Emissions Analysis Techniques for TCMs
Overview - The bus replacement spreadsheet estimates the emission impacts of one-for-one replacements within an existing bus fleet, or purchases of vehicles not dedicated to specific service improvements. The methodology can assess the replacement of older diesel buses with new diesel or alternative fuel buses.
Strategies Addressed - Alternative fuel vehicles.
Methodology - The approach for estimating the emissions reductions of vehicle replacements is based on the average daily revenue miles per vehicle of in-service vehicles, the procurement/replacement schedule and the difference in emissions between retired vehicles and the replacement vehicles. Emissions are estimated based on the year of manufacture of old vehicles and the technology of new vehicles. The spreadsheet converts factors in terms of g/bhp-hr to g/mile.
Data Requirements - Data are required on the number of new buses procured by year and the number of buses retired by model year. Data on annual vehicle revenue miles and the number of vehicle operating during maximum service are obtained from the National Transit Database. The average speed of bus operation locally is also required, to adjust emission factors.
Outputs - Annual and cumulative emission reductions.
Level of Effort - This method is easy to apply.
Advantages - Data requirements for the spreadsheet are modest. The spreadsheet provides a quick way of estimating the emission benefits of new bus purchases.
Limitations - Emission factors and conversion factors may need to be updated by the user to reflect current data on bus emission characteristics. The method does not account for differences in activity patterns (distance driven, driving cycles, etc.) among individual buses in the fleet.
Source/Availability - The Bus Replacement Spreadsheet was developed by COMSIS for the Pennsylvania DOT and updated in 1998 by Cambridge Systematics, with E.H. Pechan for the Atlanta Regional Commission. The spreadsheet can be downloaded from the Travel Model Improvement Program web site, http://www.fhwa.dot.gov/planning/tmip/. Contact: Cambridge Systematics, Inc. - Chris Porter (617-354-0167).