** Subject to significant gaps and uncertainty in the underlying data
The San Francisco Chronicle recently published an article titled, “This map shows the most dangerous streets for pedestrians and bicyclists in California.” Featuring a searchable map, it spotlighted an urgent public safety issue: pedestrian and bicyclists fatalities in California.
But because the data behind the maps is incomplete, the maps are highly questionable. In Alameda’s case, for example, over two thirds of the fatalities were missing.
Here’s what the map in the article looks like:
Here’s what it would look like with the other five fatalities included:
It tells a very different story.
Why is the data incomplete? Much of the discrepancy appears to stem from constraints in the state’s crash reporting pipeline.
Here’s how it works: Maps like this are sourced from the Transportation Injury Mapping System (TIMS) at UC Berkeley, a resource widely used by transportation professionals. TIMS pulls its data from the California Highway Patrol’s database, the Statewide Integrated Traffic Records System (SWITRS). In turn, SWITRS gets its crash data from local police departments. The problem is that local municipalities sometimes don’t report crashes to the CHP within the window of time currently allowed by the CHP. Crash data is basically finalized 18 months after the crash event. If a crash isn’t reported within that window, it won’t ever appear in the database, or on the maps that pull from it.
To raise awareness about this inaccuracy — and perhaps initiate a fix — Bike Walk Alameda wrote a letter to the article’s author and editor (click to expand):
The Chronicle subsequently updated the article with the addition of this caveat:
The database, however, is not complete. California’s crash records freeze roughly 18 months after each incident year, with no mechanism to add verified deaths afterward. Missing fatalities in the Bay Area include the deaths of KTVU News Director Fred Zehnder and champion cyclist Ethan Boyes. TIMS confirmed the gaps in state records, likely because local police departments did not submit reports in time.
Their reference to Ethan Boyes, who was killed in San Francisco, confirms that this issue is not limited to Alameda.
Not surprisingly, the Chronicle did not update the map — that would be a massive endeavor. The real fix is most likely at the state level.
Alameda maintains accurate local records and can produce its own fatality maps. However, it is unfortunate that the city cannot fully leverage TIMS and its powerful analytical tools to better understand local street safety patterns and trends. More concerning is the very real possibility that regional and statewide transportation policies may have been — and may continue to be — informed by datasets that are incomplete.
It would indeed be great to have a map that shows the most dangerous streets for pedestrians and bicyclists in California, but until this issue is addressed, this map — or the many others sourced from SWITRS data — is not it.