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Why does the presence of red-light running cameras increase my crash frequency?

2024-05-15T16:26:53+00:00May 13, 2024|
Dr. Fabio Sasahara
Dr. Fabio Sasahara

Have you ever evaluated the possibility of installing a red-light running camera in your signalized intersection and found that it increases the crash frequency?

When a signalized intersection is modeled using the Highway Safety Software using all default distributions from the Highway Safety Manual, a Crash Modification Factor (CMF) of 1.012 will be computedThis means the total crashes are expected to increase by 1.2% when red-light camera enforcement is present at the intersection.

CMF6 (Red Light Cameras) calculated in HSS using base distributions

CMF6 (Red Light Cameras) calculated in HSS using base distributions

Research has demonstrated that red light cameras effectively reduce right-angle crashes but also increase the frequency of rear-end crashes. A study by Persaud et. al, mentioned in the Highway Safety Manual (HSM), suggests a CMF for red light camera installation of 0.74 for right-angle collisions and a CMF of 1.18 for rear-end collisions.

When is it recommended to install red light cameras?

Based on the evidence provided by research and considering the trade-offs between right-angle and rear-end crashes, the economic benefits of a red light camera will become more evident at locations that experience higher proportions of right-angle crashes.

Calibrating crash proportions in the HSS

When modeling an intersection in HSS, open the “Parameters” section to start calibrating model parameters, including crash distributions:

Calibrating crash distributions in HSS

Calibrating crash distributions in HSS

Two parameters can be adjusted and are taken into account in the calculation of the CMF for red-light cameras:

  • Proportion of multi-vehicle crashes by right-angle collisions
  • Proportion of multi-vehicle crashes by rear-end collisions

As these parameters are calibrated, the calculations for the red-light camera CMF will be automatically updated. The figure below illustrates the sensitivity of this CMF when proportions are changed (right-angle proportions increased by 10%, and rear-end proportions decreased by 10%):

Comparison of CMF6 based on different crash distributions

Comparison of CMF6 based on different crash distributions

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