A handful of San Francisco's curbside parking meters will hit the $5.25 mark for the first time as the city continues its quest to find the sweet spot for pricing.

The Municipal Transportation Agency announced the seventh parking-rate adjustment under the experimental SFpark program, which attempts to manage parking with meter rates. The goal is to set the price so there's approximately one parking spot always available on every metered block. The cost is adjusted based on demand.

The prices, which can be changed no more than once a month, fluctuate by location and time of the day.

For example, afternoons on the 400 block of Battery Street in the Financial District, when the average parking space occupancy rate is between 92 and 94 percent, the cost to park will be set at $5.25 an hour, a 25-cent increase. But before noon, when just 25 percent of the spaces are filled, the cost will be $1 - 50 cents less than the current charge. The drop in price is intended to lure more drivers to park there.

About 8,200 parking meters, or a quarter of the city's stock, are part of SFpark.

Using the measurement of metered hours, parking officials calculated that the hourly price will go up 25 cents for 26 percent of the operating hours, decrease 25 cents for 24 percent, fall 50 cents for 2 percent and stay the same for 48 percent.

"We did see the highest percentage of meters staying the same, which suggests we're hitting the right price for hitting our goals," said Paul Rose, spokesman for the San Francisco Municipal Transportation Agency.

Once the rate adjustments go into effect this week, 1.7 percent of SFpark meters will cost $5.25 an hour and 4.3 percent will cost 25 cents an hour. The largest number - 43 percent - are priced at $2 or less; 2.4 percent cost $5 or more. The rest fall in between.

The most the city will be able to charge under the SFpark program is $6 an hour, unless there's a special event, such as a ballgame or street fair. The cap for those times has been set at $18 an hour.

The meter rates aren't the only things changing. So are the parking policies. The agency plans to expand meter operations into the night around the Giants' China Basin ballpark, and starting citywide on Jan. 1, drivers will have to start plugging the meters on Sundays.

- Rachel Gordon

Ending the free ride: Clipper cards will soon cost $3 for adults, and transportation officials hope the new fee will encourage riders to reuse their cards instead of discarding and getting new ones.

When the universal fare cards were rolled out in June 2010, the main goal was to get as many people using Clipper as possible - so the cards were free.

But since the cards have been introduced, the system has had a few glitches - including a negative-balance bug that lets riders with a few dollars on their card catch a ride that costs more than they have loaded and ditch the card for a new one.

Starting Saturday, adults will be charged $3 for a new Clipper card. Youth and senior cards will stay free, and Regional Transit Connection Clipper cards for people with qualifying disabilities will stay at the current $3 price.

The fee doesn't completely stop the negative-balance loophole: Riders can still get on expensive trips that cost much more than the $3 replacement fee. About 60 percent of the negative-balance trips take place on BART, where the most expensive route (Pittsburg/Bay Point to SFO) is $11.05.

Currently, BART riders who don't have enough value on their cards to pay for their trip can still exit the station as a convenience and pay the next time they load their card. But plans are in place to change that policy by early 2013, said John Goodwin, spokesman for the Metropolitan Transportation Commission, which oversees the program. After that date, Clipper users on BART will be subject to the same rules as paper ticket riders who must pay for their fares on machines in stations before they can exit.

- Ellen Huet