Road Q
Although Road Runner attempts to make Road Q questions and answers short and sweet, this one's unusually long because it's a complicated subject, and we've received lots of questions about it. In order to clear things up for drivers, we're including unabridged responses to the question.
Reader Steve Kurtz submitted this question:
There are two intersections that have the "Michigan left" turns. If I'm eastbound on Grant and want to go north on Oracle, the turning lane features a flashing yellow arrow allowing me to perform the U-turn without waiting for a green arrow. Then, when I get to Oracle, I can turn right on red.
If I'm eastbound on Ina and want to go north on Oracle, the turning lane does not give a flashing yellow arrow. I'm forced to sit in the turning lane until I get a green arrow. Then, when I get to Oracle, I cannot turn right on red even if the way is clear.
I understand one is in the city and one in the county, but why are they not both the same? Personally, I think the method instituted on Grant is the more sensible, as it allows traffic to keep flowing when the way is clear. Ina forces me (and several others) to sit and wait.
What is the reason for the two turns being implemented differently?
Michael Graham of the city's transportation department responded:
The reader is correct, the Grant/Oracle indirect left is in the city of Tucson. I cannot speak to why the county has a different system.
As for the city, no left turns are permitted from Grant Road to Oracle Road. To make a left turn from Grant to Oracle, drivers must drive past Oracle Road, make a U-turn at a traffic signal specially designed for U-turns, and then make a right turn at Oracle Road.
The “U-turn” signals, located near 14th Ave and 10th Ave use a special signal — a protected-permitted flashing yellow arrow, or “PPLT.”
This protected-permitted flashing yellow arrow signal usually displays a flashing yellow arrow to U-turning drivers. The flashing yellow arrow allows drivers to complete their turn without stopping provided it is safe to do so. When the flashing yellow arrow is displayed, oncoming traffic has a green light and turning traffic must yield.
If a driver wishing to make a U-turn is unable to complete their turn within about 30 seconds, the traffic signal will display a green arrow to allow them to safely make a U-turn while the oncoming traffic is stopped.
After the turning vehicles have completed their turns, the green arrow will turn yellow, then red to allow oncoming cars to enter the intersection. No turns are permitted during the red arrow. The arrow only stays red for a few seconds before returning to the flashing yellow arrow display.
The city of Tucson Department of Transportation designed this three-intersection indirect left turn system to work as a coordinated unit. This allows the maximum number of vehicles to safely pass through the intersections with the minimum possible delay, and without inconveniencing other modes of transportation.
Priscilla S. Cornelio, director of the Pima County Department of Transportation, had this response:
The intersection improvements on Ina Road and Oracle Road is called the “indirect left” — slightly different from the “Michigan Left.”
The intersection improvements on Grant Road and Oracle are slightly different from the improvements on Ina Road and Oracle. The improvements at the respective intersections address different factors, although the concept of the indirect left is the same.
Here are some factors to compare:
The Ina/Oracle intersection has approximately 100,000 average daily trips (ADT) in comparison to Grant/Oracle at 75,000 ADT.
Oracle at Ina is an Arizona State Highway within the jurisdiction of the Arizona Department of Transportation (ADOT). Pima County and Oro Valley are the two jurisdictions involved with the indirect left signals at this intersection. ADOT is coordinating all three signals since this is considered a "system" with input from the two local jurisdictions.
Grant Road is three lanes and 35 mph whereas Ina Road is two lanes and 45 mph.
The reader’s question regarding the right turns and their differences involve two things: a. Jurisdiction policy and b. Right-turn volume differential.
a. This design was jointly approved by not only the transportation jurisdictions, but the local residents at the time of design and was guided by the "Manual of Uniform Traffic Control Devices."
b. The traffic movement of this project was initially trying to solve was the westbound to northbound right turn lane queue and wait time. The westbound to northbound movement has two dedicated right turn lanes regulated by a signal. This signal compensates for the fact that the inside lane in the dedicated right turn lanes has no sight distance to see cars proceeding north on Oracle Road and provides positive control and allows for a safe movement onto Oracle Road.
Although the concept is the same, the mitigating factors for the two intersections were different.
