Signal timing and coordination involves traffic data collection, speed evaluation, sophisticated optimization algorithms and field calibration. At an individual intersection, signal timing is tied closely to local traffic demand.
For example, at the intersection of Veterans Boulevard and 23rd Avenue E., traffic goes north/south 8-35 times more during the peak hours compared to the traffic turning east or west and thus requires more time.
Green Light Corridors
Traffic signals are coordinated along the major corridors of Veterans Boulevard, 32nd Avenue, 13th Avenue, Main Avenue and Sheyenne Street. This means they are strategically timed to move large groups of traffic through efficiently.
Signal coordination requires careful consideration of traffic speeds, distance to upstream signals, amount of green time available at adjacent signals, protected turn phasing and a mix of other factors. Because of this mix of factors, perfect coordination is impossible. However, when the City first implemented coordination in the spring of 2016, before and after travel time studies found that overall stops in the City were reduced by a staggering 26 percent.
This also reduces crash potential, vehicle emissions and overall delays. Spread over an entire year, it is estimate that signal coordination saved commuters over 12,000 hours of total traffic delays.
Signal Light Cycles
One of the downsides of system-wide coordination is that you must wait on side-streets to enter the coordinated major corridors. Although this can often feel like an agonizing amount of time, the signals cycle through all traffic movements between 80-110 seconds throughout the day. This means, that unless you’re forced to wait through multiple green lights, you are never waiting more than 110 seconds.
Because of the decrease in traffic at night, coordinated timing is not necessary and lights change based on motion sensor.
Factors that Impact Traffic Signal Coordination
There are a variety of factors that may cause a driver to wait through multiple green lights or hit two red lights in a row on a green light corridor. A few of the most common causes are:
- Emergency vehicle preemption causing the signal to break from it’s original plan and service the needs of emergency responders;
- Frequent pedestrian crossings of a major corridor;
- Faulty detection of vehicles;
- Construction altering traffic patterns;
- Events leading to higher than normal traffic conditions.
There are also signals in the city that are overcapacity during peak periods of the day. This means that there is more traffic than the intersection is currently designed to handle. Without millions of dollars’ worth of infrastructure improvements, we can only balance the needs of the different directions of travel and mitigate issues with signal timing.
Updates to Traffic Signal Coordination
Timing plans are constantly being updated, tweaked and monitored. Timing plans are updated every few years, when major developments occur and during construction season.
Data is collected periodically, and staff is constantly reviewing operations in the field and online via the city’s central control system. With traffic patterns constantly evolving, we also rely heavily on observations from the public.