APPLICATION OF SEASONAL ADJUSTMENT FACTORS TO SUBSEQUENT YEAR DATA

摘要

Seasonal adjustment factors are used by state highway agencies to convert short term traffic counts into estimates of Annual Average Daily Traffic (AADT). These factors are typically calculated from continuous traffic counter data. The protocol for the process is set out in the Federal Highway Administration’s (FHWA’s) Traffic Monitoring Guide (TMG). This protocol specifies that temporary counts collected during a year should be adjusted by seasonal factors computed from continuous data collected during the same calendar year. It had been suggested that, if the prior year seasonal factors could be used, AADT estimates would be available soon after temporary counts were conducted. This study investigated whether the seasonal factors from sequential years could be applied without loss of statistical accuracy. It was shown that there is no significant loss of accuracy in estimating AADT when prior year seasonal adjustment factors are applied to current year short term traffic volume counts. There is likewise no significant loss of accuracy when vehicle miles of travel are computed using prior year seasonal adjustment factors.