(Julian James/Wessex Water)

Here’s an unusual math problem: How many miles can a bus travel on five years worth of human waste?

Answer: 186.

This is the distance the Bio-Bus — dubbed the “poo bus,” the United Kingdom’s first — can drive before a refill. It hit the road on Wednesday, traveling between Bristol and Bath.

According to the BBC, the 40-seat bus, run by tour operator Bath Bus Company, actually runs on biomethane gas, a byproduct created when oxygen-deprived bacteria breaks down food scraps and the stuff we flush down the toilet. Before the gas is bus-ready, the carbon dioxide must be removed and propane added. The “impurities” are removed so the gas doesn’t smell like a potty.

(Julian James/Wessex Water)

The fuel comes from the Bristol’s sewage treatment facility, which is run by GENeco, a renewable energy company. Their motto: “We make waste work!”

The facility processes about 35,000 tons of food waste per year, producing enough biomethane to power 8,300 homes.

“The bus also clearly shows that human poo and our waste food are valuable resources,” Charlotte Morton, the chief executive of the Anaerobic Digestion and Bioresources Association, said in a statement, adding that biomethane could supply about 10 percent of the United Kingdom’s domestic gas needs.

“Gas-powered vehicles have an important role to play in improving air quality in UK cities but the Bio-Bus goes further than that and is actually powered by people living in the local area, including quite possibly those on the bus itself,” GENeco’s general manager Mohammed Saddiq told the BBC.

According to the BBC, the bus’s combustion engine is similar to that of a regular diesel bus, only it emits 30 percent less carbon dioxide. The only telltale sign the bus isn’t a run-of-the-mill gas guzzler are dome-shaped tanks on top that store the gas. Well, that and the bus wrap featuring cartoons of passengers sitting on the toilet.

The bus’s debut comes as Bristol is set to become Europe’s 2015 “Green Capital,” an award given each year to a European city with a good environmental track record. Predictably, it was greeted with potty humor: