Speed and Stopping Distance at Night

For discussion of topics relating to the Driving Standards Agency Learner Test (DSA L Test) and contribution by ADI's (Approved Driving Instructors)

Postby gcl2013 » Fri Aug 30, 2013 10:35 pm


A common rule I hear is that at night you should only drive at a speed that would enable you to stop within the distance your headlights show to be clear. I have read the distance you can see with dipped headlights is between 30 and 40 metres.

If this is correct then based on the stopping distances given in the highway code, whenever it is necessary to use dipped beam due to oncoming traffic in the distance it would only be safe to drive on a straight road at between 30 and 40mph.

I just wondered if other drivers on this forum do this too because in practice when doing 40mph or less on an unlit NSL road for a prolonged time due to multiple vehicles heading towards me I always feel like I am driving remarkably slowly and much slower than most drivers tend to do.
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Postby WhoseGeneration » Fri Aug 30, 2013 11:11 pm


gcl2013 wrote:A common rule I hear is that at night you should only drive at a speed that would enable you to stop within the distance your headlights show to be clear. I have read the distance you can see with dipped headlights is between 30 and 40 metres.

If this is correct then based on the stopping distances given in the highway code, whenever it is necessary to use dipped beam due to oncoming traffic in the distance it would only be safe to drive on a straight road at between 30 and 40mph.

I just wondered if other drivers on this forum do this too because in practice when doing 40mph or less on an unlit NSL road for a prolonged time due to multiple vehicles heading towards me I always feel like I am driving remarkably slowly and much slower than most drivers tend to do.


Now you realise why rally cars competing on night stages have lots of lighting.
Doesn't help you on public roads though but this situation is one where being very observant can help.
Which means using all sources of illumination, yours and those towards without looking directly into the lights of those towards, whilst using your main beam at every opportunity without upsetting those towards.
It is hard and requires practice and concentration.
Our eyes, basically, have not evolved to deal with this. Walking or running in the totally dark, yes and females are better evolved than males.
Try it, go somewhere in the countryside with no light pollution, after about 20 minutes you'll see so much.
Always a commentary, spoken or not.
Keeps one safe. One hopes.
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Postby TripleS » Sat Aug 31, 2013 8:07 am


WhoseGeneration wrote:...go somewhere in the countryside with no light pollution, after about 20 minutes you'll see so much.


Aye, you might find some aged idiot trying to prove he can still do a 21 mile walk. :P

Hehe, still OT for the mo., I did Scarborough to Ravenscar (approx. 12 miles along the old railway line) a couple of weeks ago in 3 hrs. 15 mins. I got it down to 3 hrs. yesterday, but I don't think I can improve on that by much. :(

OK, back to night driving. It is difficult to maintain a good pace at night when you're having to go from main beam to dipped beam, but as WG says, there are things you can do to help matters. Even so, I'd guess most of us take too much on trust in the dark :wink: but as far as driving is concerned it is all too easy to find yourself going too quickly at night, no matter how diligent we try to be.

Best wishes all,
Dave.
Last edited by TripleS on Sat Aug 31, 2013 12:03 pm, edited 1 time in total.
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Postby Gareth » Sat Aug 31, 2013 9:16 am


gcl2013 wrote:I just wondered if other drivers on this forum do this too because in practice when doing 40mph or less on an unlit NSL road for a prolonged time due to multiple vehicles heading towards me I always feel like I am driving remarkably slowly

There are a number of points that may make a difference to how you think about this.

As has already been said, the default for night driving is main beam, only dipping where necessary.

Consider the pool of light provided by dipped beam. You can see further if you are looking above the furthest directly illuminated point on the ground. You can mostly use peripheral vision for the brighter area and concentrate your vision on what is dimly lit.

You can also gather information from other light sources. This can include silhouettes of static or moving objects shown up by the lights of on-coming vehicles, and reflections of lights of on-coming vehicles such as kerb-stones.

Finally you can use the information you have already gathered for a limited period when it is no longer directly visible, such as when you have to dip your lights for an on-coming vehicle.
there is only the road, nothing but the road ...
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Postby gcl2013 » Sun Sep 01, 2013 11:58 am


Many thanks for the useful suggestions. Will take your advice on board.
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Postby WhoseGeneration » Mon Sep 02, 2013 8:03 pm


gcl2013 wrote:Many thanks for the useful suggestions. Will take your advice on board.


Something else and please don't see this as being critical but when did you last have your eyesight tested? It's worth asking whoever tests you to comment upon your potential night vision. Some, unfortunately, don't have very good night vision.

When I was an IAM Observer I always used to, carefully, ask this of Associates and always take them for at least one night session, so I could get a feel for their ability in that situation.
Always a commentary, spoken or not.
Keeps one safe. One hopes.
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Postby gcl2013 » Sun Sep 08, 2013 2:19 pm


WhoseGeneration wrote:
gcl2013 wrote:Many thanks for the useful suggestions. Will take your advice on board.


Something else and please don't see this as being critical but when did you last have your eyesight tested? It's worth asking whoever tests you to comment upon your potential night vision. Some, unfortunately, don't have very good night vision.

When I was an IAM Observer I always used to, carefully, ask this of Associates and always take them for at least one night session, so I could get a feel for their ability in that situation.


I have my eyes tested regularly but I wear glasses and think that could be part of the problem. When I get a new pair I will probably ask for an anti reflective coating like this: http://www.specsavers.co.uk/offers/free ... -treatment.
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