On Sat, 09 Jul 2005 12:04:51 GMT, Gene Kearns
wrote:

I've always enjoyed this argument.... firetrucks have flashing lights
about as bright as the sun, 200db+ worth of horns and sirens, and are
about the size of a small swiftly moving cottage......

Actually, it's less than 100 db measured by spec, but volume isn't the
problem - it's the placement of the output speakers.

In the old days, sirens could be located anywhere they wanted to put
them on the front of the truck. Which meant that the sound was
directed down, up, around, through - sometimes you could have a fire
truck enter an intersection, lights and sirens full blast and still
have an accident. All the accidents had one thing in common - "I never
saw it coming".

It puzzled a lot of folks for quite a while until some bright
engineer at a computer company got to looking into it.
He discovered that the sound disappeared to a level of 10/25 db
anywhere from 60 to 100 feet from the front of the vehicle at speed.
There were any number of variables from weather to atmospheric
pressure to time of day.

He also experimented with different siren types from PA horns to small
electrostatic high volume speakers, varied pitch, speaker placement -
nothing seemed to change the sound physics He did discover that
placing the speaker as close to nominal average height of an
automobile significantly increased the recognition factor, but that
didn't account for vehicles like motorcycles and trucks. Adding
additional speakers higher tended to work in the opposite direction
and the investigator ran out of time to investigate this particular
quirk.

The upshot of the sound thing is that with modern cars, music systems,
sound dispersed systems and the lack of really high power audio
systems, sirens don't do much at all.

With respect to light, the current move to strobes also has it's
attendant problems mostly related to too much. There have been
reports of drivers on dark nights being blinded by strobes and having
accidents as a result. The other problem with strobes is that they
are so bright that you can't tell which direction they are coming from
at an intersection - you would think differently, but it aint' so.

....... I'd think visibility wouldn't be a problem, even if they were
painted with invisible paint....

Believe it or not, it is. I retired from my volunteer rescue squad
after an ambulance/auto accident which was rather spectacular - the
result of a driver not seeing or hearing the ambulance at a wide open
intersection.