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COF 2017 #30 · Communication to the City Council · Dec 4 2017
a review of Cambridge bicycle citation and collision data as they impact bicycle and general street safety planning
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CAMBRIDGE CITY COUNCIL
CITY HALL, CAMBRIDGE, MASSACHUSETTS 02139
ckelley@cambridgema.gov
Craig A. Kelley
Phone: [phone removed]
City Councillor
Fax: [phone removed]
MEMORANDUM
To:
Cambridge City Council
From:
Craig A. Kelley, Councillor
Date:
November 30, 2017
Subject:
Review of Cambridge bicycle citation and collision data as they impact bicycle and
general street safety planning
Dear Fellow Councillors,
I have been working with another bike-safety data nerd, Ted Feldman, to try and figure out how
CPD traffic enforcement efforts correlate with bicycle safety to see where enforcement efforts might be
altered to improve bike and pedestrian safety.
The City has a variety of bicycle safety efforts—from rider education programs in schools to
infrastructure changes and DPW’s construction zone hazard management work— but the data that we
know exists and to which we have ready access is pretty much limited to data about reported crashes,
CPD citations and the ‘bike totem’ bicycle counts. The focus of this particular memo, therefore, is how
data analysis might play a role in making cycling safer through more focused infrastructure improvements
and more intentional and data-driven traffic enforcement efforts.
The majority of reported
bike collisions involve some sort
of turning movements but bike
collision (and near collision) data
is very incomplete. Complicating
data collection and analysis
efforts is the fact that accidents
such as falling on ice or hitting
potholes, or any of a number of
other ways cyclists can get hurt,
do not readily fit a ‘crash type’
and are frequently not reported.
Still, the chart to the left
(Figure 1) shows the types of
collisions we have in Cambridge
and it reflects data on bike/car
collisions elsewhere. One major
Figure 1. A chart of the prevelance of crash types. Crashes associated with turning
movements and/or intersections account for well over half of all reported crash types.
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key to making cycling safer in Cambridge, then, is to lessen dangers associated with intersections and
turning movements. Accomplishing that goal may be at least partially accomplished through a
combination of infrastructure changes like the ‘no left turn’ signs in Inman Square, bike traffic lights,
education and enforcement.
Based on the fact that
so many of our bike citations
are at places where there are
intersections, CPD seems to be
focusing on cyclists running red
lights. It is not clear whether the
police are at intersections
specifically to ticket cyclists
who run red lights or they are
there because both drivers and
cyclists run red lights and some
cyclists wind up getting ticketed
just as some drivers do.
One thing that the heat
map to the right (Figure 2)
demonstrates, though, is that
our bike citations are
concentrated along certain
popular bike routes whereas
reported bike ‘crashes’ occur all
around the city. If the goal of
bike citations is to promote bike safety, we may very well not be giving bike tickets in ways that help
meet this goal.
A graphic of the timing of bike citations, all traffic citations and bike ‘crashes’ (Figure 3 below)
reveals that, while there is not a direct correlation between citations and crashes, there are more of all
three during rush hour commutes. Conceivably, there is a link between increased bike, and maybe all
traffic, citations and fewer crashes. If one point of traffic enforcement is to reduce collisions between
bikes and cars/trucks, it seems like this is one area in which we need to do a deeper data dive. Guiding
this process, we can ask: are CPD’s enforcement efforts, for bike and motor vehicles, most appropriately
timed to maximize street safety?
It is also clear that CPD gives out very few bike citations after dark. That makes some sense, as
fewer people bike at night, but it does lead one to wonder if we’re putting enough effort into emphasizing
the importance of safe biking, especially having front lights, at night. Of course, CPD has other things it
does at night, so a discussion of evening/night bike enforcement would also include a discussion of
CPD’s overall priorities and nighttime staffing levels.
Figure 2 Locations were bicycles are most likely to receive a bicycle citation (in blue),
imposed with locations where bicyclists are likely to be involved in a ‘crash’ (in red).
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Figure 3 Graph showing the percent of reported bicyle crashes and violations, along with all violations, in
Cambridge during the reported period, and the hour in which they were recorded. Commuting hours in the
morning and early evening witness increases in both bicycle crashes and violations. While reports of
bicycle crashes increase through the evening hours between 6:00 p.m. and 9:00 p.m., the number of
citations decreases steadily.
Figure 4 Distribution of all citations by violation type. Bicycle violations total roughly 5% of all citations.
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The chart above (Figure 4) shows that roughly 5 percent of all citations are given to bicycles. I
don’t know if that reflects the percentage of bicycles on the road compared to cars and trucks, but I think
it is still a pretty big number and I think most cyclists biking in or through Cambridge have some story
involving a citation. The problem with bike citations, though, is that other than knowing when and where
they were given, we don’t seem to have ready access to knowing why they were issued.
I would like to work with CPD to change the bicycle citation form and related data collection to
allow us to readily see which offenses result in citations and which ones do not to help inform other bike
safety efforts and our overall street safety work .
Similarly, the chart tells us something about what we’re giving drivers tickets for, and things like
crosswalk violations, a pet peeve of mine, seem low on the priority list. Given the disproportionate danger
that motorists pose to other road users, to the extent that we can get drivers to pay attention to other
people on the road, especially cyclists, I think we’d make great strides in traffic safety.
About 40 percent of the drivers’ tickets are given for running stop lights or stop signs while
failure to yield is only 5 percent of driver citations even though such failure to yield is very dangerous for
cyclists and pedestrians. Cambridge would be safer if drivers paid a lot more attention to turning safely,
whether it is at a street intersection or into a driveway, and I think more intentional enforcement efforts in
this area would help make that happen. Anecdotally, the delivery economy and associated curb access
requirements and sometimes unpredictable driving and parking habits of Uber, Lyft, UPS and Amazon
drivers have created a new set of safety hazards especially pertinent to cyclists but it is not clear that we
do, or can, capture specific data on this specific street safety challenge.
In conclusion, there needs to be a broader and more detailed conversation about bicycle and street
safety and equity, reflecting the multi-faceted safety challenges and transportation needs of Cambridge’s
streets. Certainly, infrastructure improvements targeting the dangers involved with turning movements
and intersections, as well CPD’s traffic enforcement efforts, have a big role to play in keeping all of us-
cyclists, pedestrians and drivers- as safe as possible. Asking CPD to explain the rational and limitations
(such as evening staffing) behind their bike and overall traffic enforcement work would be a good place
to start this part of the street safety conversation. This conversation would dovetail well with efforts to
better capture the bike-related data we need to build safer streets for all users.
This memorandum is being forwarded to the City Clerk, Ms. Donna Lopez, to be included in the
agenda for the Regular City Council Meeting on Monday, December 4, as a Communication from City
Officers.
Linked sources:
https://data.cambridgema.gov/Public-Safety/Police-Citations/gmq6-8ver
https://safety.fhwa.dot.gov/PED_BIKE/univcourse/pdf/swless04.pdf
http://law.onecle.com/massachusetts/89/9.html