AADT

The AADT module converts commercial vehicle GPS data and reference counts into modeled Annual Average Daily Traffic estimates for the road network.

AADT is the foundational volume metric used in transportation planning, federal funding applications, infrastructure investment decisions, and environmental impact assessments.

Altitude AADT delivers segment-level estimates for three vehicle weight groups: Universal (all vehicles), Heavy (GVWR Classes 6-8), and Medium (GVWR Classes 3-5). Each estimate includes a 90% prediction interval. Altitude produces estimates annually and validates them for temporal and spatial coherence before delivery.

Use cases

Quantifying vehicle volumes by weight group. Use the getModeledAADT endpoint to retrieve segment-level estimates for a specified zone, year range, and vehicle group, then aggregate or filter results to focus on the traffic categories required for your reporting or planning use case.

Supporting federal reporting and investment decisions. Use the API response to complete HPMS submissions, justify infrastructure funding applications, and identify corridors where commercial vehicle volumes warrant attention. The response includes segment-level AADT estimates with prediction intervals, vehicle group breakouts, and estimate methods.

AADT results

This section describes how to interpret AADT outputs returned by the getModeledAADT API.

Altitude currently delivers AADT as an API-only product. Each section below explains a component of the API response and how to use it.

Result components

Each row of an AADT result represents one road segment, one vehicle group, and one year. Core fields include:

  • Segment identifier (SegmentId)
  • Modeled AADT value
  • Lower and upper bounds of the prediction interval, expressed as relative percentages
  • Estimate method
  • Geographic context such as zone identifiers, road class, and direction

Each segment may have AADT values for one or more vehicle groups (Universal, Heavy, and Medium). Not every segment has estimates for every vehicle group. Altitude excludes segments with insufficient observed data for a given group rather than reporting them with low confidence.

The isDirectional request parameter controls AADT reporting direction. When set to true, results return per direction of travel. When set to false (the default), results consolidate for the road segment as a whole.

Accuracy and validation

Accuracy metrics including R², MAPE, and benchmark comparisons against FHWA traditional counts and published probe-based AADT studies will be disclosed in an upcoming AADT Technical White Paper.

Prediction intervals

The prediction interval communicates the uncertainty around each AADT estimate using asymmetric lower and upper bounds expressed as relative percentages.

The prediction interval communicates the uncertainty around each AADT estimate. The lower and upper bounds are expressed as relative percentages of the central AADT value and are asymmetric by design. A wider interval indicates higher uncertainty for that segment, typically driven by lower observed data density, atypical road characteristics, or unusual year-over-year change.

When using AADT for planning decisions, treat the interval as the relevant range for that segment, not just the point estimate. For decisions that aggregate across many segments, for example, regional VMT, the aggregate is generally tighter than any individual segment.

Estimate method

The EstimateMethod field indicates whether each AADT estimate is directly anchored to observed reference counts or produced via time series projection.

The EstimateMethod field indicates the data source type for each estimate. Observed indicates years where HPMS reference counts were available to anchor the model directly. Projected indicates years where Altitude produced the estimate via time series projection from the observed years.

For most reporting and planning use cases, observed and projected estimates can be used interchangeably. For analyses that depend on the most current year of data, use the EstimateMethod field to identify which estimates are projections versus directly anchored.

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