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Snow is a medium of variable quality
for track reproduction. The best
quality track usually occurs in snow with moderate to high water content at
just freezing temperatures. Water can
be either frozen or liquid at 0 deg. C., and the right combination can provide
excellent results. Colder snow will
still yield results that will allow for track design determination, but the
chances of fine accidental characteristics will become less as the temperature
drops and as the age of the snow increases.
In addition, often the tire stance and wheelbase record of the
suspect vehicle can be determined at the scene, especially if left
in snow. With the measurements of the tire centers
from left to right for both axles, and the wheelbase from front to back, one
can gain much knowledge of a culprit vehicle from simply a dusting of snow on
cold pavement.
Tires can range in tread designs the same way that footwear
companies continuously vary their shoe tread designs. This variation along with the length
of time tires remain on a vehicle means that they offer great value in crime
scene examination, even if no accidental characteristics can be determined in
the tracks. A bonus is the chance that
tire designs may be mixed on the same vehicle. |
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In recording tire scenes, one must remember that at least two meters
of track should be recorded by photographic means. To do this accurately, not only
must a scale and track number be added to the photo view, but also a tape
measure running the length of the track should be visible to allow the final
photos to be correctly sequenced.
While photographing snow tracks is the normal method of recording,
for accurate reproduction of accidental characteristics, one must
cast the track, or at least sections of it. Snow wax and sulphur are two methods
normally utilized, and both require training and practice to yield quality
results.
The comparison of tire tracks and suspect vehicle tires must follow
a protocol that has been described in detail by Lawren NAUSE in his
book ‘Forensic Tire Impression Identification’, and by
Peter McDONALD in his book, ‘Tire Imprint Evidence’. Both books are required reading for anyone attempting to offer an
opinion in court on this type of evidence. |
