Breakout Session 4: Identifying CRASH Problems 2015 Traffic Safety Conference by Michael Martin, Assistant Transportation Researcher, Texas A&M Transportation Institute

1. Texas-wide GIS-based Crash Risk
Assessment
By Michael Martin
2015 Traffic Safety Conference
Corpus Christi, Texas

2. Overview
 The Concept
 The Process
– Road Segments Defined
– Crashes Assigned to Road Segments
– Crash Rates Calculated per Road Segment
– Traffic Volume Ranges Defined
– Crash Risk Categories Assigned
 Statewide Crash Risk Map

3. The Concept
• TTI report PRC 14-27-F Safety section
• To compare crash risks for like road
segments with similar:
– Functional class
– Area type
– Traffic volume

4. Road Segments Defined

5. Crashes Assigned

6. Crash Rates Calculated Per Road Segment
# 𝑜𝑜 𝐶𝐶𝐶𝐶𝐶𝐶𝐶
𝐿𝐿𝐿𝐿𝐿𝐿 ∗ 𝐴𝐴𝐴
The probability of being involved in a crash per instance of the
exposure measure (length and traffic volume combined).

7. Traffic Volume Ranges Defined
Area Type Functional Class
Volume Ranges
(ADT)
Low Medium High
Urban
Freeways <75,000 75,000 – 150,000 >150,000
Arterials <25,000 25,000 – 50,000 >50,000
Collectors <5,000 5,000 – 10,000 >10,000
Local* 0 – 20,000
Rural
Freeways <30,000 30,000 – 60,000 >60,000
Arterials <15,000 15,000 – 30,000 >30,000
Collectors <5,000 5,000 – 10,000 >10,000
Local* 0 – 15,000
*- Only one volume group.

8. Traffic Volume Ranges Defined
Crashes per Mile vs. Traffic Volume (ADT) for
Rural Freeways
Low HighMedium
0
20
40
60
80
100
0 20000 40000 60000 80000 100000 120000 140000 160000
CrashesperMile
Traffic Volume (ADT)
Inflection points where the
relationship between crash rate
per mile and volume change.

9. Crash Risk Categories Assigned
Area Type Functional Class
Volume Ranges
(ADT)
Low Medium High
Urban
Freeways <75,000 75,000 – 150,000 >150,000
Arterials <25,000 25,000 – 50,000 >50,000
Collectors <5,000 5,000 – 10,000 >10,000
Local* 0 – 20,000
Rural
Freeways <30,000 30,000 – 60,000 >60,000
Arterials <15,000 15,000 – 30,000 >30,000
Collectors <5,000 5,000 – 10,000 >10,000
Local* 0 – 15,000
*- Only one volume group.

10. Crash Risk Categories Assigned
0.0%
20.0%
40.0%
60.0%
80.0%
100.0%
0 1 2 3 4 5 6 7 8 9 10
PercentofSegments
Crash Rate (Crashes per Million Vehicle-Miles)
Inflection points where the
relationship between cumulative
percentages and crash rates change.
Low
Moderate
High
Very High
Cumulative Percentage vs. Crash Rate for
Medium Traffic Volume Rural Freeways

11. All 20 Groupings

12. All 20 Groupings with
High & Very High Risk