Diesel Towing Costs: Fuel, DEF, and Tolls by the Axle

What the diesel mile really costs

On our sample trip, fuel was $865.85 over about 1,104 miles: $0.78 a mile, 44 percent of everything we spent. If you tow with a diesel, fuel is not a line in the budget. It is the budget, with other lines attached. Here is the full shape of the diesel mile.

Fuel

Towing heavy cuts fuel economy roughly in half compared to the same truck empty, and wind matters more than speed limits: a headwind day can cost like a mountain day. A fuel card with per-gallon discounts is worth real money at these volumes, and planning fuel stops around it is part of our route planning, not an afterthought. Play the what-if before a long trip: at your miles and your price per gallon, what does a 25-cent swing do to the total? On 1,100 miles at towing economy, the answer is never small.

DEF

Diesel exhaust fluid is the quiet second fuel. Trucks use it at roughly 2 to 3 percent of fuel burn, so a long towing trip drinks gallons of it, not ounces. Buy it at the pump where it is cheapest, keep a sealed jug aboard, and never let the tank run to the warning: the truck will eventually limit itself, and it will choose the worst moment.

Tolls price you by the axle

A truck with a two-axle trailer is not a car with a trailer to a toll gantry; it is a multi-axle vehicle, and the tolls scale with it. Our sample trip paid $261.54 in tolls, $0.24 a mile, including six turnpike tolls totaling $225.54 and one $36 bridge toll. Route choices that look longer in miles are sometimes cheaper in dollars. Run both numbers.

The honest summary

On our one sample trip: $0.78 a mile of fuel, $0.24 a mile of tolls, $1.77 a mile all-in. Your numbers will differ. Count your own, and they will start making your route decisions for you.

Related: payload math, because what the rig weighs decides what the diesel burns.