Effects on Driver Speeds of In-Lane Rumble Strips on Approaches to ...

More documents

Recommendations

Info

Site 1 Table 8. Example Site Comparison of Before and After Speed Profiles. Findings Graphs 80 Speeds in the after period were noticeably lower (4 mph) between the rumble strips. Inside 500 ft the two profiles are very similar. The difference in mean speed was found to be statistically significant only at 300 ft. 85th Percentile Speed (mph) 70 60 50 40 30 After Speed 20 Before Speed Rumble Strip Set 1 10 Rumble Strip Set 2 Stop Ahead Sign 0 0 200 400 600 800 1000 1200 1400 1600 Distance From Stop Line (ft) The test for significance at each site revealed mixed results. Four of the 11 sites had a statistically significant increase in speeds at a minimum of two 100 ft (30.5 m) increments. The before and after speeds at three of the sites had either one location or no locations with any significant change in speed. The remaining four sites all had statistically significant decreases in speeds at a minimum of two 100 ft (30.5 m) increments. Aggregate Comparisons Because of the differences in location and number of rumble strip patterns, all 11 sites were not combined for an aggregate test. Those five sites with two sets of staggered rumble strips where the downstream set of strips was between 750 and 900 ft (228.6 and 274.3 m) from the stop line were combined (see Table 5). Their mean speeds were compared based on the distance relative to the upstream rumble strip. These sites from the Abilene and Dallas areas provided a more homogeneous sample of sites to use as a basis for testing. The results from testing mean speeds from the subset revealed that all of the differences in speed greater than 1.0 mph (1.6 km/h) were statistically significant at both the 0.05 and 0.01 levels of significance. Table 9 shows the variables and results for this aggregate test, and Figure 4 illustrates the mean speeds graphically, with distances adjusted to the upstream rumble strip. The negative distances in Table 9 are downstream of the rumble strip. Table 9 illustrates that differences in mean speeds were statistically significant at the 95 percent level of confidence for all distances 100 ft (30 m) upstream to 1200 ft (366 m) downstream of the upstream set of rumble strips. Furthermore, the largest difference in mean speeds occurred between the two sets of rumble strips. The next largest difference in mean speeds occurred approximately 300 ft (91 m) before the stop line. Figure 4 illustrates that the greatest difference between before and after mean speeds is found between the two sets of rumble strips, as much as 5 mph (8 km/h). Downstream of the rumble strips, the difference is not as large (between 1 and 2 mph [1.6-3.2 km/h]), until about 1000 ft (305 m), when the difference increases again to about 3 mph (4.8 km/h).
Distance from Rumble Strip (ft)* Number of Observations Before Table 9. Results of Test for Statistical Significance. Number of Observations After Standard Deviation Before (mph) Standard Deviation After (mph) Mean Before (mph) Mean After (mph) Mean Difference (mph) Significant at 0.05? -1300 44 40 2.0 2.9 6.9 7.6 -0.7 N/A -1200 369 378 6.9 6.4 17.7 14.5 3.2 Yes -1100 628 529 9.1 8.3 25.6 23.5 2.1 Yes -1000 537 496 7.2 7.9 35.0 31.9 3.0 Yes -900 540 474 6.5 6.6 40.5 38.3 2.2 Yes -800 573 501 6.7 6.4 43.5 42.1 1.4 Yes -700 620 483 6.5 6.9 45.7 43.8 2.0 Yes -600 617 558 7.3 7.4 47.0 45.6 1.4 Yes -500 629 563 7.2 7.8 48.4 46.6 1.8 Yes -400 514 600 7.6 8.0 49.3 46.7 2.6 Yes -300 306 557 8.9 7.9 51.1 49.0 2.2 Yes -200 218 515 9.9 8.3 53.0 50.5 2.5 Yes -100 148 542 10.3 8.0 55.2 50.2 5.0 Yes 0 101 532 10.1 8.0 54.5 50.5 4.0 Yes 100 48 492 12.0 8.1 52.1 51.4 0.7 N/A *A range of + 25 ft. Note: 1 mph = 1.6 km/h; 1 ft = 0.305 m 80 70 60 Mean Speed (mph) 50 40 30 20 10 After Speed Before Speed Upstream RS Approx. Downstream RS 0 -1400 -1200 -1000 -800 -600 -400 -200 0 200 Distance From Upstream Rumble Strip (ft) (1 mph = 1.61 km/h, 1 ft = 0.305 m) Figure 4. Comparison of Mean Speeds Relative to Upstream Rumble Strip (RS).
Page 1 and 2: Effects on Driver
Page 3 and 4: distance of the 85 th speed percent
Page 5 and 6: Deceleration Behavior The 1993 synt
Page 7 and 8: motorists to proceed through a Stop
Page 9 and 10: Before data were collected when the
Page 11: DISCUSSION OF RESULTS Site-by-Site
Page 15: Authors’ Information: Marcus A. B

Effects on Driver Speeds of In-Lane Rumble Strips on Approaches to ...

Create successful ePaper yourself

Delete template?

Save as template?