Survey Data and Deliverables

The three primary products of the aerial traffic surveys are:

Aerial photography was selected as the best means of collecting mobility data across the large planning regions.

During survey operations, 100% overlapping aerial photographs are acquired of all surveyed highway links at a frequency of one sample per hour, repeated weekdays between 6:30 and 9:30 a.m., and between 4:00 and 7:00 p.m. So that the effects of incidents can be identified and removed, and to reduce the effects of daily fluctuations, coverage is repeated over four different weekday mornings and evenings. After flights have been completed, photography is segregated by highway, and counts are made of the number of vehicles operating in each segment, in each direction. Raw data are entered into a database file for computation of densities, levels-of-service, and surrogate levels-of-service (the latter for interrupted-flow highways).

Once performance measures have been computed for all flights, data scrubs are conducted to screen for anomalies by comparing the results, segment by segment, across different days and time slices. This process is used to identify the effects of incidents and other non-recurring events that affect traffic quality. Where confirmed or suspected incidents / events are found, corresponding data are tagged for exclusion from the averaging process. Final (averaged) performance ratings, therefore, reflect normal traffic conditions, without the effects of non-recurring events. It is these ratings that form the technical basis for the analyses in the survey deliverables.

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