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Citation |
Seneviratne PN, Islam MN. Transp. Res. Rec. 1992; 1375: 37-43. |
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Copyright |
(Copyright © 1992, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing) |
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DOI |
unavailable |
PMID |
unavailable |
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Abstract |
Estimates of expected 85th percentile speed, E(P sub 85), are essential for highway engineering and traffic control. Often, however, E(P sub 85) differs from observed P sub 85 after the facility is fully operational because of several reasons, including the errors stemming from the model and statistical uncertainty. Data from a series of spot speed surveys suggest that the proportion of all vehicles contravening the respective limits on local roads, arterials, and freeways is as high as 90%, and when heavy vehicles are considered separately, the exceeding proportions change little, if any. It is suggested that this is rendering control devices, which are in certain cases based on inaccurate estimates of E(P sub 85), inadequate for the prevailing operating conditions. While errors from approximating speed distributions by the normal model (model uncertainty) may be easily minimized, unavailability or unreliability of data due to constraints surrounding transportation agencies and statistical uncertainty is not easily eliminated by the conventional practices. Bayesian estimates based on sample and prior (assumed or subjective) parameters are an effective method of reducing errors and data requirements. Language: en |