Tag Archives: Minnesota

Traffic and Safety

What’s the life of a sign?

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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.”

A test deck at MnROAD.
Researchers look at the test deck at MnROAD. The study panel includes city and county engineers.
Resources

Traffic Sign Life Expectancy study – Technical Summary (PDF, 1 MB, 2 pages); Final Report (PDF, 2 MB, 45 pages)

Pedestrian, Traffic and Safety

New guidebook, training to facilitate safer pedestrian crossings

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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 pedestrian crossing control device.
A pedestrian crossing control device.

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.

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.

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.

Traffic and Safety

Software Tool Cuts Time to Analyze Twin Cities Congestion

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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.

Resources
Bridges and Structures

New monitoring system gives advance warning of bridge distress

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While not inherently unsafe, MnDOT’s fracture-critical bridges — those having critical, nonredundant components — must be inspected on a regular basis. To help track the health of these bridges, MnDOT has developed a bridge health monitoring system that uses electronic instrumentation to provide advance warning of structural distress.

The system detects acoustic emissions — stress waves caused when cracks form and propagate in the steel components of a bridge. Researchers recently deployed and tested the system on the Cedar Avenue/Highway 77 Bridge in Burnsville, enabling them to develop procedures for automatically collecting and processing data.

“Ever since the collapse of the I-35W bridge in Minnesota, many states have been interested in developing a bridge health monitoring system that will help engineers address the many challenges of managing infrastructure and ensure the longevity and safety of our bridges,” said Moises Dimaculangan, MnDOT bridge rating engineer.

To help distinguish real monitoring events from false alarms, researchers conducted tests to capture acoustic emission data caused by brittle fractures in steel beams using the same bridge health monitoring system currently being used at the Cedar Avenue Bridge.
To help distinguish real monitoring events from false alarms, researchers conducted tests to capture acoustic emission data caused by brittle fractures in steel beams using the same bridge health monitoring system currently being used at the Cedar Avenue Bridge.

MnDOT will continue to use the system to monitor the Cedar Avenue Bridge, a steel tier-arched bridge over the Minnesota River. It was chosen because it is fracture-critical, but has no history of cracking. The test deployment also led to guidelines for monitoring other fracture-critical bridges.

University of Minnesota researchers recommend further investigation into acoustic emission data analysis methods, as well as using the system developed in this project to monitor another steel bridge, one with a history of cracking.

*Note: This article was adapted from the upcoming May–June 2014 issue of our Accelerator newsletter. Sign up today to receive your free print edition or to receive email notification when new issues become available online. Subscribe here.

Resources

Acoustic Emmission Monitoring of Fracture-Critical Steel Bridges – Technical Summary (PDF, 1 MB, 2 pages); Final Report (PDF, 5 MB, 236 pages)

Environment, Maintenance Operations

GPS-equipped mowers to save money, reduce noxious weeds

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Putting GPS units on MnDOT highway mowers is expected to speed mowing operations and cut herbicide usage by 50-percent in metro area ditches, reducing groundwater contamination.

MnDOT’s Metro District highway maintenance division will be one of the first — if not the first — state agencies in the country to equip the majority of its maintenance tractors with Automated Vehicle Location systems.

Not only will crews be able to effortlessly track their progress — reducing paperwork and freeing time for other maintenance activities — but the AVL’s live mapping software will help them avoid noxious weed patches, thereby reducing their spread.

Last year, MnDOT tested the GPS software on five mowers.
Last year, MnDOT tested the GPS software on five mowers.

“AVL alone enables the tracking of vehicle positions, but when combined with equipment sensors and an on-board monitor with user interface, it becomes a very innovative way to reduce operation costs,” said MnDOT Project Engineer Trisha Stefanski, who applied for funding from MnDOT’s Transportation Research Innovation Group for the pilot project.

Vehicle tracking systems have been shown to reduce chemical usage by crop farmers, improve route efficiencies in truck driving and help cities and counties track snowplows.

The on-screen mapping shows the location of weed patches, so mowers can avoid them, reducing their spread.

MnDOT Metro, which tested five AVL units last year, hopes to equip as much of its remaining fleet as possible.

In the grant application, Stefanski estimated the technology will pay for itself in about a year’s time, largely due to herbicide savings.

Noxious weeds

MnDOT is required by law to manage certain noxious weeds along its highways. Each year, weed inspectors survey one-quarter of metro ditches for weeds, which enables them to concentrate eradication efforts on the worst areas.

Touch-screen maps will contain the noxious weed locations so operators can see weed patches and mow around them.

Herbicide usage is estimated to drop an estimated $100,000 to $150,000 per year. (This estimate was based on the original funding request. Final numbers haven’t been released.)

Operators can use the on-screen map to mark the location of new patches of noxious weeds.

Noxious weeds like Wild Parsnip — which can cause painful skin boils — might even be eradicated, reducing the risk for field crews, such as construction workers and Adopt a Highway volunteers.

Until now, maintenance crews have relied on paper maps to identify weed locations, which is less effective.

“What’s better, looking at a live screen when you’re going down the road and seeing where weeds are coming up, or trying to refer to a piece of paper?” Stefanski said.

Other advantages

The AVL equipment will also allow for automated reporting.

Mower operators can use the on-board AVL monitor to mark the location of guardrail hits, potholes, washed-out culverts, debris and unmarked noxious weeds.

Operators can electronically mark the location of guardrails, debris, potholes and more.
Operators can electronically mark the location of guardrails, debris, potholes and more.

Currently, operators must track their activities using hand-written forms or spreadsheets in the office.

The AVL system will also automatically track their location history, allowing operators to optimize their routes based on how long it took to mow segments in the past.

It will also be easier to answer questions from the public, who want to know the last time a certain ditch was mowed.

“Making everything geographically located adds so much analysis opportunity,” Stefanski said.

MnDOT also has AVL technology on an herbicide applicator to better track where it’s sprayed. Other future potential applications including pothole patching and road sweeping operations, Stefanski said.

Traffic and Safety

Research Drives Change At Rest Stops

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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 state law.
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.
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.

Rest areas
Pilot locations are circled.
Bicycling, Pedestrian

Bicycle and pedestrian-counting project wins CTS partnership award

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(Feature image courtesy Michael McCarthy, Center for Transportation Studies.)

Earlier this year, we wrote about the Minnesota Bicycle and Pedestrian Counting Initiative, a project that developed guidelines and protocols to help transportation planners accurately count non-motorized traffic. This groundbreaking research involved a diverse partnership of state and local officials, University of Minnesota faculty, and private and nonprofit organizations.

On Wednesday, April 23, the project team (photo above) was honored with an award from the Center for Transportation Studies. Team members accepted the CTS Research Partnership Award in a ceremony at the McNamara Alumni Center in Minneapolis. The award is given each year to projects that have resulted in “significant impacts on transportation” and that draw on “the strengths of their diverse partnerships” to achieve their results.

The video below, produced by CTS, explains the importance of the project. MnDOT is now in the process of implementing the research results by installing permanent counters and using portable counters in select locations around the state. MnDOT plans to use the information for a variety of purposes, including planning, safety analysis, investment planning and quality-of-life analysis.

Project team members will present their research findings at the North American Travel Monitoring Exposition and Conference in July. The conference’s focus is on “Improving Traffic Data Collection, Analysis, and Use.”

*Bonus: Read about last year’s Research Partnership Award-winner, a MnDOT-led, multi-state effort to reduce low-temperature cracking in asphalt pavements.

Learn more about the project:

Bridges and Structures

Video: 3D Technology Enhances Underwater Bridge Inspection

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A new technology that uses 3D-imaging sonar will enable MnDOT engineers to visualize the substructure of a bridge in a way they never have before.

Until now, MnDOT has relied on human divers and depth finders to identify problems beneath the water.

Divers are limited by what they can see and feel in murky waters, however, and depth finders can only look down, not around.

“With this new technology, we will be able to provide high resolution three-dimensional images of underwater areas, structures and objects to show what is occurring, regardless of water clarity,” said MnDOT Bridge Waterway Engineer Petra DeWall, who has received funding from MnDOT’s Transportation Research Innovation Group to purchase the equipment.

Video imagery from a sonar inspection of Minneapolis’ Third Avenue bridge is above.

Currently, MnDOT hires engineer divers to physically inspect about 500 bridges every five years. They look for cracked concrete, exposed reinforcement and other detrimental conditions.

Although divers can spot issues, they can’t always thoroughly assess the scope of a problem, such as the amount of sediment being washed out around a bridge pier, a problem called bridge scour.

It can also be difficult — or dangerous — for divers to venture down for an inspection.

This was the situation last winter with the Third Avenue Bridge in downtown Minneapolis, where the streambed has degraded around a bridge pier, causing erosion to the pier.

“The Third Avenue inspection was not totally detailed. We knew there was a void under the bridge, but it was very hard to visualize,” DeWall said.

Early ice build-up halted further inspection in November, so MnDOT asked 3D sonar scanner manufacturer Teledyne BlueView to scan the area as a demonstration of its equipment.

A video of the inspection is below:

Multiple holes were cut in the ice sheet to deploy the sonar, which provided an image of the bridge scour by emitting sound-waves that created a point cloud.

“It gives you a large data set of where the sound reaches and comes back to the equipment,” DeWall explained.

The 3D image provides a level of detail that will enable repair and construction contractors to make more accurate bids, saving MnDOT money on projects.

Although dive inspectors are also beginning to invest in this new technology, MnDOT wants its own equipment to perform quick assessments of troublesome spots without going through the lengthy contracting process.

The Federal Highway Administration is conducting a pooled fund study to see if the technology eliminates the need for dive inspectors all-together.

MnDOT also plans to use its 3D scanning sonar to inspect repair projects and assess bridge construction.

One of DeWall’s first goals is to take a scan of the Hastings bridge after construction is complete, which will provide a baseline scan that can be compared against future inspections. The old bridge has had problems with the loss of rocks at its piers. It is unclear if the rock just sinks or is washed away downstream. Monitoring will let MnDOT see what is happening over time.

“Inspection is just one part of it,” DeWall said of the sonar equipment. “The big interest in this project is coming from our construction folks.”

Post-Construction

Imagine building a new house and not being able to complete the final walk-through.

This is the situation that transportation departments face when they build a new bridge, due to the limitations of underwater inspections.

“With 3D technology, you can go back afterward and check to make sure things were done the way they were supposed to,” DeWall said.

DeWall wishes the state had the scanner many years ago when a bridge was built that required expensive correction.

A bridge construction crew left construction material behind under the water, which wasn’t discovered until the redirected water flow caused significant erosion to the bridge pier.

Divers picked up that something was going on during a routine inspection, but engineers still had to bring in depth finders to get a better look. Due to the water current, they were limited in how close they could get to the bridge pier, and turbulence crashed their boat against the pier, damaging the transducer.

Not only would this 3D technology have provided a more thorough assessment than the depth finder, it also could have captured the imagery from a safe distance away.