Collisions between
Motor Vehicles, Pedestrians and Cyclists are governed by
some simple rules. Most reconstruction formulas are a
function of velocity, reaction time and a measure of a
road's friction called its drag co-efficient, or drag
factor. Gravity, along with the condition of the road's
surface, dictate the drag number. The simplest way to
understand a roads drag co-efficient is to know that if
you need 80 pounds of force to drag a 100 pound sled
along a road, the roads drag co-efficient is .8 Gravity
also dictates how far a launched object, like a
motorcycle driver, flies before coming back to land. On
Earth the gravitational constant is usually expressed as
32.2. In calculating Velocities, Miles per hour are often
converted into feet per second for use in these formulas
by multiplying by them by 1.45. For instance at 50 Miles
per Hour a vehicle is going about 75 feet per
second.Reaction times measure how long a motorist takes
to perceive a threat, decide on an action and undertake
it. Studies have shown that 10% of people need less than
.88 seconds to react, 50% less than 1.04 and 90% less
than 1.27 seconds in controlled experiments for simple
braking. |