A BART train in San Francisco. Justin Sullivan/Getty In an effort to turn its subway system into less of a hot and sweaty mess, San Francisco introduced the country's first transit incentives program in August, giving passengers cash rewards for commuting outside rush hour.

The six-month trial is over, and the results are mixed, as The Atlantic's CityLab reports.

First, the good news: About 18,000 people participated in the BART Perks program, well above agency's estimates.

On the downside, only 250 passengers on average actually shifted their commute to miss the rush hour of 7:30 a.m. to 8:30 a.m., when the Bay Area Rapid Transit system turns into a sardine can on rails. Of the 2,600 Perks participants who used to ride during peak time, 10% made the switch after the Perks launch.

So while the program had wide reach, relatively few took advantage of it.

The experiment, which lasted from the end of August through February, is based on the economic theory of nudging, "wherein even a small reward can lead to adjustments in behavior," according to a statement from BART.

BART passengers pay for tickets in San Francisco, California. Justin Sullivan/Getty

The program was surprisingly complicated, which may have turned off enrollees. Upon launch, it required a four-page Frequently Asked Questions document to fully explain how it worked. Plus, the payout was marginal.

The Perks program awarded points per mile traveled on BART during "bonus hours," which occurred on weekdays during the hours before and after peak time. Participants were assigned a status — bronze, silver, gold, or platinum — based on how they often traveled during bonus hours. A thousand points could be exchanged for $1.

On average, riders made just $3 a month.

BART is still analyzing the program, the results of which will help determine its next steps. In a statement, the agency said it hoped to better target individuals who are frequent riders during rush hour to reduce crowding.