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How do pelican crossings work?

  1. Dec 12, 2009 #1
    can anyone tell me how a pelican crossing works? ive found loads on web about how traffic lights in generalbut im interested in how the green man is generated one the pedestrian presses the button. is it a capacitor?

    thanks :)
     
  2. jcsd
  3. Dec 12, 2009 #2

    mgb_phys

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    They run on mains power.
    The button starts a cycle of turning on the amber, then red lights for the drivers and the green light for pedestrians. You could do it with a simple 555timer and a counter but I suspect for reliability and to allow more complicated schemes, eg shorter delays at busier times, you would use a microcontroller.
     
  4. Dec 12, 2009 #3

    Danger

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    What the hell is a 'pelican crossing'? :confused:
    Is this another instance of Florida weirdness?
     
  5. Dec 12, 2009 #4

    DrGreg

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    It's the standard name in the UK for pedestrian-controlled traffic signals.

    Pelican crossing.
     
  6. Dec 12, 2009 #5

    Danger

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    Thanks for the clarification, Dr. Greg. That's some mighty weird terminology.
    Here in Canada, a pedestrian crosswalk with a button has minimal effect. It causes the 'walk' light to illuminate upon the next normally scheduled switch of the main traffic lights. That points out to drivers the pedestrian right-of-way, which in normal traffic affects only someone turning onto the street in question (since someone already on that street is held up by the main lights). That right-of-way exists at all times, whether or not the intersection is lighted or even marked, but the light makes it more noteworthy.
     
  7. Dec 12, 2009 #6

    jtbell

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    There are also midblock crossings that aren't associated with intersections, and are activated on demand by pedestrians.
     
  8. Dec 12, 2009 #7

    Danger

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    True. That's a relatively new development in my area. There are none in my town, but Calgary has quite a few.
     
  9. Dec 12, 2009 #8

    DrGreg

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    To clarify, that is what we call a "pelican crossing" in the UK. We have lots of them (usually in places a considerable distance from a light-controlled intersection). The lights at an intersection are just called "traffic lights" regardless of whether there's a pedestrian button or not.

    One of the reasons "pelicans" have a special name is because the sequence of lights that the driver sees is slightly different: between red & green there is a flashing amber which means "give way to pedestrians, but otherwise, go".
     
  10. Dec 12, 2009 #9

    Danger

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    I guess that I won't be renting a car if I ever visit England. Staying on the wrong side of the road would take all of my concentration, never mind trying to learn your signal system. :rolleyes:
     
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