A Guide to Applying the Safe System Approach to Transportation Planning, Design, and Operations (2025)

Chapter: Appendix C: Safe System Design Practices

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Suggested Citation: "Appendix C: Safe System Design Practices." National Academies of Sciences, Engineering, and Medicine. 2025. A Guide to Applying the Safe System Approach to Transportation Planning, Design, and Operations. Washington, DC: The National Academies Press. doi: 10.17226/29147.
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APPENDIX C

Safe System Design Practices

Appendix C provides data on how respondents appraised various Safe System design practices. See Table C-1 for scores related to each practice’s feasibility and impact.

Interpretive categorization of Z-scores (Feasibility and Impact columns), with a mean of zero (0) and standard deviation of one (1).

Categories Z-scores
High > 1 SD above mean
Moderate < 1 and > 0
Low > −1 and < 0
Very Low < −1 SD below mean

Note: SD = standard deviation round the mean score of zero (0).

Page 78
Suggested Citation: "Appendix C: Safe System Design Practices." National Academies of Sciences, Engineering, and Medicine. 2025. A Guide to Applying the Safe System Approach to Transportation Planning, Design, and Operations. Washington, DC: The National Academies Press. doi: 10.17226/29147.
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Table C-1. Design practice feasibility and impact scores (n = 44).

Practice Feasibility Impact Category
Improving sight distance at intersections by restricting parking at the corners (daylighting). 0.972 0.296 Moderate Feasibility/Moderate Impact
Installing centerline rumble strips on undivided highways. 1.010 0.225 High Feasibility/Moderate Impact
Installing poles that break away when struck. 0.882 0.111 Moderate Feasibility/Moderate Impact
Installing travel lane reconfigurations (road diets) at multilane roads with fewer than 20,000 annual average daily traffic. 0.219 0.604 Moderate Feasibility/Moderate Impact
Installing edge line rumble strips with bicycle gaps on undivided highways. 0.726 −0.442 Moderate Feasibility/Low Impact
Setting default local road travel lane widths to 10 ft. 0.636 −0.397 Moderate Feasibility/Low Impact
Installing right-in–right-out junctions that only allow vehicles to enter and exit from the right. 0.161 0.064 Moderate Feasibility/Moderate Impact
Installing cable barriers in the medians of rural roads. 0.223 −0.206 Moderate Feasibility/Low Impact
Installing cable barriers on the edges of rural roads. −0.114 −0.081 Low Feasibility/Low Impact
Installing pedestrian hybrid beacons along arterials with 4+ travel lanes. −0.134 −0.142 Low Feasibility/Low Impact
Converting conventional signalized intersections to single-lane roundabouts. −0.703 0.294 Low Feasibility/Moderate Impact
Installing raised pedestrian and bicyclist crossings at driveways, minor street intersections, and midblock transit stop locations. −0.364 −0.073 Low Feasibility/Low Impact
Installing permanent barrier-protected bike lanes on arterial roads. −0.869 0.280 Low Feasibility/Moderate Impact
Employing people with skills in perceptual psychology to help design “self-explaining” roads. −0.396 −0.322 Low Feasibility/Low Impact
Creating self-explaining road designs where all local roads have narrow lanes and traffic calming, all collector roads have bicycle lanes and safe pedestrian crossings, and all arterial roads severely limit access and provide protected bicycle lanes and pedestrian crossings. −1.142 0.196 Very Low Feasibility/Moderate Impact
Providing pedestrian and bicyclist bridges or daylit tunnels at intersections. −1.108 −0.407 Very Low Feasibility/Low Impact
Page 77
Suggested Citation: "Appendix C: Safe System Design Practices." National Academies of Sciences, Engineering, and Medicine. 2025. A Guide to Applying the Safe System Approach to Transportation Planning, Design, and Operations. Washington, DC: The National Academies Press. doi: 10.17226/29147.
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Page 77
Page 78
Suggested Citation: "Appendix C: Safe System Design Practices." National Academies of Sciences, Engineering, and Medicine. 2025. A Guide to Applying the Safe System Approach to Transportation Planning, Design, and Operations. Washington, DC: The National Academies Press. doi: 10.17226/29147.
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Page 78
Next Chapter: Appendix D: Safe System Operations and Maintenance Practices
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