Category: Roadways

How many miles of roads are in your ward?

February 27, 2013 / / 10 Comments

Screenshot 1: Showing how some streets are not being counted. There should be a yellow section of road between the two existing yellow road sections. 

A friend recently asked me how many blocks of road are in his ward. He wanted to know so that he could measure how many blocks of streets would have an older style of street lighting after X number of blocks receive the new style of street lighting. For this project, I used two datasets from Chicago’s open data portal: street center lines and wards. The output data is not very accurate as there may be some overlap and some uncounted street segments; this is likely due to a shortcoming in my process. I will show you how to find the number of blocks per ward using QGIS (download Quantum GIS, a free program for all OSes).

Here’s how I did it

  1. Load in the two datasets. Wards and street center lines (zipped shapefiles). They are projected in EPSG:3435.
  2. Exclude several road classifications in the street center lines by querying only for "CLASS" > '1' AND "CLASS" < '5'. The data dictionary for the road classifications is at the end. We don’t want the river, sidewalks, expressways, and any ramps to be included in the blocks per ward analysis.
  3. Intersect. In QGIS, select Vector>Geoprocessing Tools>Intersect. The input vector layer is “Transportation” (the name of the street center lines dataset) and the intersect layer is “Wards”. Save the resulting shapefile as “streets intersect wards”. Click OK. This will take a while.
  4. Add the “streets intersect wards” shapefile to the table of contents.
  5. You’ll notice some of the issues with the resulting shapefile: missing street segments (see screenshot 1). What should QGIS do if a street is a ward boundary?
  6. Obtain street length information, part 1. Remove all the columns in the “streets intersect wards” shapefile that have something to do with geometry. These are now outdated and will confuse you when you add a geometry column generated by QGIS.
  7. Obtain street length information, part 2. With the “streets intersect wards” shapefile selected in the table of contents, select Vector>Geometry Tools>Export/Add geometry columns. Select “streets intersect wards” shapefile as your input layer, leave CRS as “Layer CRS” and save as new shapefile “streets intersect wards geom”.
  8. Add the “streets intersect wards geom” shapefile to the table of contents.
  9. You will see a new column at the end of the attribute table called LENGTH. Since the data is projected in EPSG:3435 (Illinois StatePlane NAD83 East Feet), the unit is feet.
  10. Simply export “streets intersect wards geom” to a CSV file and open the CSV file in a spreadsheet application. From there you can group the data by Ward number and add the street lengths together. (I thought it would be faster to do this in a database so I imported it into a localhost MySQL database and ran a simple query, SELECT wardNum, sum(`chistreets_classes234`.`LENGTH`) as sum FROM chistreets_classes234 WHERE ward > 0 group by wardNum. I then exported this to a spreadsheet to convert feet to miles.)

Because of the errors described in step 5, you shouldn’t use this analysis for any application where accuracy is important. There are road lengths missing in the output dataset (table with street lengths summed by ward) and I cannot tell if the inaccuracy is equally distributed.

[table id=7 /]

Wards 19 (south side) and 41 (Norwood Park, including O’Hare airport) have the highest portion of street length in the city.

Screenshot 2: Ward 41 is seen. 

Street data dictionary

Column is “CLASS”. The value is a string. This dataset lacks alleys. Adapted from the City’s data dictionary.

1. Expressway

2. Arterials (1 mile grid, no diagonals)

3. Collectors (includes diagonals)

4. Other streets (side streets, neighborhood streets)

5. Named alleys (mostly downtown, like Couch Place and Garland Place)

7. Tiered (lower level streets, including LaSalle, Michigan, Columbus, and Wacker)

9. Ramps (goes along with expressway)

E. Extent (not sure how to describe these; includes riverwalk and lake walk segments, and Navy Pier, also includes some streets, like Mies van der Rohe Way)

RIV. River

S. Sidewalk

99. Unclassified

Survivor bias: Who walks away from automobile crashes?

February 14, 2013 / / 6 Comments

This photo of a damaged car has little to do with this post. 

Then my friend Alex E. asked, “Is there a reason why?”

I can’t leave such a question hanging. I thought I read that somewhere, and it was probably in Tom Vanderbilt’s book, Traffic. What I found in there mostly referred to trucks (the semi-trailer type) because of their mass and how people not driving trucks behave around them on the road. The second part explained the statistics around who lives and dies in crashes involving a drunk driver.

Knowing that, and knowing the story I tweeted a link to, you’ll see that the event didn’t involve a truck and my relating them was perhaps unsuitable. It did involve drunk driving, but I may have misread the book text.

Here’s what Traffic says about trucks

“When trucks and cars collide, nearly nine of ten times it’s the truck driver who walks away alive.” Vanderbilt discusses how that is (page 247).

…we all likely have proof of the dangerous nature of trucks. We have seen cars crumpled on the roadside. We’ve heard news stories of truck drivers, wired on stimulants, forced to drive the deregulated trucking industry’s increasingly long shifts. We can easily recall being tailgated or cut off by some crazy trucker.

Just one thing complicates this image of trucks as the biggest hazard on the road today: In most cases, when cars and trucks collide, the car bears the greater share of what are called “contributory factors”.

Really? Car drivers caused crashes with trucks and then die from it?

Instead of relying on drivers’ accounts, he [Daniel Blower at Michigan Transport Research Institute] looked at “unmistakable” physical evidence. “In certain crash types like head-ons, the vehicle that crosses the center much more likely contributed to the crash than the vehicle that didn’t cross the center line”.

After examining more than five thousand fatal truck-car crashes, Blower found that in 70 percent of cases, the driver of the car had the sole contributing responsibility in the crash.

Basically, the car drivers in a car-truck crash caused the crash and ended up being the ones dying.

…the reason trucks are dangerous seems to have more to do with the action sof car drivers combined with the physcial characteristics of trucks and less to do with the actions of truck drivers. “The caricature that we have that the highways are thronged with fatigued, drug-addled truck drivers is, I think, just wrong”, Blower said.

“In a light vehicle, you are correct to be afraid of them, but its not because the drivers are disproportionately aggressive or bad drivers”, Blower said. “It’s because of physics, truck design, the different performance characteristics. You can make a mistake around a Geo Metro and live to tell about it. You make that same mistake around a truck and you could easily be dead.”

What Traffic says about drunk driving

Of the 11,000 drunk-driving fatalities studied by economists Steven D. Levitt and Jack Porter, 72% were the crash-causing drunk driver or their passengers, and 28% were the other drivers (most of whom were not drunk themselves) (page 251).

Current madness of the week: investigating car crashes

February 10, 2013 / / 4 Comments

Gravity should have prevented this car crash, as would not placing buildings near roadways. But we’ve figured out how to defy gravity. Photo by Katherine Hodges.

“Police closed the street to investigate”.

What a waste of time. The investigation will conclude the same way as any other, with one or more of the following contributing factors: exceeding the speed limit, alcohol, a deficiency in someone’s driving skills or knowledge, or some defect in the road (I’m excluding poor road design as it could almost always be better, designed in such a way to reduce the occurrence of poor quality driving).

The story: a person driving an SUV side swipes another SUV. The driver loses control and then hits the center concrete barrier. The SUV flips over and the driver dies. (Yes, this is in relation to an incident on I-294 in Glenview this weekend.)

We already know how to fix all of these issues.

Destination streets are rarely the best places to bike

January 29, 2013 / / 22 Comments

This family took to riding on the sidewalk of Division Street instead of in the bike lane. They’re riding the stylish workhorse WorkCycles Fr8. Once I saw them riding the blue one, I had to get a different color. 

My friend Calvin Brown, a circumstantial urban planner, is always giving me Jane Jacobs-style observations about how citizens use their cities.

“Destination streets are the ones I avoid biking on because there’s so much car traffic there. Traffic must be balanced between streets that are good for biking and ones that aren’t currently good.”

In other words, because it’s a destination street (a place where there are a lot of retail outlets, venues, points of interest) it induces a lot of car traffic. Lots of car traffic discourages people from riding bikes, and makes it difficult for those who already are.

To me, a great example of this is Division Street. There’s a bike lane there from Ashland to California Avenues, and has tons (tons!) of restaurants and some night clubs. Yet that causes a lot of taxi traffic, people driving their own cars, looking for parking, jutting into the bike lane to see why traffic is going slow or backed up (um, because there are ton of cars!), and valet and delivery drivers blocking the bike lane.

It’s exactly this traffic, though, that keeps these places vibrant, desirable, and healthy (from an economic standpoint). The solution for bicycling is easy: swap the car parking with the bike lane so that bicycling isn’t affected by a majority of the aforementioned traffic maneuvers.

Calvin’s “destination streets” examples were Grand Avenue and Chicago Avenue. Neither has bike lanes, and both have 2 travel lanes in each direction. Grand has destinations from Racine Avenue to Ashland Avenue and Chicago has destinations from Ada Street to Western Avenue. I’d wager that if you narrowed those roadways by installing a protected bike lane you’d get slower traffic and higher business receipts.

Chicago Avenue at Hoyne Avenue is a particularly stupid part of Chicago Avenue: The Chicago Department of Transportation installed a pedestrian refuge island here. After several years and at least 4 replaced signs due to collisions of automobiles with it, the design hasn’t been modified. The island in and of itself did not change the speed of those who drive here, as the roadway’s width remained static.

What abysmal pavement quality on a brand new bike lane means

January 4, 2013 / / 16 Comments

Approaching the intersection and bike lane minefield. 

I find it very embarrassing that Chicagoans are supposed to ride their bicycles in this. I feel embarrassed riding my bike in this. I rode my bike on this pavement of abysmal quality and then felt ashamed and uncomfortable that I exited the bike lane and rode elsewhere.

The bike symbol succumbs to flooding which occupies half the bike lane’s width. 

I felt like a person in a wheelchair given an “accessible” theater seat behind a column that blocks a majority of my view of the stage. I felt like I was a reporter at a newspaper given a new computer where the keyboard was missing 42 keys. The bike lane was unusable, I was the butt of a cruel joke. This felt like a pittance, throwing crumbs to the masses.

2013 April Fool’s Day came early, in fall 2012. 

The photos in this post show a bike lane in Douglas Park against the curb, with a painted buffer, running in a minefield of patches and potholes on asphalt pavement. The bike lane was installed in the fall of 2012, as part of Mayor Emanuel’s efforts to construct 100 miles of protected bike lanes. The goal has since been reduced after the definition of a protected bike lane was surreptitiously changed. The change was revealed by Grid Chicago.

You can find this at the intersection of Sacramento Boulevard and Douglas Boulevard in Lawndale on the Near Southwest Side of Chicago. View more photos of this and the other West Side Boulevards bike lanes on my Flickr. They’ve probably been the most controversial: there were complaints because of ticketing cars parked in the under construction bike lane on Marshall Boulevard; then there were complaints about the “decreased safety” of the protected bike lane on Independence Boulevard which has prompted CDOT to agree to remove it and replace it with a buffered bike lane. The Independence Boulevard debacle started because of ticketing cars parked in the under construction bike lane – I doubt it would have become an issue if cars weren’t ticketed.

Franklin Boulevard at Kedzie Avenue, taken on the same day. Thankfully it’s wide enough that you can bike around it while still being in the bike lane.