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Developing a method to score Divvy station connectivity

January 4, 2014 / / 2 Comments

A Divvy station at Halsted/Roscoe in Boystown, covered in snow after the system was shutdown for the first time to protect workers and members. Photo by Adam Herstein.

In researching for a new Streetsblog Chicago article I’m writing about Divvy, Chicago’s bike-share system, I wanted to know which stations (really, neighborhoods) had the best connectivity. They are nodes in a network and the bike-share network’s quality is based on how well (a measure of time) and how many ways one can move from node to node.

I read Institute for Transportation Development Policy’s (ITDP) report “The Bike-Share Planning Guide” [PDF] says that one station every 300 meters (984 feet) “should be the basis to ensure mostly uniform coverage”. They also say there should be 10 to 16 stations per square kilometer of the coverage area, which has a more qualitative definition. It’s really up to the system designer, but the report says “the coverage area must be large enough to contain a significant set of users’ origins and destinations”. If you make it too small it won’t meaningfully connect places and “the system will have a lower chance of success because its convenience will be compromised”. (I was inspired to research this after reading coverage of the report in Next City by Nancy Scola.)

Since I don’t yet know the coverage area – I lack the city’s planning guide and geodata – I’ll use two datasets to see if Chicago meets the 300 meters/984 feet standard.

Dataset 1

The first dataset I created was a distance matrix in QGIS that measured the straight-line distance between each station and its eight nearest stations. This means I would cover a station in all directions, N, S, E, W, and NW, NE, SE, and SW. Download first dataset, distance matrix.

Each dataset offers multiple ways to gauge connectivity. The first dataset, using a straight-line distance method, gives me mean, standard deviation, maximum value, and minimum value. I sorted the dataset by mean. A station with the lowest mean has the greatest number of nearby stations; in other words, most of its nearby stations are closer to it than the next station in the list.

Sorting the first dataset by lowest mean gives these top five best-connected stations:

  1. Canal St & Monroe St, a block north of Union Station (191), mean of 903.96 feet among nearest 8 stations
  2. Clinton St & Madison St, outside Presidential Towers and across from Northwestern Train Station (77), 964.19 feet
  3. Canal St & Madison St, outside Northwestern Train Station (174), 972.40
  4. Canal St & Adams St, north side of Union Station’s Great Hall (192), 982.02
  5. State St & Randolph St, outside Walgreens and across from Block 37 (44), 1,04.19

The least-connected stations are:

  1. Prairie Ave & Garfield Blvd (204), where the nearest station is 4,521 feet away (straight-line distance), or 8.8x greater than the best-connected station, and the mean of the nearest 8 stations is 6,366.82 feet (straight-line distance)
  2. California Ave & 21st St (348), 6,255.32
  3. Kedzie Ave & Milwaukee Ave (260), 5,575.30
  4. Ellis Ave & 58th St (328), 5,198.72
  5. Shore Drive & 55th St (247), 5,168.26

Dataset 2

The second dataset I manipulated is based on Alex Soble’s DivvyBrags Chrome extension that uses a distance matrix created by Nick Bennett (here’s the file) that estimates the bicycle route distance between each station and every other station. This means 88,341 rows! Download second dataset, distance by bike – I loaded it into MySQL to use its maths function, but you could probably use python or R.

The two datasets had some overlap (in bold), but only when finding the stations with the lowest connectivity. In the second dataset, using the estimated bicycle route distance, ranking by the number of stations within 2.5 miles, or the distance one can bike in 30 minutes (the fee-free period) at 12 MPH average, the following are the top five best-connected stations:

  1. Ogden Ave & Chicago Ave, 133 stations within 2.5 miles
  2. Green St & Milwaukee Ave, 131
  3. Desplaines St & Kinzie St, 129
  4. (tied) Larrabee St & Kingsbury St and Carpenter St & Huron St, 128
  5. (tied) Clinton St & Lake St and Green St & Randolph St, 125

Notice that none of these stations overlap with the best-connected stations and none are downtown. And the least-connected stations (these stations have the fewest nearby stations) are:

  1. Shore Drive & 55th St, 11 stations within 2.5 miles
  2. (tied) Ellis Ave & 58th St and Lake Park Ave & 56th St, 12
  3. (tied) Kimbark Ave & 53rd St and Blackstone Ave & Hyde Park Blvd and Woodlawn Ave & 55th St, 13
  4. Prairie Ave & Garfield Blvd, 14
  5. Cottage Grove Ave & 51st St, 15

This, the second dataset, gives you a lot more options on devising a complex or weighted scoring system. For example, you could weight certain factors slightly higher than the number of stations accessible within 2.5 miles. Or you could multiply or divide some factors to obtain a different score.

I tried another method on the second dataset – ranking by average instead of nearby station quantity – and came up with a completely different “highest connectivity” list. Stations that appeared in the least-connected stations list showed up as having the lowest average distance from that station to every other station that was 2.5 miles or closer. Here’s that list:

  1. Kimbark Ave & 53rd St – 13 stations within 2.5 miles, 1,961.46 meters average distance to those 13 stations
    Blackstone Ave & Hyde Park Blvd – 13 stations, 2,009.31 meters average
    Woodlawn Ave & 55th St – 13 stations, 2,027.54 meters average
  2. Cottage Grove Ave & 51st St – 15 stations, 2,087.73 meters average
  3. State St & Kinzie St – 101 stations, 2,181.64 meters average
  4. Clark St & Randolph St – 111 stations, 2,195.10 meters average
  5. State St & Wacker Dr – 97 stations, 2,207.10 meters average

Back to 300 meters

The original question was to see if there’s a Divvy station every 300 meters (or 500 meters in outlying areas and areas of lower demand). Nope. Only 34 of 300 stations, 11.3%, have a nearby station no more than 300 meters away. 183 stations have a nearby station no further than 500 meters – 61.0%. (You can duplicate these findings by looking at the second dataset.)

Concluding thoughts

ITDP’s bike-share planning guide says that “residential population density is often used as a proxy to identify those places where there will be greater demand”. Job density and the cluster of amenities should also be used, but for the purposes of my analysis, residential density is an easy datum to grab.

It appears that stations in Woodlawn, Washington Park, and Hyde Park west of the Metra Electric line fare the worst in station connectivity. The 60637 ZIP code (representing those neighborhoods) contains half of the least-connected stations and has a residential density of 10,468.9 people per square mile while 60642, containing 3 of the 7 best-connected stations, has a residential density of 11,025.3 people per square mile. There’s a small difference in density but an enormous difference in station connectivity.

However, I haven’t looked at the number of stations per square mile (again, I don’t know the originally planned coverage area), nor the rise or drop in residential density in adjacent ZIP codes.

There are myriad other factors to consider, as well, including – according to ITDP’s report – current bike mode share, transit and bikeway networks, and major attractions. It recommends using these to create a “demand profile”.

Station density is important for user convenience, “to ensure users can bike and park anywhere” in the coverage area, and to increase market penetration (the number of people who will use the bike-share system). When Divvy and the Chicago Department of Transportation add 175 stations this year – some for infill and others to expand the coverage area – they should explore the areas around and between the stations that were ranked with the lowest connectivity to decrease the average distance to its nearby stations and to increase the number of stations within 2.5 miles (the 12 MPH average, 30-minute riding distance).

N.B. I was going to make a map, but I didn’t feel like spending more time combining the datasets (I needed to get the geographic data from one dataset to the other in order to create a symbolized map). 

Divvy isn’t a real bike

January 2, 2014 / / 0 Comments

Riding on Divvy in the snow.

Divvy, for the first time in its short, seven-month existence, shut down today at 12 PM on account of the weather and keeping members and workers – who move bikes, shovel snow, and drive vans around town – safe.

Every news media in town reported on the shutdown. Chicagoist, ABC 7, NBC 5, FOX 32, Chicago Tribune, Sun-Times – you name it they had it.

But nothing has been published, except parts of this story from DNAinfo Chicago, that discusses how bicycling – whether on Divvy or your own bike – is very difficult in Chicago winters because of the poor coordination between the Streets & Sanitation and Transportation departments’ snow removal efforts, and the slow pace at which CDOT gets around to removing snow from the protected bike lanes. (I was quoted, alongside someone I recommended the author get in touch with, and we have differing views on the matter.)

In winter the protected bike lanes are the only bikeable kind of bike lane as conventional bike lanes become snow storage areas because plows can’t reach further right when there are parked cars (to avoid knocking off car mirrors).

This problem is not unique to Chicago and other cities have solved it. The cold isn’t why people in Chicago stop biking: it’s that snow and ice make it even more difficult in a region with little, separated (meaning safe and desirable) cycling infrastructure. There are climes with similar and worse winters where a large portion of people who bike in the summer keep biking in the winter. Places like Boulder, Minneapolis, Montréal, and Copenhagen.

A well-plowed, separated bike lane in a Copenhagen winter. Stranded? Put your bike on the back of a taxi (their buses don’t allow bikes).

I think it’s good that news media have recognized Divvy’s position as a transit system in the area, which they do by holding it to the same, weird standard they do Chicago Transit Authority and Metra, and posting about it frequently. When the CTA or Divvy has some marginal or perceived issue with its finances or service, an article gets written. But when it comes to bicycle infrastructure they give the city a pass where it doesn’t deserve one.

The media cares about Divvy, but it doesn’t care about bicycling. It might be the 11,000 Divvy members (more than Active Transportation Alliance or The Chainlink), however, that gets the city to kick up its bike lane snow removal efforts up a notch and I anxiously await that day.

Mapping a campground that doesn’t exist: a before and after view of OpenStreetMap

December 27, 2013 / / 8 Comments

Pretty soon there will be a campground shown in OpenStreetMap, and added to its geocoding database, when I’m done adding it.

I temporarily become addicted to mapping places on OpenStreetMap. In my quest to find and map all campgrounds in Chicagoland – in order to publish them in the Chicago Bike Guide – I came across a campground that was constructed this year and opened in August 2013. This is the story of figuring out how to map the Big Rock Forest Preserve campground in Big Rock, Illinois.

I found on the Kane County Forest Preserve District website that the organization operated a campground at Big Rock Forest Preserve. I couldn’t locate the campground in Google Maps by the address the website gave. I couldn’t find it in OpenStreetMap, either, because no one had mapped it, but it’s there now.

When I searched for the park by name, Google Maps zoomed me to the main entrance of the park, but I still couldn’t see a campground. I downloaded the forest preserve district’s park map (always as a PDF) and followed the roads in Google Maps until I came across the campgrounds approximate position. There was a new road here so I followed that to find a campground under construction.

Google Maps shows the campground and artificial lake under construction.

Google’s imagery of the under-construction campground was taken on May 23, 2013 (get the date from Google Earth). This was great because now I could open JOSM, a powerful desktop OpenStreetMap editor, and locate the site, load Bing’s imagery and start tracing the campground to upload to OSM.

Bing’s imagery in JOSM, the OpenStreetMap-editing app, doesn’t show the campground.

The problem was that Bing’s imagery – and this is typical – was outdated. I could easily compare the imagery side-by-side and based on other landscape features (like the forest edge) guess where to trace the campground, but OSM needs better quality data. Enter MapWarper.

Read the rest of this post on Web Map Academy.

Compiling and mapping Chicago-area campgrounds

December 26, 2013 / / 0 Comments

I’m adding Chicago-area campgrounds to the Chicago Bike Guide to entice new users and to espouse the enjoyment of medium-distance bike camping (which I’ve now done officially once, earlier this year).

<The Chicago Bike Guide is available for Android and iOS.>

I’m taking a systematic approach to finding all the publicly-owned campgrounds in the area by looking at primary sources.

First, though, I’ve used Overpass Turbo to create a list of all existing campgrounds in OpenStreetMap. You can see a gist of these places.

Camp sites at Greene Valley forest preserve I mapped.

Camp sites at Greene Valley forest preserve I mapped.

The next method is to find out which campgrounds are operated by the county forest preserves, which are usually well-documented on their respective websites. Then I will look at state parks in Illinois, Indiana, and Wisconsin, operated by states’ respective Departments of Natural Resources (DNR). Next I will look at national parks and finally commercial campgrounds.

The app will display campground information such as alcohol rules, if cabins or lodging is available, and how you can get there (which trails or train lines).

I’ve so far mapped the campgrounds in two ways, as nodes and as areas. At the Greene Valley forest preserve in DuPage County, for example, I’ve mapped the 11 individual camp sites (see map), but at Blackwell forest preserve in the same county, I’ve mapped the area as the camp site (see map).

Blackwell has over 50 sites in a discrete area and it’s more efficient to map them as a single node, while Greene Valley had far fewer sites but scattered over a couple areas.

Cross-posted to Web Map Academy.

Getting a little closer to understanding Chicago’s pothole-filling performance status

December 21, 2013 /

Tom Kompare updated his web application that tracks the progress of potholes based on information in the city’s data portal in response to my query about how many potholes the city fills within 72 hours, which is the Chicago Department of Transportation’s performance measure.

He wrote to me via the Open Government Chicago group:

Without completely rewriting http://potholes.311services.org, I added a count of the number of open (not yet addressed) pothole repair tickets (requests) that exceed 3 days old. As of today, the data from the City of Chicago’s Data Portal shows 1,334 or the 1,404 open tickets in the 311 system are older than three days.

Full disclosure: The web app actually looks for greater than 4 days old. The Data Portal’s pothole data are only updated once a day, so these data are always a day old. 4 – 1 = 3.

Keep in mind that this web app only shows how many are yet to be addressed, and does not count how many have been patched within CDOT’s 3-day goal during some arbitrary time period. That is a much more intense calculation that this pure client-side Javascript web application can handle due to bandwidth restrictions on mobile (3/4G). This web app already pushes the mobile envelope with the amount of data downloaded. I can fix that, but, again, not without a rewrite.

Still, 1,334 open repair requests (12/16/2013 Data Portal data) is quite different than the number of open repair requests reported by CDOT (560 in Alley, 193 on street) on 12/16/2013. I’m not sure what is the difference.

This reminds me of a third issue with the way CDOT is presenting pothole performance data online (the first being that it’s PDF, the second that it doesn’t work in Safari). The six PDF files are overwritten for every new day of data. If you want information from two days ago, well you better have downloaded the PDF from two days ago!