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Nationally, crashes that occur at or near intersections are responsible for one-fourth
of all traffic-related fatalities and about half of all injuries.
Many states such as South Carolina have made reducing crashes at intersections a high priority.
Joey Riddle: “This project began in 2009.
At the time, our Strategic Highway Safety Plan had a goal to reduce fatalities and serious
injuries by 25 percent.
This systemic approach and this project was one of the ways we wanted to achieve that goal."
The agency conducted a five-year analysis of traffic crash data and identified intersections
as a place where low-cost safety improvements could be made.
Jeff Shaw: “Traditionally, you would take the number of crashes over a three-year period
and design very customized improvements to fix an intersection.
The problem with that is, it’s reactive, time consuming, and very expensive.”
Instead of the traditional approach, it involves three steps.
First, analyze system-wide data to identify a problem.
Next, look for similar risk factors present in many severe crash locations, then look for
other locations with similar risk factors.
Finally, deploy low-cost countermeasures.
The key, however, is to do this on a large-scale across a community or region.
Joey Riddle: “I think in the past our typical approach was to install hot spot locations
which may involve a signal or a left-turn lane.
The cost of such projects would be roughly a half a million dollars.
This systemic approach allowed us to treat nearly 80 projects for the same price as one.”
The South Carolina DOT identified and targeted more than 2,000 locations across the state
to receive improvements, mostly in the form of updated signing and pavement markings.
The intent was to reduce the frequency and severity of crashes at stop-controlled intersections
by alerting drivers to the presence and types of an approaching intersection.
They started with a standardized package of enhanced signing and pavement markings and
tailored each site as necessary.
The standardized package included signs on both the left and right side of the road;
larger, oversized signs with high-intensity fluorescent sheeting;
retroreflective sign post panels; solar-powered, sign post-mounted flashing beacons.
Pavement marking improvements included properly placed stop bars; double-solid yellow centerlines
and dashed lane edge lines; lane use arrows and word messages.
Additional systemic treatments can include removing obstructions that limit sight distance,
advance transverse rumble strips, or high-friction surface treatment.
Jeff Shaw: “Friction at intersections is important because of the constant patterns
of slowing, turning, yielding, and stopping.
Higher friction can reduce the critical distance needed to stop so higher friction at an intersection
can be the difference between a close call and a crash.”
A scientific analysis of more than 400 improved stop-controlled intersections in South Carolina,
over a ten-year period, showed a 10 percent decrease in fatal and injury crashes.
Each intersection improvement cost an average of $6,000, resulting in a benefit-cost ratio
of 8 to 1.
Joey Riddle: “I’ve been in the traffic safety field for over 20 years, and this project
has had the greatest safety impact of any that I’ve been involved with.”
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