Wednesday, January 13, 2010

Left Turn on Red

I was driving today in downtown Boston where most of the streets are one-way and you find yourself going along rectangles of the streets again and again to find a parking spot. Like in an old computer game game.

A puzzle has startled me when I had to turn left and I am hoping you can help me figure it out. Imagine, that you are driving on a one-way street and you are turning left into another one-way street:

Can you turn left on red, from the leftmost lane, after stop? Why?

I felt unsure and decided not to risk turning. No one beeped from behind, seemingly agreeing with me. On the one hand, you would never turn left on red. But on the other hand, you could turn right on a red light in Massachusetts, if it is safe and unless a "No Turn On Red" signal is posted in front.

The left turn situation above is just a vertical flip of the right turn situation. If right turn is allowed, then left should also be.
What do you know?
What do you think?

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Kim said...

In many places, left on red from a one-way street to a one-way street is legal, which makes sense as you suggest.

According to wikipedia, it's legal in 37 states (see:, and one is my home state of Massachusetts:

I've certainly done this, and it does feel weird.

Maria said...

Very interesting!
I love to see that on so many states traffic laws follow the rules of logic. The rest of the states hopefully have some valid reasons to disagree.
In New York, for example, you can't turn right on red. So prohibiting left turn is also logical.

Kim is catching up with Alin!

MITBeta said...

This is also evidenced by the fact that you frequently see, in places like Boston, "No Turn on Red Signs" posted on the poll opposite the left lane on a one way street, when the crossing street is also one way to the left (as in your example).

If this were never legal, there would be no need to post a sign advising you of the law. In Manhattan, there is no turning on red at all, so you don't see any No Turn on Red signs anywhere.

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