Speed Limits - 85 percentile

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Re: Speed Limits - 85 percentile

Postby Strawburger » Thu Oct 18, 2012 6:26 pm

mikesbytes wrote:Straight line reaction and braking distance is a documented metric. Using this example, how is the required stopping distance on a piece of road determined?


Going from memory here, I will look it up when i am back at work.

Reaction time is set depending on type of road and surrounding either 1.5 or 2.5 seconds), then the stopping distance looks at type of road surface, vehicle type and weight, rate of deceleration then there is a slope (grade) of road factor. Once you have that distance then you need to calculate that distance linearly to the road geometry (which is generally curved) from the drivers eye height (varies between states of aust but between 1.1m and 1.2m from the ground) and eye offset from lane (usually 1.5m) to the linear object target which in this example is 0.2m (but can vary depending on what is calculated : object height, lane line height 0.0m, tail light which is 0.6m or vehicle which is eye height and all these values change the calculated distances).

Does that cover what you are asking?
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by BNA » Thu Oct 18, 2012 8:26 pm

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Re: Speed Limits - 85 percentile

Postby tubby74 » Thu Oct 18, 2012 8:26 pm

For the example of Anzac bridge I was thinking weekend and off peak times when traffic is flowing, its always well over the speed limit. Obviously at peak times neither the speed limit nor a drivers own choice is the limiting factor in speed.
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Re: Speed Limits - 85 percentile

Postby mikesbytes » Tue Oct 23, 2012 10:35 am

Strawburger wrote:
mikesbytes wrote:Straight line reaction and braking distance is a documented metric. Using this example, how is the required stopping distance on a piece of road determined?


Going from memory here, I will look it up when i am back at work.

Reaction time is set depending on type of road and surrounding either 1.5 or 2.5 seconds), then the stopping distance looks at type of road surface, vehicle type and weight, rate of deceleration then there is a slope (grade) of road factor. Once you have that distance then you need to calculate that distance linearly to the road geometry (which is generally curved) from the drivers eye height (varies between states of aust but between 1.1m and 1.2m from the ground) and eye offset from lane (usually 1.5m) to the linear object target which in this example is 0.2m (but can vary depending on what is calculated : object height, lane line height 0.0m, tail light which is 0.6m or vehicle which is eye height and all these values change the calculated distances).

Does that cover what you are asking?


Yes, except I suspect that the type of car wouldn't be in the calculation, as they would need to use the poorest performing vehicle for the calcuation
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