Category: Roadways

Why do speeding crashes in Chicago lead to worse injuries?

November 21, 2013 / / 6 Comments

Don’t git behind me. Photo by Richard Masoner. 

A discussion about Chicagoans’ proclivity for tailgating (on a post about speed cameras) prompted me to look at the prevalence of this in causing crashes. I looked at the three-year period of 2010-2012 first, mainly so the numbers wouldn’t be so large, and left this information in a comment. But considering the prerequisites* for a crash to be reported in this dataset, and my desire to compare two multi-year periods, I switched my analysis to the single four-year period 2009-2012.

2009-2012

Total crashes: 318,193. Total fatalities: 554 people.

Tailgating crashes

62,080 crashes, 19.53% of all crash types

Tailgating crashes, injuries breakdown:

  • Killed: .0012 (this represents the number of deaths per crash). 75 people died in these crashes, representing 13.54% of all deaths.
  • Incapacitating injuries: 8.53% (the average distribution of people’s injuries in all tailgating crashes)
  • Non-Incapacitating: 46.32%
  • Possible injury: 45.15%

The share of all crash types that are tailgating has increased steadily from 18.11% in 2009 to 20.79% in 2012.

Speeding crashes

10,339 crashes, 3.24% of all crash types

Speeding injuries:

  • Killed: .0118 (this represents the number of deaths per crash). 122 people died in these crashes, representing 22.02% of all deaths.
  • Incapacitating injuries: 15.55% (the average distribution of people’s injuries in all speeding crashes)
  • Non-Incapacitating: 51.95%
  • Possible injury: 32.50%

The share of all crash types that are tailgating has decreased slightly from 3.72% in 2009 to 3.02% in 2012. While speeding leads to fewer crashes, it leads to a greater incidence of death and serious injury. The probability of a speeding crash leading to at least one death seems to stay steady through the period while the probability of seeing a person with an incapacitating injury versus a different kind of injury varies more, but not so much in a range that overlaps the rates for tailgating crashes.

A future comparison at injuries should look at the top crash causes for death and serious injury.

N/A and Unable to determine crashes

237,729 crashes, 74.71% of all crash types

N/A and unable to determine injuries:

  • Killed: .0013 (this represents the number of deaths per crash). 305 people died in these crashes, representing 55.05% of all deaths.
  • Incapacitating injuries: 9.38% (the average distribution of people’s injuries in all N/A crashes)
  • Non-Incapacitating: 48.26%
  • Possible injury: 42.35%

Notes

Updated December 4, 2013

I updated the wording on how to interpret these numbers. For example, previously for “killed” there was a percentage saying this number represented the amount of crashes that had at least one death. This wasn’t accurate: the same number represents a rate of deaths per crash of that type. Injury percentages represent the distribution of injury types experienced by all the people injured in crashes of that type.

Reliability

Analyzing crash causes is not very reliable as 45.60% of the reported crashes in 2012 had “N/A” or “unable to determine” listed as the primary cause! The third and fourth most frequently ascribed causes were the two tailgating codes (described below). There are some crashes that had the one of these two causes in the secondary cause field but I haven’t calculated that.

Cause code descriptions

Each crash has two cause codes. For tailgating crashes I searched for reports where “failing to reduce speed to avoid crash” or “following too closely” in either the primary or secondary cause field (it’s possible that a report had both of these causes ascribed). For speeding crashes I searched for “speed excessive for conditions” or “exceeding speed limit” in either the primary or secondary cause fields.

Prerequisites

This data excludes crashes where there was no injury or no property damage greater than $500 (2005 to 2008) and $1,500 (2009 to 2012). You cannot compare the two datasets when you want to see a share of all crashes because the number of “all crashes” will be underreported in the second dataset.

Queries

These are some of the MySQL queries I used to get the data out of my own crash database (I’m figuring out ways to make it public, using a shared login). “Cause 1 code” indicates the primary cause of the crash according to the police officer’s judgement. “Cause 2 code” indicates the secondary cause of the crash according to the police officer’s judgement.

1. Crash cause reliability: SELECt count(casenumber), sum(`Total killed`), `Cause2`, `Cause 2 code` FROM `CrashExtract_Chicago` WHERE year = 12 GROUP BY `Cause 2 code`  ORDER BY cast(`Cause 2 code` as signed)

2. Speeding crashes: SELECT count(casenumber), sum(`Total killed`), sum(`totalInjuries`), sum(`A injuries`), sum(`B injuries`), sum(`C injuries`) FROM `CrashExtract_Chicago` WHERE (`Cause 1 code` = 1 OR `Cause 1 code` = 27 OR `Cause 2 code` = 1 or `Cause 2 code` = 27) AND year > 8

3. Tailgating crashes: SELECT count(casenumber), sum(`Total killed`), sum(`totalInjuries`), sum(`A injuries`), sum(`B injuries`), sum(`C injuries`) FROM `CrashExtract_Chicago` WHERE (`Cause 1 code` = 3 OR `Cause 1 code` = 28 OR `Cause 2 code` = 3 or `Cause 2 code` = 28) AND year > 8

4. N/A and Unable to determine crashes: SELECT count(casenumber), sum(`Total killed`), sum(`totalInjuries`), sum(`A injuries`), sum(`B injuries`), sum(`C injuries`) FROM `CrashExtract_Chicago` WHERE (`Cause 1 code` = 18 OR `Cause 1 code` = 99) AND year > 8

Desplaines Street bike lane design facilitates right hooks for bicyclists

September 16, 2013 / / 4 Comments

Photo 1 of 2: At Randolph Street I approach the “mixing zone” and position my bicycle to ride from the bike lane to the left side of the drivers waiting to turn right. 

In some of my social circles where bicycling is frequently discussed (with fellow transportation planners, advocates, or just people who bike commute frequently) we talk about Chicago’s new protected bike lanes, which started appearing in 2011.

The subject of their design is brought forth: they exacerbate turning conflicts between bicyclists going straight and drivers turning right (and to a lesser extent, left). Participants in these discussions usually express appreciation for the protected bike lanes, largely because of their ability to  reduce injuries overall and influence in bringing new people to bicycling, but are hard pressed to ignore this issue.

The issue is created in some instances when bicyclists are removed from sight of drivers because the bike lane is separated from the travel lanes by a vision-blocking lane of parked cars. However, the Chicago Department of Transportation has attempted to mitigate the turning issue by creating “mixing zones” where turning cars are and through-bicycles are mixed into the same, very wide lane prior to the intersection. When there is a green light, drivers typically merge into the mixing zone without much deceleration and then make the turn regardless of the bicyclist’s position.

Allowing turning cars and through-bicycles to go through these movements in the same place at the same time is a situation of incompatible demands.

Photo 2 of 2: I apparently didn’t position myself far enough to the left because the driver of this black Toyota turned right across my path. 

It’s highly unclear where the bicyclist is supposed to go and how they’re supposed to maneuver themselves in the mixing zone. If the bicyclist follows the lane and then the sharrows, they will be stuck behind cars. One of the pavement markings shows a small arrow above a bicycle symbol possible indicating that bicyclists must turn here (even though a sign says bicyclists and buses don’t have to turn from the lane).

The mixing zones on Desplaines Street are the worst at this, possibly because of the street’s nature as one that moves drivers exiting the city onto streets that lead into the Kennedy Expressway. People are gunning for the highway to get home and people bicycling tend to be in the way.

Additionally, the mixing zones on Desplaines Street differ from other protected bike lane installations (like the first one on Kinzie and subsequent ones on Elston, 18th, and Milwaukee) in that they lack the green lanes that CDOT has been using to highlight where car traffic crosses bike lane traffic.

Desplaines Street has another issue that arises when the signal is red and a bicyclist and a driver are both waiting for a green light. The bicyclist is between the car and the curb. The driver then makes a right turn on red (disregard whether or not a sign control makes this illegal) across the path of the stopped bicyclist. No harm done, right? Maybe, but there are a couple possibilities where this could be dangerous: the driver makes this movement as the light turns green and the bicyclist is attempting to move straight. Or there’s the possibility that the bicyclist also wants to turn right and the driver and bicyclist do so simultaneously without accommodating what the other may be doing. Both situations could lead to the dreaded “right hook”.

The driver of this white Hyundai makes a legal right turn from a “mixing zone” to Madison Street. However, what if the bicyclist wanted to also turn right, or the driver made this as the light was turning green?

The solution to the incompatible desire for one group of roadway users to turn and for the other group to go straight is to separate their movements with traffic signals, which CDOT has done on Dearborn Street.

With these situations in mind, it’s not unexpected to see a bicyclist move through the intersection on a red light to avoid a potential incident at the intersection, the site of most bike-car crashes. CDOT has reported that the red light compliance of people bicycling on Dearborn Street – the only street with bike-only signals – “has increased from only 31 percent of cyclists stopping for reds before the lanes and bike-specific traffic signals were installed, to 81 percent afterwards”.

I don’t think there’s not a problem with protected bike lanes but their precarious design in Chicago as well as the variations within Chicago and across the United States.

Department of Road Diets: the carbon tax

September 16, 2013 / / 6 Comments

Grand Avenue over the Kennedy Expressway. Its four lanes look like this – empty – most of the day. But then there are times of the day where people who bike, take the bus, and drive all need to “share the road”. That failed strategy has led to increased road rage, slow transit, and dead bicyclists. Time to put roads like this on a diet. 

My friend Brandon sent me an article about the one-page solution to (mitigating) climate change in the United States that NPR posted this summer.

But Henry Jacoby, an economist at MIT’s business school, says there’s really just one thing you need to do to solve the problem: Tax carbon emissions.

“If you let the economists write the legislation,” Jacoby says, “it could be quite simple.” He says he could fit the whole bill on one page.

Basically, Jacoby would tax fossil fuels in proportion to the amount of carbon they release. That would make coal, oil and natural gas more expensive. That’s it; that’s the whole plan.

This new carbon tax would support different infrastructure construction and expanded government agencies with which to manage it. It would support a Department of Road Diets. Road diets are projects that reduce the number of lanes for cars on a roadway, either by reducing the width of the roadway, or converting the general purpose lanes to new uses, like quickly moving buses or giving bicycles dedicated space.

See, in the carbon taxed future, people will want to drive less and use more efficient modes of transportation like transit and bicycles. And those uses will need their own space because the status quo in our cities (except the ones in the Netherlands) of having each mode compete for the same space isn’t working. It results in frustration, delay, and death.

Enter the Department of Road Diets. We have millions of miles of roadways that will need to go on diets so a department dedicated to such transformation would be useful. The agency would be in charge of finding too-wide roads and systematically putting them on diets, I mean, changing their cross section to less carbon-intensive uses.

What Complete Streets means to DOTs: the case of widening Harrison Street

September 5, 2013 / / 28 Comments

What Harrison Street looks like in 2013, replete with additional lanes and no “bicycle ways”. 

The Chicago and Illinois Departments of Transportation completed a project in 2012 to rebuild the Congress Parkway bridge over the Chicago River and build a new interchange with Lower Wacker Drive. It also rebuilt the intersections of Harrison/Wacker and Harrison/Wells.

Harrison prior to the project had two striped travel lanes (four effective travel lanes) but now has six travel lanes (including two new turn lanes). Bicycle accommodations were not made and people who want to walk across the street at Wacker and Wells must now encounter a variety of pedestrian unfriendly elements:  they must use actuated signals (waiting for a long time), cross long distances or two roadways to reach the other side, avoid drivers in the right-turn channelized lane, and wait in expressway interchange-style islands. Additionally, Wells Street was widened and all corner radii were enlarged to speed automobile traffic and presumably to better accommodate large trucks.

That is how IDOT interprets its “complete streets” law (which took effect on July 1, 2007) and how CDOT interprets its “complete streets” policy (decreed by Mayor Daley in 2006). The full text of the Illinois law, known as Public Act 095-0665, is below:

AN ACT concerning roads.

Be it enacted by the People of the State of Illinois,
represented in the General Assembly:

Section 5. The Illinois Highway Code is amended by adding
Section 4-220 as follows:

(605 ILCS 5/4-220 new)
Sec. 4-220. Bicycle and pedestrian ways.
(a) Bicycle and pedestrian ways shall be given full
consideration in the planning and development of
transportation facilities, including the incorporation of such
ways into State plans and programs.
(b) In or within one mile of an urban area, bicycle and
pedestrian ways shall be established in conjunction with the
construction, reconstruction, or other change of any State
transportation facility except:
(1) in pavement resurfacing projects that do not widen
the existing traveled way or do not provide stabilized
shoulders; or
(2) where approved by the Secretary of Transportation
based upon documented safety issues, excessive cost or
absence of need.
(c) Bicycle and pedestrian ways may be included in pavement
resurfacing projects when local support is evident or bicycling
and walking accommodations can be added within the overall
scope of the original roadwork.
(d) The Department shall establish design and construction
standards for bicycle and pedestrian ways. Beginning July 1,
2007, this Section shall apply to planning and training
purposes only. Beginning July 1, 2008, this Section shall apply
to construction projects.

Section 99. Effective date. This Act takes effect July 1,
2007.

Here is the case: a “bicycle way” should have been incorporated into the Harrison/Congress/Wells modification.

Here is the evidence:

  1. The project location is a transportation facility in the State
  2. The project location is in or within one mile of an urban area.
  3. The project widened an existing traveled way, from 52 feet (two marked travel lanes, four effective travel lanes) to approximately 64 feet (six marked travel lanes).
  4. Local support for bicycle and pedestrian ways is evident; see the “Streets for Cycling Plan 2020” planning process and the addition of a concrete deck (to reduce bicycling slippage) on the sides of the Harrison Street bridge over the Chicago River approaching the project location.
  5. The project was constructed after July 1, 2008.

The missing piece of evidence, though, is whether or not the Secretary of Transportation, based upon documented safety issues, excessive cost or absence of need, made an exception for this project.

The Chicago “complete streets” policy is less specific than the Illinois “complete streets” law, printed below:

The safety and convenience of all users of the transportation system including pedestrians, bicyclists, transit users, freight, and motor vehicle drivers shall be accommodated and balanced in all types of transportation and development projects and through all phases of a project so that even the most vulnerable – children, elderly, and persons with disabilities – can travel safely within the public right of way.

One of the examples CDOT gives on how this policy can be implemented is “Reclaim street space for other uses through the use of ‘road diets’ e.g., convert 4-lane roadway to 3-lane roadway with marked bike lanes” – they accomplished the opposite on Harrison Street.

In a 2010 traffic count, 16,800 cars were counted here, an amount handled by roads with fewer lanes and less than the amount in CDOT’s guidelines for implementing road diets and narrowing a road from 4 lanes to 2, yet in 2012, the agencies increased capacity.

Before: An aerial view from November 7, 2007. Image from Google Earth’s historical imagery feature. These two images represent the same zoom and area so you can compare the land changes from before to after the infrastructure modification. 

After: An aerial view from April 4, 2013. Image from Google Earth. Notice the additional lanes, roadway width, land taken south of Harrison Street, and the widened intersection at Wells with increased curb radius.