SAN FRANCISCO (CBS/AP) — Motorists in San Francisco are being introduced to demand-based parking fees ranging from 25 cents to $6 an hour, depending on how many spaces are available.

During ball games, festivals and other special events, however, prices could jump to $18 an hour.

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The city-run SFpark flex pricing program on city streets and in public parking garages is debuting April 21.

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Under the program, rates at curbside meters will be adjusted block by block in an attempt to have at least one parking space available at any time on a given block.

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Transportation planners figure drivers will spend less time circling for parking, which will ease congestion and pollution.

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