Traffic-Safety Department studies safety; maintains approximately 1,500 signals & 150,000 road signs.
If you've ever noticed the safety problems that occur when a traffic signal goes "black," you can appreciate the vital 24-hours-a-day, 365-days-a-year mission of the Road Commission for Oakland County's Traffic-Safety Department.
But that's not all. The department also:
- Conducts traffic studies
- Handles pavement marking
- Installs/maintains guard rails, 150,000 traffic signs, and 1,500 signals on all county roads, most state trunk lines, and many city streets.
The electricity alone for traffic signals costs about $1 million a year.
Based on traffic information, various standards and regulations, accident pattern statistics and other data, department personnel conduct studies to evaluate speed limits and the need for new or different signs or signals. Before they can be installed, traffic signals must meet criteria called "warrants." Speed studies analyze driving patterns to see if speed limits should be adjusted -- either up or down. Studies are also done after major injury or fatality accidents. Sight distance -- which might limit visibility for drivers entering roads or intersections -- is also measured, and changes are made when necessary.
During power outages, department workers use portable generators to provide emergency power for traffic signals. They may also place temporary stop signs at "black" intersections. Repairs and resetting signal time clocks are done after power is restored. Traffic volume and intersection visibility problems dictate which signals are serviced first.
In response to growing traffic congestion and limited funding for road widening and construction, a computer-controlled traffic management system called FAST-TRAC was developed.
This innovative, federally-funded system has helped maximize the capacity of existing roads, improved traffic flow, and reduced serious intersection accidents. FAST-TRAC has given the Road Commission a global reputation in Intelligent Transportation Systems (ITS).
Visit the FAST-TRAC section of this Web site for more information.
Aside from FAST-TRAC signals, three types of signals are used: pre-timed, semi-actuated, and fully-actuated.
- Pre-timed signals have 24-hour clocks which change signal timing for morning and evening rush hours, and again when traffic is lower.
- Semi-actuated signals, often used where side streets meet busy roads, maintain "green" on the primary road until sensors detect side-road vehicles and then turn the light green for the side road.
- Fully-actuated signals have sensors to adjust traffic flow in all directions. Some traffic signals detect oncoming police, fire, and ambulance vehicles and automatically give them a green light.
For more information view our Speed Limits publication: