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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
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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.
×
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
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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.
×
Page 78
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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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