Guidance for the Design and Application of Shoulder and Centerline Rumble Strips (2009)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

158 A P P E N D I X E This appendix presents the SPF results developed based on all nontreatment sites (i.e., sites without shoulder rumble strips: BA-No RS and CS-No RS) in the four roadway categories for the four crash types of interest (Tables E-1 to E-4). These SPFs were developed using negative binomial regression analysis. Each line in each table provides the regression coefficients and their precision estimates for a given SPF. For example, using Table E-1 for urban freeways in Pennsylvania: An empty cell in a table indicates the corresponding regres- sion coefficient was not statistically significant at the 0.15 level or the coefficient’s sign was not of the expected direction. Note that inside RHR does not apply to rural two-lane roads. Expected total crashes mi yr A= − +exp . . ln8 17 0 83 DT RHR RHR e ADT e Out IN+ +( ) = × ×− 0 10 0 19 8 17 0 83 . . . . 0 10 0 10. .RHR_Out RHR_Ine× SPF Results for TOT, FI, SVROR, and SVROR FI Crashes on Selected Roadways Without Shoulder Rumble Strips It should be noted that the analyses for SVROR crashes includes SVROR crashes to the right and to the left. No effort is made to distinguish crashes by side of the road; however, by including RHR for both the outside and inside shoulders/ roadsides of divided highways, the analyses account for the differences between ROR crashes to the right and left. Also, for states that treat both sides of a divided highway as sepa- rate sites (i.e., Missouri and Pennsylvania), the RHR variables in the models represent the values for a single side of the divided highway. When both sides of a divided highway are treated as a single site (i.e., Minnesota sites), the RHR variables in the model represent average values for both directions of travel. Similarly, the RHR variable in the model for rural two-lane roads represents the average RHR for both sides of the roadway. Thus, the analysis accounts for SVROR right and SVROR left crashes, without necessarily distinguishing between the two crash types.

Intercept lnADT Outside RHR Inside RHR Overdispersion Roadway type State Number of sites Estimate SEa Estimate SE p–valueb Estimate SE p–value Estimate SE p–value Estimate SE R2LR Urban freeways PA 90 –8.17 1.07 0.83 0.11 <.0001 0.10 0.05 0.051 0.19 0.05 0.0001 0.10 0.03 0.70 MO 35 –11.69 2.79 1.31 0.28 <.0001 0.16 0.05 0.37 Rural freeways PA 34 –0.15 2.59 0.08 0.27 0.782c 0.10 0.06 0.002 MN 33 –8.10 1.36 0.87 0.15 <.0001 0.23 0.08 0.005 0.11 0.04 0.62 MO 26 –12.84 4.42 1.50 0.47 0.002 0.64 0.19 0.25 Rural multilane divided highways (nonfreeways) PA 13 –13.01 6.58 1.48 0.69 0.033 0.28 0.15 0.26 MN 56 –4.75 0.58 0.44 0.08 <.0001 0.33 0.07 <.0001 0.21 0.06 0.60 MO 37 –5.95 2.68 0.51 0.25 0.039 0.61 0.34 0.075 1.49 0.39 0.15 Rural two–lane roads PA 110 –4.99 0.91 0.62 0.11 <.0001 0.31 0.06 0.23 a SE: standard error of estimate. b p-value: significance level. c ADT not significant at 0.15 significance level. Table E-1. SPF results for TOT crashes based on all nontreatment sites. Table E-2. SPF results for FI crashes based on all nontreatment sites. Intercept lnADT Outside RHR Inside RHR Overdispersion Roadway type State Number of sites Estimate SEa Estimate SE p–valueb Estimate SE p–value Estimate SE p–value Estimate SE R2LR Urban freeways PA 90 –8.42 1.32 0.77 0.13 <.0001 0.11 0.06 0.079 0.22 0.06 0.0001 0.12 0.04 0.61 MO 35 –13.37 3.20 1.36 0.32 <.0001 0.12 0.05 0.36 Rural freeways PA 34 –4.54 3.38 0.45 0.35 0.199c 0.10 0.09 0.05 MN 33 –8.00 1.74 0.75 0.19 <.0001 0.20 0.11 0.064 0.15 0.06 0.44 MO 26 –18.77 4.73 2.01 0.51 <.0001 0.46 0.20 0.35 Rural multilane divided highways (nonfreeways) PA 13 –13.12 7.75 1.42 0.82 0.082 0.33 0.20 0.19 MN 56 –5.71 0.65 0.43 0.09 <.0001 0.33 0.07 <.0001 0.08 0.05 0.59 MO 37 –7.03 2.65 0.44 0.25 0.078 0.77 0.32 0.018 1.24 0.36 0.18 Rural two–lane roads PA 110 –6.05 1.08 0.68 0.13 <.0001 0.38 0.09 0.20 a SE: standard error of estimate. b p–value: significance level. c ADT not significant at 0.15 significance level.

Intercept lnADT Outside RHR Inside RHR Overdispersion Roadway type State Number of sites Estimate SEa Estimate SE p–valueb Estimate SE p–value Estimate SE p– value Estimate SE R2LR Urban freeways PA 90 –6.22 1.23 0.60 0.12 <.0001 0.11 0.06 0.083 0.12 0.06 0.030 0.10 0.03 0.46 MO 35 –10.23 3.71 1.09 0.37 0.003 0.26 0.08 0.19 Rural freeways PA c 34 0.22 0.10 0.16 0.09 nc MN 33 –9.81 1.82 0.99 0.19 <.0001 0.17 0.07 0.44 MO 26 –16.28 4.81 1.76 0.52 0.001 0.53 0.19 0.29 Rural multilane divided highways (nonfreeways) PA 13 –20.34 7.42 2.21 0.78 0.005 0.19 0.14 0.37 MN 56 –3.62 0.74 0.07 0.10 0.475d 0.49 0.09 <.0001 0.21 0.10 0.40 MO 37 –5.68 2.77 0.25 0.26 0.331d 0.82 0.35 0.019 1.40 0.39 0.16 Rural two–lane roads PA 110 –3.05 1.11 0.34 0.13 0.012 0.48 0.10 0.05 a SE: standard error of estimate. b p-value: significance level. c Means model; R2LR not calculated. d ADT not significant at 0.15 significance level. Intercept lnADT Outside RHR Inside RHR Overdispersion Roadway type State Number of sites Estimate SEa Estimate SE p–valueb Estimate SE p–value Estimate SE p–value Estimate SE R2LR Urban freeways PA 90 –6.88 1.36 0.62 0.13 <.0001 0.11 0.08 0.130 0.12 0.05 0.25 MO 35 –10.33 4.04 1.01 0.40 0.012 0.21 0.09 0.15 Rural freeways PAc 34 –0.52 0.11 0.14 0.12 nc MN 33 –8.61 2.26 0.79 0.24 0.001 0.23 0.10 0.25 MO 26 –17.50 5.08 1.82 0.54 0.001 0.44 0.20 0.28 Rural multilane divided highways (nonfreeways) PA 13 –20.03 9.38 2.11 0.99 0.032 0.33 0.22 0.26 MN 56 –3.73 1.06 0.15 0.14 0.258d 0.58 0.24 0.02 MO 37 –6.00 2.61 0.13 0.26 0.611d 0.93 0.31 0.003 1.10 0.39 0.21 Rural two–lane roads PA 110 –3.58 1.25 0.32 0.15 0.034 0.49 0.13 0.04 a SE: standard error of estimate. b p-value: significance level. c Means model; R2LR not calculated. d ADT not significant at 0.15 significance level. Table E-3. SPF results for SVROR crashes based on all nontreatment sites. Table E-4. SPF results for SVROR FI crashes based on all nontreatment sites.