Texas-wide GIS-based Crash Risk Assessment

By Michael Martin

2015 Traffic Safety Conference Corpus Christi, Texas

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

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

Road Segments Defined

Crashes Assigned

Crash Rates Calculated Per Road Segment

# 𝑜𝑜 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐿𝐶𝐿𝐿𝐿𝐶 ∗ 𝐴𝐴𝐴

The probability of being involved in a crash per instance of the exposure measure (length and traffic volume combined).

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.

Traffic Volume Ranges Defined Crashes per Mile vs. Traffic Volume (ADT) for

Rural Freeways

Low High Medium

0

20

40

60

80

100

0 20000 40000 60000 80000 100000 120000 140000 160000

Cras

hes p

er M

ile

Traffic Volume (ADT)

Inflection points where the relationship between crash rate per mile and volume change.

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.

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

Perc

ent o

f Seg

men

ts

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

All 20 Groupings

All 20 Groupings with High & Very High Risk