Traffic Signals

A traffic signal is any power-operated device by which traffic is warned or directed to take some specific action. The Washtenaw County Road Commission adheres to the regulations and guidelines provided by the Michigan Manual of Uniform Traffic Control Devices (MMUTCD). The MMUTCD specifies the size, shape and color of all traffic signs and signals. It also provides guidelines for installing signals.

The decision to install a traffic signal is based upon the following factors:

  • Vehicular and pedestrian volumes
  • Crash history
  • Vehicle delay
  • Vehicle progression

Traffic signals operate on one of three principles: pre-timed, semi-actuated and fully-actuated. Below is a brief summary of how the three operate.

  • Pre-timed Signal: A pre-timed signal runs a set timing plan independent of the existing traffic. It also has the capability of running different cycle lengths depending on the time of day.
  • Semi-actuated Signal: A semi-actuated signal includes a mechanism installed on the minor road that detects when traffic is present. This detection switches the green phase to the minor road to allow traffic to clear.
  • Fully-actuated Signal: A fully-actuated signal includes mechanisms installed on both the major and minor roads that detect the volume of traffic present. Based on the amount of traffic, the signal provides enough time to accommodate all of the vehicles.

The Road Commission receives many requests for traffic signals based on safety concerns. However, traffic signals do not always prevent crashes. In many instances after the signal is installed, the total number of crashes increases while the severity of the crashes decreases. While a properly placed traffic signal improves the flow and decreases serious injury crashes, an unnecessary one can be a source of danger and annoyance to all who use an intersection: pedestrians, cyclists and drivers.



Intersection Control Beacons (Flashers)

An intersection control beacon is a standard traffic signal head having flashing Yellow or Red indications in each face. They are intended for use at intersections where traffic or physical conditions do not justify conventional traffic signals but where high crash rates or potential exists and indicate a special need.


Dark Signals: What happens when a traffic signal loses power? 

During storms and high winds, the Washtenaw County Road Commission (WCRC) recieves many phone calls about loss of power at signalized intersections. Residents often ask how WCRC responsds to "dark signals" and how to drive safely through intersections where a traffic light has lost power. 


What are WCRC’s next steps after a signal loses power?

We appreciate the public notifying us of traffic signals that have lost power. When the public calls to report power outages at traffic signals WCRC contacts the power company immediately. Once we have determined that the outage is due to local power loss, we monitor the progress of the repair and operation of the signal.  

There are a number of factors that are taken into account when determining the appropriate course of action in response to the loss of power at a signalized intersection. The Washtenaw County Road Commission follows the Michigan Department of Transportation’s policy on “Dark Signals” caused by a power outage and utilize the policy’s options 1 and 2 for responding to “dark signal.”

“1.No action taken. Traffic shall proceed as per the Michigan Vehicle Code, Section 257.649, Right-of-Way; Rules; Violations as Civil Infraction

2. Traffic control is provided by uniformed police officers at the sole discretion and responsibility of the police enforcement agency in a manner determined solely by the police enforcement agency. (BOH IM 2004-24 -2- October 7, 2004)”

WCRC typically takes no action when a signal goes dark and drivers should obey the “Right-of-Way” rules (see “Driving Safely through ‘Dark Signals” section below). Citizens often request that WCRC place temporary stop signs at traffic signals that have lost power. WCRC does not place temporary stop signs at dark signals for several reasons which include:

  • Avoiding Driver Confusion:  Often it only takes a few hours before power companies are able to get signals back on. WCRC chooses to allow signals to return to stop and go automatically when the power is restored. If WCRC placed stop signs at dark signals, WCRC would have to turn the signal to an “all way red flash” mode to eliminate confusion of a conflicting message to drivers on whether they should obey the stop signs or the traffic signal indications when power is restored.  Additionally, it requires staff resources and time to return to intersections to remove signage and reconfigure the intersection to normal stop and go operation.
  • Crew Availability: Due to limited resources, WCRC does not have the staff capacity or resources to place temporary stop signs at every dark signal and be able to respond promptly to remove temporary signage when the power comes back on. When signals go dark, it’s often because of a wind, ice or other storm event and there are multiple signals out at the same time. 


Driving Safely through “Dark Signals”:

Many motorists believe that when a traffic signal loses power it becomes a 4-way stop. According to the Michigan Vehicle Code, when a signal loses power, the intersection becomes uncontrolled and reverts back to the basic right-of-way requirements. The intersection does not become a four-way stop.

Right-of-Way at a Dark Signal (Michigan Vehicle Code, Section 257.649, Right-of-Way; Rules):

1. “The driver of a vehicle approaching an intersection shall yield the right of way to a vehicle which has entered the intersection from a different highway or roadway.

If two cars meet at an intersection, the car that arrived first has the right of way.

2. “When 2 vehicles enter an intersection from different highways/roadways at approximately the same time, the driver of the vehicle on the left shall yield the right of way to the vehicle on the right.”

Always yield to the driver on the right; cars take turns in a counter-clockwise order