Transport
Fuel per mile, not miles per gallon alone
Fleet analysis converts activity into energy: annual fuel = miles ÷ MPG (or hours × idle rate). Baseline the fleet by vehicle class, duty cycle, and route profile, because city stop-and-go favors hybridization and regenerative braking while highway miles favor aerodynamics and gearing. Telematics (GPS, engine data, idling reports) is the audit instrument - it replaces assumptions with measured idle time, hard acceleration events, and route deviations.
Comparisons across fuels require a common basis. Electricity is roughly 0.3–0.4 kWh per mile for light-duty vehicles, with charger and drivetrain losses of about 10–15%. CNG and propane are priced per gasoline-gallon-equivalent (GGE: CNG ≈ 1 GGE per 125 ft³; propane ≈ 1 GGE per 1.35 gal). State whether comparisons are tank-to-wheel or well-to-wheel. Total cost of ownership must include infrastructure (charging, compressors, dispensers), maintenance differences, and resale.
Traps. Comparing $/gallon to $/kWh without converting to cost per mile; using rated range instead of real-world range; assuming 1 gallon per hour of idling universally (it varies from about 0.5 to over 1.5 gal/h by engine size); ignoring infrastructure capital; and forgetting driver training and tire-pressure programs, which are usually the fastest paybacks in any fleet audit.
Worked example
Fifty trucks idle 6 hours per day, 250 days per year: 50 × 6 × 250 = 75,000 idle hours. At a conservative 0.8 gal/h that is 60,000 gallons; at $4.00/gal, $240,000 per year. Idle-reduction controls, auxiliary power units, and a policy with telematics enforcement typically remove 40–60% of that.