Transportation: Which is more significant in reducing free flow speed on a freeway, narrower lanes or...

Transportation: Which is more significant in reducing free flow speed on a freeway, narrower lanes or a narrower right side shoulder? Does this make sense to you? Why?

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Expert Solution

Narrowing the lanes can cause traffic to slow down as this will reduce level of psychological comfort of driver so that drivers will slow down the vehicles due to chances of accidents. Hence there will be decrease in Free Flow Speed. Right shoulder clearance also known as lateral clearance if decreased then there will be decrease in free flow speed due to increase in discomfort of the driver.

When comparing both, effect of narrowing lanes will be higher in decreasing free flow speed as it will effect drivers moving in all lanes. Whereas, decreasing right side shoulder width will effect only driver moving in right side lane. Therefore narrow lanes are more significant than narrow right side shoulder in reducing Free Flow speed.

Same effect can be observed from Highway capacity manual where decrease of lane width by 1ft reduce the FFS by 1.9 mile per hour and decrease right shoulder by 1ft decrease FFS by 0.1 to 0.6 mile per hour depending upon number of lanes in one direction.

Ally Wells answered 5 months ago

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