Average Daily Traffic(ADT)
It is the average 24-hour volume at a given location for some period of time less than a year. For this minimum of 7 days count is done to include the daily variation like on Saturday and Sunday.
Annual Average Daily Traffic(AADT)
It is the average 24 hours traffic volume at a given location over a full 365 days. Total traffic and classified traffic are calculated. It helps in deciding the relative importance of a route and road development. It includes seasonal variation also.