🚀 go-pugleaf

rhl@valhalla.mitre.org (Roger Lincoln) writes:
>Is it just blind luck or are the traffic lights on Rt 2, between 128
>and the Concord Rotary, *purposely* timed to make you stop ...
> after a year I've noticed a pattern

Traffic lights are driven by synchronous motors similar to electric
alarm clocks.  In the past, at least, traffic engineers deliberately
set up the timers along fairly long stretches so they'd have the same
overall cycle time.  That means that if two of them are on the same
circuit, they'll stay in sync regardless of power outages, because
they essentially count off ticks of the 60-Hz line frequency.

The trouble is that they usually aren't on the same circuit, at least not
for more than a few blocks.  If power goes out to a whole town and comes
back on simultaneously, the lights will stay in sync.  But if power is
shut off to a specific locality, its traffic lights will come back on
randomly with respect to others.

The net effect is that over time, entropy takes over and the lights wind
up having cycles that show exactly the "blind luck" Roger's talking about,
forcibly grinding traffic to a halt repeatedly for weeks or months until
the next power outage randomizes the cycle in a different direction.

In high school, one learns that entropy must be counteracted by
judicious application of energy.  I.e., tax dollars for traffic
maintenance.  Someone has to go to each traffic light controller and
adjust it whenever the power goes out.

Whatever happened to this seemingly necessary task?  Environmental types
like myself have come to wonder how much extra gas, pollution, and tire
rubber is consumed or built up due to this lack of attentiveness.

-rich