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Re: Monitor traffic speed



Mark Sylvester wrote:

If you could set up two light gates that could do the
job, [of measuring speeds of cars] but one would not
want to leave the setup unattended.

Practical issues aside, a one gate system may also work.
Assume the light detector probe is sensitive to your
laser beam. Send that beam to the other side of the
street, reflect it at 45 degrees and bring it back to
the same side (after the second 45 reflection) where
the light probe is located.
/ --> \


I I
/ \ I
I I
I \ /
I I

Laser Light probe

The distance between the two crossing beams should be
longer that the length of a bus or track. For each vehicle
there will be TWO "dark pulses". Suppose time records are
kept for the arrivals of dark pulses, something like I had
for the Vernier Geiger counter. Knowing the distance between
beams and the times of arrivals one can calculate the v of
each car. The assumption is that two cars never pass each
other between the beam lines.