User`s manual

TDC Ultra User’s Manual
10-2
Spot Speed Studies
The Spot Speed study in the TDC Ultra is designed to allow you to measure
the speed characteristics at a specified location, typically an approach to an
intersection. This study is not meant to replace a formal speed study using
an automatic traffic recorder like those of the JAMAR TRAX series. Rather,
it is meant to be used when the approach speed of traffic is required as part
of a capacity analysis at an intersection, or possibly as a preliminary study
to find appropriate locations for a formal speed survey at a later date.
The procedure implemented in the TDC Ultra is based on accurately
measuring the time it takes a vehicle to travel over a known distance. The
observer presses one button when the vehicle passes over one point (called
the start line) and then presses another button when the same vehicle passes
over another point (the end line) which is usually 100-200 feet away. The
start and end lines may be cracks in the road, or markers on the side of the
road. The TDC Ultra accurately measures the time between button presses,
and calculates the speed.