MnROAD is hosting pavement researchers from around North America this week to discuss research conducted at its cold weather pavement testing facility in Albertville, Minnesota.
Participants at the three-day conference (June 10 to 12) are reviewing the findings of recent pooled fund studies, sharing their implementation experience and recommending what projects should be picked for the next round of research.
We recently blogged about a research project to evaluate a new type of rumble strip that produces significantly less external noise than traditional designs. The above video, shot near Thief River Falls, Minnesota, shows a comparison between traditional rumble strip designs and the newer, “sinusoidal” rumble strips (a.k.a. “mumble strips”).
The life-saving benefits of rumble strips are well-established, but traditional designs produce external noise that residents consider to be a nuisance. The issue has pit safety concerns against quality-of-life concerns in some parts of the state. Researchers are investigating whether sinusoidal rumble strip designs, which are much quieter, are effective enough to combat drowsy or inattentive driving.
The video is not exactly a scientific comparison, but it does give the viewer a good sense of the difference in noise levels produced by the two styles of rumble strips. The results of the actual research project are expected to be available later this year.
A large percentage of Minnesota’s local highways were built in the 1950s, the same era that birthed the modern interstate system. But the golden age of highway construction has caught up to counties, who are struggling to maintain and rehabilitate aging road systems with fewer and fewer dollars.
“Our economic resources do not meet the financial investment needed as the bulk of our pavements surfaced in the 1950s reach the end of their useful life all about the same time,” said Freeborn County Engineer Susan Miller.
In rural Otter Tail County alone, the cost of road construction has climbed 10.5 percent per year for the past 10 years.
Meanwhile, there has been only one increase in funding — an 8.5-cent bump in the state gasoline tax “that was eaten up the moment it was enacted,” said County Engineer Rick West.
Otter Tail’s funding gap? An estimated $11 million in year 2011 alone.
With no change in sight, counties across the state are banding together in a research project through the Local Road Research Board to identify ways to reduce the size of their road systems and lower preservation costs.
The LRRB launched the study at the behest of counties who were considering turning some paved highways back to gravel just to get by — even though it would probably increase long-term maintenance costs.
In addition to providing expertise on that topic, consultants worked with a group of pilot counties to develop other strategies of stretching county road dollars further. These include: changing maintenance schedules; using different gravel road materials; transferring roads to city or township ownership; adopting different road performance measures; and raising local revenue.
“This project of how five different counties approach funding limitations and how to manage a system with constrained resources is one of the best that I have been a part of through the LRRB,” said Miller, who found the data critical to convincing her county board to pass a wheelage tax.
Although the ideas developed through the study aren’t entirely new, for a busy county engineer with few staff, the assistance to implement them has been very valuable.
“We’re practitioners — not researchers,” said Otter Tail’s Rick West. “It’s really forced us to look at our system in its entirety and from a long-range perspective. For us, that’s huge.”
The LRRB selected pilot counties (Dakota, Otter Tail, Freeborn, Stearns and Anoka) that reflect the diversity of the state. After researchers help them implement their chosen strategies, they will hold informational workshops for others throughout the state.
“Other counties with similar roadway preservation issues or management structures can follow these best practices,” said Michael Marti of SRF Consulting Group. “There are a lot of tools out there, there just needs to be more demonstration or training on each of these tools.”
Anoka County, for example, undertook a detailed analysis to determine which roads should become city-owned and which roads the county should assume.
The evaluation system used by Anoka, which examines travel data and other factors, could be adopted by other counties.
Public education
While some ways of changing the system of road maintenance may not be immediately popular, the community will get on board if they understand why, said Otter Tail County Board Chairman Wayne Johnson.
For instance, Otter Tail had to explain why it’s more cost-effective to sealcoat four-year-old roads than reconstruct beat-up, low-volume roads.
“That’s hard to get your arms around when it’s been the other way for 50 to 60 years,” Johnson said.
Community residents did, however, reject one possible strategy discussed at eight public outreach meetings: unpaving roads.
Otter Tail’s entire county road network is paved — a reflection of investments made back in the 1950s that have become somewhat of a community ethic for Ottertail’s 57,000 residents (a population that triples during the summer).
Tools used in the study enable counties to illustrate just how far behind they are in terms of maintenance and prioritize where to make improvements.
“Everyone wants roads to be maintained, but until the road system preservation study, nobody understood the magnitude of the funding gap between where we are and what we need to do to preserve the system,” said Johnson, who recently shared his county’s findings at the National Association of County Engineers conference.
The data is critical for the public to understand why a county might seek a local tax or different method of road maintenance.
“It’s far better to try to tell them what the problem is on the front end, rather than defend the decision on the back end,” Johnson said. “We’re after them to buy into something because it’s their roads and their money.”
Traffic signs provide important information to drivers, and are a critical component of traffic safety. In order to be effective, their visibility and readability must be maintained under both day and night conditions.
Key to signs’ effectiveness is a quality known as retroreflectivity — the ability for signs to bounce light back toward a driver’s eyes, making them appear brighter and easier to read. Retroreflectivity deteriorates with time, so transportation agencies need to actively maintain their signs.
A research project funded by the Local Road Research Board is developing a guide to help cities and counties better manage their signs, and also to meet a new Federal Highway Administration retroreflectivity management requirement while getting the lowest life-cycle costs.
Cities and counties have until June to establish a sign assessment or management method that will maintain minimum levels of sign retroreflectivity.
“Right now there’s a mixture of different management methods, with very little guidance as to what’s appropriate for your agency based on the signs you have and your labor force and equipment,” said Matt Lebens, a MnDOT research project engineer.
Since 1993, the Manual on Uniform Traffic Control Devices has included guidelines for minimum retroreflectivity of pavement markings and signs. The standards are meant to ensure that drivers, especially the growing population of elderly drivers, are able to detect, comprehend and react to traffic signs. The LRRB project is designed to help fill certain knowledge gaps in this area.
Possible methods for ensuring retroflectivity include night-time inspection; use of a reflectometer; spot-checking a sampling of signs that are the same age; or blanket replacement of signs once they reach a certain age.
Although the retroreflectivity of a sign is guaranteed by its manufacturer to last a certain number of years, it commonly lasts much longer.
“Currently, we don’t have expected sign life guidance for agencies to use. Through this project, we are establishing a control deck for sign sheeting used in the state, and an expert panel will make recommendations on expected sign life ranges,” Lebens said.
Researchers reviewed retro-reflectivity studies from other states and also measured the retro-reflectivity of signs out in the field across Minnesota using a retroreflectometer. As part of this project, MnDOT is providing training on the retroreflectometer and will also make it available for loan to local municipalities. (Watch a video demonstration.)
At MnDOT’s MnROAD site, control decks contain dozens of signs. In addition to measuring retroreflectivity, the MnDOT Materials lab is monitoring color fade, which has been a larger issue in Minnesota.
“By getting better data as to the real life in-field life span of the signs, agencies will have a more realistic and better informed value for sign life expectancy, as well as potentially reducing costs,” said MnDOT Senior Engineer Mark Vizecky.
There’s been no definitive studies to date as to what the life of a sign is, said lead project investigator Howard Preston of CH2M Hill, but the research so far shows it is in well excess of manufacturer warranties.
Cities and counties will be advised to pick an expected sign life that goes beyond the warranty – and then stay tuned.
“The notion is to watch these signs until they fail,” Preston said. “The sheeting material is better than it used to be. The failure might be 20 or 30 years out.”
There are two basic types of reflective sheeting material: beaded and prismatic.
Although beaded is guaranteed to last 10 years, researchers anticipate a retroreflectivity life of between 12 and 20 years old.
For the prismatic material – which has a 12-year warranty – the life cycle is anticipated to be 20 to 30 years.
“Nobody knows for sure, because nobody has actually followed this material to failure in a controlled condition,” Preston said. “On the road, there are so many variables: vandalism, knock-downs, etc.”
Traffic Sign Life Expectancy study – Technical Summary (PDF, 1 MB, 2 pages); Final Report (PDF, 2 MB, 45 pages)
Despite their more similar roles at work and home than ever before, U.S. men and women continue to have different travel behavior. Historically, employed men have spent more time traveling to work and less time on household and family support trips than women. While this difference is well-documented, explanations for the difference vary widely: some theories say it’s due to biologically driven differences in gender, while others attribute it to socially constructed gender roles or to gendered structural contexts such as labor market segregation and economic inequality.
While much research has examined these theories, few studies have tested their validity based on evidence—which prompted U of M researchers to examine the theories more deeply. “We believe a greater understanding of the underlying reasons for these enduring travel differences is necessary to effectively address the gender equity issue in transportation policy,” says Yingling Fan, assistant professor in the U’s Humphrey School of Public Affairs.
Researchers set out to test the competing theories by analyzing publicly available data from the American Time Use Survey (ATUS) in various ways across groups of workers with different types of family structures. (ATUS is an ongoing time diary study funded by the U.S. Bureau of Labor Statistics.)
First, they tested the theory that travel behavior differences were based on biologically driven gender differences. “If this theory was true, travel differences between men and women could be applied across all population groups regardless of family structure, but this was not the case,” Fan explains. “We found that single female workers and single male workers exhibit no significant difference in travel behavior.”
Next, the team studied the impact of gendered structural contexts, such as women’s greater presence in pink-collar occupations and significantly lower earnings. The team found moderate support for this theory. “These factors are associated with shorter work travel time among some—but not all—family structures,” Fan says.
Researchers did find strong support, however, for the theory that socially constructed gender roles explain travel behavior differences. “We discovered that while marriage alone doesn’t differentiate travel behavior between men and women, parenthood does have a significant impact,” Fan says. “Interestingly, we found that even being the sole breadwinner does not insulate mothers from socially constructed gender roles—female breadwinners in married single-worker households with children have shorter work commutes and more household support travel than male breadwinners in the same family structure.”
According to the researchers, these findings have important implications. First, policies to minimize auto travel (for environmental purposes, for example) may be unfair to women who wish to reach more job possibilities through longer commutes. In addition, the findings highlight the importance of incorporating parenthood as a prime variable in understanding the gender and mobility connection.
Finally, this research provides insights on how future growth or decline in specific family structures may shape travel demand. “As childless households continue to grow in relation to households with children, it’s possible that fewer female workers will be confined by short work commutes and may choose to spend more time commuting to more desirable jobs, placing new demands on the transportation system,” Fan says.
The research was funded in part by a Minnesota Population Center Program Development Grant.
Reprinted from the May 2014 issue of CTS Catalyst.
City and county engineers often struggle with how to respond to safety concerns about pedestrian crossings, with no scientific method for evaluating them.
In Long Lake, for example, the police department received numerous complaints about the safety of a particular pedestrian crossing. But when the crossing was videotaped, no one was observed using it.
This example — which was part of a research project funded by the Local Road Research Board — exemplifies the difficulties local governments face when they receive requests for a stop sign or signals at a crossing.
A new manual and June 5 training workshop being held by the Minnesota Local Technical Assistance Program will provide cities and counties with step-by-step tools for evaluating a pedestrian crossing and identifying whether improvements are warranted.
The soon-to-be released guidebook* recommends when to install marked crosswalks and other enhancements based on the average daily vehicle count, number of pedestrians, number of lanes and average vehicle speed. It guides users how to rate a crossing for pedestrian service, and includes a flow chart to assist in decision-making.
The training is unique because it is based on actual video footage of existing crosswalks and the pedestrians which use them.
Although vehicles are legally required to stop for pedestrians crossing at intersections and within marked crosswalks, they don’t always yield the right-of-way. And areas with high traffic volumes may not have adequate gaps for pedestrians to cross safely, leading to risk-taking.
Alan Rindels, a MnDOT research engineer, had previously looked for a methodology to evaluate a crosswalk’s effectiveness, but could not find an appropriate engineering analysis.
“What I kept coming up with were results based on the experience of an engineer or planner for what they ‘felt’ was a better crosswalk, such as additional pavement markings, lights or maybe a signal system,” he said.
Rindels finally found guidance in a Transportation Research Board webinar two years ago. Based on that, he asked the LRRB to develop a training methodology for Minnesota practitioners.
Unless specifically marked otherwise, every intersection is a pedestrian crossing, regardless of the existence of crosswalk markings or sidewalks. At mid-block locations, crosswalk markings legally establish the pedestrian crossing. Uncontrolled pedestrian crossings (which the guidebook focuses on) are locations that are not controlled by a stop sign, yield sign or traffic signal.
Defining where to place pedestrian crossing enhancements — including markings, signs and or other devices — depends on many factors, including pedestrian volume, vehicular traffic volume, sight lines and speed.
The LRRB developed a worksheet that engineers can use to evaluate an uncontrolled pedestrian crossing location in a systematic way, in accordance with the 2010 Highway Capacity Manual. Users note the level of lighting, distance from the nearest all-way stop and whether another location might serve the same pedestrian crossing more effectively.
The guidebook’s 11-step evaluation can identify what level of treatment is appropriate, ranging from overhead flashing beacons and traffic calming devices, such as curb bump-outs, to more expensive options like building overpass or underpass.
Hennepin County Senior Transportation Engineer Pete Lemke, who went through pre-training, said the guidebook will help engineers measure the pedestrian experience by “quantifying the delay at non-signalized intersections.”
“It will inform how we respond to concerns — whether that response is ‘the crossing fits the needs of what’s there’ or ‘we need to make changes or enhancements,'” he said.
Putting Research Into Practice: A Guide for Pedestrian Crossing Treatments at Uncontrolled Intersections – Technical Summary (1 MB, 2 pages); Final Report.
Training workshop – June 5 (register here)
* Consultant Bolton & Menks prepared the guidebook with guidance from a 21-member project team that included University of Minnesota researchers and engineers from the city of Eagan, Hennepin County, Carver County, Scott County, MnDOT, the Center for Transportation Studies and the Federal Highway Administration.
The design of long-lasting roads requires knowing how many cars and commercial trucks travel over them. To collect this data, engineers rely on traffic counters.
But at a cost of $50,000 to $200,000 each, MnDOT must be judicious about where it places its permanent automatic traffic recorders (ATR) and weigh-in-motion (WIM) sites.
In a new MnDOT-funded research project, University of Minnesota researchers are studying how to optimize ATR placement and other collection methods to improve the quality of the data while reducing costs.
ATRs and WIMs are devices embedded in the pavement surface that continuously collect traffic data. The state has 91 ATR/WIM sites, as well as 32,500-plus short-duration (i.e. “short-count”) sites where traffic data is collected for 48-hour periods and then used to estimate average daily traffic counts.
“We place permanent traffic counters at key locations across the state and try to logically apply patterns from them to similar locations across the state,” explained MnDOT Project Advisor Alan Rindels. “Short-count locations draw on seasonal patterns from individual or clusters of ATRs to convert 48-hour counts into annual average daily traffic estimates.”
The information collected is used by MnDOT’s Traffic Monitoring Unit to analyze traffic patterns and travel trends. An increase in traffic may cause the department to consider increasing the number of lanes or add a traffic light to an intersection that becomes busier. The data is also submitted to the federal government to determine highway funding.
Fifteen WIM sites also collect axle loadings, vehicle and axle configuration and truck volume characteristics. This information is useful for pavement and bridge design, as well as size and weight enforcement.
It’s too early to say what the ultimate outcome of the study will be, but University of Minnesota researcher Diwakar Gupta believes it may involve reducing the number of permanent count locations, while increasing the frequency of counts at short-count locations — which are deployed only once or twice every two, four, six or 12 years. He said research is showing that these snapshots in time may be insufficient for short-duration locations with seasonal commercial truck traffic.
Another option may be retaining all the permanent ATRs, but only collecting data from them every few years. This could reduce site maintenance costs and the manpower needed to analyze continuous traffic count data.
Researchers are also looking at how to better match short-count sites with individual or groups of continuous count locations to improve the accuracy of seasonal adjustments that are used to create annual estimates.
“We think, in the end, Traffic Data Management will transition to a different way of sampling and collecting data,” Gupta said.
When a semi carrying millions of bees crashed three years ago on Interstate 35, a five-mile stretch of freeway near Lakeville had to be shut down, and it took several hours to re-open.
A new pilot project under way in southern Minnesota would move traffic more quickly during accidents like these by having a predetermined route along I-35 to redirect motorists.
Currently, when the Minnesota State Patrol decides to close a freeway, motorists are left to their own devices to determine where to go.
“The use of emergency alternate routes are very helpful in rural areas where other roadway options might be limited,” said project consultant Andy Mielke of SRF Consulting, who helped the state of Wisconsin establish similar routes along its interstate.
The MnDOT-funded research project establishes a permanent alternate route parallel to the interstate in Freeborn, Steele and Rice Counties.
MnDOT worked with local officials to identify the best alternative roads and is in the process of procuring signs to permanently affix along the I-35 alternate route this summer.
Identifying an emergency route wasn’t easy. Engineers had to consider the proximity to the freeway, whether a route was direct enough and whether the roads could handle heavy truck traffic.
A planning committee that included MnDOT, the State Patrol and three county engineers developed a route and procedures for everyone to follow.
“All of the responders know where the traffic is going, so they’re all operating off the same sheet of music,” Mielke said.
The alternate route system is intended to reduce traffic delays, minimize secondary crashes, speed the emergency response and keep truck freight moving during a large accident.
More than 5,000 trucks per day travel Interstate 35.
“If you’re a truck driver sitting in congestion, time is money,” Mielke said.
The planning team identified messages that can be automatically deployed on message boards along 35 during an emergency. The route will only be activated if the freeway is fully blocked or once all other methods of moving traffic are exhausted.
The interest for the project came from MnDOT District 6 Traffic Engineer Mike Schweyen, who participated in Wisconsin’s planning for an emergency alternate route in the La Crosse area.
An I-35 Corridor Emergency Alternate Route Operations Guide has been created. The route plans just need final approval now from the county boards.
This project could be an example for the rest of the state to follow. Other MnDOT districts are considering establishing alternate freeway routes in their districts.
Alternate route plans for Freeborn County, Steele County and Rice County (PDFs) (subject to final county board approval).
Crossroads 