Average Annual Daily Traffic (AADT) is a measurement that tells transportation planners how many vehicles use a particular road on an average day throughout the year. It's calculated by counting all vehicles that pass a point on the road over a year, then dividing by 365. Municipalities and provincial transportation departments use AADT data to decide which roads need widening, where to install traffic lights, and how to prioritize road maintenance budgets. A residential street might have an AADT of 500, while a major highway could have an AADT of 50,000 or more.