Boston is the only major municipality in the state that does not report its traffic crashes, even though an average of 16 people are killed in traffic-related crashes annually in the city, the victims both inside and outside of vehicles. And for those hit by vehicles, more than 1,000 pedestrians and bicyclists are injured each year in Boston. The city is taking part in a program called "Vision Zero," to reduce those numbers. WGBH News’ Isaiah Thompson found in his reporting that it is hard to chase after that goal without hard numbers to look at. He spoke with WGBH All Things Considered anchor Barbara Howard about what he calls a “Boston-sized hole” in state safety data. The below transcript has been edited for clarity.

Barbara Howard: Explain why it’s important to have these numbers.

Isaiah Thompson: For many years, the Massachusetts Department of Transportation has been collecting detailed traffic crash data from the state's police departments, and all of that data goes into a big crash database called the Crash Portal. State officials use it for everything from determining safety studies to improvement projects, to reduce or eliminate crashes on some of the most problematic intersections in the Commonwealth.

Howard: You found out that the city of Boston is not handing that data over to state officials. Who's responsible for doing that?

Thompson: The responsibility is that of the Boston Police Department, and it turns out that for years now, since before the Walsh administration, the Boston Police Department has really been unique in not sending this detailed crash data to state officials. It appears that this has been the case for many years — Boston appears to be the only municipality, or at least the only one of any size, that just does not submit these numbers to the state year after year.

Howard: Is it that they’re not handing over the data, or they just don't have the data?

Thompson: It becomes a complicated question to answer. The Boston Police Department does make reports when there's a crash, but the police department doesn't seem to collect those reports in any way that they're publicly available or really even able to be analyzed. Meanwhile, the mayor's office, as part of its Vision Zero program, does collect its own crash data, but that data is limited and it's problematic, because it's based entirely on EMS reports.

Howard: EMS of course being emergency responders. Ambulances only?

Thompson: That's right, as opposed to police reports.

Howard: Are the ambulance reports as detailed as a police report would be?

Thompson: No, they're definitely not, because the job of the emergency responder is to respond. Police reports, which are often finished after the fact, are supposed to and usually do contain a lot more detail. For example, was one of the parties speeding? Was there some kind of issue with the intersection? Was there some other factor that contributed to the crash?

Howard: So did the city explain why they're not reporting the data?

Thompson: The explanation for why the police department doesn't collect and submit this information to the state is not entirely clear. The city told me that the Boston Police's record keeping system is somehow incompatible with the state’s. And again, that appears to have been the case for a long time. The city did tell me that they are working to fix that, to make the Boston Police's records more compatible with the state, but the mayor's office did not give a specific timeline for when that might happen.

Howard: What are the potential consequences for this lack of data? Does it really matter?

Thompson: One of the people I talked to for this story is Stacy Thompson. She's the executive director of the LivableStreets Alliance, and she put it this way: Think about plane crashes and what we do when those happen.

“We don't call plane crashes 'plane accidents.' A tremendous amount of effort goes into being able to collect data so that someone can figure out what went wrong and then likely make some sort of structural change,” Stacy Thompson said.

And what she said is, you can think about exactly the same thing in terms of traffic crashes. There's so much information that can be collected from a traffic crash, and also from looking at crashes over time to see if there is a reason that traffic crashes are happening at a particular intersection. Is there something about that intersection, the way the street is designed? One of the things she really emphasized is that any given crash could just be a freak accident, but when you begin to see patterns, that's no longer an accident. That's a real safety issue that can be addressed.

Howard: What else did you find?

Thompson: I looked at this separate data that the city of Boston does keep from EMS reports but that does not go to the state, and I found at least eight more intersections on Boston streets that were as dangerous or even worse when it came to crashes that just were not on the state list of the worst intersections.

Howard: That's WGBH Radio's Isaiah Thompson, who's been looking into how Boston has not been reporting crashes on its city streets to state officials, who rely on that information to make safety improvements. This is WGBH’s All Things Considered.