Changes to parking fees at ­Metro-operated lots and garages start Monday — part of a six-month experiment with innovative pricing methods. But there are already concerns that the pilot program could alienate suburban transit users who are smarting at the prospect of extra fees.

The changes to Metro's pricing policy will expand the hours parking fees are charged, eliminate some weekend parking that had been free and expand a program that charges "non-riders" more to park at Metro lots and garages. It's part of an effort by the agency to wring more revenue out of its operations and to help it gather more data about how people use its facilities.

The new pricing structure has been applauded by some transit advocates and planners, but critics — including riders and some suburban elected officials — say the changes may ultimately undercut transit usage in places where people are easily lured back to their cars.

They also fear that the new fees could hurt Metro's weekend ridership — when parking traditionally has been free — and discourage people from using other forms of transit, such as Virginia Railway Express, the MARC commuter rail and the Fairfax Connector bus system.

"The good news here is that this is a pilot, so we'll be able to analyze what the impact is and then make a decision about how to go forward," said Fairfax County Supervisor Pat Herrity (R), many of whose constituents use the Franconia-Springfield Metro station.

It's one of the stations that will begin to charge non-Metro-riders who use its parking nearly double, even if they are using the station to take VRE.

Herrity said he wants to make sure that the fee changes aren't counterproductive to the ultimate goal — getting more people to use transit.

"We really need to be designing our mass transit so people want to ride it, and not just have to ride it," Herrity said.

The hours during which Metro will charge for parking weekdays will start two hours earlier, beginning at 7:30 a.m. — and extend until 12:30 a.m., except for Fridays, when fees will be charged until 2 a.m.

And for the first time, the agency will charge for parking on Saturdays; a flat $2 fee will be collected from 10 to 2 a.m. Sunday parking will remain free.

Lastly, the agency is expanding its program of non-rider parking fees, which charges significantly higher rates for people who use Metro's parking facilities but don't pay with a SmarTrip card that is also swiped into the rail system.

Those daily fees range from $8.70 to $10. Previously, the special rates were only charged at New Carrollton, Twinbrook and White Flint. Now, the higher rates also will be charged at the Branch Avenue, Greenbelt, Suitland, Huntington, Dunn Loring, Minnesota Ave., Franconia-Springfield, Largo Town Center, Rhode Island Avenue and Rockville stations.

The one bright spot: Metro is lowering parking fees at the Landover and West Falls Church stations — from $4.70 and $4.95, respectively, to $3 daily — as part of an effort to entice more people to use them and perhaps switch from other parking garages that frequently reach capacity on weekday mornings.

The pilot program is estimated to bring in $4 million of revenue for Metro and is scheduled to last until July 30, although the Metro board could vote to make the changes permanent before then.

The gains for the agency could be significant. For example, officials estimate that had they charged a $5 parking fee the Saturday of the January 2017 Women's March, the agency could have made $500,000 based on the day's record ridership.

Still, the extensive changes have riled some local jurisdictions, who say that Metro failed to loop them in on the project and that the agency's eagerness for more revenue may discourage people from using the system.

In Fairfax, the Board of Supervisors approved the changes to the weekday schedule — going so far as to preemptively agree to make the changes permanent, if Metro chooses to do so — but opposed charging for Saturday parking.

"Parking usage and Metrorail ridership are lowest on weekends when it is currently free to park. . . . Typical economics would lead to charging for parking when usage is in high demand and supply is low, rather than the reverse," the Fairfax board wrote in a memo last month. "The result may mean some modest increase in parking revenue at the expense of weekend ridership."

Supervisors also worried that Saturday parking fees would discourage low-income transit riders "who can least afford another increase in transit costs."

Supervisor Catherine M. Hudgins (D-Hunter Mill) took her colleagues' concerns to the Metro board, on which she also serves. She asked that Fairfax stations be exempted from the weekend fee pilot but was unsuccessful. Still, the Board of Supervisors ultimately voted to exclude the ­Wiehle-Reston station parking lot, which is owned by Fairfax County, from instituting the weekend fee.

The policy also will impact MARC and VRE riders. Three of the stations introducing "non-rider" fees — Greenbelt, Franconia-Springfield and Rockville — are also commuter train stations.

Officials from the Maryland Transit Authority did not respond to a request for comment. But in an email to a rider who had asked whether MARC commuters would pay "rider" fees, the agency said it had not been able to discuss the change with Metro.

"MARC has had no success reaching out to WMATA regarding the parking rate increase," David Johnson, MARC's chief transportation officer, said in an email to a rider. "WMATA is not affiliated with MTA and we do not have an agreement with them regarding parking."

Metro spokeswoman Sherri Ly said there are no plans to accommodate MTA, VRE or other regional transit systems under the "rider" parking fee, which requires paying with a SmartTrip card that has been used to tap out of the same station where the garage or lot is located.

A similar pricing strategy has been used at the New Carrollton station for years, and only 15 percent of people who park at the station are paying the non-rider price, she said.

"The non-rider fee affects a relatively small percentage of customers," Ly said.

Still, the changes are bad news for Sasha McMurry, 36, who lives two miles from Rockville Metro station. She commutes to Silver Spring, and MARC is her method of choice.

She usually parks at Metro stations, but now that the daily cost of parking will increase by at least $3.50 per day — almost $900 per year, she calculated — she's going to start riding her bike to the station.

"It feels very anti-transit of WMATA to not have some sort of partnership in place with MTA," McMurry said.

She said she finds it "puzzling" that the changes don't include a provision for people who use non-Metro forms of transit, especially because MARC and Metro already have a partnership to honor one another's tickets if there are service disruptions.

"It feels like WMATA is trying to cash in on the people who ride MARC," McMurry said.