Category: Data

Which is safer: Bike without helmet, or drive without seatbelt?

December 3, 2011 / / 0 Comments

Cycling on Milwaukee Avenue at Grand Avenue and Halsted Street, one of the most crash-likely intersections on Milwaukee Avenue.

Someone asked me on Twitter: “What’s more dangerous, biking with no helmet or driving with no seatbelt?” It’s an odd comparison, but I decided to try to crack the question.

Here’s my answer:

If your definition of “dangerous” is “the likelihood that you’ll receive an injury while traveling in/on the vehicle”, assuming that the likelihood of being in a crash is the same*, then you are more likely to sustain an injury while cycling while wearing a helmet than while driving or being a passenger in a car while wearing a seatbelt.

Here’s the data, for crashes in Chicago in 2007-2010:

Table 1: Yes, recorded to be wearing a helmet while bicycling

Injury Type Frequency (each number is a person) Percent of total
No injury 3 7.32%
Possible injury 6 14.63
Non-incapacitating injury 26 63.41
Incapacitating injury 6 14.36
Fatality* 0 0
Total 41 100%

A value of 0 fatalities in four years for people wearing a helmet absolutely DOES NOT mean that a helmet prevented a fatality. The “contrary” data for “Recorded to not be wearing a helmet or having safety equipment” shows that there was 1 fatality in four years – the data do not suggest that the fatality would be prevented if the person was wearing a helmet. The sample size is so small that this data is meaningless.

Table 2: Yes, recorded to be wearing a seatbelt as driver or passenger

Injury Type Frequency (each number is a person) Percent of total
No injury 423,096 89.42%
Possible injury 21,667 4.58
Non-incapacitating injury 23,956 5.06
Incapacitating injury 4,338 0.92
Fatality 93 0.02
Total 473,150 100%

*I don’t think we can determine the likelihood of being in a crash when riding a bicycle because we don’t know the “device miles traveled” of Chicago cyclists. It’s probably possible to approximate the number of vehicle miles traveled by drivers in Chicago, though; I’m not sure about passengers.

Download the data for this article, which includes these additional tables:

  • Bicycling: All injuries
  • Bicycling: No safety equipment or helmet wearing
  • Bicycling: Unknown usage of safety equipment
  • Auto: All injuries
  • Auto: No safety equipment or helmet wearing
  • Auto: Unknown usage of safety equipment

Last minute vote on bicycle data visualization project

November 28, 2011 / / 0 Comments

The United States Department of Transportation is holding a data visualization competition and Chicago bike crash locations are one of the topics.

From Michael Carney:

I started this project because, basically, I thought it would be interesting to make a map of bike crash locations around Chicago and present it to my GIS class at UIC. Sebastian Lew and I collaborated for several months and it evolved into something more. Using ArcGIS, we were able to symbolize streets by level of overall crash intensity, calculate crashes per mile on streets, perform hot spot analysis to identify areas with high numbers of crashes, compare ridership levels with crash levels, examine temporal trends in crash activity, and perhaps most importantly, assess the effectiveness (at least at a basic level) of current bicycle infrastructure. At the very least I hope our project can help you plan a safe route to work, at the most I hope it can be used by policymakers and planners when considering how and where to expand Chicago’s bike infrastructure.

Vote today only. View the project.

Expanding data collection to include other modes

October 31, 2011 / / 0 Comments

I think the Census Bureau should start collecting “journey to work” data on trips made by electric or gas-powered standing scooters as well as Segways. And that we need to start organizing vehicle crashes by this category.

Saw this electric scooter locked up outside the Active Transportation Alliance headquarters a couple weeks ago, 9 W Hubbard Street. 

Alderman Laurino should start work on “leveling the playing field” between texting while driving with texting while biking to include a ban on texting while Segwaying. Seen at 2030 S Archer. 

Rambling about automobile crash data and cellphone distraction

October 4, 2011 / / 0 Comments

How often do bicyclists get involved with crashes because of cellphone distraction? See the table below. And how many crashes are caused by the bicyclist being distracted by a cellphone? We won’t and don’t know. 

The Chicago City Council will vote tomorrow on ordinance 02011-7146 to add a new section in Chapter 9 of the Municipal Code of Chicago: “9-52-110 Use of communication devices while operating a bicycle.”

In a Chicago Sun-Times article today, Matthew Tobias, the Chicago Police Department’s deputy chief of Area 3 patrol, reported on the number of citations that the department has issued to drivers in violation of the cellphone ban: “from 2,577 administrative violations in 2008 to 10,920 in 2009 and 19,701 last year” (known as “citations issued” in the table below).

I looked at the crash data to see how many crashes were coded as having been caused by “Distraction – operating an electronic communication device (cell phone, texting, etc)”.

Out of 274,488 recorded crashes in 2008, 2009, and 2010, there were 331 crashes which had a Cause 1 or Cause 2 of “Distraction – operating an electronic communication device (cell phone, texting, etc)”. The table below compares the rates of crashes to the rates of citations issued and the number of crashes that the police noted were caused by cellphone distraction. It also shows the number of these “cellphone distraction” crashes that involved bicyclists and pedestrians.

Year Citations issued Automobile crashes Cellphone distraction crashes % of cellphone distraction crashes Involved with bicyclists? Involved with pedestrians? National VMT (billions)*
2008 2577 111,701 91 0.081 3 10 2973.47
2009 10920 81,982 130 0.159 1 7 2979.39
2010 19701 80,805 110 0.136 6 8 2999.97

Maybe this data shows that the increased enforcement is causing fewer crashes?
However data for cyclists’ involvement in crashes and their cellphone use WON’T BE recorded unless there’s a rule change as the cause is only recorded for the vehicle involved in the crash, and bicycles are devices, not vehicles.

None involved fatalities.

*Yep, that’s 2 thousand billion. Read it like this, 2 trillion 973 billion and 470 million. VMT data from Bureau of Transportation Statistics.

Are protected bike lanes going in the right places?

September 29, 2011 / / 0 Comments
Bike crash map of Ogden, Milwaukee, Chicago

Common bike-car crash locations in West Town. The bottom blue circle identifies Ogden/Milwaukee, where there is a yellow trap for northbound, left-turning motorists (from Milwaukee to Ogden) that makes them run into southbound bicyclists who have a green light.

My contribution to a discussion on The Chainlink, Are protected bike lanes going in the right places?

Kelvin, Milwaukee/Ogden/Chicago is the intersection along Milwaukee Avenue with the highest number of bicycle crashes. I created this table and map to show them, using data from 2007-2009.

The blue rings on the map are called, in GIS parlance, “buffers” and are circles used to select things (in this case, bike crashes) within a certain distance of the circle center. In this map I used 50 feet radius buffers (100 feet diameter). While this distance encompasses the intersection from center to all four curbs, it doesn’t encompass the crashes that happened just outside the buffer that were still most likely influenced by the intersection (like drivers’ turning movements).

I am working on a project with three friends to create a better map and “crash browser”. I mentioned it in the last story on Grid Chicago in this post. For this project, we are using 200 feet radius (400 feet diameter) buffers to ensure we encompass the entire intersection and the area in which it still has an effect. This also grabs the bike lane “pinch points”, places where a bike lane doesn’t start until 100-200 feet beyond the intersection.

I am also concerned with the strategy and approach CDOT is using to choose locations. It’s not transparent; at MBAC, CDOT said they were choosing locations “without controversy and that could be implemented quickly”.

Read more about Kinzie Street, Chicago’s first protected bike lane, and my other thoughts on protected bike lanes.