Temporal disaggregation of travel demand for high resolution emissions inventories

The commonly used photochemical air quality model, the Urban Airshed Model (UAM), requires emission estimates with grid-based, hourly resolution In co ntrast, travel demand models, used to simulate the travel activity model in puts for the transportation-related emissions estimation, typically only pr ovide traffic volumes for a specific travel period (e.g. the a.m. and p.m. peak periods). A few transportation agencies have developed procedures to a llocate period-based travel demand data into hourly emission inventories fo r regional grid cells. Because there was no theoretical framework for disag gregating period-based volumes to hourly volumes, application of these proc edures frequently relied upon a single hypothetical hourly distribution of travel volumes. This study presents a new theoretical modeling framework th at integrates traffic count data and travel demand model link volume estima tes to derive intra-period hourly volume estimates by trip purpose. We prop ose a new interpretation of the model coefficients and define hourly alloca tion factors by trip purpose. These allocation factors can be used to disag gregate the travel demand model 'period-based' simulation volumes into hour ly resolution, thereby improving grid-based, hourly emission estimates in t he UAM. (C) 1998 Elsevier Science Ltd. All rights reserved.