A Metro train pulls into McPherson Square station. (John McDonnell/The Washington Post)

Taken individually, each of the principles behind Metro’s fare policy sounds great. They include: Satisfy the customers, be fair about fares, keep them simple, make the most of the transit system’s capacity, encourage riders to use efficient payment systems like SmarTrip, and generate adequate revenue while maximizing ridership.

But as the transit authority and the riders begin to consider proposals for a 2014 round of fare increases, they’re going to have to put the principles in a room and let them fight it out.

Some principles endorsed by the Metro board may turn out to be more sacred than others.

For example, transit planners can make a good case that Metrobus fares are too low, given what other big cities are charging for bus rides. Also, Metrobus equipment and service have gotten the sort of upgrades in recent years that a marketer would label “new and improved.”

Mark Schofield, a Metro official who works on the transit budget, said the Metrobus fare of $1.60 paying with a SmarTrip card is well below going rates of $2 or $2.25 charged by some other transit agencies.

If you’re with him on that, then how much should the Metrobus fare go up? It’s not just a question of adequate revenue. You want to apply fare principles about fairness and efficiency while maximizing ridership.

But cash customers, who now pay $1.80 for the bus, including the cash surcharge, hate to fumble with change when they’re boarding. And how often do all those nickels actually make it into the farebox?

It would be easier for the cash customers — and a lot easier for the riders behind them who are waiting to board — to pay with two dollar bills. But that’s an 11 percent increase for the cash customers. Not very fair.

So here’s what the transit staff is thinking: Quarters aren’t so hard to handle. How about charging everybody $1.75, whether they pay cash or use a SmarTrip? That will generate more revenue for Metro while holding down the rate of increase in the fare.

But won’t that destroy the incentive to pay by tapping the farebox with a SmarTrip card, something that’s more efficient and moves boarders along more smartly than feeding in real money?

Yes, Schofield told Metro board members at a meeting this month, some people would lose the will to pay electronically if there were no cash surcharge. “But we’re not terribly worried about that,” he said.

For bus riders, there are other reasons to go plastic. Using a SmarTrip card allows riders a free bus-to-bus transfer and provides a discount on a Metrorail transfer. They also can load a seven-day bus pass onto the card for a potential savings.

Besides, Schofield said, there are some riders who treat SmarTrip as the near-equivalent of cash. They load their cards with enough money to cover just one or two rides.

The transit staff suspects that it’s these riders who are most likely to abandon SmarTrip for cash payment. But they already are slowing down the boarding line to the point where they might as well be paying cash.

If this proposal survived public hearings and Metro board review this winter and spring, it would leave our fare principles somewhat bent, but unbroken.

But the initial transit staff proposals rarely survive that process without some modification.

Bus hikes aren’t the only fare proposals that will emerge in the next few months. The cost of an average Metrorail ride could increase 10 cents. Daily parking could cost 25 cents more.

On parking, the staff also would like the board to give General Manager Richard Sarles more flexibility in setting the rates for specific stations. Schofield noted that the garage at East Falls Church fills up, while the Wheaton station garage may be half empty. Parking prices could rise or fall — somewhat — in response to demand.

Before that idea or any other new fare or fee takes effect in July 2014, look for a lot more debate over principle vs. principle.

Dr. Gridlock also appears Thursday in Local Living. Comments and questions are welcome and may be used in a column, along with the writer’s name and home community. Write Dr. Gridlock at The Washington Post, 1150 15th St. NW, Washington, D.C. 20071 or e-mail drgridlock@washpost.com.