AARoads Forum

Please login or register.

Login with username, password and session length
Advanced search  

News:

New rules for political content in signatures and user profiles. See this thread for details.

Author Topic: Graphic: Speeding on the Illinois Tollway  (Read 2345 times)

Brandon

  • *
  • Offline Offline

  • Posts: 9884
  • Mr. Accelerator is our friend; Mr. Brake is not.

  • Age: 41
  • Location: Joliet, IL
  • Last Login: Today at 07:39:13 PM
Graphic: Speeding on the Illinois Tollway
« on: November 30, 2013, 08:05:26 PM »

Graphic: Speeding on the Illinois Tollway

Methinks the problem is the 55 mph limit, not the speeds at which people are going.  They do not change much between the 55 and 65 mph zones, if at all.

The Tribune also has this article behind a paywall (free if you already subscribe to the paper):

Speed limits largely ignored, Tollway report finds

Quote
As the state prepares to increase the maximum speed to 70 mph on some interstates starting Jan. 1, the Tollway studies and other research suggest that those large black numbers posted on roadside signs don't dictate how fast people really go. Instead, drivers are influenced by other factors, from road conditions to traffic flow and even some basic traits of human psychology.

Quote
The data, gathered in April, May and September, showed that, depending on which tollway stretch was tested, 91 to 98 percent of drivers exceeded the 55 mph speed limit. In those stretches, the average speed ranged from 66 to 70 mph.

Quote
Illinois State Police spokeswoman Monique Bond said she was reluctant to draw conclusions from the Tollway data. Vehicles would have been more likely to slow down if their drivers had seen a state police squad car than engineers atop overpasses, she said.

Bond acknowledged that speeding citations have decreased statewide but added that officers assigned to the tollways are among the most productive. A Tribune analysis of the agency's ticket data showed troopers assigned to the tollways write an average of 72 citations a day in metro Chicago.

Did it ever occur to her that the limit might be too low?  The Michigan State Police did the same study and concluded that limits around Metro Detroit should be raised to 70 mph.  Maybe the ISP needs to ask the MSP for their study results.

Quote
Those 72 citations a day pale in comparison to the volume of traffic on the tollway. Nearly 100,000 vehicles cross its busiest spots every day, and the job of deciding how fast they should be allowed to go falls to the Illinois Department of Transportation. The agency is required to set limits that are "reasonable and safe," IDOT spokeswoman Jae Miller said.

And to figure that out, engineers study crash history, ramp locations, traffic volume and traffic flow, among other factors.

But perhaps the most fundamental metric in deciding where to set a speed limit is a concept known as the 85th percentile, or the speed at which 85 percent of drivers are either traveling at, or below. In essence, it measures the limit that most drivers place on themselves, regardless of posted speed limits.

Tollway data showed that the 85th percentile speed ranges from 71 to 75 mph.

Then the limit along the entire Tollway should be 70 mph.  Makes sense, eh?  Good geometry, good distance between exits, etc.

Quote
Citing the safety argument, Tollway engineers say the interstates near Chicago are too congested to raise 55 mph limits, with some exceptions.

I call bullshit.  People are already going 70-75 mph even with the congestion.

Quote
Not everyone agrees. Supporters of higher limits note research showing that most drivers reach a comfortable maximum speed of 70-75 mph, regardless of how high the limit is set.

And Tollway research suggests higher limits may have very little effect on drivers' speed.

Consider two stretches of highway I-94 through Lake County and I-88 west of Aurora. The I-88 stretch has a 65 mph limit 10 mph higher than the I-94 stretch but drivers are traveling about the same speed on each road. In fact, the 85th percentile speed is just 3 mph faster where the speed limit is 10 mph faster.

Quite in contrast to the IIHS's claims:

Quote
In an April 2013 report, the Insurance Institute for Highway Safety pointed to research showing that raising limits that high would lead drivers to push down on gas pedals even more, creating a cycle of ever-increasing speeds.

"The 85th percentile is not a stationary point," the IIHS states in the report. "It is, rather, a moving target that increases when speed limits are raised."

As shown by the Tollway's own data, the IIHS's claims are baseless junk.

Quote
One of the experts who advocate higher limits is Leon James, a psychology professor at University of Hawaii who has been studying aggressive driving for 20 years.

"The way they set speed limit is somewhat subjective and arbitrary," he said. "It's not an exact science."

He maintains that research supports the 85th percentile approach; that "if most of the people travel at the same rate, that's the safest way of going, regardless of the speed limit."

To add to that in the article,

Quote
One is Jan Allen, a retiree from southwest suburban Wilmington. Her priority is to "go with the flow."

"I don't think it's a good idea to reduce your speed too much when everybody else is whizzing past you," said Allen. "I think that has the potential for causing more trouble."

Good advice.  Go with the flow, and then set the limit somewhere near the flow speed.
« Last Edit: November 30, 2013, 08:10:35 PM by Brandon »
Logged
"If you think this has a happy ending, you haven't been paying attention." - Ramsay Bolton

Illinois: America's own banana republic.

Screw the KSA; Stand with Canada.

JREwing78

  • *
  • Offline Offline

  • Posts: 992
  • Location: Janesville, WI
  • Last Login: Today at 08:57:39 PM
Re: Graphic: Speeding on the Illinois Tollway
« Reply #1 on: November 30, 2013, 11:33:17 PM »

Heh - learn something new every day. I just assumed the limits around Chicago were posted at 55 for Clean Air Act reasons. The absurdity of the existing limits is obvious whenever you drive these highways. 70mph is perfectly appropriate on these stretches of highway.
Logged

ET21

  • *
  • Offline Offline

  • Posts: 1925
  • Age: 26
  • Location: Chicagoland, USA
  • Last Login: Today at 02:18:17 PM
Re: Graphic: Speeding on the Illinois Tollway
« Reply #2 on: December 01, 2013, 09:28:14 PM »

Little late on the report, been like this for 5-10 years
Logged
The local weatherman, trust me I can be 99.9% right!
"Show where your going, without forgetting where your from"

Clinched:
IL: I-88, I-180, I-190, I-290, I-294, I-355, IL-390
IN: I-80, I-94
SD: I-190
WI: I-90, I-94
MI: I-94, I-196
MN: I-90

Henry

  • *
  • Offline Offline

  • Posts: 4444
  • Age: 48
  • Location: Chicago, IL/Seattle, WA
  • Last Login: Today at 03:58:50 PM
    • Henry Watson's Online Freeway
Re: Graphic: Speeding on the Illinois Tollway
« Reply #3 on: December 03, 2013, 01:35:23 PM »

I agree, 55 is too low for this region. At least raise it to 65 in metro areas, and 70 in rural parts.
Logged
Go Cubs Go! Go Cubs Go! Hey Chicago, what do you say? The Cubs are gonna win today!

Brandon

  • *
  • Offline Offline

  • Posts: 9884
  • Mr. Accelerator is our friend; Mr. Brake is not.

  • Age: 41
  • Location: Joliet, IL
  • Last Login: Today at 07:39:13 PM
Re: Graphic: Speeding on the Illinois Tollway
« Reply #4 on: December 03, 2013, 05:45:15 PM »

I agree, 55 is too low for this region. At least raise it to 65 in metro areas, and 70 in rural parts.

Illinois (DOT, ISTHA, etc) is supposed to use the results of a speed study to help determine speed limits.  Since ISTHA did a speed study and discovered the median and 95th percentile, then the limits should be 70 on the tollways, all tollways.
Logged
"If you think this has a happy ending, you haven't been paying attention." - Ramsay Bolton

Illinois: America's own banana republic.

Screw the KSA; Stand with Canada.

 


Opinions expressed here on belong solely to the poster and do not represent or reflect the opinions or beliefs of AARoads, its creators and/or associates.