Would speed limits per second make drivers more aware of their speed?

[Cudzoziemiec]

The thread title is a little clumsy. My ideas is as follows:

We give speed limits in miles/kilometres per hour, which is practical for calculating roughly how long it will take to reach our destination, but not for safety. The only vehicles likely to travel at a constant speed for as long as an hour are ships and aeroplanes, or perhaps trains in the Australian outback. Speed limits are supposed to be related to safety concerns, and what matters for safety is what is about to happen, or what the driver thinks is about to happen, in the next few seconds. So it occurs to me that measuring road speed per second would give drivers a feeling for the distance they will cover in the next few foreseeable seconds, that is not given by speed measured per hour.

For instance, 60 mph is 29.3 recurring yards per second. Remember the two-second rule? A driver can then easily think "In two seconds at this speed I will cover 60 yards" and have more of a feeling that he needs to look and plan at least a hundred-odd yards ahead than one who knows he will cover 60 miles in an hour. Who can see the traffic an hour ahead?!

Obviously any such change would lead not only to some genuine confusion ("What's that in old money?") but also to a wonderful Daily Froth about persecution and confubbling of motorists, but if it ever took off, would it change our perspective on speed and 'thinking ahead' when on the road? That's what I'm after.

[Greenbank]

Interesting idea but, as with most things related to driving, any attempt to change the behaviour or thinking of motorists is a lost cause with most existing drivers.

Who can see the traffic an hour ahead?!

Never cycled in Lincolnshire then?

[Ham]

No, it wouldn't work, most people are crap at estimating distance.

[andygates]

When I drive it is to go from a place to another place in driver-scale distances, in a human-scale time.

Metres per second is a meaningless measure on those scales.  It doesn't tell me anything useful.

If you're trying to educate drivers with a splat threshold, "twenty's plenty" is, I contend, going to be much more successful with the seething masses.

[clarion]

And that's what my bike now says

[Charlotte]

Sorry Cudzers, it's a rubbish idea.

You could measure it in rods per helek, furlongs per samay or even parsecs per sidereal year, but people will still ignore it.

At least miles per hour is something we're all used to.

[RJ]

At least miles kilometres per hour is something we're all used to.

FTFY, since the 70s when maps went metric and converting 2cm to 1km to miles was harder than to start thinking in km - and resetting one's computer to display distances in km and speed in km/h.

But mph to kmh is an easy calculation to do; changing both bits of the fraction (to ms^-1 for example) starts getting waaaayyy too complicated for any real-time conversion back to what we're actually used to in Real Life.

[Cudzoziemiec]

So nobody likes my idea. Boo hoo. 

Actually, I have to concede all the points made above, especially that we are all familiar with the present measurement and that many/most people are bad at estimating distances in the tens or hundreds of metres/yards (myself included, I admit). This idea just popped into my head when I woke up this morning, so I thought I'd try it out here. 

Sorry Cudzers, it's a rubbish idea.

I don't mind you rubbishing my idea, but I'm not at all sure about the abbreviation "Cudzers"...

[Clandy]

If you're trying to educate drivers with a splat threshold, "twenty's plenty" is, I contend, going to be much more successful with the seething masses.

You would think, but no, see comments here.

[Kim]

Furlongs per fortnight ftw.

[gordon taylor]

You have a point, but it's the numbers that are relevant to a driver, not the units, IMHO.

I've tried before, when discussing cycle paths, to talk about the time taken to ride them. Foe example, planners get excited about a 60 metre facility, but at 20kph, that only takes just over ten seconds to ride.

[Panoramix]

Actually on a boat it is easy because 1 knot = 0.5 m/s

That is useful to know when racing, at a windward mark you need to start setting up you spinnaker ready to hoist as late as possible so for a 10m boat doing 6.5 knots that is one boat length (easier than meters to guesstimate) every 3 seconds. A good bowman will start to move around 10-15 lengths before the mark.

[andygates]

Cudzolicious, the driving test includes stopping distances.  That gives an idea just how far a vehicle is travelling.

Clandy: Comment threads are twitching reactionary cretin pits.  I can see little reason to pay attention to a bunch of self-aggrandising blowhards who no better reflect reality than my blancmange scupltures do.

Panoramix: That is, actually, pretty cool.  I didn't know that.

[Greenbank]

As the OP shows, mph to yards/s is not exactly tricky.

Dividing the number by two is a perfectly usable estimate.

kph to m/s isn't so easy (multiply by 10, divide by 6, divide by 6 again).

60 -> 600 -> 100 -> 16.67 (2dp).

[hellymedic]

It's not really that difficult in imperial units either, but I don't think people really think that way.
60mph = 88 ft/s or approx 30 yd/s
30mph = 44ft/s or 15 y/s.

What would be more useful would be for people to understand how kinetic energy (and hence damage potential and stopping distance) rise as the square of the speed.

The Powers That Be never (want to) get that message across.

[Cudzoziemiec]

I think the bit about stopping distance rising as the square of speed is made apparent in the distances given on the back cover of the HC (don't know if still on the back cover, used to be). I remember working it out IIRC eg at 70mph it's 70 feet + 70 squared/20.

And feet per second! Wee, I knew there was more than just yards! Despite having pretty much grown up in Imperial, I'm now so used to metric that I forgot about feet, whereas yards remain in my brain as a rough equivalent of metres. Or perhaps I was still a bit sleepy when I did the maths this morning.

[Cudzoziemiec]

You have a point, but it's the numbers that are relevant to a driver, not the units, IMHO.

I've tried before, when discussing cycle paths, to talk about the time taken to ride them. Foe example, planners get excited about a 60 metre facility, but at 20kph, that only takes just over ten seconds to ride.

And even I can ride at 20km/h 

[Cudzoziemiec]

Cudzolicious, the driving test includes stopping distances.  That gives an idea just how far a vehicle is travelling.

This name I actually like!

Yes, the test includes stopping distances. But do people learn what they're based on (I did, it was pretty obvious to me and I'm not particularly mathematically inclined, so I have hope that people do) or do they just learn them by rote? And whichever is the case, don't they just forget it all shortly after receiving the pink card from Swansea? I'm afraid they probably do.

[hellymedic]

<<Stopping distances>>
Do they just learn them by rote? And whichever is the case, don't they just forget it all shortly after receiving the pink card from Swansea? I'm afraid they probably do.

I would think you're right about this, unfortunately.

[Kim]

Yes, the test includes stopping distances. But do people learn what they're based on (I did, it was pretty obvious to me and I'm not particularly mathematically inclined, so I have hope that people do) or do they just learn them by rote?

I learned them by rote for the 30 minutes it took to do the theory test, then promptly forgot them.  This is, I'm sure, entirely typical.

Not that a table of numbers really means that much to you when driving a car.  A proper intuitive sense of how a car actually stops based on experience would be much more relevant.  I think the test would be better to include couple of hours of running over cones in a controlled environment and some skid-pan training.

[Greenbank]

Given a speed v in m/s the stopping distance (in m) is:-

d = 0.6818v + 0.07626v²

Handy if you can convert mph to m/s in your head and do that kind of mental arithmetic.

[Cudzoziemiec]

Handy. But not for me!

I think the test would be better to include couple of hours of running over cones in a controlled environment and some skid-pan training.

Skid-pan experience, even test, yes. Cones in a car park, no. That's what happens in Poland, and it's totally unrealistic - tests only low-speed clutch control and steering, really. Great for parking, but not much else.

[andygates]

 I think the test would be better to include couple of hours of running over cones in a controlled environment and some skid-pan training.

No driving instructor, examiner or road-safety maven I've heard has ever said otherwise - but the time and cost doesn't easily scale.  I'd welcome it.

Mind you, I've never volunteered and ponied up for skidpan training myself, either.  I doubt many of us have.

[clarion]

I'd go with the opinion that the stopping distances are learned by rote.  An examiner could sit with the candidate in a car and ask 'If you were travelling at xmph, and were here when you saw a hazard you needed to make an emergency stop for, where would your car likely come to rest?'.

But they don't.  The numbers are completely meaningless. 

[Kim]

Skid-pan experience, even test, yes. Cones in a car park, no. That's what happens in Poland, and it's totally unrealistic - tests only low-speed clutch control and steering, really. Great for parking, but not much else.

I was thinking more race track than car park...