Methodology

FEC has the capability to estimate emissions as a function of engine-load, using a load surrogate known as Scaled Tractive Power (STP).  This same STP modeling approach is employed in the US Environmental Protection Agency (USEPA) emission rate model known as the MOtor Vehicle Emissions Simulator (MOVES).  MOVES is the current federally approved emission rate model for use in regional and microscale air quality impact analyses for regulatory purposes.  MOVES emission rates are now employed in the Calculator and resulting emissions are based upon the user-supplied vehicle operating parameters that affect fuel consumption and emissions.  With the added modules, the Calculator provides more accurate Greenhouse gas emissions, using a combination of load-based emissions estimated from MOVES and life-cycle emissions estimated from the Department of Energy’s Greenhouse Gases, Regulated Emissions and Energy Use in Transportation (GREET) model.

The Georgia Tech research team added four embedded modules based on the original developed emission calculator.  Those four modules include:

  1. A scaled tractive power (STP) operating mode bin calculator
  2. A MOVES-matrix emissions rates lookup table
  3. A hybrid bus energy balance model designed to shift energy demand across STP operating mode bins
  4. New algorithms and analytical processes for electric and diesel-electric rail operation

The updated calculator retains all of the functionalities of the original calculator, including summary charts and tables for greenhouse gas emissions, cost-effectiveness comparisons, etc.  The updated calculator now allows emissions comparisons to be performed across vehicle operating modes, allowing users to compare fuel consumption and vehicle emissions across energy technologies based on route characteristics such as road grade, number of stops, average speed, etc.  Attention has also been given to electric drive and hybrid vehicles to enable transit agencies to assess the benefits of these vehicles as fleet candidates.