Every year, the Massachusetts Department of Transportation publishes a list of the 200 most dangerous roadway intersections across the commonwealth.

But for years those reports, and the data that underlie them, have had a gaping hole — one the size of the city of Boston: Unlike every other municipality in the state, Boston’s police department does not collect and submit standardized traffic crash data to state officials.

Even as the city of Boston pursues its Vision Zero plan, announced by Mayor Marty Walsh in 2015 — with the goal of ending traffic-related fatalities and serious injuries by 2020 — the commonwealth’s largest city has yet to comply with basic data collection and reporting practices followed for years by other towns and cities across state.

And when it comes to Boston, the numbers in question are alarming: In recent years, the city has seen an average of more than 20 traffic-related fatalities and crashes, injuring between 700 and 800 pedestrians and between 400 and 500 bicyclists, per year.

That's according to data the city of Boston maintains separately from the Boston Police Department. But that data isn't reported to MassDOT and is drawn from emergency medical response reports, instead of police reports. Safe streets advocates say that approach is problematic — it doesn’t capture crashes in which EMS isn’t called, and the reports are far less detailed than the reports collected by state officials from local police departments.

“It’s a real issue,” says Brendan Kearney, a spokesperson for Walk Boston, a pedestrian advocacy group.

The standardized crash data reported to the state by every other municipality, says Kearney, informs not just reports but state-funded improvement projects and studies, called “safety audits.”

“If they're not sending in all this full police report data,” Kearney points out, key crash sites “could possibly be missing from some of these road safety audits.”

Exactly what the consequences might be of Boston’s annual omission aren’t entirely clear; MassDOT communications officials did not answer repeated questions about what impact the missing data has on state reports, funding or safety interventions.

Nor did MassDOT officials answer questions about the extent to which the state’s own data and reporting on crashes might be incorrect as a result of the known absence of records from the Boston Police Department.

But there’s evidence that the state’s own lists of the most dangerous intersections around the commonwealth may be missing chronically crash-prone intersections across Boston.

The state’s most recent 200 “Top Crash Locations Report,” serves as an example.

That report, published in 2017 and covering data for the years 2013 to 2015, lists only eight “top crash locations” within the city of Boston — all of them state roads, over which the Massachusetts State Police, and not the Boston Police Department, have jurisdiction.

But separate crash data maintained by the city of Boston’s Vision Zero program — data not reported to state officials — reveal at least as many additional intersections, on Boston streets, with equally high or even higher numbers of crashes over roughly the same amount of time.

That means state officials might not know where some of the most dangerous intersections are.

Exactly why Boston has failed to adhere to state reporting standards is unclear.

In an email, a spokesperson for Walsh told WGBH News that the records-keeping system used by the Boston Police Department is incapable of generating reports compatible with the state’s crash data analysis program.

The problem is hardly new: In 2014, a year before Walsh announced his Vision Zero initiative, the Boston Globe reported on the data disconnect.

And safe streets advocates say they have been pressing the administration for years to adopt better and more transparent data-collection practices when it comes to traffic crashes.

Because data, they say, is key to preventing more deaths and injuries.

“We don’t call plane crashes plane accidents,” notes Stacy Thompson, executive director of the nonprofit Livable Streets Alliance.

When a plane crashes, Thomas says, “A tremendous amount of effort goes into accessing data and being able to collect data, so that someone can access that data and figure out what went wrong, and then likely make some sort of structural change.

”And you can use that process when you're thinking about traffic data,” Thomas says. “It's not random.”

A few years ago, using grant money, the city did hire a data analyst for the Boston Police Department, but the funding ran out — and the position vanished.

A spokesperson for the Boston Mayor’s Office told WGBH News in an email that the police department “is currently working with a vendor to be able to automatically populate a crash report that will be submitted to MassDOT.”