Mpg Trip Cost Calculator

Trip fuel cost is a two-step calculation: gallons equal distance divided by miles per gallon, and cost equals gallons times the pump price. The subtlety hides in the first step, because miles per gallon is a reciprocal measure of consumption rather than a linear one. Fuel saved per mile is proportional to the difference of the reciprocals, not the difference of the MPG numbers, so moving from 15 to 20 MPG saves far more fuel over the same distance than moving from 30 to 40 MPG. Larrick and Soll named this the MPG illusion in a 2008 paper in Science, and it is the reason most of the world quotes liters per 100 kilometers instead, a directly proportional measure obtained here as 235.215 divided by MPG. Useful reference values: compact cars manage 30 to 40 MPG on the highway, midsize sedans 28 to 35, crossovers and SUVs 22 to 30, half-ton pickups 18 to 25, and full hybrids 45 to 55. The Department of Energy estimates that fuel economy typically peaks between 45 and 55 mph and falls sharply above 60 mph as aerodynamic drag dominates. The EPA figure of 8,887 grams of carbon dioxide per gallon of gasoline burned, about 19.6 pounds, drives the emissions line. The main caveat is that a single MPG number cannot represent a real trip: grade, headwind, cargo and roof racks, tire pressure, air conditioning load, and traffic all move actual consumption by 10 to 30 percent.

Systematic fuel economy measurement in the United States began with air pollution work rather than with economics. The Federal Test Procedure driving cycles developed for emissions certification in the late 1960s and early 1970s measured tailpipe carbon, and because carbon in equals carbon out, fuel consumption could be derived from the same test by the carbon balance method that is still used today. The Energy Policy and Conservation Act of 1975, passed in the wake of the 1973 oil embargo, created Corporate Average Fuel Economy standards and directed the EPA to publish the annual Fuel Economy Guide and the mileage figures that appear on the Monroney window sticker required since the Automobile Information Disclosure Act of 1958. Those laboratory numbers proved optimistic against real driving, and the EPA adjusted them twice. A downward correction was applied in 1985, and a more thorough revision took effect for 2008 model year vehicles, adding high-speed, air conditioning, and cold-temperature cycles to the original city and highway tests. Public per-gallon price reporting has an older lineage still, with AAA tracking retail fuel prices since the 1910s and the Energy Information Administration publishing weekly national and regional averages since 1990. Crowd-sourced station-level pricing arrived with GasBuddy in 2000, which is what makes route-level trip cost planning practical rather than merely approximate.