Exclusive bus-only lanes, like the semi-exclusive HOV ("high-occupancy vehicle") lanes that are common in the United States, further lessen the inherent efficiency of cars. Mr. O'Toole calls HOV lanes "fampool lanes" — because family size alone typically determines the number of people in any particular car at any particular time.

Approximately 80 percent of all carpools are made up of family members — "fampools" — who would commute together regardless of HOV incentives, according to Alan Pisarski, author of "Commuting in America."

In other words, you pay for the Jones family's trip, but you don't get to use their lane….

There are ways to align consumer demand with transit costs that create supply, however, that Massachusetts hasn't tried. Express toll lanes make drivers who want less congestion to pay for it, thereby generating revenue for new capacity. HOTV lanes — high occupancy lanes limited to car and vanpools paid for by employers who want to get their employees to work on time — eliminate the "fampool" subsidy of HOV lanes.

It is difficult to be optimistic regarding a renaissance in carpooling. Most carpooling today is not carpooling in the sense we knew it just a few years ago—a voluntary arrangement among co-workers or neighbors. That is dying—most of the surviving "carpool" activity consists of family members with parallel destinations and timing. Maybe these need a new name—fampools?