When Sonoma-Marin Area Rail Transit commute service kicks off later this year it will be free until the Fourth of July.

That could mean a loss of $700,000 in revenue, but rail officials want a way to lure riders to the system.

“They are going to see how this is going to be a replacement for Highway 101,” said Farhad Mansourian, SMART’s general manager. “We want people to come and see our service and be familiar with it.”

The loss of revenue assumes a May start date for the service, but that is not firm, Mansourian said.

“We are looking forward to offering people the opportunity to try our new service free of charge for a limited time,” said Debora Fudge, SMART board president, in a statement.

Once the free period is over, there will be more savings in store for riders under a plan approved by the rail board Wednesday.

From July 5 through Sept. 4 all fares will be cut by 50 percent on all non-discounted regular adult fares. That half-off plan could cost the rail agency up to $500,000.

“There are good reasons to believe that the free and reduced fairs will lead to a more rapid change on commute behavior making our ridership base stronger at the end of the reduced-fare period than without it,” Mansourian wrote in his staff report to the board.

The free and reduced fare periods will allow passengers to get calibrated to the operation, including trying out Clipper for the fare system. During the free period using Clipper will not be required, but encouraged. Using Clipper will make it easier for SMART riders to transfer to other transportation systems, like Golden Gate ferries and buses.

The Clipper card system is similar to FasTrak, which allows drivers to pass through Bay Area toll booths without having to stop and hand over cash. Clipper works much in the same manner, with patrons signing up and allowing their credit cards to have bus, ferry or rail fares deducted.

Clipper users can scan or “tag” their cards on a reader. A computer chip inside the card reads the transaction, information is displayed on the screen and a beep sounds to alert the passenger the card has been read.

The Clipper system automatically deducts the correct fare and applies any discounts — including transfers — for each trip.

The free period will also allow passengers to better understand operations, including how long it takes to get off and on trains, how to get to stations and how and where to park bicycles or bring them on board.

The board also approved a $200 pass good for 31 days. With that pass, a commuter who works 20 days will pay an average of $10 a day for roundtrip train service. A pass for passengers with disabilities, those 65 and older and youth 5 to 19 for the same period will sell for $100.

Once full-price fares are implemented, riders will see a one-way base fare of $3.50, plus another $2 each time a zone is entered.

SMART has five zones from downtown San Rafael to the Santa Rosa Airport.

Under the structure, a passenger would pay $11.50 one way to pass through all five zones. SMART officials believe the majority of commuters — 61 percent — would pass between two and three zones. There would be a pass that caps a daily fare at $23 to allow more travel if passengers wanted to get off and on the system.

SMART will offer discounts of between 75 cents and $1.50 for passengers using Clipper-enabled North Bay bus systems to get to the train. There would be senior, disabled, youth and veterans discounts as well.

Rail planners hoped revenue from fares would generate about $5 million a year for its assumption of 3,070 daily riders during the work week. The system expects about 300 riders on each weekend day.

But the adopted base price and zone charges will only produce about $4 million annually. Train officials did not want to set fares too high the first year of service for fear people would be deterred from riding. Money could be pulled from a $19 million reserve if fares fall short.