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TRAFFIC
FATALITIES AND INJURIES: THE EFFECT OF CHANGES IN INFRASTRUCTURE AND OTHER
TRENDS
Robert B. Noland
Centre for Transport Studies
Dept. of Civil and Environmental Engineering
Imperial College of Science, Technology and Medicine
London, SW7 2BU
An analysis of how various road infrastructure improvements affect traffic-related
fatalities and injuries is conducted while controlling for other factors
known to affect overall safety.
The road infrastructure elements analysed include total lane miles, the
fraction of lane miles in different road categories (interstates, arterial,
and collector roads), the average number of lanes for each road category,
and lane widths for arterials and collector roads. Other variables that
are controlled for in the study include total population, population age
cohorts, per capita income, per capita alcohol consumption, seat-belt
legislation (and seat-belt usage),
and a proxy variable that represents underlying changes in medical technology.
The data used is a cross-sectional time series database of U.S. states
and is analysed using a fixed effects negative binomial regression that
accounts for heterogeneity in the data. Data from all
50 states over 14 years is used. Results strongly refute the hypothesis
that infrastructure improvements have been effective at reducing total
fatalities and injuries. While controlling for other effects it is found
that demographic changes in age cohorts, increased seat-belt use, reduced
alcohol consumption and increases in medical technology have accounted
for a large share of overall reductions in fatalities.
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