I love speed
That’s one reason I have fibre broadband. And SSDs. But I’m a petrolhead as well so it won’t come as a surprise I like speed on wheels.
Four wheels and two.
Well, it was two for a while … I stopped riding a motorbike (a rather fun CBR600) a couple of years ago. It was a great decade but getting knocked off was always going to be the end - it just wouldn’t be worth even trying to have that argument with my wife 
I’ve always had interesting cars. A V8 MGB, Corrado VR6, Impreza Turbo, TVR Chimaera 500 and now an E39 M5.
Learner
Since I love driving I’ve taken several training courses. Mainly because they’re fun but partly because I thought they’d make me a better / safer driver.
- A skid control day (a noddy car in a cradle meant under & over steer was simulated at low speed)
- Several track days (Brands Hatch, Bedford Autodrome - awesome, Bruntingthorpe)
- Better than Wetter (a car handling course)
- Rally day (for my stag do, immense fun and the instructor just encouraged sliding)
- Drift day (Caterhams with sticky front tyres and 60psi bald tyres meant sliding was easy)
- The usual karting stuff doesn’t really count … but it is fun
- A motorbiking day with a RoSPA-qualified instructor
Oops
Driving up the A12 late last year on a nice clear dry day I was pressing on past someone which, unfortunately, meant I didn’t see the copper on a motorbike with a hairdryer in a lay-by. Darn.
The dreaded letter arrived a few days later… Well, it’s been more than a decade (and I’d guess around 80,000 miles) since I last got nicked so I guess my number was up.
Punishment
Having been caught red-handed I’ll take my punishment like a good boy. This time that meant a driver awareness training course. Four hours of tedium beckoned.
These courses are obviously held during the week so some holiday would be required. Perhaps unusually I decided to take the course on my birthday - well, if I’m going to take time off it may as well be then rather than some other random day. At least I get the morning off. And get home early.
(In fact I managed to use that time to get a couple of useful jobs down … including taking down my old shed 
)
It didn’t take long to get to the centre where the course was being held and to find the room full of sheepish looking people and a couple of instructors who wouldn’t have been out of place in The Office.
Having said they’d treat us with respect and wouldn’t patronise us, they went on to patronise us for most of the four hours. It wasn’t a completely wasted afternoon: I did learn something (20 mph zones are probably coming to us all … perhaps in 2020?) and I enjoyed being right about which decade contained the worst year for road deaths (and why it was worst).
And that’s a fact
The instructors enjoyed telling us some facts. And that’s where I smelt a rat. But by this stage I’d interacted enough and was looking forward to the end. Unfortunately someone else also smelt a rat and asked a question…
Admitting their lack of knowledge of physics is fine. Truly, I have no problem with it. But don’t cite an equation (E=mc2) that has nothing to do with speeding (KE=½mv2 would be more relevant).
Further, don’t try to shock me with incorrect stats. Shock me with correct stats.
Let’s suppose you’re doing the speed limit on a motorway: 70mph. Now assume a lorry has jack-knifed in front of you and you whack the brakes and stop just before hitting the lorry. Phew, a lucky escape.
Now suppose you were doing 80mph before you hit the brakes at the same distance from the lorry. What speed would you be doing when you hit?
What if you were doing 90mph?
100mph?
They said you’d hit the lorry at 38mph … if you’d started out at 80mph. That sounded high. Starting at 90mph would mean you’d hit the lorry at 57mph so they said. 100mph starting speed means thumping the lorry at 71mph. That also sounded wrong.
Which brings me back to the question someone asked.
10mph faster start speed (90mph vs 80mph) resulted in 19mph higher impact speed.
Yet another 10mph (100mph vs 90mph) resulted in only another 14mph impact speed.
That feels wrong. And they didn’t answer the question, they ignored it. Which only made me more suspicious.
So what’s the truth?
I thought I’d work it out. Thinking back to school-level physics I assumed the brakes / tyres would be able to translate kinetic energy to heat at a constant rate. Of course since kinetic energy increases with the square of velocity there’s four times as much energy to translate for each doubling of speed.
I found CSGNetwork a useful site but in the end only used its estimate of deceleration as an input to my crude spreadsheet.
Stopping from 70mph at 15 feet per second (fps) per second (it’s a rate of change hence the two _per second_s) would require just under eight seconds and you’d’ve travelled nearly 454 feet before stopping. At 80mph, at the same deceleration, you’d still be doing 39mph at 467 feet … hmm.
At 90mph, again with the same deceleration, you’ll be doing 59mph after 461 feet. So far my calculations tally reasonably with the stats given on the course. Which is both comforting (my spreadsheet is accurate) and annoying (they were right).
On to 100mph? 74mph after 465 feet (rougher calculation because you’ll do this between seconds three and four and I only put my spreadsheet together with per-second granularity ). But again it tallies reasonably well. Perhaps the instructors deceleration rate was higher.
I certainly hope it was as 454 feet is pretty poor performance. Especially given the highway code quotes a braking distance of 315 feet from 70mph (ignoring thinking time). To hit that we need 25fps per second deceleration.
If you can decelerate that quickly, you’d expect the impact speeds to come down right? No. Because the distance travelled at 70mph also comes down. So the impact speeds, for higher start speeds, actually go up.
So we come to what’s actually important: how far ahead can you see is clear? More importantly, how far ahead do you look?
A football pitch is 100-130 yards long (a fact I find disturbingly inconsistent) which means you’ll take 3-4 seconds to cover a football pitch at 70mph (103 fps).
So how far ahead do you look? Cruise at 90? Make sure you’ve got 500 feet of clear space. Plus reaction time … which is likely not as quick as you’d like. Assume a second at best. That’s another 130 feet. So give yourself about one seventh of a mile. That’s hard to visualise … some football pitches and some buses for their supporters perhaps?
In the end
It wasn’t a waste of time. It’s made me think about stopping distances. I doubt it’ll slow me down much and I’ll still be frustrated about middle lane hogs … but I will aim to leave more space than I think is truly necessary. Now … where to get bonnet mounted missiles to stop people stealing that space I’m so carefully leaving?
If any coppers happen to read this … would you mind pulling over tail-gaters and middle-lane hoggers a bit more often please. The instructors said this would happen (indeed is happening already). I’m not sure I believe them.