Evaluating Safety and Health Impacts
TDM Impacts on Traffic Safety, Personal Security and Public Health
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Victoria Transport Policy Institute
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Updated
22 July 2008
This chapter describes how road risk is measured, and how to evaluate the safety and health impacts of different TDM strategies. For more detailed analysis of this issue see Litman and Fitzroy, 2005 (www.vtpi.org/safetrav.pdf).
How
Mileage Affects Crash Frequency
Other
Public Safety and Health Risks
Safety
and Health Impacts of Specific TDM Strategies
Pay-As-You-Drive Vehicle Insurance
Improved Automobile Availability
Safety
and Health Impacts Summary
Evaluating
Traffic Safety Impacts Of Vehicle Travel Changes
References
And Resources For More Information
Road risk is a general term for the costs to society of road traffic crashes.
Road safety refers to a reduction in road risk and crash costs. There are various ways to improve road safety:
· Reduce total vehicle mileage.
· Reduce per mile crash rates (more caution drivers, safer roads).
· Improved vehicle occupant protection (energy absorbing vehicle designs, seat belt use, helmet use, air bags).
· Improved emergency response and trauma care.
· Improved long-term medical treatment and rehabilitation for traffic victims.
· Reduced vehicle repair costs.
|
Reduced
Crashes Versus Safe Crashes There
are two general approaches to increasing road safety. One is to prevent
crashes, for example, by reducing vehicle traffic volumes and speeds,
designing and building roadways with fewer conflicts (such as
grade-separating intersections and replacing traffic signals with roundabouts), increasing traffic law enforcement,
reducing intoxicated and other high-risk types of driving, and imposing more
rigorous requirements on driving privileges. These strategies are intended to
promote crash-free traffic operations. Another
approach to road safety involves reducing the amount of damage that occurs in
a crash, particularly for vehicle occupants, by building crash protection
into roadways (wider shoulders, break-away light standards, etc.) and in
vehicles (increased vehicle weight, energy absorbing vehicle design, air
bags, etc.), and by requiring vehicle occupants to use seatbelts, child
restraints, motorcycle and bicycle helmets. These strategies are intended to
mitigate crash injuries. Critics call this approach “safe crashing”
(Birnbaum). Some argue that this approach has been overemphasized by
government policies and traffic safety agencies (Gladwell, 2001). As
described later in this chapter, “safe crashing” safety strategies tend to
have a Rebound Effect: as individual drivers feel
safer they take somewhat greater risks, which offsets some of their expected
safety benefits, and may increase risk to others, particularly vulnerable
road users such as pedestrians, cyclists and motorcyclists. As a result, net
safety benefits may be smaller than expected. This is called risk
compensation or risk homeostasis. |
Traffic safety researchers measure crashes (also called collisions, accidents or incidents), injuries, fatalities and damages. Injuries and fatalities together are called casualties. Many road safety experts prefer the term crash to accident, because “accident” implies a random event, while “crash” emphasizes that such events have a cause (driver error, mechanical failure, poor roadway design, etc.) and so are preventable.
Traffic crash Statistics are available from the following sources:
·
Bureau of Transportation Statistics (www.bts.gov). The BTS National Transportation
Statistics report provides annual information on transportation activities
and impacts, including traffic crashes. North American Transportation in
Figures, provides crash data for
·
National Highway Traffic Safety
Administration (www.nhtsa.dot.gov)
provides comprehensive information on traffic crashes and safety programs in
the
·
·
·
Transport
· Eurostat (www.europa.eu.int) provides transportation and crash data for European countries.
· European Conference of Ministers of Transport (www.oecd.org/cem/stat) provides traffic crash data for European countries.
·
G-7 Transportation Highlights (www.bts.gov/itt/G7HighlightsNov99/G-7book.pdf)
provides transportation data for European countries, the
· International Road Traffic and Accident Database, (www.bast.de/htdocs/fachthemen/irtad//english/we2.html) provides international crash data.
Data used to evaluate transport risks often different between jurisdictions, times and modes. For example, some data sets only include deaths that occur at a crash site, others include deaths within a certain number of days or months. Some transit and rail fatality data include suicides (which represent a significant portion of rail fatalities), and passengers who suffer a heart attack or assault on a transit vehicle or train stations.
Crash Severity Scales (FHWA, 1994)
Crashes are categorized by severity using indices such as the KABC Scale and the Abbreviated Injury Scale, as illustrated in tables 1a and 1b.
Table 1a
|
KABC Scale |
||
|
Severity |
Descriptor |
Cost (1994) |
|
K |
Fatal |
$2,600,000 |
|
A |
Incapacitating |
$180,000 |
|
B |
Injury Evident |
$36,000 |
|
C |
Injury Possible |
$19,000 |
|
PDO |
Property Damage Only |
$2,000 |
Table 1b
|
Abbreviated Injury Scale (AIS) |
||
|
Severity |
Descriptor |
Cost (1994) |
|
AIS 6 |
Fatal |
$2,600,000 |
|
AIS 5 |
Critical |
$1,980,000 |
|
AIS 4 |
Severe |
$490,000 |
|
AIS 3 |
Serious |
$150,000 |
|
AIS 2 |
Moderate |
$40,000 |
|
AIS 1 |
Minor |
$5,000 |
These tables show two commonly-used crash severity indices.
Police and traffic safety organizations collect traffic
crash and casualty data (
Insurance actuaries measure claims and claim costs (insurers’ expenses for managing and compensating crash damages). Less than half of all vehicle insurance claims are crash-related (glass damage, fire, theft and vandal damage do not usually involve a crash). About 70% of crashes involve multiple vehicles, which usually result in multiple claims. An average crash produces about 1.5 insurance claims, so a 10% reduction in total crashes reduces crash-related claim costs by 15%, all else being equal.
Crash costs refer to damages (also called losses)
caused by collisions, and costs of crash damage avoidance activities. Total
crash costs include both of monetary and non-monetary losses. Monetary costs
include damages to vehicles, medical costs, lost productivity due to
disabilities and death, emergency services, and expenditures on safety programs
and equipment to reduce crash damages. Non-monetary costs include pain, grief
and lost quality of life due to crash injuries and deaths, and reduced mobility
to non-motorized modes due to crash risk. Several techniques are be used to
estimate the value that people place on these non-monetary costs (Miller,
1991), resulting in various estimates of the total cost per injury or death, as
indicated in tables 1a and 1b. Table 2 summarizes an estimate of total
Table 2
|
|
All Vehicles |
Passenger Cars |
Motor-cycles |
Light Trucks/Vans |
Single Unit Trucks |
Combination Trucks |
|
Police Reported Crashes |
6,261,000 |
5,307,000 |
89,000 |
2,209,000 |
154,000 |
214,000 |
|
Minor-Moderate
Injuries |
3,433,000 |
3,020,000 |
78,000 |
1,183,000 |
65,000 |
85,000 |
|
Serious-Fatal
Injuries |