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From page 221... ... A-1 This appendix supplements Chapter 4, Safety, to provide details of literature reviews and findings on the safety performance of diverging diamond interchanges (DDIs) Read the entire page →
From page 222... ... A-2 Diverging Diamond Interchange Informational Guide The safety evaluation at the project-level accounts for the influence of the DDI treatment in the entire footprint of the interchange. The findings include: • The highest crash reduction was observed for fatal and injury (FI) Read the entire page →
From page 223... ... Safety Details A-3 (e.g., angle, rear-end, sideswipe, all types combined) , crash severity categories (e.g., FI crashes, PDO crashes, and for all crash severities combined) Read the entire page →
From page 224... ... A-4 Diverging Diamond Interchange Informational Guide No. Road Names City State AADT (vpd) Read the entire page →
From page 225... ... Safety Details A-5 and are shown in Exhibit A-2. They can be compared with those obtained from a spreadsheet prepared by Nye et al. Read the entire page →
From page 226... ... A-6 Diverging Diamond Interchange Informational Guide No. Before Control Type1, Terminal 1 Before Control Type1, Terminal 2 Crossroad Lane Drops2 Area Type Stop Line to Stop Line Distance3, ft Crossroad Speed Limit, mph Median Width4 Before, ft Median Width4 After , ft signal signal 2 Urban 600 40 1 17 signal signal 2 Urban 435 40 1 15 signal signal 0 Urban 600 35 4 81 signal signal 2 Urban 620 25 1 55 signal signal 0 Urban 710 45 16 30 signal signal 2 Suburban 600 35 40 64 signal signal 0 Suburban 640 40 1 22 signal signal 0 Suburban 375 40 16 15 signal signal 1 Suburban 670 45 6 24 stop stop 0 Rural 700 40 1 21 sig/sig signal 0 Suburban 810 40 1 30 full clover full clover 0 Suburban 750 40 8 40 signal signal 2 Urban 465 35 8 33 signal signal 1 Suburban 525 35 1 17 signal signal 2 Suburban 325 25 16 28 signal signal 1 Urban 645 30 4 36 stop signal 0 Suburban 860 45 4 50 stop stop 2 Rural 590 45 1 30 signal signal 0 Suburban 605 45 1 12 signal signal 1 Urban 760 30 4 34 signal signal 0 Suburban 815 50 10 27 signal stop 0 Urban 890 45 1 78 signal signal 1 Suburban 710 45 1 26 stop stop 1 Rural 740 30 1 23 signal signal 0 Rural 1,020 30 42 45 stop stop 0 Rural 613 40 1 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Notes: 1. Read the entire page →
From page 227... ... Safety Details A-7 An examination of the computed variance of the odds ratio indicated that (1) it is likely biased to a value that is smaller than the true value, and (2) Read the entire page →
From page 228... ... A-8 Diverging Diamond Interchange Informational Guide No. Read the entire page →
From page 229... ... Safety Details A-9 formulations for the CMF functions. A suboptimal formulation will bias the model predictions at some factor levels. Read the entire page →
From page 230... ... A-10 Diverging Diamond Interchange Informational Guide wi = weight of CMF observation i (from Equation A-2) ; CMFi = value of CMF observation i; CMFi = predicted value of the CMF for observation i; si = standard error of CMF observation i; and p = 3.14159 . Read the entire page →
From page 231... ... Safety Details A-11 1.0 ln ln ln Equation A-32 2 2R w CMF CMF w CMF L t i i i i i ∑ ∑ ( ) Read the entire page →
From page 232... ... A-12 Diverging Diamond Interchange Informational Guide The number-of-crossroad-through-lanes variable Nlanes describes the number of lanes on the crossroad that serve vehicles traveling as a through movement. Each through lane can be traced as a continuous traffic lane through the interchange (including both crossroad ramp terminals) Read the entire page →
From page 233... ... Safety Details A-13 database. It is likely due to factors at site 18 that are different from the other jurisdictions and not represented in the database (e.g., signing, pavement condition, weather, or curve radius) Read the entire page →
From page 234... ... A-14 Diverging Diamond Interchange Informational Guide Statistics Value Degrees of Freedom p-value Number of observations 26 Treatment Chi-Square 180 8 0.001 Homogeneity Chi-Square 83.0 18 0.001 0.68 Estimated Effect of... Variable Coefficient Value Standard Error t-statistic Intercept b0 -1.0919 0.174 -6.25 Crossroad lane drops at DDI (crossroad to ramp) Read the entire page →
From page 235... ... Safety Details A-15 a. CMF comparison for FI CMFs. Read the entire page →
From page 236... ... A-16 Diverging Diamond Interchange Informational Guide Traffic Control Type before Conversion Crossroad Speed Limit, mph Change in Crossroad Through Lanes1 Crossroad Lane Drops2 CMF, FI CMF, PDO CMF, Total Change in crossroad through lanes Signal 30 2 0 0.20 0.26 0.25 Signal 30 1 0 0.25 0.30 0.29 Signal 30 0 0 0.32 0.35 0.34 Number of crossroad lane drops at DDI Signal 30 0 0 0.32 0.35 0.34 Signal 30 0 1 0.47 0.53 0.51 Signal 30 0 2 0.70 0.81 0.79 Conversion from specific traffic control type to signalized DDI3 Unsignalized 30 0 0 0.38 0.50 0.48 Signal 30 0 0 0.32 0.35 0.34 Crossroad speed limit Signal 25 0 0 0.23 0.24 0.23 Signal 30 0 0 0.32 0.35 0.34 Signal 35 0 0 0.43 0.53 0.49 Signal 40 0 0 0.59 0.78 0.71 Signal 45 0 0 0.80 1.17 1.03 Notes: 1. Number of through lanes at the DDI minus the number of through lanes at the interchange before conversion (i.e., = , − , ) Read the entire page →
From page 237... ... Safety Details A-17 The CMFs in the last section of Exhibit A-10 describe the best estimate of the influence of DDI design on safety. It is noted that the total-crash CMF associated with a speed limit of 45 mph is greater than 1.0, which suggests that the conversion to a DDI with a 45-mph crossroad is likely to increase crash frequency -- most notably, it will increase the PDO crash frequency. Read the entire page →
From page 239... ... Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing America's Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) Read the entire page →

From page 221...

... A-1 This appendix supplements Chapter 4, Safety, to provide details of literature reviews and findings on the safety performance of diverging diamond interchanges (DDIs)