Saturday, January 26, 2008

Red light, green light, go go go

The mainstream press and bloggers from both sides of the aisle made a controversy this week about the Kentucky Transportation Cabinet's Elizabethtown district office's decision to install a left-turn traffic light on a turnoff that leads to the subdivision where new KYTC Secretary Joe Prather lives.

Unlike many others, we didn't get worked up over this. To the contrary, we think this was probably a good decision and one that should be emulated statewide.

We have a very reliable source in Transportation, so we checked with them to get information about not this situation in particular, but about traffic lights in general. Here's what we learned.

There are basically four types of signals or cycles that can be used at intersections with left turns. At intersections that have no specific signal or cycle to deal with left turns, the setup is called a "permitted left." That means that if traffic going through the traffic signal has a green light, traffic can turn left on green but only while yielding to oncoming traffic. This was the previous situation at the traffic light on Ring Road in E-town.

If one signal in one direction turns red before the signal for traffic in the oncoming direction does, or if the signal stays red after oncoming traffic gets the green, this is called a delayed or advanced red or green, depending on local terminology. Kentucky does not use this setup very frequently, but the best example that Kentuckians may be familiar with is the main drag in Gatlinburg. This setup is used at Traffic Light #8, for southbound traffic turning left onto Airport Road.

The third signal type is called a "protected left" and is when there is a special signal specifically for the left-turn lane. In Kentucky, those signals usually have red, yellow or green arrows instead of balls. You can only turn when the light above the turn lane is green. If the light for the turn lane is red but the light for the through lanes in the same direction of travel is green, you can't turn. A protected left is the safest left turn because the only time there will be oncoming traffic is if someone runs the red light.

The fourth signal type, which was the one installed in E-town, is called a "permitted/protected left" and probably is the most common signal used at left-turn intersections. When turning traffic has a green arrow, it has the right of way because oncoming traffic is being held by a red light. But when turning traffic has a green ball, it must yield to oncoming traffic from the opposite direction. The unofficial slang term for this type of light setup is called a "doghouse" because you have one red light in the center of the assembly, then four lights below the red (yellow arrow, yellow ball, green arrow and green ball) in a 2x2 setup.

Installing some form of a protected left is a highway safety issue. These lights are the safest. A permitted/protected left still offers a margin of safety because even if oncoming traffic is heavy, there will be a cycle for a protected left and motorists can be assured they'll get a chance to turn without having to judge the speed and distance of oncoming traffic.

We favor the installation of some type of dedicated left turn signals, be they protected or protected/permitted, at all traffic lights in Kentucky as a highway safety improvement. So we won't complain about Secretary Prather getting one for his neighborhood -- although we wonder if Prather is still living in E-town, and if so, does he get to drive a state car home every night. His predecessor, Bill Nighbert, moved from Williamsburg to Lexington. We wonder if Prather has any plans to relocate closer to his new Mero Street office in Frankfort.

And in case anyone wonders, the headline on this post is a song lyric taken from an old Kiss song circa 1977.


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