Why is it so hard to figure out how much a trip on a Metro train will cost, while buses are a flat rate? Why don’t trains either have a set rate—like those in Chicago and New York—or a simple zone system—like in London?

Subway fares correspond to the distances that passengers travel. Despite being confusing, Metro considers the system is the fairest way to charge people for their trips, according to transit authority spokesperson Candace Smith.

The system’s only hitch, Smith says, is that riders have to look at the rates posted above the fare card machine or station manager kiosk in order to figure out how much their ride will cost.

Metro made the decision to put the current system in place in August 1975, when Metro officials decided the mileage-based system was the best way to encourage riders to take short trips. A zone system, like the London Underground’s, might have required passengers traveling from Rosslyn to Foggy Bottom to cross zones for a one-stop commute, while a flat fare, like the New York City Subway or Chicago “L” systems, would have required urban riders to subsidize suburbanites commutes, says George Mason University history professor Zachary Schrag, who detailed the history of the Metro in his book The Great Society Subway.

“Metro planners were starting fresh, which allowed them to do things very differently than older subways,” says Schrag, noting that machines capable of calculating varying fares for a mileage-based system did not exist before the 1960s.

At the same time that Metro planners decided on the mileage-based system, they also considered using a mileage-based system for buses but later changed their minds after deciding that it was not technologically feasible.

Every Monday, the ‘Huh?’ Bub takes your questions. Got one?