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The effect of rainfall on freeway travel speeds
Abstract
Studies on the effect of rainfall on freeway capacity found that capacity during wet conditions was 8 percent to 24 percent lower than average capacity during dry conditions. Based on these findings, Greenshield's speed-flow model was calibrated with hypothetical free-flow speed and j am density parameters to predict speed during wet and dry conditions. The model predicted lower wet speeds than dry speeds for given volumes, and differentials increased as volume approached wet capacity. At volumes exceeding wet capacity, the differential decreased until dry speed at dry capacity was equal to wet speed at wet capacity. Wet and dry speed data were collected during September 1995 along US 290 in Houston and analyzed with analysis of variance tests. Wet and dry speed differentials were quantified over different volume regimes. Assumptions about the volume regimes were based on the time of day of data collection. The evening period represented the lowest volume regime, the mid-day period represented a mid-level regime, and the PM peak period represented volumes at or near capacity. Wet and dry speed differentials ranged from 1.7 kph to 6.3 kph and averaged 4.8 kph for evening data. Differentials ranged from 10.7 kph to 16.3 kph and averaged 13.1 kph for mid-day data. Average wet speeds were 0.2 kph to 37.9 kph lower than average dry speeds for the peak period, and the average differential was 13.9 kph. Assuming that volume increases from each period to the next, these findings suggest that differentials do increase as volume approaches wet capacity. However, it is difficult to determine if differentials during the peak period behaved according to the model without observing continuous volume data. The magnitudes of mid-day and peak period rainfall events were also greater than those observed during the evening period, and this may have resulted in increased differentials. The findings suggest that rainfall can have a statistically significant negative effect on speed data. Additional study is recommended to illustrate the relationship between wet and dry speeds and continuous volume data and to study the effect of increasing rainfall magnitude. If statistically significant differentials are quantified, the results can be applied to develop more accurate historical speed profiles and robust incident detection algorithms.
Description
Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.Includes bibliographical references: p. 104-106.
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Citation
Holdener, Douglas Joseph (1997). The effect of rainfall on freeway travel speeds. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1997 -THESIS -H654.
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