Tuesday, March 14, 2017 - 3:15 PM

Traffic Lights: Affixed vs. Hanging

The City of St. John’s favours hanging traffic signals over affixed. Affixed signals are not always the best option because they shorten the life of the pole. As the number of lights required on a pole increase, the likelihood they can be affixed decreases. 

Traffic engineers have to take all factors into consideration and make the best possible decision for the conditions and infrastructure.
 
Affixed vs. Hanging
When wind blows on a traffic light that is affixed, the load is transferred to the pole, which fatigues it, requiring more robust poles and risks failure of the entire pole. When wind blows on a traffic light that is hanging, the load is dissipated by the signal, which is hung so it can move with the wind.

The City has two types of hangers for light fixtures:

  • The rigid mount has a spring cushion that allows for some movement. This type is most commonly used throughout the city.
  • The swivel mount allows much more movement, providing it 90 degrees in either direction to swivel. 

Additionally, our light fixtures are not hung by chains – rather, the chains are a safety precaution should the mount break. This gives crews time to remove the fixture before it falls to the ground.

Although more than 140 fixtures were damaged during the recent wind storm, they did not all fall from the poles. In fact, most of the safety chains held and many of the lights missing from poles were removed by staff.

The City of St. John's continuously reviews traffic mount designs, and improving the safety chain mount is a priority. The winds experienced in the city on Saturday were far from typical. This strength of wind hasn’t been recorded in St. John’s for 40 years.

View our photo album showing damaged traffic signals, mounts and chains.