Use of Wireless Data for Work Zone Performance Measures

The second TRB paper I would like to discuss is paper number 14-2186: “Using Private Sector Travel Time Data For Project-Level Work Zone Mobility Performance Measurement” by Michael Fontaine, PilJin Chun and Benjamin Cottrell of the Virginia Center for Transportation Innovation and Research. It analyzes the value of mobile phone data as a measure of work zone performance.

They began by noting the need for more and better work zone data to be used in measuring work zone performance. They focused only on performance measures, and did not touch on safety. The measures they chose were delay time and queue length. They felt those were the two most commonly accepted measures in use today.

They did mention the potential use of this data to determine work windows in real time. This is something we have discussed before but it is interesting that they see value in that, too. They also said, “Installing new, temporary sensors specifically to monitor work zone mobility is an option, but it is often only cost effective for long-term, major projects.” That was true at one time, but it is not usually true today. And it assumes you are collecting the data only to measure performance. It does not consider its added use for queue warning and other safety enhancements.

Wireless data is collected and analyzed over road segments which they call Traffic Message Center (TMC) Links. These are a standard reporting format created by mapping companies. They are generally a section of road between major intersections or between interchanges. So in cities they are fairly close together, but in rural areas they are often much farther apart.

The limitation of this data is that a work zone two miles long may be in the middle of a TMC 10 miles long. In that case it will under report delays because speeds will be averaged over that segment rather than just through the work zone.

Longer segments will over report queue lengths. Queuing is defined as anytime speeds are reduced to less than X% of the norm anywhere in the segment. So if a queue develops somewhere in that 10 mile long segment, it is reported as a queue 10 miles long even when it is actually less than a mile long.

These issues are less consequential in urban areas where they found average segment lengths of .56 and .71 miles on the two projects studied. The amount of any error will be much smaller and would probably be fair to both agency and contractor if used in an incentive/disincentive program for work windows.

But there are still issues if this data is to be used to report delay times to travelers or to warn them of queuing. For the delay times, there will be an error. For the agencies and contractors this error averages out. But individual travelers will see the error when it occurs and that will undermine their perception of the value of such systems.

For queue warning, even in these urban areas, the spacing is set. In some cases it will provide ample warning, but on longer segments it may not. The spacing cannot be adjusted as needed.

And in rural areas, the long road segments mean both delay and queue length measures are significantly inaccurate. And they are almost useless for reporting delays or queuing to motorists.

We have not discussed whether this data can be used to trigger portable message sign messages in a timely manner. If not today, they will most likely be capable of it in the very near future. But this study does point out the weaknesses of this data for work zones. If an agency wants the data solely for internal performance measurement, it is probably an option.

But if that agency also wants to use it for contractor incentives or for reporting delays or queuing to the public, they should stick with portable systems. Only portable sensors can be spaced to meet the needs of that project. Only portable sensors can be adjusted to provide useful data in a changing work zone environment. And only portable sensors can tell you precisely where in that work zone the queue begins so that traffic control can be adjusted to minimize the disruption to traffic.

TTI Response to March 31 Post

In my post dated March 31 I wrote about the TTI website known as My35. In the post I said it would be nice to see some data on the number of people using it, and especially the number who changed their route based on what they saw there.

I just received an email from Bob Brydia, the principal investigator on this project. I will let him tell the story.

Bob writes, “Allow me to introduce myself, Bob Brydia, with the Texas A&M Transportation Institute. I’m the Principal Investigator of the project you referenced in your Feb 18 and March 31 blog articles and also the designer of the real-time map you provide the link to. I also wrote the article in ITS International that you referenced in the blog posting.

Your article states that you’d like to see some usage statistics, so I thought I’d reach out and try to provide you with some information. I’d like to thank both Jerry Ullman and Chad England for forwarding your blog articles to me and I obviously need to sign up.

I’m going to caveat my response by saying that we suffer, on the I-35 corridor, with (a lack of) good ways of reaching the public. Given that 2/3rds of the traffic is through, and we don’t have billboards, we have a decided lack of market penetration to a huge portion of the driver base. The communications component of the project team is constantly searching for new ways to get to the public. As an example, 4 new rest stops recently were completed and we’re putting pull up banners in those locations, showing a corridor graphic with completion dates by section and a QR code that goes straight to the real-time map. We also link to the map from newsletters, our daily automated lane closure announcements, tweets, Facebook, etc.

As you can see from the table below, we’ve averaged over the past 4 months, more than 10,000 visitors and upwards of 12,000 pageviews. Since we went live with the corridor traffic map in October 2012 and started with less than 1500 visitors, most of which were testing, we’ve been building our user base from scratch.


Additionally, since we deployed the new tabbed interface for information (Feb 2014), we’re tracking the tab clicks and the percentages of information has a breakdown as shown in the table below. The map tab is underrepresented as the desktop view always has the map present and the mobile view defaults to the map tab. Approximately 1/3 of the site traffic originates from mobile devices.


From a survey that recently concluded (yesterday!, so the results aren’t published yet), of the respondents that were aware of the real-time map, nearly 90% (89.33) found the information to be useful. 8% said the information wasn’t enough, outdated, or incomplete, and 2.67% provided no answer to that question.
You also asked if drivers have changed their plans based on the available information traveler information resources (which is a wider set than just the map). From the responses, 32.58% said “Never”, 12.92% did not respond, and a total of 54.49% answered anywhere from Once or Twice to Frequently. Nearly 25% of the respondents answered “Frequently”.

I hope this information provides some follow-up to the questions you posed in your March 31 blog. Please feel free to contact me if you need or would like any additional information.
Thank you for the opportunity to respond to your questions.”

Thank you Bob for your detailed response! We exchanged a few more emails, then he wrote back with this additional information, “Just one additional note on the map. If you click on options, you can customize all the information to your trip, so by direction, and by the type of information you want to see. That customization will persist across all tabs, so if you click Option and indicate you only want to see northbound information, the lane closure list will filter down to NB only and when you click to say…travel times, only the NB travel times will show. There’s no other traffic map in the nation that puts information together in this manner.”

I agree. And the more useful we can make these websites, the more users can customize their experience, and the fewer unwanted notifications they receive, the more folks will use them.


New app helps the visually impaired navigate work zones

By Melissa Turtinen

The Minnesota Department of Transportation has funded a smartphone application that will help the visually impaired navigate construction zones.

MnDOT says approximately 17 percent of work zone fatalities nationwide are pedestrians, and those who are visually impaired are even more at risk. That’s why MnDOT funded the University of Minnesota research, led by Chen-Fu Liao, to develop a cell phone app that can guide visually impaired pedestrians around those construction zones, MnDOT says. The final report on the U of M’s research was released last month.

Before developing the app, researchers surveyed visually impaired people about what information would be helpful when navigating a work zone, MnDOT said.

All a pedestrian needs is a smartphone – and on the construction site, to make the app work, a small box is added to a traffic signal box. The app uses GPS and Bluetooth technologies to find a person’s location and, once a work zone is detected, the smartphone vibrates and announces an audible message describing what street he or she is facing, how many lanes of traffic there are, and how and when to walk through the intersection safely, KARE 11.

“This information can be used to guide them, which direction they are going and tell them when it’s the appropriate time to cross the intersections. Making a decision at the intersection is very critical and it could be life threatening,” Liao told KARE 11 in 2012.

The user can also tap the smartphone to repeat the messages if needed, MnDOT says.

The U of M research team tested the smartphone app by attaching four Bluetooth beacons to light posts near a construction site in St. Paul, MnDOT says.

And after years of research, the navigational app could become available to more than 50 million visually impaired Americans in the near future, KARE 11 reported. But first, researchers need to conduct a few more tests to evaluate how reliable and useful the app is.

For those who don’t have smartphones, state officials are also looking into special equipment that could relay the same audible warnings at affected work zones.