Motorists may soon have to pay $9 to cross the Bay Bridge if voters approve a ballot measure next month.

Regional Measure 3 will add $3 to every Bay Area toll bridge except the Golden Gate Bridge. If approve, the $3 jump will be phased in over seven years and is projected to raise just over $4.4 billion.

On Monday, the mayors of San Francisco, San Jose and Oakland held a press conference calling the measure an investment in the Bay Area's future. The bulk of the money from the measure would go to fun extensions and improvements of the Bay Area's Rapid Transit system.

"Our trains are more crowded than ever before," San Francisco Mayor Mark Farrell said. "Our buses are more crowded than ever before."

Farrell on Monday was joined by Oakland Mayor Libby Schaaf and San Jose Mayor Sam Liccardo in calling for infrastructure spending.

But some motorists are not in favor of having to spend more to cross bridges.

"It's crazy," said Diddy Sykes of Mission Viejo. "I think it's ludicrous for them to raise it up to $9."

Election Day is June 5.