The Traffic Signal Modification Process

Red, yellow, and green are three colors that engineers cannot forget when preparing design plans for a roadway widening project.  Almost every roadway widening project – when the widening extends through an intersection or multiple intersections – requires one or more traffic signal modifications.  Signal modifications are required due to new curb locations which require new pole locations.  With new pole locations come new signal head locations since the signal heads need to line up properly with the traffic lanes.

Traffic Signal Modification

This article will explore the process of designing and constructing traffic signal modifications.

There are several steps involved in preparing a traffic signal modification plan and constructing the traffic signal modifications.  These steps are as follows:

  1. Prepare an accurate base map

Preparing an accurate base map is key to ensuring that there are no issues during construction and thus no contract change orders requested by the Contractor.  Key components of preparing an accurate base map for a traffic signal modification plan include:

  • Measure existing mast arm lengths
  • Determine location of existing signal heads
  • Determine location of existing traffic signal poles relative to existing curb returns

2.  Construct new traffic signal poles in locations that the existing traffic signal can remain in operation at all times.  Cover new traffic signal heads to avoid driver confusion

The photo below shows the construction of a traffic signal at the Jamboree Road and Michelle Drive intersection in Irvine, California.  The photo below shows an existing traffic signal fixture in operation with the new, unactivated traffic signal fixture behind it.

Traffic Signal Modification

When the new traffic signal equipment is installed, tested, and is ready for full operation, the old traffic signal equipment will be removed.  The new traffic signal equipment is activated, and the traffic signal modification is complete.  Well, almost.

Lastly, the traffic signal timing will be adjusted according to observation of the new traffic signal in action.



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