Speed averaging cameras

[obi_waynne]

If the posted limit is 50 would a camera be triggered (assuming it is set for a zero tolerance at exactly 50) in the following scenario.

1. Over a 4 mile distance, 2 miles are covered at 60 and 2 miles are covered at 40!
2. What about if half the time you were doing 60 and the other half of the time you did 40?

This is quite a perplexing maths question which I thought was easily answered but the more I think about it the less convinced I am.

 

[TCJBOLDIE]

They are used on our major highways to monitor heavy transport vehicles. Am unsure if they also check cars.
Will leave the math to the resident boffins

 

[HDi fun]

1. 2 minutes at 60mph covers 2 miles. 3 Minutes at 40mph covers the next 2 miles. Average speed 48mph.

Will go and look at the next bit.................. I am thinking that given the 4 mile distance is fixed then you would average 50mph if driving half the time at 40mph and half the time at 60mph.

Same as if you drove half the time at 5mph and the other half the time at 105mph??

 

[obi_waynne]

I can't really fault your logic. I wouldn't be totally convinced its correct but I was thinking along similar lines.

Speed average = average speed over distance but speed is also a function of time in MPH! The more I think about this the more my head wants to explode!

So as long as you cover the distance in the time it would expect at the posted limit you should be ok! But it's not a simple as doing scenario 1 - the time at speed is critical as you cover different distances.

I'll just mark your answer as correct then!

 

[HDi fun]

Waynne, in situation 2 the distance is immaterial.

Drive for 11 hours at 60mph and then another 11 hours at 40 mph and you will have averaged 50mph over 22 hours.

 

[herb]

What's saying the distance between cameras is 4 miles?

The easiest thing to do is either set the cruise control to 50mph or use the speed limiter set at 50mph that way there is no risk of a speeding ticket

 

[HDi fun]

What's saying the distance between cameras is 4 miles?

The easiest thing to do is either set the cruise control to 50mph or use the speed limiter set at 50mph that way there is no risk of a speeding ticket

Yes, but that's not the point of the question. Waynne suggested 4 miles by way of example. That's all.

 

[herb]

Yes, but that's not the point of the question. Waynne suggested 4 miles by way of example. That's all.

But if you were going to speed then drive slow to get to the exact speed you need you would need to know the exact distance between cameras to make this applicable

 

[HDi fun]

But if you were going to speed then drive slow to get to the exact speed you need you would need to know the exact distance between cameras to make this applicable

I know. Waynne has arbitrarily suggested 4 miles by way of example. Same answer from me to the same question from you.

You're missing the point totally.

 

[obi_waynne]

It was intended as a maths questions to get people to think about average speed cameras and how they work. If you drift over the posted limit for a certain distance you should reduce your speed accordingly for the same distance to make up the difference.

These things pop into my head when I'm driving along and sometimes they stick with me and I talk myself out of the solution i've worked out.