The National Academies Press

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Pages 185-207

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From page 185... ... 185 Field Speed Study A P P E N D I X D Study Objective The objective of the study was to quantify the effects of RPMs on a motorist's speed. The desired goal was to study roadways where only RPMs were replaced in order to isolate the effects of RPMs. Read the entire page →
From page 186... ... 186 Performance Criteria for Retroreflective Pavement Markers lighting on this road. Road tubes were placed over 1,000 ft from the start of the curve. Read the entire page →
From page 187... ... Field Speed Study 187 Farm to Market Road 2517 Counters were placed at two data collection sites on FM 2517: one location was on a tangent segment, and the other location was at a horizontal curve. This road is a two-lane rural highway with a speed limit of 75 mph. Read the entire page →
From page 188... ... 188 Performance Criteria for Retroreflective Pavement Markers degree of curvature. The curve has a steep drop-off for vehicles traveling through the outside of the curve. Read the entire page →
From page 189... ... Field Speed Study 189 State Highway 47 SH 47 is a four-lane highway with a speed limit of 75 mph. The facility has higher traffic volumes compared to FM 1971 and FM 2517. Read the entire page →
From page 190... ... 190 Performance Criteria for Retroreflective Pavement Markers Figure D-5. Data collection sites for SH 21 (Map Data: Google) Read the entire page →
From page 191... ... Field Speed Study 191 Table D-1. Summary of data collection sites. Read the entire page →
From page 192... ... 192 Performance Criteria for Retroreflective Pavement Markers temperature, and weather condition (e.g., cloudy, foggy) Read the entire page →
From page 193... ... Field Speed Study 193 Descriptive Statistics The raw data from the road tubes had entries for unclassified vehicles (i.e., no axle count) and entries with no speed recorded. Read the entire page →
From page 194... ... 194 Performance Criteria for Retroreflective Pavement Markers Figure D-6. Box plot of initial database. Read the entire page →
From page 195... ... Field Speed Study 195 Table D-5. Final database speed statistics. Read the entire page →
From page 196... ... 196 Performance Criteria for Retroreflective Pavement Markers Table D-6. Speed statistics according to daytime and nighttime conditions. Read the entire page →
From page 197... ... Field Speed Study 197 highest. After RPMs were replaced, the 85th percentile speed was similar to the 85th percentile speed observed during the day. Read the entire page →
From page 198... ... 198 Performance Criteria for Retroreflective Pavement Markers SH 47 NB Tangent 71.09 71.99 0.90 0.00001* SH 47 SB Tangent 71.86 70.13 -1.73 < 0.00001* Read the entire page →
From page 199... ... Field Speed Study 199 analyzed nighttime data under wet-weather conditions. The second model used data for SH 47 because there was no rain event in the after period of the study for SH 21. Read the entire page →
From page 200... ... 200 Performance Criteria for Retroreflective Pavement Markers from SH 47. The average speed of the subset was 70.49 mph, and the median value was 71. Read the entire page →
From page 201... ... Field Speed Study 201 Normally distributed data plots a roughly straight line on a Q-Q plot. The line shown in Figure D-8 is roughly straight, meaning that the data are adequate for linear regression. Read the entire page →
From page 202... ... 202 Performance Criteria for Retroreflective Pavement Markers Figure D-9. Histogram of the speeds for wet, nighttime data for four-lane highways. Read the entire page →
From page 203... ... Field Speed Study 203 The model coefficient shows that speeds would be 0.013 mph slower with barely visible or no RPMs. This coefficient was not statistically significant in the model. Read the entire page →
From page 204... ... 204 Performance Criteria for Retroreflective Pavement Markers Linear Regression Model for Two-Lane Rural Highways, Nighttime Conditions The sites at FM 2517 and FM 1917 were used in the analysis. Speed data were taken at three different sites on two different roads, allowing for geometric factors such as lane width and shoulder width to be used in the model. Read the entire page →
From page 205... ... Field Speed Study 205 LW = lane width of the travel lane (ft) Read the entire page →
From page 206... ... 206 Performance Criteria for Retroreflective Pavement Markers Figure D-12. Q-Q plot for two-lane rural road linear regression model. Read the entire page →
From page 207... ... Field Speed Study 207 The ANOVA showed that there was a significant difference in average speeds during nighttime under clear weather conditions. The statistically significant conditions were observed on four-lane highways, and on two-lane rural roads where the speed limit was 75 mph. Read the entire page →

From page 185...

... 185 Field Speed Study A P P E N D I X D Study Objective The objective of the study was to quantify the effects of RPMs on a motorist's speed. The desired goal was to study roadways where only RPMs were replaced in order to isolate the effects of RPMs.