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Signal Warrant Studies, New Left Turn Arrows

Typically left turn arrows reduce delay for left turning vehicles and increase delay for through traffic.  By definition, a green arrow for left turning traffic means a red light for other traffic.  Also, left turn arrows may reduce accidents involving left turning vehicles but may increase other type of accidents.

Prior to the installation of left turn arrows at an existing traffic signal in Scottsdale, a thorough study is completed that analyzes the anticipated advantages and disadvantages of the proposed left turn arrows. The analysis considers three factors; traffic volume, traffic delay, and traffic accidents.

The traffic volume consideration compares the number of vehicles turning left to the number of vehicles traveling straight in the opposite direction. The traffic delay consideration evaluates the decreased delay for left turning traffic to the increased delay for all other traffic. All traffic accidents - including those involving left turning vehicles - are analyzed.

Questions contact Traffic Engineering staff at 480-312-7696