Baker Institute report: Houston’s red-light cameras reduce accidents

Baker Institute report:
Houston’s red-light cameras reduce accidents

Rice News staff

Cameras placed at intersections across Houston to monitor
compliance with traffic laws reduced the number of accidents by almost 30
percent per camera, according to a new study published by the James A. Baker
III Institute for Public Policy. The report estimates that camera-surveilled intersections
prevented about 792 collisions between September 2006 and December
2009 — the period when the cameras were in place.


Moreover, the study found the presence of a second camera
at an intersection further reduced accidents. Installing one camera to monitor
one approach at a four-way intersection curtails accidents on that particular
approach, according to the report, but it has no impact on the other three
approaches. A second camera monitoring a second approach, however, reduces
“the number of collisions substantially more than one camera alone.”

“Statistical tests showed that camera installation
does reduce collisions, but the size of the effect depends on how many cameras
are installed, which approach we study and how long the camera is in
place,” the Baker Institute report said. “In every case, the benefits
of having cameras on an intersection grow with time, perhaps as drivers learn
to watch for the cameras.”

Robert Stein, the Lena Gohlman Fox Professor of Political
Science at Rice University and a fellow in urban politics at Rice University’s James
A. Baker III Institute for Public Policy, co-authored the study, which was
funded by Rice University and the Baker Institute. The study is based on collision
data by intersection and approach from the Crash Record Information System
database compiled by the Texas Department of Transportation. Graduate students Matthew
Loftis and Aleksander Ksiazkiewicz co-authored the paper with Stein.

“If the Houston program were an experiment, the
cameras would have been installed at intersections chosen at random,” the
authors wrote. “To get around the problems with making simple comparisons,
we chose to use all of the data available to us to build a statistical model of
traffic accidents. We use this model to simulate the number of collisions at an
average intersection approach with or without cameras installed. The simulation
approach solves our problem because it provides a baseline for comparison that
is built from the information collected at all 50 intersections and 200
intersection approaches and incorporates everything we can measure about what
causes traffic accidents.”

The study’s authors controlled for a number of factors
that could have an effect on the frequency of traffic accidents, including
weather, geography, the natural decline in the number of accidents across all
intersections in Houston between 2003 and 2009 and seasonal differences in
traffic patterns.

“Within 12 months of installing one camera at a
high-risk intersection, we estimate there will be about one less collision
every month, and this drop will be permanent,” Stein wrote. “The data
indicate that the effect of one camera on the other three approaches in the
intersection is virtually nil.”

However, the installation of a second camera at the
intersection not only cut the number of accidents from that approach but also
had a spillover effect of reducing collisions even on the two approaches
without any camera.

Red-light cameras were first installed in Houston in 2006.
Their presence has prompted a good deal of discussion, and activists seeking to
remove the cameras collected more than 20,000 signatures on a petition to place
the issue on the 2010 ballot. Voters agreed, and the cameras were turned off
until a federal judge overturned the referendum’s results in June. The issue is
still up in the air, with the Houston City Council expected to decide on the
future of red-light cameras soon.

To read the report, go to



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