Category: Research/Study

Where does this road diet rule come from?

April 17, 2013 / / 14 Comments

55th Street road diet from summer 2012. This is the best road diet photo I’ve got. Traffic counts here indicate 15,700 cars daily (based on a single day of measurement in 2006).

“Roadways with Average Daily Traffic (ADT) of 20,000 or less may be good candidates for a road diet and should be evaluated for feasibility”, via FHWA. The documents – here’s the second one – I’ve found so far on FHWA’s website don’t explain the research behind this assumption. How should a road be evaluated for feasibility? The second one bases review of a street on crash type, severity, and rate.

View 4600 W Foster Avenue in a larger map. Alderman Laurino is correct in her description of how many lanes are here. The road is only striped for 1 lane in each direction.

This concerns me because CDOT seems to have adopted this as a policy. They are using it as a reason to not consider a road diet on Foster Avenue. However, though, Foster Avenue between Pulaski Road and the Edens Expressway has only “1 and a half lanes” in each direction, according to local Alderman Marge Laurino of the 39th Ward (see John Greenfield’s interview below, which is an expanded version of one published on Grid Chicago in two parts).

Interview

Greenfield: Where in your ward would you like to see speed cameras installed?

Laurino: Well right now I don’t know that we have locations that would fit some of the criteria that we’re looking at. Currently I think the ones that they’re putting in are going to be where there have been pedestrian fatalities and I don’t know that I have anything that fits that really strict criteria but I would… Just a suggestion, Foster Avenue in front of Gompers Park. I mean it’s often times an area where cars really speed because for whatever reason, where there are no homes and that and it’s just wide-open parkland people just seem to hit the accelerator. I don’t know why that it but it appears to be the case.

JG: Is that a long stretch with no stoplights?

ML: From Pulaski to Cicero it’s a long stretch and it’s not one lane. I want to call it one-and-a-half lanes. There really shouldn’t be two lanes of traffic going in one direction but they seem to squeeze that in. So anyway that might be a potential place for a camera. We’re also looking at something called a road diet, where we just, through paint markings and paint striping, make the street narrower. That would be on Foster Avenue, let’s say between central Park and Cicero.

JG: Is there any talk of putting in bike lanes there to take up the extra space?

ML: No, for whatever reason it doesn’t fit their criteria.

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).

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.

Tell it, Sue Baker! Car crashes are not accidents

October 29, 2012 / / 0 Comments

“It was an accident!”, said the driver. Photo by Katherine Hodges. 

Because of Hurricane Sandy, the New York Times paywall is down so I’m reading every article I can, starting with “Safety Lessons from the Morgue“:

As she explains it, “To say that a car crash is an accident is to say it’s a matter of chance, a surprise, but car crashes happen all the time, and the injuries that people sustain in those crashes are usually predictable and preventable.”

Another car crash-related excerpt from the article about Sue Baker, injury prevention researcher extraordinaire:

In one of her recent projects, Baker looked at another aspect of highway deaths. The study, which Baker prepared with David Swedler, a doctoral candidate, examined more than 14,000 fatal crashes involving teenage drivers. They found that male drivers were almost twice as likely as female drivers to have had high levels of alcohol in their blood and were also more likely to have been speeding and driving recklessly. Significantly, 38 percent of 15-year-old drivers, both male and female, were found to have been speeding, but by age 19, female speeders dropped to 22 percent, while male speeders remained steady at 38 percent.

Those differences, Baker says, suggest that boys and girls should not automatically receive the same driver training — and that boys should perhaps receive their license at an older age than girls. “Males might scream foul,” Baker acknowledges, “but let them.”

Yes, let them. It’s too easy to get a driver’s license in this country.  I love her style:

In 1979, at a Department of Transportation public hearing about the dangers faced by truck drivers, Baker angrily explained, “Isn’t it time we did some crash testing with trucks and dummies, rather than with drivers themselves?” Later, according to Baker, the trucking industry hired a researcher to try to discredit her driver-safety studies. Unable to uncover problems with her work, he eventually gave up and called to tell her about his assignment. [emphasis added]

Not everything is perfect with injury prevention studies, though.

In the mid-1970s, [Sam] Peltzman did research on highway fatalities that suggested that mandatory safety features like seat belts and padded dashboards actually encouraged people to drive less cautiously.

Tom Vanderbilt talked about that in “Traffic“, which is basically my favorite transportation book, even mentioning Mr. Peltzman. Flip to page 181 to read it. Vanderbilt lists all of the different labels for that behavior:

  • the Peltzman effect
  • risk homeostasis
  • risk compensation
  • offset hypothesis

He summarizes: “What they are saying, to crudely lump all of them together, is that we change our behavior in response to perceived risk, without even being aware that we are doing so”. But Sue has a response:

Baker acknowledges that there may be some individuals in cars with anti-lock brakes, for example, who may not apply the brakes as soon as they did with the old brakes. But she insists there is no evidence that better brakes or air bags have encouraged recklessness — that they have in fact saved many thousands of lives. “What concerns me,” she says, “is that these spurious arguments are used by companies to bolster their opposition to beneficial safety regulation.

I think it’s safe to say now that she’s a personal hero of mine. But way, there’s just one more thing!

As she talked about what still needed to be done, her voice was tinged with anger: “Buildings need to be designed so it’s not so easy to fall down stairs. All new homes should have sprinklers. Traffic lights should be timed for pedestrians, not to move as many cars as possible through an intersection.

Yep. Exactly what we don’t do. We make ’em wait. And wait. Without even telling people the traffic signal’s even acknowledged their presence.

More

Links between pedestrian safety and crime

October 25, 2012 / / 4 Comments

Chicago Pedestrian Plan

Safety item 20: Analyze the relationship between pedestrian safety and crime (download the plan)

The 2011 Chicago Pedestrian Crash Analysis identified a strong correlation between community areas with high numbers of pedestrian crashes and community areas with high crime rates. Correlation does not indicate causation and further study is necessary to understand this relationship and the potential broader benefits of pedestrian safety improvements. [From page 62 in the 2012 Chicago Pedestrian Plan.]

ACTIONS

Short Term

  • Identify and obtain funding for this study.
  • Identify a location for safety improvements and obtain data for the “before” conditions.

Mid Term

  • Design and implement pedestrian safety improvements.
  • Develop a pedestrian safety enforcement plan for the area for the duration of the project.
  • Analyze the effects on pedestrian safety and crime.

MILESTONES

  1. Initiate this study by 2013 and complete by 2015.

ADDITIONAL RESOURCES

National Highway Traffic Safety Administration. Data-Driven Approaches to Crime and Traffic Safety (DDACTS). 2011. [I don’t fully see the connection, but this reference was linked to a page on NYC Department of Transportation’s website.]

Pedestrian Crash Analysis

The summary report didn’t contain the word “crime”. The technical report contained 2 mentions, with an additional chart. They are quoted in the ordered list below. Download the summary report.

  1. In an examination of various factors including crime, income, race, language spoken, and Walk Score®, the strongest correlation found was between pedestrian crashes and crime
  2. Finally, crime statistics were compared to pedestrian crashes to determine if a correlation could be identified, using data from the Chicago Police Department (CPD) annual reports for 2005 through 2009. The annual reports include incidences of crime by Chicago Community Area (CCA). The statistics for the years 2005 through 2009 were averaged and compared to the aver- age number of fatal and serious injury pedestrian crashes over the same time period in each CCA. Of these factors, crime was the only variable that correlated to pedestrian crashes. Figure 1 shows the correlation between crime and pedestrian crashes was very high. However, there may be many variables responsible for this correlation.
  3. Figure 1: Crime vs. Fatal and Serious Injury Pedestrian Crashes by Chicago Community Area

Figure 1.

I have a few criticisms of this analysis: it lacks raw data; the data tables included in the technical report are of limited length, listing only the “top” items of any metric; the summary report lists many silly factoids; the maps are low resolution and of a limited scale – their design could be modified to improve their usefulness in communicating the crash frequencies of the marked locations. The analysis is reliable.

The technical report includes the state’s guide on how police officers are trained to fill out a crash report form. It also includes relevant crash reporting laws in Illinois. Download the technical report.

Special post for S.M.