So it occurred to me today while I was running some errands, that I don't quite understand stop lights. Weird, huh? It's one of those things I question while I'm sitting there waiting for the light to turn green, but then quickly forget to ask somebody about later.
Today as I was once again questioning this issue, I realized I had wondered about it for YEARS, but haven't ever remembered to figured it out later on!! Well, I was on my last errand I was running for the day, so I forced myself to think "stop lights" "stop lights" "stop lights" all the way home, so I could GET SOME ANSWERS. I got some answers from my grandparents, who I had dinner with tonight, but I have more ponderings...
-So some intersections are timed and some have sensors?
-Do the timed intersections' "timings" differ at different times throughout the day? For instance, during rush hour time, are the timings quicker?
-The sensors only can read the first car there, right? What good does that do if there are 15 cars lined up on one street and only one car on the other? Shouldn't the intersection with more cars have a longer light than the one with one? And go first?
-How do the "stop light peeps" decide which intersections to sensor? Is it just based on the traffic count that flows through it?
Geez, so many questions! Can anyone enlighten me on the art of stop lights?
Gratefully appreciated,
Sarah
3 comments:
http://en.wikipedia.org/wiki/Traffic_lights
click on 6.3 Coordinated control
Its about like I thought, but its good hearing some of the details.
The basics:
Some operate under timed
Some operate under dynamic (using sensors in the pavement/cameras)
- may revert to timed if a button to cross is pushed
- also may adjust this depending on the time of day / expected direction of traffic
Bigger systems use coordination between intersections in an effort to give as many green lights to drivers as possible (based on expected speed between lights - sometimes this is regulated in an effort to prevent speeding)
- many adjust for rush hour to prevent congestion
- the most expensive systems (hundreds of thousands $ per intersection) adjust traffic continuously by using multiple sensors and sophisticated computers
Additionally police and emergency vehicles have encrypted frequency lights that can force the lights to change if they need.
Hope that helps
haha I was coming to leave you a comment about wikipedia and steve o already beat me to it.
The other thing to keep in mind is that you will see none of these techniques used effectively in Ames, IA - in fact, it's quite the opposite. If you ever have a spare 45 minutes, ask me what I think of our traffic infrastructure here.
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