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From page 41... ... In summary, reliable estimates of the safety effectiveness of shoulder rumble strips for different roadway types are not available, and in all likelihood the safety beneﬁts of shoulder rumble strips vary by roadway type because the different types of roadways are built to varying standards (e.g., lane widths, shoulder widths, roadside) , accommodate varying traffic volumes and distributions, serve different driver populations, and accommodate a range of operating speeds. Read the entire page →
From page 42... ... This section describes the general scope of the safety evaluation conducted to resolve these issues, the site selection process, the videolog data collection procedures, the database development, the analysis approach, and the analysis results. Scope of Safety Evaluation The primary objectives of the safety evaluation conducted as part of this research are to do the following: • Quantify the safety effectiveness of milled shoulder rumble strips on speciﬁc types of roads including urban freeways, urban multilane divided highways (nonfreeways) Read the entire page →
From page 43... ... A list of selection criteria was provided and explained to the DOTs in an effort to develop a list of treatment sites that could be used in a before-after safety evaluation. The following were selection criteria for identifying candidate treatment sites: • Roadway type -- Identify locations along the following roadway types where shoulder rumble strips have been installed: – Urban freeways, – Urban multilane divided highways (nonfreeways) Read the entire page →
From page 44... ... 0.00 0.61 66.6827.482sdaorenal-owtlaruR 55.75308.925sepytyawdaorllassorcaslatoT Table 10. Total mileage of Minnesota treatment and nontreatment sites considered for inclusion in the safety evaluation of shoulder rumble strips. Read the entire page →
From page 45... ... considered for inclusion in the safety evaluation of shoulder rumble strips. Based on the total mileage of both treatment and nontreatment sites across all three states, Table 13 suggests that analyses of the data for urban freeways, rural freeways, rural multilane divided Roadway type Treatment sites (mi) Read the entire page →
From page 46... ... 0.00 0.00 Rural two-lane roads 23.34 99.49 Totals across all roadway types 164.94 177.84 Table 12. Total mileage of Pennsylvania treatment and nontreatment sites considered for inclusion in the safety evaluation of shoulder rumble strips. Read the entire page →
From page 47... ... Similarly, none of the sites included in the safety evaluation include centerline rumble strips. When conﬁrming the presence of the milled shoulder rumble strip at a site, the beginning and ending locations of the milled shoulder rumble strips were recorded. Read the entire page →
From page 48... ... Only those treatment sites where shoulder rumble strips were not installed over a very long stretch of highway were the boundaries of the treatment sites modiﬁed to reﬂect numerous or signiﬁcant breaks in the continuous shoulder rumble strips. Based purely on observation, the urban treatment sites tended to have more natural breaks within the sites compared to the rural treatment sites. Read the entire page →
From page 49... ... Thus, the locations of some of the treatment sites in Pennsylvania were initially identiﬁed as being high-crash locations compared to the rest of the highway network. For the other treatment sites included in the safety evaluation but not initially identiﬁed through the low-cost safety improvement database, the rumble strips may or may not have been installed as part of a broader proactive safety policy to install shoulder rumble strips on certain types of roadways. Read the entire page →
From page 50... ... Because of insufﬁcient number of sites and mile-years or lack of comparison sites for a number of roadway types and states to conduct the safety evaluation, it was decided to focus the safety evaluation of shoulder rumble strips on the following four categories: • Urban freeways in Pennsylvania only; • Rural freeways in Missouri and Pennsylvania only; • Rural multilane divided highways (nonfreeways) in all three states; and • Rural two-lane roads in all three states. Read the entire page →
From page 51... ... CS-RS 3 2.88 13.49 0 0 SRoN-AB BA-RS 0 0 0 CS-No RS 2 1.90 17.08 1 1.92 19.20 1 0.46 4.58 Urban multilane undivided highways (nonfreeways) CS-RS 0 0 0 19.699.6SRoN-AB BA-RS 1 1.40 4.19 0 3 1.23 3.69 CS-No RS 0 3 3.15 31.50 29 26.88 261.60 Urban two-lane roads CS-RS 1 1.01 5.06 0 0 SRoN-AB 313.00 80.09 BA-RS 0 29 52.08 156.00 18 15.43 57.02 CS-No RS 8 23.42 210.75 6 7.91 79.20 16 25.23 245.60 Rural freeways CS-RS 28 109.15 495.67 12 25.65 77.90 41 55.40 146.30 BA-No RS 100.00 109.00 32.57 BA-RS 6 20.00 60.00 14 19.11 51.20 5 4.18 4.61 CS-No RS 27 73.17 658.49 12 15.04 150.00 8 3.43 32.88 Rural multilane divided highways (nonfreeways) Read the entire page →
From page 52... ... Due to the lack of variability in either shoulder widths within a given roadway type and/or due to a high correlation with roadside hazard ratings, it was decided to exclude shoulder width from all modeling efforts. The use of RHRs discussed below addresses how shoulder width information is being captured in the statistical models. Read the entire page →
From page 53... ... Rumble strip offset, measured in inches, is available for treatment sites only. A preliminary check of offset measurements on a continuous scale led to considering this variable as a categorical variable in two ways for the statistical analysis: • Two categorical levels: – Edgeline rumble strips (i.e., offset distances of 0 to 8 in. Read the entire page →
From page 54... ... Crash data. Four crash types are considered in the safety evaluation of shoulder rumble strips: 1. Read the entire page →
From page 55... ... Analyses of TOT crashes are performed primarily because several previous safety evaluations of shoulder rumble strips analyzed this crash type. However, analyses of TOT crashes include many other crash types besides SVROR crashes (i.e., the target crash type) Read the entire page →
From page 56... ... Distribution of inside shoulder width by state and site type. crashes because the analyses include only those crashes expected to be most directly impacted by shoulder rumble strips. Read the entire page →
From page 57... ... Comparisons of the crash frequencies are made separately for each state and across states for three of the four roadway types of interest. The following two statistical approaches are used to evaluate whether installing shoulder rumble strips has an effect on crash frequencies: 58 Outside RHR Roadway type State Site type Number of sites Minimum Maximum Mean Standard deviation BA 53 1.0 4.0 3.3 0.7 CS-No RS 37 1.0 5.0 3.6 1.0 Urban freeways PA CS-RS 48 2.7 4.0 3.6 0.4 BA 29 2.0 4.0 3.0 0.5 CS-No RS 6 3.0 3.7 3.2 0.3 MO CS-RS 12 2.0 4.0 3.0 0.4 BA 18 2.0 4.0 3.4 0.6 CS-No RS 16 2.0 4.0 3.2 0.7 Rural freeways PA CS-RS 41 2.2 4.1 3.6 0.5 BA 6 2.0 2.0 2.0 0.0 CS-No RS 27 2.0 4.0 2.9 0.9 MN CS-RS 27 1.0 3.3 2.2 0.6 BA 14 2.0 3.1 2.9 0.4 CS-No RS 12 2.0 4.0 3.0 0.7 MO CS-RS 1 3.0 3.0 3.0 BA 5 3.0 4.0 3.5 0.5 CS-No RS 8 2.8 4.4 3.5 0.6 Rural multilane divided highways (nonfreeways) Read the entire page →
From page 58... ... Before-After EB Analysis to Determine the Safety Effectiveness of Shoulder Rumble Strips on Different Roadway Types The EB method is now the most widely used method to evaluate the safety effectiveness of a countermeasure given a set of matched before-after sites and a set of reference sites. The EB method, which adjusts for the effects of regression to the mean, is based on the comparison of observed crash frequencies in the after period to predicted crash frequencies in the after period had the treatment not been implemented. Read the entire page →
From page 59... ... or shoulder with (ft) a Number of sites 4+ 100 Non-edgeline 0-4 1 4+ 82 Urban freeways PA No rumble strips 0-4 8 Edgeline 4+ 24 Non-edgeline 4+ 17 MO No rumble strips 4+ 35 Edgeline 4+ 4 4+ 53 Non-edgeline 0-4 2 4+ 32 Rural freeways PA No rumble strips 0-4 2 Edgeline 4+ 7 Non-edgeline 4+ 26 MN No rumble strips 4+ 33 4+ 4 Edgeline 0-4 1 Non-edgeline 4+ 10 4+ 25 MO No rumble strips 0-4 1 Edgeline 4+ 1 Non-edgeline 4+ 8 4+ 12 Rural multilane divided Highways (nonfreeways) Read the entire page →
From page 60... ... Total number of crashes Crash frequency (crashes/ mi/yr) 27.013146.189272.113288.242520.281SRoNBA RS 53 35.51 129.58 394 3.04 162 1.25 198 1.53 97 0.75 No RS 37 19.88 194.52 1,325 6.81 648 3.33 556 2.86 265 1.36 Urban freeways PA CS RS 48 28.44 103.98 601 5.78 314 3.02 281 2.70 143 1.38 97.084279.171633.171432.4423,170.313SRoNBA RS 29 52.08 155.69 827 5.31 241 1.55 300 1.93 115 0.74 No RS 6 7.91 79.15 310 3.92 102 1.29 177 2.24 63 0.80 MO CS RS 12 25.65 77.90 200 2.57 64 0.82 107 1.37 42 0.54 56.02543.170157.00626.103190.08SRoNBA RS 18 15.43 57.02 107 1.88 44 0.77 63 1.10 28 0.49 No RS 16 25.23 245.62 429 1.75 207 0.84 273 1.11 136 0.55 Rural freeways PA CS RS 41 55.40 146.29 302 2.06 126 0.86 215 1.47 102 0.70 02.00233.03303.00327.02700.001SRoNBA RS 6 20.00 60.00 59 0.98 16 0.27 28 0.47 10 0.17 No RS 27 73.17 658.49 1,770 2.69 550 0.84 567 0.86 248 0.38 MN CS RS 27 103.32 508.56 1,205 2.37 373 0.73 476 0.94 193 0.38 46.00731.132199.080124.246220.901SRoNBA RS 14 19.11 51.18 196 3.83 66 1.29 114 2.23 44 0.86 No RS 12 15.04 150.37 458 3.05 122 0.81 152 1.01 65 0.43 MO CS RS 1 2.32 2.32 5 2.16 2 0.86 3 1.29 2 0.86 04.03170.15385.09144.17475.23SRoNBA RS 5 4.18 4.61 6 1.30 2 0.43 4 0.87 2 0.43 No RS 8 3.43 32.88 113 3.44 62 1.89 79 2.40 48 1.46 Rural multilane divided highways (nonfreeways) Read the entire page →
From page 61... ... Total number of crashes Crash frequency (crashes/ mi/yr) Nonedgeline edgeline edgeline edgeline edgeline edgeline edgeline 53 35.51 129.58 394 3.04 162 1.25 198 1.53 97 0.75 BA No RS 53 35.51 182.02 524 2.88 231 1.27 298 1.64 131 0.72 Non- 48 28.44 103.98 601 5.78 314 3.02 281 2.70 143 1.38 Urban freeways PA CS No RS 37 19.88 194.52 1,325 6.81 648 3.33 556 2.86 265 1.36 Edgeline 16 28.42 47.10 288 6.11 68 1.44 114 2.42 41 0.87 Non- 13 23.66 108.58 539 4.96 173 1.59 186 1.71 74 0.68 BA No RS 29 52.08 313.07 1,324 4.23 417 1.33 617 1.97 248 0.79 Edgeline 8 13.46 16.97 85 5.01 23 1.36 35 2.06 9 0.53 Non- 4 12.19 60.93 115 1.89 41 0.67 72 1.18 33 0.54 MO CS No RS 6 7.91 79.15 310 3.92 102 1.29 177 2.24 63 0.80 Edgeline 3 3.14 3.14 2 0.64 1 0.32 1 0.32 0 0.00 Nonedgeline 15 12.29 53.88 105 1.95 43 0.80 62 1.15 28 0.52 BA No RS 18 15.43 80.09 130 1.62 60 0.75 107 1.34 52 0.65 Edgeline 1 0.94 1.89 1 0.53 0 0.00 0 0.00 0 0.00 Non- 40 54.46 144.40 301 2.08 126 0.87 215 1.49 102 0.71 Rural freeways PA CS No RS 16 25.23 245.62 429 1.75 207 0.84 273 1.11 136 0.55 Edgeline 3 10.40 31.20 28 0.90 7 0.22 11 0.35 4 0.13 Nonedgeline 3 9.60 28.80 31 1.08 9 0.31 17 0.59 6 0.21 BA No RS 6 20.00 100.00 72 0.72 30 0.30 33 0.33 20 0.20 Edgeline 4 14.24 67.19 189 2.81 49 0.73 44 0.65 18 0.27 Non- 23 89.08 441.37 1,016 2.30 324 0.73 432 0.98 175 0.40 MN CS No RS 27 73.17 658.49 1,770 2.69 550 0.84 567 0.86 248 0.38 Edgeline 5 5.72 7.50 15 2.00 2 0.27 11 1.47 2 0.27 Non- 9 13.39 43.69 181 4.14 64 1.46 103 2.36 42 0.96 Rural multilane divided highways (nonfreeways) Read the entire page →
From page 62... ... Edgeline 1 1.16 1.16 3 2.59 1 0.86 1 0.86 1 0.86 Nonedgeline edgeline edgeline edgeline edgeline 4 3.02 3.45 3 0.87 1 0.29 3 0.87 1 0.29 BA No RS 5 4.18 32.57 47 1.44 19 0.58 35 1.07 13 0.40 Non- 4 1.18 2.35 6 2.55 2 0.85 3 1.28 1 0.43 PA CS No RS 8 3.43 32.88 113 3.44 62 1.89 79 2.40 48 1.46 Edgeline 19 62.33 174.00 116 0.67 38 0.22 19 0.11 6 0.03 Non- 9 33.18 111.68 104 0.93 32 0.29 24 0.21 9 0.08 BA No RS 28 95.51 478.41 296 0.62 100 0.21 61 0.13 24 0.05 Edgeline 42 140.01 655.58 413 0.63 141 0.22 154 0.23 74 0.11 Nonedgeline 11 39.20 196.02 98 0.50 33 0.17 23 0.12 14 0.07 MN CS No RS 28 86.66 776.29 515 0.66 199 0.26 162 0.21 76 0.10 Edgeline 1 3.80 3.80 3 0.79 0 0.00 1 0.26 0 0.00 Non- 4 6.72 26.88 70 2.60 15 0.56 32 1.19 6 0.22 BA No RS 5 10.52 63.97 77 1.20 27 0.42 41 0.64 19 0.30 Nonedgeline 1 2.33 2.33 2 0.86 0 0.00 0 0.00 0 0.00 MO CS No RS 32 77.20 771.97 1,630 2.11 567 0.73 499 0.65 207 0.27 Edgeline 15 18.38 59.97 79 1.32 54 0.90 39 0.65 24 0.40 Non- 5 4.96 9.92 7 0.71 2 0.20 2 0.20 0 0.00 BA No RS 20 23.34 136.18 171 1.26 101 0.74 118 0.87 64 0.47 Rural two-lane roads PA CS No RS 90 99.49 933.20 1,080 1.16 617 0.66 643 0.69 345 0.37 Read the entire page →
From page 63... ... 07.082127.013130.0646.189220.281SRoNBA RS 53 35.51 129.58 198 1.53 3 0.02 79 0.61 82 0.63 No RS 37 19.88 194.52 556 2.86 15 0.08 236 1.21 246 1.27 Urban freeways PA CS RS 48 28.44 103.98 281 2.70 42 0.40 111 1.07 133 1.28 57.053228.055274.064179.171670.313SRoNBA RS 29 52.08 155.69 300 1.93 51 0.33 108 0.69 103 0.66 No RS 6 7.91 79.15 177 2.24 26 0.33 76 0.96 82 1.04 MO CS RS 12 25.65 77.90 107 1.37 15 0.19 39 0.50 34 0.44 06.08416.09443.07243.170190.08SRoNBA RS 18 15.43 57.02 63 1.11 5 0.09 34 0.60 23 0.40 No RS 16 25.23 245.62 273 1.11 15 0.06 115 0.47 125 0.51 Rural freeways PA CS RS 41 55.40 146.29 215 1.47 15 0.10 125 0.85 90 0.62 31.03112.01250.0533.03300.001SRoNBA RS 6 20.00 60.00 28 0.47 1 0.02 24 0.40 5 0.08 No RS 27 73.17 658.49 567 0.86 14 0.02 308 0.47 266 0.40 MN CS RS 27 103.32 508.56 476 0.94 14 0.03 320 0.63 211 0.42 04.04454.09440.0431.132120.901SRoNBA RS 14 19.11 51.18 114 2.23 6 0.12 51 1.00 53 1.04 No RS 12 15.04 150.37 152 1.01 8 0.05 55 0.37 57 0.38 MO CS RS 1 2.32 2.32 3 1.29 1 0.43 2 0.86 1 0.43 34.04194.06130.0180.15375.23SRoNBA RS 5 4.18 4.61 4 0.87 1 0.22 2 0.43 1 0.22 No RS 8 3.43 32.88 79 2.40 12 0.37 40 1.22 33 1.00 Rural multilane divided highways (nonfreeways) PA CS RS 4 1.18 2.35 3 1.28 0 0.00 3 1.28 0 0.00 70.04360.07220.0731.01614.874SRoNBA RS 28 95.51 285.67 43 0.15 5 0.02 25 0.09 23 0.08 No RS 28 86.66 776.29 162 0.21 3 0.00 68 0.09 68 0.09 MN CS RS 53 179.21 851.60 177 0.21 10 0.01 119 0.14 77 0.09 41.0972.07160.0446.01479.36SRoNBA RS 5 10.52 30.67 33 1.08 3 0.10 19 0.62 8 0.26 No RS 32 77.20 771.97 499 0.65 26 0.03 160 0.21 192 0.25 MO CS RS 1 2.33 2.33 0 0.00 0 0.00 0 0.00 0 0.00 44.00653.08430.0478.081181.631SRoNBA RS 20 23.34 69.90 41 0.59 2 0.03 19 0.27 22 0.32 Rural two-lane roads PA CS No RS 90 99.49 933.20 643 0.69 28 0.03 281 0.30 322 0.35 Table 24. Read the entire page →
From page 64... ... A comparison of the three sets of results is discussed later in Analysis Results. Cross-Sectional Analysis to Determine the Impact of Rumble Strip Placement on the Safety Effectiveness of Shoulder Rumble Strips The analysis of the effect of rumble strip placement was performed using the same GLM approach used for the safety evaluation of shoulder rumble strips on different roadway types. Read the entire page →
From page 65... ... Estimating the Safety Effectiveness of Shoulder Rumble Strips on Different Roadway Types Before-After EB Analysis Results The EB analysis consisted of the following two steps: • Develop SPF models based on all nontreatment sites. • Using the SPFs, evaluate the safety effectiveness of shoulder rumble strips using crash data from the before-after sites only. Read the entire page →
From page 66... ... For each crash type, roadway type, and state, the safety effectiveness of shoulder rumble strips was estimated in accordance with the approach discussed earlier. The ﬁnal results are shown in Tables 25 through 28 for TOT, FI, SVROR, and SVROR FI crashes, respectively. Read the entire page →
From page 67... ... Table 26. Safety effectiveness of shoulder rumble strips on FI crashes using the EB method. Read the entire page →
From page 68... ... Table 27. Safety effectiveness of shoulder rumble strips on SVROR crashes using the EB method. Read the entire page →
From page 69... ... Cross-Sectional GLM Analysis Results The safety effectiveness of shoulder rumble strips was also evaluated using a repeated measures analysis of variance approach based on all treatment and nontreatment sites as discussed in the Analysis Approach part of this section. This approach takes advantage of crash information on all study sites of interest. Read the entire page →
From page 70... ... Table 30. Safety effectiveness of shoulder rumble strips on FI crashes based on all site types using the GLM method. Read the entire page →
From page 71... ... PA 17 125 –32.9 –61.3 16.4 0.18 Not significant at 90% CL Combined 257 2,124 –37.3 –54.3 –13.9 0.01 Significant at 95% CL MN 109 726 3.6 –26.4 45.7 0.85 Not significant at 90% CL MO 38 366 –59.4 –97.3 510.3 0.25 Not significant at 90% CL Rural two-lane roads PA 110 1,032 –37.4 –61.1 0.8 0.06 Significant at 90% CL Table 31. Safety effectiveness of shoulder rumble strips on SVROR crashes based on all site types using the GLM method. Read the entire page →
From page 72... ... Comparison of Results from the Different Analysis Approaches The previous discussion covers two statistical methods -- EB and GLM -- applied to three different sets of data to assess the safety effectiveness of shoulder rumble strips on different roadway types. A direct comparison of the three sets of results is presented in Tables 37 through 40 for the four crash types, respectively. Read the entire page →
From page 73... ... PA 13 117 –25.7 –59.6 36.4 0.37 Not significant at 90% CL Combined 203 1,871 –5.5 –27.7 23.5 0.65 Not significant at 90% CL MN 56 474 17.9 –0.6 39.7 0.09 Significant at 90% CL MO 37 365 –15.3 –86.2 421.0 0.74 Not significant at 90% CL Rural two-lane roads PA 110 1,032 –24.4 –48.1 10.1 0.14 Not significant at 90% CL Table 33. Safety effectiveness of shoulder rumble strips on TOT crashes based on before-after sites and nontreatment cross-sectional sites using the GLM method. Read the entire page →
From page 74... ... PA 13 117 –21.5 –47.4 17.1 0.32 Not significant at 90% CL Combined 203 1,871 –39.6 –59.5 –9.9 0.02 Significant at 95% CL MN 56 474 –22.6 –52.5 26.1 0.36 Not significant at 90% CL MO 37 365 –56.9 –97.4 617.0 0.29 Not significant at 90% CL Rural two-lane roads PA 110 1,032 –37.4 –61.1 0.8 0.06 Significant at 90% CL Table 35. Safety effectiveness of shoulder rumble strips on SVROR crashes based on before-after sites and nontreatment cross-sectional sites using the GLM method. Read the entire page →
From page 75... ... PA 5 –40.1 42.5 0.94 13 –43.8 –68.0 –1.2 0.10 17 –41.5 –65.4 –1.2 0.09 Combined 53 –8.0 8.0 0.99 203 –14.4 –34.1 11.2 0.23 257 –27.5 –42.4 –8.6 0.01 MN 28 5.1 12.7 0.41 56 7.0 –20.0 43.1 0.66 109 –12.7 –27.6 5.3 0.16 MO 5 –19.2 21.8 0.88 37 –35.4 –85.5 188.1 0.40 38 –39.7 –86.1 162.4 0.32 Rural two-lane roads PA 20 –18.0 11.6 1.55 110 –16.4 –45.6 28.5 0.36 110 –16.4 –45.6 28.5 0.36 Table 37. Comparison of results from three approaches to estimate safety effectiveness of shoulder rumble strips on TOT crashes. Read the entire page →
From page 76... ... PA 5 –19.9 56.9 0.35 13 –21.5 –47.4 17.1 0.32 17 –32.9 –61.3 16.4 0.18 Combined 53 –36.4 9.7 3.75 203 –39.6 –59.5 –9.9 0.02 257 –37.3 –54.3 –13.9 0.01 MN 28 –32.4 17.6 1.84 56 –22.6 –52.5 26.1 0.36 109 3.6 –26.4 45.7 0.85 MO 5 –44.6 23.2 1.93 37 –56.9 –97.4 617.0 0.29 38 –59.4 –97.3 510.3 0.25 Rural two-lane roads PA 20 –36.7 13.3 2.75 110 –37.4 –61.1 0.8 0.06 110 –37.4 –61.1 0.8 0.06 Table 39. Comparison of results from three approaches to estimate safety effectiveness of shoulder rumble strips on SVROR crashes. Read the entire page →
From page 77... ... In summary, the average safety effects of installing milled shoulder rumble strips on the following roadway types and 78 Read the entire page →
From page 78... ... . The two safety evaluations report similar expected reductions in SVROR due to shoulder rumble strips, while the results from this research indicate more than double the safety effectiveness of shoulder rumble strips in reducing SVROR FI crashes along rural two-lane roads compared to that reported by Patel et al. Read the entire page →
From page 79... ... Determine the Impact of Rumble Strip Placement on the Safety Effectiveness of Shoulder Rumble Strips The effect of shoulder rumble strip offset on SVROR FI crashes was evaluated based on all treatment and nontreatment sites using the approach discussed previously in the Analysis Approach part of this section. The analysis focused on SVROR FI crashes because this crash type and severity level yielded the most consistent results when analyzing the safety effectiveness of shoulder rumble strips on different roadway types. Read the entire page →
From page 80... ... Safety effectiveness of rumble strip placement on SVROR FI crashes based on all sites using GLM method. Read the entire page →
From page 81... ... The estimates for the percent change due to offset of a given distance are the following: • 28.8 percent reduction in SVROR FI crashes for edgeline rumble strips and • 8.9 percent reduction in SVROR FI crashes for non-edgeline rumble strips. For rural freeways, these results provide evidence that offset distance impacts the safety effectiveness of shoulder rumble strips. Read the entire page →
From page 82... ... Table 44 presents the results of the analyses designed to determine the impact that rumble strip placement measured at three levels has on the safety effectiveness of shoulder rumble strips. The two most interesting results from this analysis are for rural freeways (combined data) Read the entire page →
From page 83... ... Offset regression coefficient Estimate Lower 95% CL Upper 95% CL P-value Type 3 p-value 78.068.06.227.51–7.120.002-9999831APsyaweerfnabrU 0-8 –0.34 –28.8 –51.0 3.6 0.08d 9-20 –0.11 –10.4 –32.7 19.2 0.45 Combined 122 776 21+ –0.08 –7.4 –21.4 9.0 0.35 0.14 0-8 –0.28 –24.6 –49.5 12.6 0.17 9-20 –0.72 –51.1 –56.2 –45.4 <.001c15374OM 21+ 0.02 2.0 –13.1 19.8 0.81 0.13 0-8 9-20 Rural freeways PAb 52457 21+ 0-8 –0.30 –25.8 –46.9 3.8 0.08d 9-20 0.06 6.4 –18.0 38.1 0.64 Combined 104 788 21+ 0.15 15.8 –29.5 90.4 0.56 0.31 0-8 –0.35 –29.2 –50.2 0.4 0.05c 9-20 0.26 29.9 –1.0 70.6 0.06d42406NM 21+ –0.30 –25.9 –47.8 5.2 0.09d 0.02c 0-8 –0.54 –41.7 –63.5 –6.8 0.02c93272OM 21+ 0.25 28.3 –17.8 100.2 0.27 0.13 0-8 9-20 Rural multilane divided highways (nonfreeways) PAb 52171 21+ 0-8 –0.40 –33.2 –53.1 –4.9 0.03c 9-20 –0.47 –37.7 –60.4 –2.0 0.04cCombined 257 2,124 21+ –0.84 –56.7 –84.8 23.4 0.12 0.07d 0-8 0.10 10.0 –24.9 61.2 0.63 9-20 –0.24 –21.2 –55.3 39.0 0.41 627901NM 21+ 0.45 57.5 –26.0 234.9 0.24 0.54 0-8 MOb 66383 21+ 0-8 Rural two-lane roads PAb 230,1011 9-20 a Percent change is relative to no rumble strip. Read the entire page →
From page 84... ... performed to assess the impact that placement has on the safety effectiveness of shoulder rumble strips, it appears that Table 42 provides the most reliable results. The results of the analysis of edgeline rumble strips versus non-edgeline rumble strips as compared to no rumble strips reveals the following: • On rural freeways, edgeline rumble strips are more effective in reducing SVROR FI crashes than non-edgeline rumble strips, and • On rural two-lane roads, there is no difference in the safety effect of rumble strips placed close to the edgeline (i.e., edgeline rumble strips) Read the entire page →
From page 85... ... Safety effectiveness of combined rumble strip offset and recovery area on SVROR FI crashes based on all sites using the GLM method. Read the entire page →
From page 86... ... c Percent change is relative to no RS with 5+ ft shoulder. d Significant at 95 percent confidence level. Read the entire page →
From page 87... ... This implies that the current dimensions of shoulder rumble strips installed along rural freeways provide sufﬁcient levels of stimuli to alert inattentive and/or drowsy drivers of heavy vehicles and that it is not necessary to design rumble strip patterns that are "more aggressive" based strictly on the needs of drivers of heavy vehicles. • Concerning the accuracy of the estimated safety effect of shoulder rumble strips on SVROR crashes involving heavy vehicles (i.e., approximately a 40 percent reduction) Read the entire page →
From page 88... ... Safety effectiveness of shoulder rumble strips on SVROR crashes involving heavy vehicles. Table 47. Read the entire page →
From page 89... ... Table 48. Safety effectiveness of shoulder rumble strips on SVROR crashes under low-lighting conditions. Read the entire page →
From page 90... ... Given the level of detail of this analysis and the confounding issues, only a general conclusion can be drawn stating that shoulder rumble strips likely result in a positive safety beneﬁt during low-lighting conditions by providing positive guidance along the travel lanes. Summary of Key Findings The primary objectives of the safety evaluation of shoulder rumble strips are to do the following: • Quantify the safety effectiveness of milled shoulder rumble strips on speciﬁc types of roads, and • Quantify the safety effectiveness of shoulder rumble strips placed in varying locations with respect to the edgeline. Read the entire page →

From page 41...

... In summary, reliable estimates of the safety effectiveness of shoulder rumble strips for different roadway types are not available, and in all likelihood the safety beneﬁts of shoulder rumble strips vary by roadway type because the different types of roadways are built to varying standards (e.g., lane widths, shoulder widths, roadside) , accommodate varying traffic volumes and distributions, serve different driver populations, and accommodate a range of operating speeds.