Category: Data

Crashes by bike or by foot at different intersections

January 16, 2012 / / 0 Comments

While working on a private web application that I call Chicago Crash Browser, I added some code to show the share of pedestrian and pedalcyclist crashes. The site offers users (sorry I don’t have a web server that can make it public) a list of the “Top 10” intersections in terms of bike crash frequency (that’s bike+auto crash). You can click on the intersection and a list will populate showing all the pedestrian and pedalcyclist crashes there, sorted by date. At the bottom of the list is a simple sentence that tells what percentage pedestrian and pedalcyclists made up at that intersection.

I’m still developing ideas on how this information may be useful, and what it’s saying about the intersection or the people using it.

Let me tell you about a few:

Milwaukee Avenue and Ogden Avenue

I mentioned in my article Initial intersection crash analysis for Milwaukee Avenue that this intersection is the most bike crash-frequent.

23 crashes within 150 feet of the center, 2005-2010

82.61% bike crashes **

17.39% ped crashes.

Ashland Avenue and Division Street

28 crashes within 150 feet of the center, 2005-2010

46.43% bike crashes

53.57% ped crashes **

Milwaukee, North and Damen Avenues

46 crashes within 150 feet of the center, 2005-2010

39.13% bike crashes

60.87% ped crashes **

Halsted Street, Lincoln and Fullerton Avenues

38 crashes within 150 feet of the center, 2005-2010

42.11% bike crashes

57.89% ped crashes **

Montrose Avenue and Marine Drive (Lake Shore Drive ramps)

11 crashes within 150 feet of the center, 2005-2010

90.91% bike crashes **

9.09% ped crashes

Why do you think some intersections have more of one kind of crash than the other?

People walking at Milwaukee-North-Damen.

The Chicago Crash Browser can be made public if I have a host that offers the PostgreSQL database. Do you have one to offer?

Some crash analysis based on gender/sex in Chicago

December 13, 2011 / / 0 Comments

A friend sent me an article saying that in London, women were experiencing crashes more often than men while cycling (BBC article). He asked if this was true about Chicago. So I crunched the numbers. This is very low-level, initial, take it with a grain of salt analysis. It appears that that is not the case for Chicago.

It appears that men walking or cycling are involved in disproportionately more crashes with automobiles than women, but not very disproportional.

1. Men make up 72.73% of people cycling (to work, the only trip purpose for which I have data). And they experienced 75.75% of the crashes with automobiles (to where is unknown).

2. Men make up 48.45% of people walking (to work, again, the only trip purpose for which I have data). And they experienced 53.38% of the crashes with automobiles (again, to where is unknown).

This analysis also points out shortcomings in our data. Even with National Household Travel Survey I don’t think I could get very detailed (as the statistics would be too aggregated and the sample size for Chicago would be small). This data is based on two sources: motorist crash reports from 2007-2010 from the Illinois Department of Transportation (IDOT); and American Community Survey “means of transportation to work”. The last time a household travel survey was done in Chicago was 2008 and I just acquired that data last week. I need to figure out how to connect the people and trip tables and then I can do more analysis, getting exposure data for all trips, not just work.

Who bikes?

December 12, 2011 / / 0 Comments

Who bikes? pie chart

From April 2011, via Sightlines Daily, using data from John Pucher and Ralph Buehler, who got it from the 2009 National Household Travel Survey.

Contrary to popular convention, the biggest share of bicyclists isn’t yuppies, it’s low income people. In fact, the lowest-earning quarter of Americans make nearly one-third of all bike trips. Among that group, I would expect to find at least some fraction of working poor, students, the unemployed, and retired people of modest means. No doubt there are almost as many reasons to bike as there are cyclists, but it’s clear that bikes are a favored choice among those on a budget.

The big takeaway for me, however, is looking beyond low-income riders. Bicycling is remarkably evenly distributed among the remaining three quartiles. With the exception of the over- represented bottom quartile, bike trips don’t appear to be the province of any one income class more than any other.

Dumke fighting the open data fight for Chicagoans

December 4, 2011 / / 0 Comments

Dan O’Neil mails a FOIA request to Chicago’s 311 service in 2007. Now, you can email most places (or fax!). 

I like to say that for every dataset a government agency proactively publishes, there’s one fewer FOIA* request it has to respond to.

City officials say they get so many FOIA requests that responding to them all has become a serious resource drain. But this is one of the reasons why—we don’t have any other way to get information about our government.

As a result, I will be adding to their workload and submitting another FOIA request. I don’t mind saying this publicly since it won’t be a secret anyway. That’s because the Emanuel administration has resumed Daley’s old habit of posting FOIA requests online. It’s also kept up Daley’s habit of not posting any information showing how responsive the city is.

That’s Chicago Reader author Mick Dumke talking about his troubles obtaining some data from the Chicago Department of Human Resources. Read the entire article, where he also gives a pretty good description of the “Chicago FOIA way”, the process for getting information in Mayor Emanuel’s transparent administration.

Note: I submit a FOIA request to some agency at least once a month. My most frequent FOIA requests go to the Chicago Transit Authority (CTA) and the Chicago Department of Transportation (CDOT). I also query the Chicago Police Department, and the Department of Administrative Hearings. Derek Eder has a story on how he and his colleagues worked with some Chicago staff to add new data about lobbying to the Chicago Data Portal.

*Freedom of Information Act. In California, it’s called FOIL, or Freedom of Information Law.

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