AP-G84/04 Best practice in road use data collection, analysis ... - WIM

Accessed by AR - ARRB TRANSPORT RESEARCH on 04 Feb 2005
APPENDIX A – NATIONAL GLOSSARY OF TERMS
Austroads 2004
— 58 —
Best Practices in Road Use Data Collection, Analysis and Reporting
Annual Average Daily Traffic AADT is a measure of the average daily traffic passing a
roadside observation point over the period of a calendar
year. One method of calculating AADT is by counting the
total volume of traffic passing an observation point and
divided by the number of days in that year (365 or 366 days).
Annual Average Weekday Traffic AAWT is the average 24 hour traffic volume on weekdays
(Mondays to Fridays excluding public holidays) throughout a
12 month period, at a specific observation point.
Average Daily Traffic ADT is a sample of the AADT and is the traffic count
averaged over a particular month, a week or a few days.
Average Weekday Daily Traffic AWDT is taken as the average 24-hour count over a
consecutive seven-day period from Monday to Sunday. It is
often considered because of the empirical observation that
the longer the counting period used to observe a traffic
stream, the better the resulting estimates of the design
parameters AADT or HHV.
Average Weekday Traffic AWT is taken as the average 24-hour count over the period
Monday to Friday. In some situations the average seven-day
weekly traffic may be required and referred to as Average
Weekday Daily Traffic (AWDT).
Axle counts This is the number of actuations on an axle sensor such as a
pneumatic tube as the wheels of vehicles cross over the
sensor.
Axle pair counts This is one half of the number of axle counts and is used as
an indication of the number of vehicle counts. Axle pair
counts are always less than the number of vehicles and can
only be an approximation because a traffic stream will have
vehicles with more than two axles. A correction factor is
usually applied after calibration.
Design Hour Volume DHV is the traffic flow rate chosen as the design traffic load
for a facility over its design life. Common practice is to
choose an ‘nth’ HHV as the design volume, with the 30 th
highest hourly volume often used in a rural environment and
the 80 th HHV in an urban area. The 100 th HV (or 100 HV) is
used on National Highways. This probabilistic concept is
chosen because it is uneconomic, if not impossible, to
design a facility realistically to meet the highest traffic flow
rate.