New Tool Measures Impact of Heavy Trucks

A new tool developed by the Local Road Research Board helps cities and counties assess how much increased heavy vehicle traffic affects local roads.

Researchers created an analysis method and corresponding spreadsheet tool that city and county engineers can use to calculate the impact of heavy vehicles on asphalt roads beyond what was planned in the original pavement design.

The information will help agencies optimize services, such as garbage collection, for the least amount of damage. It will also help agencies better plan roads in new developments, as well as redesign existing roads that are nearing the end of their lives.

Lack of Data

Heavy trucks cause local roads to deteriorate more quickly than passenger vehicles, but it is challenging to quantify the impacts, especially for areas where traffic was not forecast at the time a road was designed.

Many local engineers in Minnesota have requested information about the impact of heavy vehicles in light of new construction, commercial distribution facilities and hauling routes. This information is needed to assist in local road planning and maintenance.

Two Methods

In a newly completed study, investigators developed two methods for calculating heavy vehicle impact:

  • Calculate the additional bituminous material (and associated costs) that would have been required to construct the pavement had the heavy truck traffic been predicted when the pavement was designed.
  • Calculate the portion of a pavement’s design life, measured in equivalent single-axle loads (ESALs), consumed by unanticipated vehicles.

“Before this project, there wasn’t an easy way for an engineer to determine how much a specific truck was going to decrease the life of a road,” said  Deb Heiser, Engineering Director, City of St. Louis Park.

Whereas previous research has calculated the impact of extremely heavy vehicles over the short-term (typically the course of a construction project), this project calculates the impact of long-term increases in traffic from vehicles that are heavy, but still mostly within normal legal weight limits.

The tool can be used for a single street segment or an entire road network. Users can also compare current situations with proposed ones to evaluate the impact of potential changes in heavy traffic levels.

Related Resources

New permitted left-turn model helps improve intersection safety

In recent years, the transportation community has introduced significant changes to improve left-turn safety at signalized intersections—and for good reason. Nationally, intersection crashes represent one-fifth of all fatal crashes, and most of these are crashes involving left turns.

In response to this serious safety problem, the FHWA has adopted a new national standard for permissive left turns: the flashing yellow arrow. This signal warns drivers that they should proceed with a left turn only after yielding to any oncoming traffic or pedestrians. Flashing yellow arrow signals can help prevent crashes, move more traffic through an intersection, and provide additional traffic management flexibility.

Many transportation agencies, including MnDOT, are interested in using the new flashing yellow arrow signals to accommodate within-day changes: protected left turns (signaled by a green arrow) could be used when needed to lower crash risk, while permitted left turns (signaled by a flashing yellow arrow) could be used to reduce delay when crash risk is low.

“Of course, this requires being able to predict how the risk of left-turn crashes changes as intersection and traffic characteristics change within the course of a day,” says Gary Davis, a professor of civil, environmental, and geo- engineering at the University of Minnesota.

To help engineers make more informed decisions about when to use flashing yellow arrows, Davis is leading the development of a model that could help predict the probability of left-turn crash risk at a given intersection at different times of day. This model—which will ultimately be available as a set of spreadsheet tools—will help traffic engineers determine when the crash risk is sufficiently low to allow for the safe use of flashing yellow arrows. The project is sponsored by MnDOT and the Minnesota Local Road Research Board.

To develop the statistical model, the researchers needed to determine how the risk for left-turn crashes varies depending on time of day, traffic flow conditions, and intersection features (such as number of opposing lanes, number of left-turn lanes, and median size). The process included developing a database containing left-turn crash information, intersection features, and traffic volumes, as well as developing a set of 24-hour traffic pattern estimates to help fill gaps where hourly traffic volume counts were not available. The resulting statistical model uses this information to determine relative crash risk for every hour of the day at a given type of intersection.

Currently, Davis and his team are using the model to develop a spreadsheet tool that will allow traffic engineers to choose their type of intersection and enter the available turning movement count. The tool will then generate a specialized graph for that intersection showing the relative crash risk by time of day. Any time the crash risk is at or below the level identified as acceptable, engineers can consider using flashing yellow arrows.

“By simulating how crash risk changes as traffic conditions change, this model could help identify conditions when permitted left-turn treatments would be a good choice and what times of day a protected left turn might be a better option,” Davis says.

Moving forward, Davis is leading an additional project related to the use of flashing yellow arrows, funded by the Roadway Safety Institute. The project will first review video data of drivers making permitted left turns to characterize left-turn gap acceptance and turning trajectories. Then, Davis will incorporate the findings into the existing statistical model. To further improve the model’s accuracy, the study will compare the crashes described by the simulation model with reconstructed real-world left-turn crashes.

How Better Sign Management Could Save Minnesota Millions

Replacing traffic signs at the right time is an important science.

Waiting too long can endanger lives and expose an agency to a lawsuit. But replacing traffic signs prematurely could cost a single city tens of thousands of dollars per year.

If fully implemented, new recommendations developed by MnDOT and the Local Road Research Board (LRRB) could save public agencies as much as $41 million over three years by helping them better manage their signs and meet new federal requirements on retroreflectivity without replacing signs prematurely. Here’s how:

Reducing Inventories

At a purchase price of $150 to $250 a piece, plus $20 per year for maintenance, the cost of an unnecessary traffic sign adds up. (Maintenance costs involve replacing signs that have been vandalized, knocked down, or that no longer meet required levels of retroreflectivity.)

In a case study of townships in Stevens County, Minnesota, researcher Howard Preston found that nearly a third of traffic signs were not required and served no useful purpose. The average township has 180 signs, which results in an annual maintenance cost of $3,600. The average county has 10,000 signs — an annual maintenance cost of $200,000.

Public agencies could save a collective $26 million* just by removing unnecessary or redundant signs from the field, Preston said. A traffic sign maintenance handbook developed by the LRRB and MnDOT guides agencies through that process.

Longer  Lives

Traffic signs have more life in them than the typical 12-year manufacturer’s warranty, Preston said. But how often agencies replace them varies throughout the state.

Whereas small municipalities may replace signs on an individual basis through spot-checking for retroflectivity, MnDOT has a schedule. Each of the agency’s 400,000 signs is replaced within 18 years of installation.

Preston found that MnDOT could safely extend the service life of its signs to 20 years, which would save an estimated $1.3 million within the first few years of implementation.

Assuming (in lieu of a research-backed benchmark) that local municipalities would likely start replacing signs around the 15-year mark to ensure compliance with the federal law, Preston estimates that townships, cities and counties could avoid a collective $6 million in unnecessary costs per year just by adhering to the minimum 20-year replacement schedule recommended by the study.

Agencies are required by federal law to have a method in place for ensuring that signs maintain adequate retroreflectivity. A replacement schedule based on science is one way; regular physical inspection is another.

Researchers, who consulted other state’s studies and also examined signs in the field, determined that the life of the modern sign in Minnesota is at least 20 years.

It’s possible that traffic signs actually retain their retroreflectivity for 30 years or more, but further study is needed since sheeting materials on today’s traffic signs haven’t been deployed long enough to know, researchers say.

A test deck at the MnROAD facility will track the condition of Minnesota signs over the next decades — and perhaps push the  recommended replacement cycle longer.

*This figure  and the $41 million total above account for cost savings calculated over an initial, three-year period. Ongoing cost savings thereafter may be different, according to Preston.

Related Resources

Sign Maintenance Management Handbook (PDF, 13 MB, 119 pages)

Traffic Sign Life Expectancy study

Auto-Flaggers Keep Road Crews Safe, Save MnDOT Money

Like a traditional flagger, an Automatic Flagger Assistance Device directs drivers through work zones and other problem areas. But whereas traditional flagging requires workers to stand dangerously close to moving traffic, AFADs can be operated remotely, keeping the flaggers out of harm’s way.

“This is a very risky environment from our employees,” said MnDOT Research Services Project Advisor Alan Rindels said. “Any flagger you talk to can recount a time he or she had to jump in a ditch to avoid a vehicle.”

Using a remote control, a single worker can easily operate two AFADs simultaneously, freeing up personnel to perform other tasks and speed up the completion of a road project. MnDOT estimates that the resulting cost savings can cover an AFAD’s purchase costs within two years.

MnDOT recently undertook a pilot implementation of three sets of AFADs, introducing them to maintenance staff and identifying the most appropriate situations for their use. Researchers reviewed past AFAD use in Minnesota, observed traditional flagger and AFAD operations in action, interviewed MnDOT maintenance personnel about their experiences and held two hands-on training sessions that were attended by more than 60 people.

Results showed that drivers obeyed the AFAD instructions and that AFADs work well for stationary construction projects. These successful demonstrations should encourage the wider use of AFADs and enhance worker safety in a cost-effective way.

MnDOT Research Services & Library produced the video above, which details the experiences of a MnDOT road crew who recently started working with AFADs.

(Bonus: Watch MnDOT flagger Joe Elsenpeter talk about jumping into a ditch to avoid being hit.)

*Note: This blog post was adapted from an article in the latest issue of our newsletter, Accelerator. Click here to subscribe.

Related Resources

Snow Control Tools Webinar Jan. 28

Tune in to this free webinar at noon CST on January 28 to learn about the Blowing Snow Control Cost-Benefit Web Tool. This online tool allows transportation agencies to calculate the amount they can pay private landowners (farmers) to establish a living snow fence (shrubs) or to leave standing corn rows or other structures like hay bales or silage bags to reduce blowing snow on sensitive highways.

The tool also analyzes grading and structural snow fence benefits. Reducing blowing snow on highways decreases highway maintenance costs and improves traffic safety in winter driving conditions.

To watch, register online by January 23. For more information, please visit the event web page.

New crash report interface will improve usability and data quality

The data collected at the scene of a crash by law enforcement officers are important for more than just drivers and their insurance companies. The information is also used on a much larger scale by state agencies and researchers to analyze and evaluate crashes, trends, and potential countermeasures.

“Big decisions get made based on that data—million-dollar decisions,” says Nichole Morris, a research associate at the U of M’s HumanFIRST Laboratory. “So you have to be sure that what goes in to that report is high quality and reflects what actually happened at the scene of the crash.”

As part of an effort to improve this data quality in Minnesota, Morris is leading a team of HumanFIRST researchers in a project to redesign the electronic crash report interface used by law enforcement officers. The team’s goal is to create a new interface that improves the accuracy, speed, reliability, and meaningfulness of crash report data.police_guy

The project is occurring in conjunction with a redesign of Minnesota’s crash records database and is being sponsored by the Traffic Records Coordinating Committee (TRCC) at the Minnesota Department of Public Safety (DPS) and by MnDOT.

“In industry, they do this work all the time, looking at usability and design. But when you think about what a state does in terms of usability, nothing like this to our knowledge has ever been done. This makes it a very exciting and revolutionary project for Minnesota,” Morris says.

In the first phase of the project, the researchers completed a human factors analysis on the existing crash report interface to identify potential problem areas. This included a step-by-step task analysis and in-depth interviews with law enforcement officers.

During this process, the researchers identified several areas they hoped to improve. For instance, they wanted the new interface to be smarter, making better use of autofill features to reduce the amount of manual data entry.

Following the analysis, the team built two versions of a mock crash report interface for usability testing: a wizard and a form. In both versions, the researchers added decision aids to ease usability. They also significantly improved the system’s autofill capabilities, reducing the ratio of officer to system data entry from 6:1 to nearly 1:1.

The researchers then conducted four rounds of usability testing with law enforcement officers for both the wizard and the form. Results were split: half the officers preferred the wizard and half preferred the form. Because of these findings, the TRCC is planning to build full versions of both, Morris says, which will allow officers to use the version they prefer.

Going forward, the researchers plan to make a few more adjustments to the research prototype before handing it off to the state vendor, Appriss, which will build the new system. The team will then work collaboratively with Appriss to complete additional beta and usability testing before the new interface launches in January 2016.

“The results of the HumanFIRST prototypes are being combined with the vendor’s prior experience for a best-of-breed approach,” says Kathleen Haney, traffic records coordinator at DPS. “This is a fantastic project, and the results will be relevant for years to come.”

Read more about the project in the December 2014 CTS Catalyst.

MnDOT Appoints First Scholar-in-Residence

It’s back to school at the Minnesota Department of Transportation.

University of Minnesota Professor Greg Lindsey was recently appointed as MnDOT’s first Scholar-in-Residence.

Lindsey, who is spending his sabbatical on bicycle and pedestrian counting research projects, will be working in the Office of Transit’s Bicycle and Pedestrian Section until June 2016.

Since Lindsey was going to be spending much time at MnDOT anyway conducting his research, the agency invited him  to be a Scholar-In-Residence and also office at MnDOT part-time.

“We’ll be working on institutionalizing bicycle and pedestrian counting — so local engineers and planners have evidence for planning and investing in new facilities and establishing priorities for investments to increase safety,” Lindsey said.

Lindsey will help MnDOT develop a district-based plan for permanent and long-term bicycle and pedestrian monitoring following new guidance in the Federal Highway Administration’s Traffic Monitoring Guide.

Lindsey’s appointment expands on MnDOT’s existing partnership with the University of Minnesota’s Center of Transportation Studies and builds on his work for the Minnesota Bicycle and Pedestrian Counting Initiative, a collaborative effort between MnDOT and the university (see Final Report (PDF) ) .

“We are excited about this new collaboration with the University and believe it establishes an important precedent for the future,” MnDOT Commissioner Charles Zelle stated in a letter to Lindsey.

This is believed to be the first time MnDOT has appointed an in-house scholar.

A former Humphrey School of Public Affairs associate dean, Lindsey specializes in environmental and transportation planning, policy, and management. His current research involves non-motorized transportation systems. Partners in his research include the MnDOT, the Minneapolis Department of Public Works, Transit for Livable Communities and the Minneapolis Parks and Recreation Board.

“[Lindsey’s] work to institutionalize bicycle and pedestrian monitoring throughout Minnesota, is central to our efforts to establish the evidence we need to maximize the efficiency of our investments in infrastructure and the safety of our transportation facilities,” Zelle wrote.

MnDOT, LRRB Pick New Research Projects with Financials in Mind

Minnesota’s transportation research governing boards put a new emphasis on financial benefits when selecting next year’s round of transportation research projects.

MnDOT’s Transportation Research Innovation Group (TRIG) and the Local Road Research Board announced their Fiscal Year 2016 funding awards this week after hearing proposals from researchers in several states. They selected 20 research proposals hall-marked by novel approaches to improving the environment, increasing transportation safety, improving construction methods and boosting the bottom line.

“We asked the principal investigator to present the safety and financial benefits up front, and how they can be implemented to improve the transportation system and economic viability of Minnesota,” said MnDOT Research Management Engineer Hafiz Munir. “We’re making a point early in the process to identify those potential benefits, quantify them and document them in our tracking system.”

Researchers will test new technology that could make crack-free pavements; find better, faster and less expensive ways to reclaim roads; and even explore how to use waste material from road construction projects as part of the landscaping to absorb water runoff.

Links are provided below to brief descriptions of each of the projects:

Bridges and Structures

Environment

Maintenance

Materials and Construction

Multimodal

Policy and Planning

Traffic and Safety

Decoding the Deicers

The results of last season’s deicing study are in — just in time for our next snow.

Last winter, Minnesota State University researcher Steve Druschel set up experimental lanes at two Shakopee entertainment parks and a test site on a Mankato bridge to examine the life cycle of winter maintenance, from plowing and the application of chemicals to the drainage of chemical residue after the roadway has been treated.

What the Study Found

  • The majority of chloride appears to leave the roadway by plow ejection, vehicle carry-away or tire-spray spreading, rather than through storm drainage, even in warmer storms.
  • Pavements don’t hold chloride very long in a precipitation event, even after anti-icing/pre-treatment.
  • Deicer effectiveness. Warmer temperatures provide more melt from the deicer. Little melt was observed below
    10 degrees Fahrenheit unless sunlight provided warming, and prewetting produced no significant difference in deicer performance.
  • Dry pavements may be better candidates for pretreatment, with researchers noting that any wetness on the pavement ahead of a storm limited anti-icer effectiveness.
  • Truck traffic after deicer application was found to significantly improve deicer performance, resulting in both a wider and quicker melt.
  • Plow effectiveness. Even with different snow and temperature conditions, the evaluation of plow speed provided the same findings: snow rises higher in the curvature of the plow at higher speeds, creating a broader spray off the plow ends, and higher speeds decrease scrape quality.
Students pour water to form ice on a test lane in Shakopee.
Students pour water to form ice on a test lane in Shakopee.

What’s Next?

The research team has proposed a third phase of this project to continue their work in the field, which is expected to include further examination of the impact of truck traffic on deicer effectiveness, variations in plow setup and expanded testing under varying weather conditions and snow structure.

Related Resources

Field Effects on Deicing and Anti-Icing Performance – Technical Summary (PDF, 1 MB, 2 pages); Final Report (coming soon)

Salt Brine Blending to Optimize Deicing and Anti-Icing Performance -Technical Summary (PDF, 1 MB, 2 pages) and Final Report (PDF, 11 MB, 151 pages) (previous study) 

The 411 on Sign Management

A revised handbook offers Minnesota cities and counties the latest tips on how to meet new sign retroreflectivity requirements, as well as the 411 on sign maintenance and management – everything from knowing when it’s time to remove a sign to creating a budget for sign replacement.

The best practices guide – produced in conjunction with a new sign retroreflectivity study – also offers case studies from around the state.

“The life cycle of traffic signs, from installation to replacement, is a pretty complex issue and it can be a challenge to get your arms around,” said Tim Plath, Transportation Operations Engineer for the city of Eagan. “This handbook really boils it down into some basic concepts and also gives you the resources to dig deeper if necessary. It’s a good resource to have at your fingertips.”

2014RIC20-1

This handbook updates a previous version issued in 2010, to include new FHWA  retroreflectivity and maintenance and management requirements and deadlines.

“Maintenance/management of a large number of signs can potentially be an administrative and financial challenge for many local road authorities,” explained Sulmaan Khan, MnDOT Assistant Project Development Engineer.

Here’s a video demonstration of a sign life reflectometer (the Gamma 922), another resource MnDOT has available for local government agencies. Cities, townships or counties may borrow the reflectomer by contacting the Office of Materials and Road Research, (651) 366-5508.

Related Resources

Traffic Sign Maintenance/Management Handbook (PDF)

Traffic Sign Life Expectancy – Technical Summary (PDF) and Final Report (PDF)

Gamma 922 demonstration (video)

Minnesota transportation research blog

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