Making the grade
National Transportation Operations Coalition tool helps departments focus resources.
Developed in 2005 and updated in 2007, the National Traffic Signal Report Card covers management, signal operations at individual intersections, signal operations in coordinated systems, signal timing practices, traffic monitoring and data collection, and maintenance.
“We decided to concentrate on maintenance because we felt we could get the greatest return for the smallest initial investment,” says Peggy Allen, deputy director of the Traffic Engineering Department of DeKalb County, Ga. “Also, with congestion a major concern for metropolitan Atlanta, of which DeKalb County is part, we wanted to see how an effective program would affect congestion.”
When the department formalized preventive maintenance in 2005, its self-assessment grade in the report card's maintenance category was one point lower than the national average of 67, and congestion was costing the region almost $2 billion annually.
The department calculates “cost of congestion” using data from the Texas Transportation Institute's Annual Urban Mobility Report. In 2005, according to the report, the per-person value of the extra time and fuel consumed by vehicles traveling at slower-than-allowed speeds was $14.60/hour; and metropolitan Atlanta commuters were spending 60 hours annually stalled in traffic.
Thus, that year traffic delay added $876 to the average commuter's travel costs.
Let's look at how a malfunction at one of DeKalb County's largest intersections — Peachtree Industrial Boulevard and the I-285 eastbound ramp (pictured above) — affects traffic flow. The former has annual average daily traffic (AADT) of 109,800 vehicles and a peak-hour volume of 5,916; the latter an AADT of 32,038 vehicles and a peak-hour volume of 1,783. A one-hour repair at this intersection creates $112,405.40 in congestion/delay costs.
By 2007 the department's maintenance grade was 78 — eight points above the national average — and commuters were avoiding millions in congestion costs. –Stephanie Johnston
Source: DeKalb County Traffic Engineering Department