Signal Pole Design Changes
By: Sue Zarling, State Signal and Lighting Engineer, MnDOT Office of Traffic Engineering
MnDOT is changing the traffic signal poles that we have used for more than 30 years. The old PA signal poles were designed using standards from the early 1990’s. While they have served us well it was decided that we should begin to use the current AASHTO LRFD standards for the design or our signal poles. While making the decision to change, design standards from several other states were reviewed and it was found that many others were also using updated AASHTO standards.
Changes to the new signal pole, called a TS pole, include using a round pole, rather than a multi-sided pole, and removal of the transformer base. While the vertical poles have not changed greatly in size the mast arm sizes have increased. Minnesota’s continued practice of allowing signs on our signal mast arms contributes to the overall size of our signal structures. The foundations have also changed to meet AASHTO LRFD requirements. These changes were required to meet the wind load requirements. MnDOT has kept the truss style mast arm since this minimizes bouncing of the mast arm, therefore preventing fatigue stresses on the pole. For maintenance purposes MnDOT will be extending the foundation 27 inches out of the ground with the vertical pole being placed on top of that.
Cities and counties are not required to follow MnDOT’s signal pole standards on their roadways. They can change designs along with MnDOT or continue to use the signal structure that they have been. MnDOT’s Standard Plates for the PA pole and associated foundations have been retired, but can be found under the discontinued plates on the Standard Plates webpage.
If a city or county is installing a signal on a MnDOT owned roadway they will be expected to include the new TS pole in the design. Please keep this in mind as you begin designs so you do not have to redo your work.
If you have any questions on the design of the new TS signal pole please contact Sue Zarling at susan.zarling@state.mn.us or 651-234-7052.