Work Zone Traffic Control “Down-Under”

We just returned from a wonderful trip to Australia where we spoke to the Traffic Management Association of Australia (TMAA) about work zone ITS. Their members were all excited and focused on finding safer, more efficient ways to manage their work zones.

The program was packed full of interesting speakers and a variety of timely topics. They also gave us all just the right amount of time to discuss those topics between sessions. It was very well run.

The attendees seemed to enjoy talking to Americans and all asked what we thought of the meeting. My first answer was always the same: traffic control companies in both countries share the exact same set of problems:

1) Speeding in work zones.

2) End-of-queue crashes.

3) Hiring, training and retaining good employees.

4) A perception by the driving public that we are there to make their lives miserable.

5) Insufficient funding for maintenance and construction.

6) Changing standards and levels of enforcement from one state to the next.

7) Varying commitment and funding levels from one state to the next.

Just like ATSSA, the TMAA brings contractors, manufacturers, academia and government agencies together to discuss these problems and identify solutions. The TMAA does an especially good job of this. We look forward to learning more from them in the years to come!

Distracted Driving and Work Zones

We all know that distracted driving is resulting in increased fatalities on our roadways. The National Safety Council reported a 6% increase in fatalities in 2016. According to the National Work Zone Safety Information Clearinghouse, overall roadways fatalities increased 13% from 2013 to 2016. And during that same period, work zone fatalities increased 28%!

We enjoyed a period of dramatic decline in these numbers in the early 2000’s and then in 2013 they suddenly began to climb again. A small part of that change was due to improving economic activity and the increase in vehicle miles traveled that came as a result. But far more is due to other factors and distracted driving certainly tops the list.

The National Safety Council reports that 47% of drivers feel comfortable texting while they are driving. But we know that, in fact, texting while driving often increases reaction times more than driving under the influence.

But the problem is bigger than just that. In a recent article by Dr. Carl Marci, a neuroscientist writing in the January 4th issue of Perspectives magazine (http://www.nielsen.com/us/en/insights/news/2018/perspectives-driving-while-distracted-the-challenges-of-measuring-behavior-in-complex-environments.html), he said that our cars may be contributing to the distracted driving problem as well! This question occurred to him driving home one night so he ran a test using standard bio-metric equipment on a short drive on an unfamiliar road in Boston. The results showed the driver looked at his or her phone 60 times during a ten minute trip! A study by Zendrive reinforces these findings. They found that drivers use their phones for 88% of their trips.

Dr. Marci explains this by examining the way we use our phones outside of our vehicles. Any time we are bored, we look at our phone. Sitting at home in front of the TV, standing on a street corner waiting for a bus, or sitting in slow a meeting at work – we all check our phones when we get bored. And then we are often rewarded for doing so with a response from others. Email and social media have changed the way we act in very profound and far-reaching ways. And that can’t be turned off when we get behind the wheel.

Furthermore, our cars are becoming very comfortable. They resemble our living rooms more every day. Elaborate electronics help guide us to our destination, provide entertainment, and interface with our phones calling and communications applications.

We do use our cars electronics and phones for legitimate reasons while driving. They give us directions to our destination. They warn us of traffic problems along our planned route. They tell us of weather changes that may be important. So our phones & automotive electronics can help us get where we are going more safely. But once we use these for legitimate reasons, we can’t put them down. Or our drive becomes boring or our phone beeps to announce a new text, and we can’t seem to wait until we stop to check those messages.

So, back to work zones. A 28% increase in work zone fatalities cannot be ignored. Distracted driving is a growing and potentially catastrophic trend for work zones. Work zone ITS has always helped to reduce crashes. But this trend in distracted driving makes the use of work zone ITS all the more important. End of queue systems, dynamic merge systems, and variable speed limit systems can all get drivers attention, improve their work zone awareness, and help mitigate the effects of distracted driving. Let’s get ahead of this trend now before it gets any worse.

The Importance of Crash Modification Factors to Work Zone ITS

A webinar was held December 5th on work zone crash data collection and analysis. It was organized by Wayne State University and included speakers from the University of Missouri and Michigan State University. A recording of the webinar will be made available soon.

Several very good resources were made available as the webinar began including “A Guide for Work Zone Crash Data Collection, Reporting, and Analysis” which was produced for the FHWA by the Wayne State University College of Engineering. This guide can be found at:  https://www.workzonesafety.org/files/documents/training/fhwa_wz_grant/wsu_wz_data_collection_guide.pdf

As a work zone ITS practitioner, I have deployed many systems over the years but have very little data to prove the effectiveness of those deployments. The problem has always been establishing a base line of the probable number of crashes given the traffic control, project duration, traffic volumes, etc. Only with that base line can we compare our actual crash numbers to determine whether the system was cost-effective.

The crash data guide states the problem very succinctly, “In order to perform an effective work zone safety analysis, the appropriate work zone crash data needs to be available. The availability of this data is only as good as what is collected on the state crash report form.”

The webinar pointed to several states’ best practices in this regard. At a minimum, states are required to include a checkbox on their form to indicate if the crash was work zone related. But states including Connecticut, Iowa, Minnesota, Pennsylvania and Virginia collect much more. They go into detail about the location of the crash within the work zone, and what types of traffic control and construction activity was in place at the time of that crash.

That data will help them develop Crash Modification Factors (CFMs) for different traffic control treatments. In time we hope to see CFMs for queue warning systems, dynamic merge systems, variable speed limit systems, and much more. Those CFMs could be specific to high volume multi-lane facilities, rural four lane highways, etc.

Once CFMs are developed, the rest of the process is fairly simple. Compare the CFM associated with your proposed system to the traffic volumes where that system will be used, and you will know immediately whether the use of that system is justified. The use of these systems is already taking off, but there is still some guess work involved in the decision to use or not use work zone ITS. By developing CFMs we could speed that process along and make it more scientific.

Variable Speed Limit Systems – Revisited

In a post on April 24th we discussed a recent webinar on variable speed limit signs. The speakers voiced their disappointment in the technology and found very little if any benefit from their use. But now a new study by the University of Missouri saw far better results for VSL signs used in work zones.

“Evaluation of Variable Advisory Speed Limits in Congested Work Zones” by Praveen Edara, Carlos Sun and Yi Hou found far better, but still mixed results when using Variable Advisory Speed Limit signs in work zones.

As we have known for some time, the VSL results depend to a great extent on the algorithm used. In the Missouri study the original algorithm used in the field resulted in shorter queue lengths and reduced speed differentials. In fact the maximum speed differential was reduced by a remarkable 10 MPH. However it also reduced throughput by 7 to 11% and travel time increased by 4 to 8%. So the results were mixed.

They then experimented through simulation. Using the same traffic data they tried two other algorithms. One smoothed over a one minute period and the other over a 5 minute period. The original field algorithm smoothed over a 30 second period.

The 5 minute smoothing algorithm still reduced throughput but only by about 1%. At the same time it reduced end of queue conflicts by 30% and lane changing conflicts by 20%. Speed variances remained low. And they saw medium to high compliance with these advisory signs.

Compliance is key, of course, and the Missouri experience was very different from previous installations in places such as Utah and Oregon. Even where VSL posted limits were enforceable, compliance only occurred when message signs explained the reason for the speed limit reduction or when law enforcement was present and actively enforcing those limits.

The reasons for this could be many. Maybe Missouri drivers are just more law abiding. It was not discussed in the study but perhaps MoDOT did a better job of explaining VSLs to the public before they were installed. Or perhaps the need for variable limits is more apparent to drivers in a congested urban work zone. But whatever the reason, it is clear we should not give up on variable speed limit systems just yet. More studies are needed, especially on the subject of the best applications for these systems and the algorithms driving them.

Variable Speed Limit Webinar

Variable speed limits systems have always, at least intuitively, promised benefits for work zones including greater throughput, reduced speed variance, and as a result, fewer crashes. We discussed these systems in a post in October 2015 after a presentation at the National Rural ITS meeting in Utah. The concept made sense and we looked forward to greater use of VSL systems.

A webinar was just offered April 4th by the US DOT Office of Assistant Secretary for Research & Technology entitled, “Variable Speed Limit Systems – Are They For Everyone?” The speakers, and there were several of them, did a great job of explaining the advantages and disadvantages of these systems. Those speakers included Jimmy Chu of FHWA, John McClellan of MnDOT, Bryan Katz of Toxcel, Jiaqi Ma of Leidos, and Vinh Dang of WsDOT.

There wasn’t a lot of new information. Instead they presented a comprehensive history of VSL systems from around the country. They looked at different uses for these systems, including work zones. In all, more than a dozen different projects from 9 different states were discussed. Some projects were relatively small, and others like those in Minneapolis and Seattle, were quite large.

But in almost every case, the results of these systems have not met expectations.  This was true for weather related systems, work zones, and congestion management applications. Reductions in speed variance and crashes were very small if not non-existent. And the reason in every case was a lack of conformance by the traveling public. There was some smoothing, but very little.

Many of the system designers anticipated this and included variable message signs alongside the VSL signs to explain why the speed reduction was justified. But drivers either misunderstood when they were supposed to slow or simply chose to continue at their current speed until they saw the problem for themselves.

Law enforcement is critical for these installations. Without enforcement, compliance will never reach levels that will result in the benefits designers expected. But law enforcement often became distrustful of the data they received, or didn’t get timely notifications at all. They also ran into serious resistance from the courts. So enforcement slowed, and compliance tanked.

There is still hope that these issues will one day be resolved. But for now, variable speed limit systems just aren’t providing the benefits we all hoped to see.  The webinar closed with a short discussion of future considerations. One thought was to combine these systems with a larger big data process (as discussed in our last post). They might look at not just weather, or work zone conditions, but also at traffic speed and volume data approaching the area, timing of major events, and more to improve drivers trust of VSLs.

Another thought was with regard to automated vehicles. Will VSL systems be more effective when the information is sent directly to each vehicle? If a pop-up display recommends slowing to 35, will they be more likely to do so? Or will they continue to ignore them as they apparently do now? Once autonomous (driverless) cars are on the road, the recommendations from these systems will be adopted automatically. But until then, compliance will remain the biggest problem for VSLs.

Portable Variable Speed Limit Systems

Late last year the FHWA Every Day Counts initiative held another wonderful webinar. This one covered two more work zone ITS products: variable speed limit systems and dynamic lane merge systems. This webinar was so chock full of information that I will discuss them one at a time. You can view the recorded webinar at: https://connectdot.connectsolutions.com/p1rhnco4915/?launcher=false&fcsContent=true&pbMode=normal .

Today let’s start with variable speed limit systems. Todd Peterson of FHWA began by explaining the basic structure and goals of a variable speed limit (VSL) system. These are portable, trailer-mounted signs that move as the work zone moves.

Josh Van Jura of Utah DOT described VSL experience in his state. Utah began with static (manually adjusted) signs. He says they have many interstates posted at 80 MPH. And for construction, especially where workers are exposed to traffic, they like to reduce those speeds significantly – sometimes as much as 30 MPH or more. He later said these systems are especially useful for slab replacement work where you have a relatively long work zone, but workers are present and visible only in one or two small locations. So the system gets the speeds down in advance of the work. It also drives down the speed variance.

UDOT VSL1 UDOT VSL2

So far they have chosen to use these systems where queuing is unlikely. They don’t want to solve one problem, only to cause another upstream. They have been pleased with the results and now want to move to dynamic VSL systems. They applied for and won a grant to finance their research. Kimley-Horn is doing the work.

Mr. Van Jura made an interesting point. He said that this project was especially susceptible to scope creep. As they discussed their wants and needs folks asked for CCTV, weather detection and more. Much of that was for the testing phase primarily. But even then those features would have driven the cost up significantly, so they chose to do without them.

The basic system uses sensors to measure speeds in and near the work zone. Those speeds are sent over a cellular link to a server where they are processed by an algorithm that then adjusts the posted speed limit to match the measured 85th percentile. The displayed speed limit is adjusted no more than every 10 minutes. Everything is date and time stamped showing the posted speed limit at that time at that location.

Todd Foster of VerMac asked what type of sensors they plan to use. As he said, doplar has occlusion issues but side-fire radar is a pain to set up. Josh said they plan to make that decision on a project by project basis. For two lane roads, they will use doplar. For projects on larger facilities they will weigh the need to relocate the sensors, the space available to place those sensors, and the costs associated with each to decide what should be required for that application.

A survey during the webinar asked the audience if their agency was considering using VSL systems in their work zones. 70% said yes. It then asked whether they were considering a regulatory system or an advisory system. 73.8% plan to use a regulatory system. Utah Highway Patrol cooperated fully with this UDOT initiative. Apparently other states don’t see that as an issue either.

We look forward to the final publication of Utah’s research. But it sounds like portable VSL’s should be another tool in our work zone ITS toolbox.

In our next post we will look at their discussion of lane merge systems.

Variable Speed Limit Signs

VSL UtahAt the recent National Rural ITS show held in Utah, a workshop was presented on the subject of variable speed limit signs. The speakers included Lynne Randolph from the Southwest Research Institute who talked about VMS use in Texas, Brian Christensen of Horrocks Engineers and Glenn Blackwelder of Utah DOT who discussed the local VMS installation on I-80 between Salt Lake and Park City, and Josh Crain of DKS who talked about the use of VMS in Oregon.

This technology remains one that makes good sense in theory, but whose complete affect on traffic is still not fully understood. This workshop filled in some of the blanks but there is more work to be done.

In short, a variable message sign system measures traffic speeds as conditions change and then displays the 85th percentile speed rounded down to the nearest 0 or 5 on regulatory speed limit signs upstream. The idea is to smooth traffic flow and reduce the speed variance that occurs as drivers begin to respond to changes in weather, traffic volumes and construction work.

The speakers shared some interesting lessons learned. Utah’s installation seemed to be the most successful. They have a total of 15 VSL signs through Parleys Canyon, a very steep climb from Salt Lake City east to Park City. There are 8 signs eastbound and 7 signs westbound. The other deployments discussed had far fewer signs or in Oregon’s case, they are single installations spread over the state.

Utah also posts VARIABLE SPEED LIMIT SYSTEM AHEAD signs at each end of the canyon. For these reasons they are far more visible and, I suspect, gets better results.

Utah did find that the white LED displays washed out behind a sign covered in the standard white reflective sheeting. To overcome this they added a black band around the speed display. You can see in the photo above that this change greatly improved the contrast so the signs are now easy to read in all light conditions.

The four speakers seemed to agree that drivers were more inclined to respect lower VSL speed limits when weather or construction activity justified the change. They did not respond as well when limits were lowered due to congestion downstream. Drivers need to know why they should slow before they respond.

Utah’s signs are enforceable. Texas’ signs are not. Oregon has installed some of each. They have developed a decision tree that weighs local conditions and the reasons for the installation to determine which type should be used in each situation.

It was a very informative workshop. I encourage you to download it when it becomes available.