Monday, May 5, 2008

Another eternal question

It's obvious I've got some savvy Chicago natives reading this blog, so maybe y'all can help me comprehend the incomprehensible, as my Google-fu has failed me:

How the heck do they switch the direction of the Interstate express lanes?

I understand they've got a series of gates at the entrances to the reversible lanes, which swing shut to keep traffic from pouring into them. But given the non-stop nature of Chicago highway traffic, how do they clear those entrance ramps long enough to shut the gates? At virtually any given moment, it seems like there'd be someone driving into the entrance, who'd unavoidably smash through one or more of the closing gates. How do they do it??

8 comments:

Eric Allix Rogers said...

I've been quite curious about that for a while, too. I don't know, unfortunately. If I had to guess, they probably have sensors in the lanes leading up to the entrance, that they can use to find a clear moment to close the gates once the decision has been made to do so. Since you'd want the lanes open to the side with the heaviest traffic, they shouldn't reverse until traffic is lower, at which point they'd probably be able to find the time to close them.

That said, I mainly commented so that I'd get a notification if anyone posts the *real* answer...

BWChicago said...

http://www.timeout.com/chicago/articles/out-there/17777/whats-up-with-that
http://www.gapersblock.com/detour/high_on_lsd_and_stuck_in_traffic_again/

Robert Powers said...

an emergency foreman keeps tabs on traffic by driving up and down the Kennedy along the shoulder, and gives the go-ahead to reverse the flow.

So... basically they just have to watch for a gap in traffic and shut the gates when it comes? Whoa. Sounds risky!

BWChicago said...

Well, there are flashing warning signs that say DO NOT ENTER too, so theoretically they shouldn't be entering at that point.

Robert Powers said...

Ah, see, that's a crucial piece of information! I don't think I've ever seen these signs, certainly not while they're in operation. Guess I've always been too busy trying not to kill any of my fellow drivers to admire the scenery.

BWChicago said...

http://maps.google.com/maps?f=q&hl=en&geocode=&q=&layer=c&ie=UTF8&ll=41.971775,-87.747073&spn=0.013209,0.043259&t=h&z=15&cbll=41.963737,-87.749007&panoid=3CzujrjwyMyFfnl148diOA&cbp=2,95.51537519797836,,0,1.4716821630841295

The black box on the pole is one. They're designed to just look unobtrusive until they're lit, otherwise you can't really see what they are. Additionally, those overhead yellow signs that say "EXPRESS LANES CLOSED- DO NOT ENTER" are usually flipped a little while before they actually close.

http://maps.google.com/maps?f=q&hl=en&geocode=&q=&layer=c&ie=UTF8&t=h&cbll=41.966673,-87.753943&panoid=wmgAeiqUFw5TYxYCqQGPAQ&cbp=2,129.59637151729356,,0,-2.1612692774518067&ll=41.974711,-87.752008&spn=0.013209,0.043259&z=15

BWChicago said...

Those were truncated, obviously.
Unlit Sign - I should clarify that there are only on immediately before, I think they say GATES CLOSING DO NOT ENTER or something to that effect.
Overhead sign

MF said...

I assume there are videocameras along the lanes as well, so operators can visually confirm that there's no traffic heading in one direction, before they switch the gates and open it to traffic traveling the opposite direction? Now you've got me wondering!