Roadguy is behind on his correspondence, so let’s look at a little something from Elizabeth:
I have a question that’s been driving (ha ha) me crazy. There are yellow lights along the carpool lane on 394 that blink randomly. Sometimes when there’s a car in the lane, sometimes when it’s empty. What the heck are they doing?
Thanks for saving my sanity,
This question arrived some time ago, and it kept getting lost in Roadguy’s cluttered inbox, so he sincerely hopes that Elizabeth’s sanity was not actually dependent on a prompt answer. When Roadguy did finally forward the question to those in the know, he got a very thorough e-mail from Kevin at MnDOT.
…I believe the lights your questioner is seeing are part of the enforcement equipment on the MnPASS lane. As you know, people who use the MnPASS lane on I-394 who are driving by themselves during its hours of operation must pay a toll. To do this they must sign up to use the system and have a transponder. This is a small low-power radio device that interacts with antennas mounted above the lane.
The antennae are mounted on bridges or sign gantries along the corridor. On the other side of the bridge or gantry from where the antenna is mounted is a yellow beacon. It is square in shape, with a light in the middle.
Ever helpful, Kevin sent along a photo (which Roadguy has cropped down to blog size):
… When an active transponder passes under the antenna, the light that is mounted on the opposite side of the bridge or gantry flashes several times….
The lights are used by the law enforcement that patrols the lane…. The officer watches to see if the light flashes when a car passes underneath. If the light flashes, it means a valid transponder is in the vehicle. If the light does not flash, the officer will check to see if there are two or more people in the vehicle. If there are, it is a valid carpool and is allowed to use the lane for free.
If there is no flashing light, and there is only one person in the car, then that driver is illegally using the MnPASS lane and is subject to being stopped and ticketed. The ticket is $142.
The lights flash almost immediately upon transponder interaction, so if the antenna is mounted on a bridge, the car may not make it all the way past the bridge before the light is done. However, if there are a couple cars together, one in front of the other, it might appear that the light is flashing as the front car passes when the second car is actually triggering the flasher.
So there you have it, Elizabeth. Hope that helps keep you out of a padded room.
I read your blog because I like transportation. I also like to nitpick about punctuation and grammar:
I’m visualizing apostrophe imperfection.
Heh — proper punctuation is almost as rare as proper turn signal use, and almost as distracting to the well-intentioned driver.
Roadguy wouldn’t want his readers to fret too much about their own punctuation, of course. So even if you don’t know the basic pluralization rules of your native language, keep those e-mails and comments coming.