Speed data collected on an urban roadway yielded a standard deviation in speeds of 4.8 mi/h. (a) If an engineer wishes to estimate the average speed on the roadway at a 95% confidence level so that the estimate is within 2 mi/h of the true average, how many spot speeds should be collected? (b) If the estimate of the average must be within 1 mi/h, what should the sample size be?

Traffic and Highway Engineering
5th Edition
ISBN:9781305156241
Author:Garber, Nicholas J.
Publisher:Garber, Nicholas J.
Chapter4: Traffic Engineering Studies
Section: Chapter Questions
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Speed data collected on an urban roadway yielded a standard deviation in speeds of 4.8 mi/h. (a) If an engineer wishes to estimate the average speed on the roadway at a 95% confidence level so that the estimate is within 2 mi/h of the true average, how many spot speeds should be collected? (b) If the estimate of the average must be within 1 mi/h, what should the sample size be?
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