.com/creative/reaction-time-test/

Enjoy!

Well, I tried that three times and went from 35 to 27 to 25. The difference with that, of course, is that you are anticipating having to react. On a motorway, most people don't anticipate an emergency and the reaction times will therefore be very different. In terms of stopping distance, people will always use the "ah but" argument whilst not acknowledging the basic message. The faster you go, the longer it takes to stop. Your reaction time may be the same, but the distance travelled while you react will be longer.

 

[Lord Tyrion]

Well, I tried that three times and went from 35 to 27 to 25. The difference with that, of course, is that you are anticipating having to react. On a motorway, most people don't anticipate an emergency and the reaction times will therefore be very different. In terms of stopping distance, people will always use the "ah but" argument whilst not acknowledging the basic message. The faster you go, the longer it takes to stop. Your reaction time may be the same, but the distance travelled while you react will be longer.

The 'Sully' defence . (Tom Hanks dramatised it in a film. Quite correct as well)

 

[jim8flog]

A
No, I think many of these braking figures are measurements from years gone by that, like speed limits themselves, are not reviewed much.

.

Problem is that there are still many vehicles around from years gone by and in the main it is always best to quote worst possible scenario.

Many years ago I was used to driving cars with disc brakes but without realising I was driving a car with drum brakes - the difference was staggering probably around 50% more stopping distance needed at 60mph plus.