A statistic about car-pool lane scofflaws raised eyebrows — but it might not be true

Transportation Secretary Stephanie Pollack. The Boston Globe/Globe Staff

The state’s transportation secretary raised eyebrows this week when she revealed a shocking statistic: The vast majority of vehicles using the car-pool lanes into Boston — “as much as 80 or 90 percent,” she said — carry only drivers.

Except that may not be true.

When Stephanie Pollack made the comment, she was basing it not on any hard data, offering an “anecdotal reference,” state officials acknowledged Thursday.

A recent report on the state’s high occupancy vehicle lanes said scofflaws make up far fewer of the drivers using them — roughly 18 percent — than Pollack had described.

The discrepancy comes as state officials wrestle with how to address the growing congestion that’s choking Greater Boston’s highways, be it through the addition of “managed lanes” or by creating a new network of travel lanes and parking lots to encourage more carpooling.

Currently, there are HOV lanes on Interstate 93 south and north of Boston. But as a sweeping congestion study the Baker administration compiled pointed out, they cover relatively short distances and “do not necessarily provide sufficient travel time savings to achieve their objectives.”

“Enforcement appears to be an issue, at least for the HOV lane on the north side of Boston,” the report added.

But that didn’t even scratch the surface, at least how Pollack described it.

Speaking Tuesday at a meeting of the Local Government Advisory Commission, Pollack told municipal officials she was “shocked” to learn that drivers had resorted to using a Twitter group to alert each other when police were monitoring the HOV lanes, the State House News Service reported.

“And,” Pollack said, “we think as much as 80 or 90 percent of the traffic is actually just individual people in cars, and it’s not functioning as a car-pool lane.”

Pressed about those figures, Department of Transportation officials said Thursday that Pollack was making an “anecdotal reference” to the use of the HOV lane north of Boston, through Somerville and Medford.

That car-pool lane has been temporarily opened to all vehicles “as a congestion relief” while construction crews work on the Tobin Bridge and Route 1, which feeds traffic into the city from the north, MassDOT spokeswoman Jacquelyn Goddard said.

Actual figures show far fewer car-pool lane violators than what Pollack cited, according to a 2017 study of morning traffic on I-93, north and south. It was conducted by the Central Transportation Planning Staff, which works under the Boston Region Metropolitan Planning Organization.

According to its count of the 4,092 cars that used the HOV lanes heading into Boston on a morning that June, 738 of them, or about 18 percent, had only one person in them, though the share of scofflaws north of the city, 24 percent, was somewhat higher.

More than 72 percent of the cars between both the northbound and southbond HOV lanes carried two people.

Chris Dempsey, director of the advocacy coalition Transportation for Massachusetts, said that figures aside, the implication “behind the secretary’s statement remains valid,” and MassDOT needs to better manage the HOV lanes — be it through technology or through enforcement.

“Whether the status quo is 15 percent or 90 percent, the goal should be zero percent,” Dempsey said. “The point of HOV lanes is to reward bus riders and car-poolers for taking up less space on our crowded roads and reducing congestion. We’re only going to solve our worst-in-the-nation congestion if we start moving more people in fewer vehicles.”

State officials have said they’re committed to reexamining car-pool lanes, given that there hasn’t been a comprehensive effort to consider adding more since the state was planning the Big Dig in the 1990s.

That now includes launching a “yearlong” process of identifying potential places for a network of HOV lanes and commuter park-and-ride lots that could allow drivers to get out of their cars sooner and onto buses or shuttles to finish the trip into the city.