Mapping Milwaukee for Cyclists

The Chicago Department of Transportation (CDOT) has prioritized bike infrastructure improvement in recent years. In 2023, CDOT released the  Chicago Cycling Strategy , with goals to connect currently disconnected bikeways and make cycling safer throughout the city. In line with these goals, CDOT plans to implement 150 miles of new bikeways, and improve existing bike infrastructure toward lower-stress options. Milwaukee Avenue has been the target of some recent bike lane improvements. We want to find out: have these improvements prevented bike crashes?

We were able to find bicycle traffic data from Replica, a private data collection company that focuses on city mobility data. Replica provides data per season. We chose to focus on fall of 2019 (before many bike lane improvements were made) and fall of 2023. Replica's data stores traffic volumes in small line segments, which we combined to make longer line segments. We took the mean traffic for all smaller line segments to use as our traffic count for the longer line segments. Our first conclusion:

We found traffic crash data from the City of Chicago Data Portal and cleaned it to only use bicycle crash data for our selected time periods. The total number of crashes remained relatively consistent. In Fall 2019 there were 22 crashes. In Fall 2023 there were 21. But bike volumes increased. How do crashes per rider compare for each year? We normalized our Milwaukee crash data by rider to get a more accurate picture of changes in safety over time.

Next, we wanted to look at how bike lane type has played a role in decreasing crashes. We used bike route data from the City of Chicago Data Portal from 2019 and 2023 to visualize what type of infrastructure existed where crashes occurred.

There is significant clustering around the stretch of Milwaukee with no bike lane. There are also fewer crashes near the loop in 2023, though minimal change in the bike infrastructure occurred.

Protected bike lanes still had a high number of crashes per mile. This could be a result of higher bike traffic on protected lanes as indicated above; there are only a few parts of Milwaukee in 2019 with protected lanes, and they are a part of the highest-traffic section.

Crashes per mile went down for many bike lane types after four years, but not all. No crashes occurred on buffered sections and are therefore not present in the 2023 chart.

Note how in the bike lane map further above, crashes are concentrated in two clusters around lanes labeled as "Bike" (non-buffered, non-protected lanes). This cluster is reflected in the 2023 crashes per mile chart above.

Crashes per 100,000 riders and crashes per mile decreased on protected segments as bicycle infrastructure improved on Milwaukee. But crashes continued to occur in some stretches of road that upgraded their lane type. This points to other factors that may have caused crashes, like traffic speed and proximity to intersections, and prompts questions about the details of actual bike lane quality.

Because our bike traffic data could only be used in one season, we were limited to looking at crashes in a three-month time span. Longer term crash data may reveal more trends, but accurate bike traffic data would be needed to get an accurate crashes per rider number.

Next steps might involve further exploration of the bike lane types. While the City of Chicago categorizes a certain type of bike lane as "protected," there are different types of protected lanes, which includes parking-protected, curb-protected, and flex-post-protected, among others. Differing street conditions may also affect bicycle safety. A more in-depth analysis that breaks down bike lane type even further could yield instructive results.