Transportation Research Update
 MULTIMODAL - The City of Richfield’s new Complete Streets program, known as “Sweet Streets,” has improved quality of life and enthusiasm for bicycling and nondriving transportation since 2013, although researchers found that construction impacts still shadow local perceptions.
New facilities that offer better lighting of pedestrians, improved crosswalks, new bike lanes and bus pullouts leave business owners and citizens confident that safety will be improved. New concerns over potential conflicts between bicyclists and parked cars, as well as roundabout visibility and pedestrian safety have arisen, particularly with residents who have families.
Safety studies of roundabouts in Richfield show increased pedestrian safety. Traffic times across the city appear to have been reduced, since roundabouts significantly reduced delays when compared to earlier traffic signals. Health and economic data proved somewhat elusive, and the impact of the program on home values and public health remains uncertain.
 ENVIRONMENTAL - From 2012 through 2018, researchers monitored an iron-enhanced sand filter (IESF) basin installed near Trunk Highway 610 and County Road 81 to determine how well the IESF was removing phosphorus from roadway stormwater runoff. Researchers examined the first three years of data and then continued monitoring from 2016 to 2018 after installing more measuring devices and developing a computer hydrology model to account for the filter’s inflow and outflow. They determined that if IESFs are to be monitored, then certain features need to be incorporated into the design of the pretreatment wet cell, berm and filtration basin. Methods of monitoring IESFs also need to be a part of the system’s initial design, with close attention paid to limiting uncontrolled aspects of the site. Researchers recommended many future IESF designs and protocols for monitoring to avoid erroneous information.
 BRIDGES - Opened to traffic in 2008, the new Interstate 35W St. Anthony Falls Bridge, a smart bridge with over 500 gauges and sensors embedded in the structure, continues to collect useful information. A 10-year check-in found that 90% of the successfully installed instruments still gather and report data.
Key systems track temperatures in the structure, displacements from the natural creep and shrinkage of concrete, and strains in bridge elements. The original corrosion detection system has not, at any point, produced usable information. Data shows that the bridge manages significant thermal strains caused by temperature variations in the environment, such as sunlight heating or rainfall cooling the top of a deck but not the underside, forcing uneven expansion or contraction in the concrete. Conservative design choices protect the structure from these stresses.
In future smart bridges, designers may adjust instrumentation plans based on these findings, electrically grounding systems for stormproof performance, providing a wider distribution of temperature gauges and possibly using wire-based strain gauges rather than fiber optic sensors. Researchers recommended design standards and modeling options for Minnesota locations based on data trends observed with the St. Anthony Falls Bridge.
 MATERIALS - Permeable pavement proves helpful when snow and ice are thawing, but insulate so well that snow and ice are slower to melt than on standard pavements treated with salt until temperatures rise and stay at or above freezing. Researchers used photography, friction testing and temperature gauges to evaluate the performance of permeable pavements untreated by road salt and impermeable pavements treated with road salt at shared locations throughout Minnesota.
At freezing and below temperatures, permeable pavements seem to retain snow and ice on the surface longer than regular paving treated with road salt, and friction testing during winter showed mixed performance for permeable pavement in terms of driving safety. Used in residential and parking applications by a number of Minnesota road agencies, permeable pavement moves water well in nonfreezing weather and improves the impact of runoff and water quality. It also works well during periods of thaw, when regular pavement experiences pooling and refreezing that makes driving treacherous. For residential streets and parking lots, permeable pavement can function to capture (infiltrate) meltwater before it refreezes and eliminate the most dangerous conditions on these surfaces.
 SAFETY - A longitudinal study funded by the Local Road Research Board found some long-term benefit for participants in an innovative MnDOT project conducted in 2015 that tracked and warned teen drivers of risky behavior using dash-mounted smartphones. The original study compared a control group of users who received no alerts on their phones to a second group of users who received text and audio alerts for speeding, aggressive turning and other risky behaviors, and a third group of teens who received warnings and notifications that their parents had been informed. Drivers in the two warned groups took fewer driving risks in their first year of driving.
Five years later, researchers recruited 150 of the original participants and analyzed their driving records and responses to a survey that mirrored much of the survey from the original study. Drivers from the original study who had a lower incidence of risk-taking while driving had fewer driving citations later. Safety impacts were less clear. A new system based on the original Teen Driver Support System has been applied with success to a small group of senior drivers.
 Researchers analyzed Minnesota public fleet vehicle performance data to help local agencies determine the benefits of using hybrid and conventionally powered vehicles.
For urban stop-and-go uses, hybrid powertrains offered significant benefit, with 20% to 25% improvement in fuel consumption. However, for rural and highway routes, hybrids provided only modest benefit—about a 5% improvement in fuel consumption.
Overall, plug-in hybrids offer the greatest fuel economy benefits. Hybrid use in winter produced improved cold weather fuel economy, possibly due to lower driving speeds and regenerative braking technologies.
 Stop lines are relatively inexpensive, and citizens frequently request them at intersections with frequent stopping violations. However, local agencies may have hundreds of such intersections, and at approximately $1,000 for annual maintenance, stop line upkeep can become a sizable expense.
The LRRB investigated whether stop lines provide a quantifiable safety benefit. Two comprehensive studies concluded that installing stop lines doesn’t directly correlate to improved traffic safety. The study concluded that traffic engineers may want to reconsider where to invest the dollars they currently spend on stop lines and their maintenance.
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