AADT, ADT and the language of traffic counting
Traffic planning has its own vocabulary, built in an era of two-week tube counts. Here are the terms in plain language, and what happens to them when measurement becomes continuous.
Traffic engineering grew up with expensive, short measurements, and its vocabulary shows it: annual averages estimated from samples, correction factors for the season the tubes happened to lie on the road, and figures that live for a decade because remeasuring costs money. The terms below are the ones that matter in most municipal conversations, explained plainly, with a note on what continuous measurement does to each. National definitions belong to the road authorities; where an official figure exists, use theirs.
AADT: the headline figure
Annual average daily traffic: a year of traffic at a point, divided by 365. It ranks roads, triggers design standards and anchors noise and safety calculations. The catch on local streets is that no one publishes it for you, and deriving it from a two-week sample means multiplying a short truth by a long assumption. A continuous series makes AADT an arithmetic fact instead of an extrapolation.
ADT and the period problem
Average daily traffic over a stated period is the workhorse for real questions: the summer street, the roadworks detour, the event weekend. With samples, every new question is a new field campaign. With a continuous series, ADT for any period is a query, and before/after comparisons, the thing municipalities actually decide on, stop depending on whether anyone thought to measure “before”.
Directional split, rhythm and class
Three descriptors turn a count into a picture. Directional split by hour reveals the commuter tide. Weekly and seasonal rhythm separates the school-run street from the weekend destination. Movement class, vehicles, cyclists, pedestrians, tells you who the street actually serves, which is the question most urban redesigns turn on. Modern sensor measurement, compared method by method in our traffic counting guide, delivers all three from one installation, continuously, anonymously.
The term that is quietly retiring: “measurement week”
The strangest convention in traffic data is that a street’s truth is whatever happened the week someone measured it. Continuous, privacy-first measurement retires the concept: the street simply has data, all year, and every term in this glossary becomes something you read off rather than estimate. What that requires from a procurement is covered in the municipal guide.
We have extensively evaluated Bumbee Labs' solution and the quality insights they produce, in combination with the efficiency of the remote installation process, make this a valuable collaboration. This alliance presents a great opportunity for our distribution ecosystem to provide a variety of service offerings to their customers, opening up new revenue streams.
Frequently asked questions
What is AADT?
AADT, annual average daily traffic, is the total yearly traffic volume at a point divided by 365: the standard headline figure for how busy a road is. National road authorities define and publish AADT for their networks; local streets usually have no official figure at all, which is where municipalities measure for themselves.
What is the difference between AADT and ADT?
ADT, average daily traffic, is the average over a shorter, stated period, a month, a season, a campaign. AADT smooths the whole year into one number; ADT answers questions about a specific time. Continuous measurement gives you both from the same series, instead of estimating the year from a two-week sample.
What is directional split?
The share of traffic in each direction, hour by hour. A 50/50 street and a commuter street with a morning tide need different signals, crossings and parking logic, and the split is often the fastest way to see which one you have.
How long should a traffic measurement period be?
With sampled methods, the honest answer is a compromise: long enough to catch weekly rhythm, short enough to afford, and hopefully a representative season. Continuous measurement dissolves the question: the period is simply the series, and any AADT, seasonal or event figure is a query rather than a new field campaign.