# Presentation: 695349

## NCHRP 17-25Crash Reduction Factors for Traffic Engineering and ITS Improvements

- UNC HSRC
- VHB
- Ryerson University
- (Bhagwant and Craig)

## Project Goals

- Develop new Accident Modification Factors where voids currently exist
- Increase the *level of predictive certainty* for existing Accident Modification Factors
- Coordination with other NCHRP and FHWA projects

## Completed Tasks

- Phase I
- Literature Review
- State Surveys and Interviews
- Research Results Digest 299
- Accident Modification Factors Knowledge Matrix
- List of 20 “credible” Accident Modification Factors
- High or Med-High level of predictive certainty (LOPC)

## Phase II Efforts

- Empirical Bayes Before-After Evaluations
- Rural signal installations
- 4-lane to 3-lane conversions (Road diets)
- Skid resistance treatment
- Left-turn signal phasing
- 8” to 12” signals
- Nighttime flash operation to normal
- Double red signal heads (“Dollys”)
- Median width on divided roadways
*Analysis-Driven* Expert Panels
- Urban/Suburban
- Rural Multilane
- Cross-sectional models
- GOAL – Develop Accident Modification Factors

**Notes:**
Notes: 
Left-turn Signal Phasing: 
Permissive to protective/permissive Left Turn phasing
Protective/permissive to protected Left Turn phasing

## Rural Signal Installations

| State | Treated Sites | Unsignalized Reference | Signalized Reference | Years of Data |
| --- | --- | --- | --- | --- |
| California | 28 | 2,330 | 63 | 1993-2002 |
| Minnesota | 17 | 1,258 | 21 | 1991-2002 |

| 3-Leg Stop-Controlled          (CA and MN independently) | 4-Leg Stop-Controlled             (CA and MN independently) |  
4-Leg Signalized             (CA and MN combined) |
| --- | --- | --- |
| All | All | All |
| Right-Angle | Right-Angle | Right-Angle |
| Left-Turn | Left-Turn |  |
| Rear-End | Rear-End | Rear-End |

- Summary of data collected

- Safety Performance Functions Developed

## Rural Signal Installations

| Crash Frequency Crash Modification Factors
 (standard error)  |  |  |  |  |
| --- | --- | --- | --- | --- |
| State | Total | Right Angle | Left Turn | Rear End |
| CA | 0.778 (0.061) | 0.221 (0.036) | 0.433 (0.065) | 2.474 (0.373) |
| MN | 0.488 (0.027) | 0.228 (0.019) | 0.374 (0.063) | 1.300 (0.141) |
| ALL | 0.559 (0.025) | 0.227 (0.017) | 0.401 (0.047) | 1.579 (0.142) |

## Rural Signal Installations

| Economic Cost Crash Modifications Factors |  |
| --- | --- |
| Characteristic | Theta Cost |
| All | 0.265 |
| California | 0.315 |
| Minnesota | 0.247 |
| 3 leg | 0.286 |
| 4 leg | 0.264 |
| 2 lanes on major | 0.265 |
| 4 lanes on major | 0.265 |
| AADT < 20,000 | 0.314 |
| AADT > 20,000 | 0.253 |
| Expected RA/Expected RE <=4.5 | 0.324 |
| Expected RA/Expected RE >4.5 | 0.215 |

## Skid Resistant Treatment

| SUMMARY OF DATA COLLECTED |  |
| --- | --- |
| Site Type | No. of Sites |
| Treated Intersection | 256 |
| Reference Intersection | 3,993 |
| Treated Segment | 36.3 miles |
| Reference Segment | 1,242.4 miles |
| Data collected in New York State for 1994 to 2003. |  |

| SAFETY PERFORMANCE FUNCTIONS DEVELOPED |  |
| --- | --- |
| Intersections | Segments |
| Total | Total |
| Wet-road | Wet-road |
| Rear-end | Rear-end |
| Dry | Dry |
| Rear-end wet-road | Rear-end wet-road |
| Right-angle | Rear-end dry-road |
| Right-angle wet-road | Single vehicle |
|   | Single vehicle wet-road |

## Skid Resistant Treatment

| Safety Effects At Intersections  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- |
| Grouping | Total (s.e.) | Wet-road (s.e.) | Rear-end (s.e.) | Dry (s.e.) | Rear-end Wet (s.e.) | Right-angle (s.e.) | Right-angle Wet (s.e.) |
| All | 0.799 (0.028) | 0.426 (0.030) | 0.582 (0.034) | 1.149 (0.051) | 0.322 (0.041) | 1.045 (0.078) | 0.799 (0.123) |
| 3 leg signalized | 0.667 (0.050) | 0.372 (0.053) | 0.554 (0.065) | 0.959 (0.093) | 0.261 (0.066) | 0.787 (0.125) | 0.470 (0.161) |
| 3 leg stop-controlled | 0.819 (0.048) | 0.355 (0.046) | 0.586 (0.057) | 1.302 (0.095) | 0.335 (0.075) | 0.828 (0.218) | 0.828 (0.218) |
| 3 leg yield-controlled | 0.590 (0.114) | 0.217 (0.103) | 0.304 (0.086) | 1.392 (0.321) | 0.221 (0.161) | n/a | n/a |
| 4 leg signalized | 0.797 (0.052) | 0.546 (0.070) | 0.585 (0.068) | 0.992 (0.081) | 0.361 (0.084) | 0.898 (0.117) | 1.105 (0.294) |
| 4 leg stop-controlled | 1.271 (0.143) | 0.597 (0.137) | 0.943 (0.188) | 1.754 (0.242) | 0.482 (0.215) | 1.687 (0.323) | 0.829 (0.351) |
| 4 leg yield-controlled | 0.589 (0.216) | 0.361 (0.371) | 0.504 (0.248) | 0.651 (0.273) | 
n/a | n/a | n/a |

- s.e means standard error    n/a means not applicable

**Notes:**
There are  bold numbered cells that indicate that the results are statistically significant at the 95 percent confidence level. The numbers are bolded for the following:
All total crashes, wet road, rear-end, dry roads, and rear end wet roads;
3 leg signalized total crashes, wet road, rear-end, rear-end wet road, and right angle wet road;
3 leg stop-controlled total crashes, wet road, rear-end, dry, and rear-end wet road;
3 leg yield-controlled total crashes, wet road, rear-end, and rear-end wet road;
4 leg signalized total crashes, wet road, rear-end, and rear-end wet road;
4 leg stop-controlled wet road, rear end wet road, and right angle crashes
4 leg yield-controlled rear end crashes  

## Skid Resistant Treatment

| Safety Effects For Segments |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Grouping | Total (s.e.) | Wet-road (s.e.) | Rear-end (s.e.) | Dry (s.e.) | Rear-end Wet-road (s.e.) | Rear-end Dry-road (s.e.) | Single-vehicle (s.e.) | Single-vehicle Wet-road (s.e.) |
| All | 0.764 (0.023) | 0.434 (0.024) | 0.828 (0.043) | 1.003 (0.043) | 0.575 (0.055) | 0.977 (0.068) | 0.698 (0.040) | 0.399 (0.039) |
| Rural 2 lanes | 0.964 (0.073) | 0.852 (0.126) | 1.047
-0.149 | 1.167 (0.114) | 0.971 (0.256) | 1.235 (0.219) | 1.078 (0.141) | 1.125 (0.287) |
| Rural >2 lanes | 0.684 (0.032) | 0.346 (0.028) | 0.776
(-0.068) | 0.875 (0.061) | 0.474 (0.079) | 0.838 (0.098) | 0.588 (0.046) | 0.292 (0.038) |
| Urban 2 lanes | 0.599 (0.082) | 0.260 (0.066) | 0.612
(-0.142) | 0.992 (0.195) | 0.344 (0.145) | 0.695 (0.216) | 0.921 (0.232) | 0.523 (0.247) |
| Urban > 2 lanes | 0.862 (0.038) | 0.538 (0.045) | 0.866
(-0.059) | 1.132 (0.065) | 0.640 (0.084) | 1.120 (0.099) | 0.800 (0.083) | 0.615 (0.115) |

- s.e means standard error

**Notes:**
There are bolded numbered cells that indicate that the results are statistically significant at the 95 percent confidence level. The numbers are bolded for the following:
All total crashes, wet road, rear-end, rear end wet roads, single vehicle and single vehicle wet road;
Notes:  
Rural area with greater than 2 lanes total crashes, wet road, rear-end, dry road, rear end wet roads, single vehicle and single vehicle wet road; 
Urban area with 2 lanes total crashes, wet road, rear-end, and rear end wet road; 
Urban area with greater than 2 lanes total crashes, wet road, rear-end, dry road, rear end wet road and single vehicle and single vehicle wet-road.  

## Road Diets in Urban Areas

*Previously discussed*

## Winston-Salem Empirical-Bayes Evaluations

- Treatments
- Left-turn signal phasing
- Permissive to protective/permissive LT phasing
- Protective/permissive to protected LT phasing
- 8” to 12” red signal heads
- Nighttime flash to normal
- Added double red signal heads (“dollys”)
- Identified treatment sites and reference group
- Obtained crash data, geometric data, and traffic volumes for treatment and reference sites

**Notes:**
Notes: 
One single reference group for all treatments 

## Winston-Salem Empirical-Bayes Evaluations

- Permissive to protective/permissive Left Turn
- 11 sites
- Protective/permissive to protected Left Turn
- 4 sites
- 8” to 12” signal heads
- 26 sites
- Nighttime flash to normal
- 12 sites
- Double red signal heads
- 8 sites

## Winston-Salem Empirical-Bayes Evaluations

- Safety Performance Function (SPF) for total crashes
- Developed using reference group
- Safety Performance Function (SPF) for target crashes
- Could not be developed with available data
- Used proportion of target crashes to adjust SPF for total crashes
- Empirical Bayes analysis almost complete
- Calibrate Safety Performance Functions separately for before and after periods
- Estimate percent change in crashes

## Median Width AMF

- Current studies are not consistent
- Accident Modification Factor for median width and validation of the approach
- Preliminary assessment of states – WA, CA, MN, IL

## Analysis-Driven Expert Panels

- Urban-Suburban Arterials (NCHRP 17-26)
- 25+ treatments addressed for segments and intersections
- Geometrics (lane/shoulder widths, median type, etc.)
- Operations (signalization, speed limits, etc.)
- Other (lighting, roundabouts, etc.)
-  Consensus on 9 Accident Modification Factors
-  Follow-up work on additional Accident Modification Factors (e.g., roadside hazards, speed)

**Notes:**
Notes:  
AMFs:
Left-turn lanes, right turn lanes, left turn phasing, on-street parking, lighting 

## Analysis-Driven Expert Panels

- Rural Multilane Roadways (NCHRP 17-29)
- 15+ treatments addressed for segments and intersections
- Geometrics (median width/type, shoulder width/type, turning lanes, alignment, etc.)
- Operations (signalization, speed limits, access, etc.)
- Other (lighting, roadside hazards, etc.)
-  Consensus on 3 Accident Modification Factors
-  Follow-up work identified for additional Accident Modification Factors (access, shoulder type) within both projects

## 

Questions??

- Questions??