Safe Speed Forums

Full report:

How important is checking the speedometer? Cars can have non-working speedometers and still function safely for long periods, alternatively after coming off a motorway and into a town, 50kph feels like you have almost come to a standstill and the speedometer is useful in that situation to ensure you do not go over the speed limit. A few major questions need to be answered about the speedometer:
1) How long does a speedometer check take?
2) How often do drivers check the speedometer (especially drivers on 9 penalty points)?
3) What are the side effects of knowing your speed?
4) How far do you travel with your eyes on the speedometer?

How long does a speedometer check take?
Research was undertaken to determine how long a speedometer check takes. The results are available in Appendix x. In the car, the check took 0.73 of a second. In the simulator the same test took 0.59 of a second. This is due to the fact that the speedometer was lower in the car than on the simulator.

At 0.59 of a second, at 50km/hr you travel 8.2m in this time. Taking the 0.73 of a second figure you travel 10.04m in that time.

How often do drivers check their speedometer?
The number of checks per minute varied widely depending on the driver. The figures are too varied to be considered a complete test. A minimum of 8 checks per minute and as high as 22 checks were recorder. Taking the average figure of 15, along with the figure of 0.59 seconds per check, the percentage of time the drivers eyes were on the speedometer was 15.74%. This does not include time it takes eyes to refocus back onto the road. This is a very worrying figure. This figure does not take into account looking in the mirror etc. so the time your eyes are off the road is higher. Further research needs to be carried out on this matter.

What are the side effects of knowing your speed?
Possible side effects include trying to reach a maximum speed, going faster than you would just because you are still below the speed limit and going slower as you realise you are over the speed limit. Further research should be carried out into the side effects of the speedometer.

How far do you travel with your eyes on the speedometer?
See Appendix x for table of speed vs. distance due to speedometer check.

Speed (km/hr) 30 50 60 80 100 120
Time
1 8.33 13.89 16.67 22.22 27.78 33.33
0.59 4.92 8.19 9.83 13.11 16.39 19.67
0.723 6.03 10.04 12.05 16.07 20.08 24.10

Full report:
A few major questions need to be answered about the speedometer:
1) How long does a speedometer check take?
2) How often do drivers check the speedometer (especially drivers on 9 penalty points)?
3) What are the side effects of knowing your speed?
4) How far do you travel with your eyes on the speedometer?

I would suggest that the speedometer is the least useful
apparatus in my car. It's only purpose is to allow me to check my speed relative to
an artificially imposed and arbitarily set constraint.

Another key question is this: do drivers check the speedometer at random moments of time,
or are they more selective, choosing to check their speed at moments of low risk?

This is important because, if it is done randomly, then taking your eyes off the road at a
random moment that coincides with a period of high risk would cause more accidents.
Whereas, taking your eyes off the road to check the speedo when there is low
hazard density is far safer.

In my view, the "how often" question is watered down, because it may occur often,
but not in the "risk window", or it could happen once randomly, at a very bad time.

Where will this report be published, please? I think it has the makings of some good PR.

Another key question is this: do drivers check the speedometer at random moments of time,
or are they more selective, choosing to check their speed at moments of low risk?

This is important because, if it is done randomly, then taking your eyes off the road at a
random moment that coincides with a period of high risk would cause more accidents.
Whereas, taking your eyes off the road to check the speedo when there is low
hazard density is far safer.

In my view, the "how often" question is watered down, because it may occur often,
but not in the "risk window", or it could happen once randomly, at a very bad time.

and finally, I used a fair few of safe speed's graphs/figures etc. I've referenced them all but do I need permission to reproduce them? It is an academic report but it will be sent to a few professional bodies in the hope of forcing a job out of them.

Please credit Safe Speed in your reference section, and please retain the SS Rondel in the corners of the graphs. Other than that Paul was extremely happy for his work to be used and I am sure Claire feels the same.

On your other question, I believe Safe Speed would be pleased to host a copy of your report - as a PDF for download (I will confirm with the management team and get back to you).

If I get a phd what I would like to do is to get a car on a closed section of road (or race track) and get people to drive a few laps with the speedometer and without the speedometer. It's my opinion (again just opinion) that the majority will actually driver slower without the speedo, while in terms of boy racers, with no speed to aim for or brag about I reckon they won't push as hard, it will still feel very dangerous but you won't be trying to beat your top speed.

I realise that this is going to be just anecdotal, but recently I've been driving around in a car with only km on the speedo, so to begin with it was producing numbers that were completely meaningless to me. I also had a GPS in the car to get the speed in mph, but as you are probably aware, GPS only works reliably as a speedo when you are doing a constant speed, and even then there is a few seconds lag, so basically I had to set my speed as I thought best, then check the GPS for validation.

Guess what, on the residential roads that I would normally do 30 on, I was consistently setting a speed of 20 +/- 2mph.

Unfortunately before venturing out further into the road network, I made sure I had accurate MPH readings available due to the camera issue, so cannot comment on higher speed roads.

If I get a phd what I would like to do is to get a car on a closed section of road (or race track) and get people to drive a few laps with the speedometer and without the speedometer. It's my opinion (again just opinion) that the majority will actually driver slower without the speedo, while in terms of boy racers, with no speed to aim for or brag about I reckon they won't push as hard, it will still feel very dangerous but you won't be trying to beat your top speed.

Side note: I know a few guys who race motorbikes, they all cover their speedo as they say that when it was uncovered they used that as a reference about how fast to go around the corner, and try beat it the next lap. without it they just use their feel

When I have done track days the only times I look at the speedo are when entering the pit lane and when in the passenger seat. If you were going to check when driving then you would be looking for peak speed before entering the next corner, that means you are not paying attention to your braking/turn in point, which can be a very bad idea.

If I drive an NSL lane where it is difficult or unlikely to significantly exceed the speed limit then I seldom if ever look at the speedo. When I am on a road where the range of safe speeds may exceed the limit then I check fairly often, it is for safety, that of my license. I definitely check on approach to a camera unless obviously doing well under the limit, this is done well ahead so my eyes are back on the road ready for the panic brakers.

Your experiment would be interesting not only to see what proportion of drivers would drive slower with the speedo visible, but also what proportion of drivers used their speedo at all.

I look forward to reading your report when you publish it.