Philip,

On Tue, 15 Jun 2004 21:30:59 -0600, Philip Stortz wrote:

> in texas it's legal to buy a bear at 7-11

Unless it's a Polar bear, of course, when it would be cruel to keep it in all that heat :-)

> it could be argued that they should have coded rf transmitters in
> emergency vehicles resounding to a call so that cars could have
> receivers to alert drivers to the distance and direction of approach of
> emergency vehicles (without depending on people hearing and usually much
> later seeing them), i know it is sometimes hard to tell at first if they
> are close and what direction they are coming from, and i don't play the
> stereo loud, with some of today's idiots it's a wonder there aren't more
> emergency vehicle collisions, and there are a lot.

Actually they could do a lot to improve things without this - experiments on the sound that emergency vehicles
make discovered that they normally produce a sine wave, albeit of a varying frequency, and the human ear is
very bad at detecting direction in this case.  They (Manchester University, I think) developed a sound that
was much more effective: it was a fast-warbling "yelp" note that lasted for about 1.25 sec, then two loud
rasping white noise bursts (with emphasis on the lower frequencies, I think, so perhaps pink noise), then
repeated.

It sounded something like:  WeeWeeWeeWee  Pzzzzt  Pzzzzt,  taking about 2 sec to do each sequence.

The warble carries well and can be heard at a distance, and starting and stopping it was found to be more
effective than having it continuous.  The white noise was very good at giving direction information because
ears work well at doing this with lots of frequencies.  They found that drivers reacted more quickly and were
more likely to take the correct avoiding action than with any of the existing sounds, and they tried lots of
other combinations, and this was the winner.   They estimated it would reduce accidents involving emergency
vehicles on "blues and twos" by about 80%.

Unfortunately it doesn't seem to have been adopted, and I've only ever heard one ambulance using it - and my
personal opinion from that one occasion is that it works!

Cheers,

Howard Winter
St.Albans, England

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