Category: Transportation

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.

I need a visualization tip for showing pedestrian and auto traffic in downtown Chicago

January 30, 2013 / / 34 Comments

Madison Street over the Chicago River. Pedestrian traffic is very high, and very constrained, near the Metra stations.

Here’s the goal:

Show that pedestrians don’t get sufficient space or time to have a high quality pedestrian experience given that they comprise the largest mode share on streets in the Loop. The trips are highly delayed at traffic signals, pedestrian space is encroached upon because of automobile turning movements, and the sidewalks aren’t wide enough for two-way or even one-way traffic at certain times of the day. It’s possible to build our way out of pedestrian traffic…

Here’s an example data set:

On October 3, 2006, for all of the 24 hours, at 410 W Madison Street, there were 17,100 automobiles counted.

On some day in summer 2007, for 10 hours, at 350 W Madison Street, there were 43,987 pedestrians counted.

The two locations are practically the same as the bridge here prevents more pedestrians or automobiles from “slipping in”.

It’s possible to download the data sets from CDOT’s Traffic Tracker so you can see the whole city on your own map, but you’ll have to do some digging in the source code to find them.

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.