 |
PPT version for Printing
Low Cost Safety Improvements Pooled Funds Study
Flashing Beacons at Stop Controlled Intersections Results
Dr. Raghavan Srinivasan, HSRC
Background on Strategy
- Alert drivers to the presence of an intersection
- Reduce angle crashes
- Initial installation costs: $2,000 to $ 100,000
- Placement Options
- STOP Sign mounted
- Overhead
| 
 |
Literature Review
- Previous Work
- Cribbons and Walton 1970
- 14 rural sites
- About 1 year before, 1 year after
- Pant et al. 1999
- 6 sites without and 7 with a beacon
- Murphy and Hummer 2007
- 34 locations in North Carolina
- Empirical Bayes study - accounted for change in traffic volume using a linear assumption
- Safety effectiveness has not been adequately quantified
Objective
- To examine the safety impact
- Target crash types considered included:
- Total intersection crashes.
- Total intersection injury and fatal crashes (including fatality (K), Injury, incapacitating (A), Injury, non-capacitating (B), and possible injury (C).
- Total intersection angle crashes.
- Total intersection rear-end crashes.
- Determine if safety impacts are function of:
- Area type (rural, suburban, or urban).
- Intersection type (Two-way versus four- way stop-controlled).
- Types of flashing beacon installations including standard and actuated.
- Location of the beacon including stop sign or overhead.
Study Design
- Based on methodology suggested by Hauer (1997)
- Literature review to determine the average number of crashes at stop controlled intersections
- Sample size
- Minimum: 53 intersection-years in the before period (ability to detect 20 percent reduction in crashes at 90 percent confidence level)
- Desirable: 260 intersection-years in the before period (ability to detect 10 percent reduction in crashes at 90 percent confidence level)
Data Collection
Data Collection – North Carolina
Total number of intersections used = 64
| Variable | Before | After |
|---|
| Site-Years | 583 | 305 |
| Major Road AADT | 3578 | 5105 |
| Minor Road AADT | 1540 | 2074 |
| Total Crashes per site-year | 2.85 | 2.99 |
| Angle Crashes per site-year | 1.66 | 1.45 |
| Injury and Fatal Crashes per site-year | 1.68 | 1.58 |
| Rear-end crashes per site-year | 0.31 | 0.42 |
Data Collection – South Carolina
Total number of intersections used = 42
| Variable | Before | After |
|---|
| Site-Years | 334 | 128 |
| Major Road AADT | 3978 | 4531 |
| Minor Road AADT | 1938 | 2192 |
| Total Crashes per site-year | 2.73 | 2.64 |
| Angle Crashes per site-year | 1.17 | 1.27 |
| Injury and Fatal Crashes per site-year | 0.94 | 0.89 |
| Rear-end crashes per site-year | 0.55 | 0.61 |
Aggregate Evaluation Results: North Carolina
| | Angle | Injury and Fatal | Rear-end | Total |
|---|
| Expected crashes without strategy | 532.6 | 533.7 | 148.0 | 973.2 |
| Observed crashes | 436 | 469 | 127 | 894 |
| Estimate of percent reduction | 18.3 | 12.2 | 14.6 | 8.2 |
| (standard error) | (4.9) | (5.1) | (9.7) | (4.0) |
Aggregate Evaluation Results: South Carolina
| | Angle | Injury and Fatal | Rear-end | Total |
|---|
| Expected crashes without strategy | 156.6 | 115.1 | 73.6 | 323.8 |
| Observed crashes | 162 | 114 | 78 | 338 |
| Estimate of percent reduction | -2.7 | 1.8 | -3.9 | -4.0 |
| (standard error) | (11.7) | (12.9) | (18.5) | (8.2) |
Aggregate Evaluation Results: NC and SC Combined
| | Angle | Injury and Fatal | Rear-end | Total |
|---|
| Expected crashes without strategy | 689.2 | 648.8 | 221.6 | 1297.0 |
| Observed crashes | 598 | 583 | 205 | 1232 |
| Estimate of percent reduction | 13.3 | 10.2 | 7.9 | 5.1 |
| (standard error) | (4.6) | (4.8) | (8.9) | (3.6) |
Disaggregate Evaluation Results: Angle Crashes
| Disaggregate Group | Sites | Estimate of percent reduction (Standard Error) |
|---|
| Rural (NC and SC) | 76 | 15.7 (5.3) |
| Suburban (NC) | 14 | 11.8 (10.2) |
| Urban (NC and SC) | 16 | -12.3 (23.4) |
| 2-way stop (NC and SC) | 95 | 12.7 (4.7) |
| 2-way stop (SC) | 31 | -10.4 (13.4) |
| 4-way stop (SC) | 11 | 27.8 (20.5) |
| Beacon Type-Standard (NC and SC) | 89 | 13.3 (5.2) |
| Beacon Type-Standard (NC) | 47 | 19.8 (5.7) |
| Beacon Type-Other (NC) | 17 | 14.0 (9.8) |
| Beacon Location-Overhead (NC and SC) | 97 | 14.7 (4.8) |
| Beacon Location-Other (NC and SC) | 9 | -5.8 (18.4) |
| Beacon Location-Overhead (NC and SC) | 97 | 14.7 (4.8) |
Economic Analysis
- FHWA cost per crash for unsignalized intersections (FHWA-HRT-05-051)
- $13,238 for rear-end
- $61,114 for right-angle
- Economic Benefit
- Based on combined results from NC and SC
- $ 12,040 per site-year
- Costs estimated for Standard and ‘Other’ types separately
- Standard Beacons:
- $ 27,500 initial installation costs (high value)
- Annual Maintenance and other costs: $ 720
- 10 year life
- Annualized costs = $ 4,636
- Benefit Cost ratio is 2.6:1
- ‘Other’ Beacons:
- Initial costs range from $ 5,000 to $ 100,000
- Benefit achieved if initial cost is less than $ 79,000
- 2:1 Benefit/Cost ratio if initial cost is less than $ 37,000
Conclusions
- NC: statistically significant reduction in total, angle, and injury and fatal crashes
- SC: very little change
- NC and SC combined: statistically significant reduction in angle and injury and fatal crashes
- Probably more effective in rural and suburban locations
- Very few locations with stop sign mounted beacons
- Standard beacons provide a benefit cost ratio of 2.6:1
- Net benefit of non-standard beacons depends on their cost
< Presentation 4 | Presentation 6 >
|
