Spatial Interpolation–Based Localized Growth Factors Compared to Statewide, Regional-Level, and County-Level Growth Factors for Local Roads

Abstract

The focus of this paper is on developing localized growth factors for estimating annual average daily traffic (AADT) of a local, functionally classified road (referred to herein as a local road). Statewide, regional-level, and county-level median and mean growth factors were computed and compared with localized growth factor estimates from spatial interpolation methods, such as Ordinary Kriging, inverse distance weighted (IDW), and natural neighbor (NN) interpolation. The use of Ordinary Kriging-based localized growth factor is recommended for a local road AADT estimation. If count-based local road AADT (c-AADT) figures for previous years are available, they, along with localized growth factors for those years, should be used to estimate the local road AADT (e-AADT) for the reporting year. The estimated AADT (e-AADT) for the base year and localized growth factors from the base year to the reporting year must be used for estimating e-AADT of a non-covered local road link for the reporting year. The c-AADT or e-AADT of the local road link can be used to compute vehicle miles traveled (VMT) for reporting purposes. The proposed methodology reduces the costs and other resources required for traffic data collection and for e-AADT accounting for spatial variations.