Comparing to Label Fuel Economy - FASTSim Documentation

What is “Label” Fuel Economy?¶

EPA window-sticker (i.e. “city”, “highway”, and “combined”) fuel economy values are published estimates based on standardized test procedures for light-duty vehicles. Because every vehicle is evaluated under the same rules, they provide a useful comparison point when checking how a FASTSim vehicle lines up with a real vehicle’s fuel economy performance.

You can search for these published values on fueleconomy.gov, a resource administered by Oak Ridge National Laboratory (ORNL) for the U.S. Department of Energy and the U.S. Environmental Protection Agency. The FuelEconomy web services page also provides an API and a downloadable CSV for programmatic access to label data.

Label Fuel Economy Simulation in FASTSim¶

FASTSim includes a label fuel economy calculation module that produces EPA-style city, highway, and combined values from a simulated vehicle. This makes it useful for model calibration and for checking whether a FASTSim vehicle is in the same general range as its published EPA window-sticker values.

Historically, EPA label fuel economy was derived from adjusted fuel economy measured over the FTP-75 and HFET drive cycles (commonly known as the 2-cycle procedure). To better capture higher speeds, harder accelerations, air conditioning use, and cold-temperature operation, the EPA later introduced the 5-cycle testing procedure. When supplying label fuel economy data to the EPA, manufacturers may either use the 5-cycle procedure or use the 2-cycle procedure together with EPA powertrain-specific adjustment equations (most recently updated in 2017).

FASTSim’s label fuel economy module emulates the latter approach by applying the EPA’s powertrain-specific adjustment equations to simulated FTP-75 and HFET results.

Example¶

import fastsim
import json

The label fuel economy values for a 2012 Ford Fusion are found here: https://www.fueleconomy.gov/feg/Find.do?action=sbs&id=31390.

The same vehicle’s full data is available at https://www.fueleconomy.gov/ws/rest/vehicle/31390 (the same id 31390 as in the URL above), with unrounded values and more vehicle specifications.

label_city_mpg = 23
label_highway_mpg = 34
label_combined_mpg = 28

print(f"Target label fuel economy:")
print(f"  City:     {label_city_mpg:.1f} mpg")
print(f"  Highway:  {label_highway_mpg:.1f} mpg")
print(f"  Combined: {label_combined_mpg:.1f} mpg")

Target label fuel economy:
  City:     23.0 mpg
  Highway:  34.0 mpg
  Combined: 28.0 mpg

Now, we will load the corresponding vehicle from FASTSim’s resources and run the label fuel economy comparison.

veh = fastsim.Vehicle.from_resource("2012_Ford_Fusion.yaml")
label_fe = json.loads(fastsim.get_label_fe(veh).to_json())

simulated_city_mpg = label_fe['adj_udds_mpgge']
simulated_highway_mpg = label_fe['adj_hwy_mpgge']
simulated_combined_mpg = label_fe['adj_comb_mpgge']

print(f"Vehicle: {veh.to_dict()['name']}")
print(f"Simulated label fuel economy:")
print(f"  City:     {simulated_city_mpg:.1f} mpg")
print(f"  Highway:  {simulated_highway_mpg:.1f} mpg")
print(f"  Combined: {simulated_combined_mpg:.1f} mpg")

Vehicle: 2012 Ford Fusion
Simulated label fuel economy:
  City:     26.6 mpg
  Highway:  33.3 mpg
  Combined: 29.2 mpg