J. Utts et al., Statistical methods for estimating speed correction factors with confidence intervals for mobile source emissions models, TRANSP R D, 5(2), 2000, pp. 103-120
Citations number
11
Categorie Soggetti
Politucal Science & public Administration
Journal title
TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT
Speed correction factors are an important component of mobile source emissi
ons models. The current "ratio of means" methodology used by the California
Air Resources Board (CARB) and the US EPA does not provide estimates of er
ror or account for the dependence in the data. A repeated measures regressi
on method that takes into account the dependence in the data and provides e
stimates of error is proposed and illustrated using recent emissions data f
rom CARE, A method for calculating confidence intervals for the ratio of me
ans is also derived and illustrated. Using the same dataset, we find that t
he method currently in use, which fits a polynomial curve to the ratio of m
ean emissions: slightly underestimates the correction factors when compared
with the repeated measures method. However, both methods appear to overest
imate values in the middle range of speeds when compared with a method that
does not assume a polynomial curve. (C) 2000 Elsevier Science Ltd. All rig
hts reserved.