- Why are traffic signals needed?
- Are traffic signals coordinated?
- Why does the signal go to the side street when no one is there?
- Why are the signals not coordinated on two way streets?
- How do timing plans work?
A. As traffic volumes increase beyond the capability of lesser controls such as four-way stops, it may be necessary to install a traffic signal. Before installing a traffic signal at an intersection, established minimum criteria must be satisfied. A review includes:
- Amount of vehicular and pedestrian traffic
- Need to provide interruption to the major flow for side street vehicles and pedestrians\
- Special conditions such as hills and curves
- Accident history of the intersection
- Proximity of schools.
A. Yes. The traffic signals within defined groups along major roads are coordinated using timing plans with common cycle lengths. Timing plans are designed to provide minimum delay and stop time within each group. This does not mean that drivers will attain a green light at every intersection, but rather delays and stops will be minimized.
A. The most common reason that a signal goes to a side street when there is no one waiting is that a car has made a right turn on red. Most signals in the County detect that no vehicle is present and will not service the side street.
A. There are computer controlled systems which time the signals on many of the major roads. The problem of designing coordination for two way streets is complex. Timing must be designed so that vehicles traveling in both directions arrive at intersections at the same time, considering traffic from the side streets and that intersections are not uniformly spaced.
A. Timing plans work by instituting a common cycle length (the amount of time necessary to display all traffic signal indications at an intersection) at intersections within a group. These plans control the points in a cycle length when the signals will be red, amber or green. By controlling the points when main street and side street greens occur, coordinated movement through an area can be achieved.
Revised June 5, 2015