The casual carpool — in which people with a fear of commitment line up and hop into complete strangers' cars for a free ride across the Bay Bridge — could forever be changed this week.

Carpools must start paying a $2.50 bridge toll tomorrow. Will drivers still want to ferry people across the bridge without the incentive of the free carpool lane? Will passengers still want to endure half an hour of NPR's Morning Edition or KOIT's Light Rock, Less Talk if the ride is no longer free?

With all the unspoken rules of casual carpool culture — riders don't speak unless spoken to, drivers get to pick the radio station — there will also have to be an awkward truce reached over how to split the new toll.

And finally, aside from all the potential social upheaval, drivers take note of this: The San Jose Mercury News reports that drivers will now have to get a Fast Trak pass to go through the carpool lane. Janis Mara writes:

Starting Thursday, drivers must have a transponder to use the carpool lane.

"If you drive in the carpool lane without a transponder, even if you have the requisite number of passengers, you will get a violation," said Randy Rentzler of the Metropolitan Transportation Commission. However, transportation officials have some mercy, he said.

"If you get a transponder within 30 days, your violation will be waived," Rentzler said.