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.
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.
Measuring retroreflectivity
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.
Expected life
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.”
Researchers look at the test deck at MnROAD. The study panel includes city and county engineers.
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.
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.
No guidance
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.
Uncontrolled pedestrian crossings
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.
Further Resources
Putting Research Into Practice: A Guide for Pedestrian Crossing Treatments at Uncontrolled Intersections – Technical Summary (1 MB, 2 pages); Final Report.
* 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.”
Traffic analysis
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.
A Weigh-In-Motion traffic counter on Highway 52, between the Lafayette Bridge and I-494.
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.
A sign similar to this will go up along the I-35 alternate route to guide redirected traffic.
“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.
Picking a route
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.
Proposed alternate route.
“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.
Newly developed software has drastically reduced the amount of time and effort required by MnDOT’s Regional Transportation Management Center (RTMC) to analyze congestion in the Twin Cities metropolitan area.
Developing MnDOT’s annual Metropolitan Freeway System Congestion Report used to be a manual process that could be applied to only a portion of the large quantity of data generated by in-pavement sensors.
The new Highway Automated Reporting Tool now automatically imports and cleans data to produce a report about the percentage of network miles congested during peak periods as well as three new reports on other performance measures.
The tool will help MnDOT engineers and planners better develop congestion reduction strategies and determine the most cost-effective investments in the network.
From RTMC’s control room, engineers monitor and manage 400 miles of Twin Cities freeway traffic using data from thousands of in-pavement sensors.
“Before HART, it took months to analyze freeway performance using traffic data from only the month of October. Now engineers can quickly analyze data from any time period, significantly improving traffic planning,” said Jesse Larson, Assistant Freeway Operations Engineer for MnDOT’s Metro District Regional Transportation Management Center.
The tool was developed in a MnDOT-funded study led by University of Minnesota researcher John Hourdos.
Note: This article was adapted from the May–June 2014 issue of our Accelerator newsletter. Sign up for your free print or email subscription by clicking here.
Rumble strips alert sleepy and inattentive motorists that they are about to veer off the highway or into the opposite lane of traffic. But the grating noise that prevents collisions can also be annoying to nearby residents.
Around Minnesota, more and more counties are facing push-back as they install shoulder rumble strips on roadways in populated areas. This is because county road shoulders are narrow — leading drivers to frequently hit the rumbles.
“There is a strong concern statewide that these noise complaints will raise enough concern that legislation may be passed reducing their use,” said technical liaison Ken Johnson of MnDOT’s Office of Traffic, Safety and Technology.
A European-developed style of rumble strip, called sinusoidal, could provide Minnesota a new means of warning drivers without as much stray highway noise.
Accident reduction
Rumble strips are patterns ground into asphalt that cause a vehicle to vibrate when its tires come close to the centerline or road edge. They help prevent lane departure crashes, which account for more than 50-percent of fatalities on the road system.
The sinusoidal rumble (below) has a sine wave pattern ground into the pavement, while the traditional rumble strip (top photo) doesn’t follow a wave pattern.
Creation of a Sinusoidal rumble strip. Photo courtesy of the Wirtgen Group
MnDOT’s Office of Traffic, Safety and Technology plans to test different designs of the Sinusoidal rumble strips to find the one with the highest level of interior vehicle noise and lowest level of exterior vehicle noise.
The navigability of sinusoidal rumbles by motorcycles and bicycles will also be evaluated. The project was recently funded with a research implementation grant from MnDOT’s Transportation Research Innovation Group.
If sinusoidal rumble strips are found to be effective, the chosen design will be used for centerlines and road shoulders in noise-sensitive areas throughout the state highway system. It is anticipated that counties will also adopt the design.
Unlike counties, most of MnDOT’s recent complaints have been for its centerline rumbles, which are required on all rural, high-speed undivided roads in Minnesota, Johnson said.
MnDOT has considered allowing more exceptions due to residential noise concern; however, doing so could result in more fatal and serious crashes. Sinusoidal rumbles are seen as a possible alternative for these noise-sensitive areas.
The Local Road Research Board is also studying different designs of sinusoidal rumble strips in Polk County.
In an effort to encourage more use of safety rest areas and reduce drowsy driving, the Minnesota Department of Transportation is bolstering amenities and plans to install new signage at select rest areas across the state.
Drowsy driving is conservatively estimated to cause at least 1,550 deaths nationwide each year and $12.5 billion in monetary damage.
Motorists would stop more frequently at rest areas if they knew what rest areas offered, according to market research completed in 2009.
MnDOT will design and install highway symbol signs to advertise the amenities at 13 rest areas in a pilot project funded by MnDOT’s Transportation Research Implementation Group.
“We are using this as a way to entice drivers to take a break, pull over and refresh before returning to the road,” said Robert Williams, MnDOT Safety Rest Area Program Manager and the project proponent.
Rest areas in Brainerd and Cass Lake, Minn., can now offer a tourism-related gift shop, thanks to a change in law.
Amenities differ greatly between rest areas within the state, as well as across the country; this depends on when they were built and whether they are located on an interstate, state highway or toll road.
Older, smaller rest areas may only have a bathroom and picnic area, while newer facilities often have features such as children’s play areas, staffed travel counters and dog runs.
In the future, the state may consider new amenities such as gift shops, adult exercise equipment to rejuvenate motorists, electrical vehicle charging stations and perhaps even electrification stations to allow truck drivers to power their TV or refrigerator without idling their vehicle.
Research has found that as the spacing of rest areas increases beyond 30 miles, the number of drowsy driving crashes goes up exponentially, Williams said.
Each sign will advertise up to six amenities.
Proposed Signage
Symbols on each sign will identify up to six amenities, such as in the example above, which depicts an assisted restroom, gift shop, ticket sales, EV charging stations, childrens’ playlot and adult exercise equipment.
MnDOT will evaluate the pilot project to determine if the symbol signs are effective in communicating to travelers the amenities offered at individual rest areas and if the signs were a factor that encouraged them to stop.
If the two-year project goes well, the state may add similar signs to the remaining 39 Class I safety rest areas (those rest areas equipped with flush toilets).
Some of the signs will require a request to FHWA for experimentation. The intent is to install the signs in the summer of 2015 at rest areas on northbound I-35, eastbound I-94, as well as at the Brainerd Lakes Area Welcome Center on Hwy. 371.
Rest Area Offerings Increase
Although travelers and state DOTs would often like to introduce new amenities, state and federal laws limit what states can offer.
Toll roads and highways built before 1960 (the Interstate era), mostly in the East Coast or Chicago area, have fewer federal restrictions than rest areas in Minnesota and may feature restaurants or convenience stores.
Changes to Minnesota state law in 2005 and recent changes to federal law in MAP-21 now allow limited commercial activities, such as tourism-related gift shops and ticket sales at rest areas. MnDOT and its partners have taken advantage of some of these changes at its visitor centers in Brainerd/Baxter and Cass Lake.
In addition, the state is exploring the concept of using rest areas as transit transfer facilities, where long-distance bus carriers and regional transit lines can exchange passengers.
These transit hubs would shorten travel times for long-distance travelers and allow the rest areas to serve multiple functions while providing a comfortable waiting area for passengers.
The new Roadway Safety Institute, a $10.4 million regional University Transportation Center (UTC) established in late 2013, will conduct a range of research, education, and technology transfer initiatives related to transportation safety. Led by the University of Minnesota, the two-year consortium will develop and implement user-centered safety solutions across multiple modes.
The Institute will be a focal point for safety-related work in the region, which includes Minnesota, Illinois, Indiana, Michigan, Ohio, and Wisconsin. Other consortium members are the University of Akron, University of Illinois at Urbana-Champaign, Southern Illinois University Edwardsville, and Western Michigan University.
Max Donath, professor of mechanical engineering at the U of M, serves as the new Institute’s director. In this month’s issue of the CTS newsletter, Catalyst, Donath shared his vision for theInstitute.
According to Donath, the Institute will focus on addressing regional traffic safety priorities, educating the public, and attracting more professionals to the safety workforce by connecting with students.
Research topics will focus on two key areas, Donath said: high-risk road users and traffic safety system approaches. The goal of this work is to prevent the crashes that lead to fatalities and injuries on the region’s roads.
One unique Institute effort will involve working with American Indian communities in the region to explore and address the unusually high number of motor vehicle crash fatalities on tribal lands. “Our research will work to better understand why this is happening and to develop more effective solutions,” Donath said.
Crossroads 