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Improving the safety of transportation networks is a key area of research at the Minnesota Traffic Observatory. The MTO’s ability to gather fine-grained data on traffic dynamics has driven significant research into the causes of vehicle crashes and potential countermeasures. In addition to studying crashes and dangerous traffic conditions, the MTO provides support to researchers seeking to understand how the design and construction of road networks affects safety and mobility.
Through efforts to expand the lab’s flexible traffic monitoring solutions, MTO staff developed TIMs. TIMs are versatile and portable traffic monitoring systems that provide high-quality video to meet a multitude of traffic engineering needs.
Recent projects utilizing TIMs in conjunction with traffic safety are outlined below.
Consistently ranked as one of the most bicycle friendly cities in the country, the City of Minneapolis has been experimenting with alternative bicycle infrastructure in an effort to attract more cyclists and improve cyclists’ safety and experience. The MTO collected video footage of campus cyclists on one of the most heavily used on-street bicycling facilities in the state using the TIM system. The lab also performed before-and-after studies to evaluate the effects of several new bicycle infrastructures, including the country’s first advisory bike lane, bicycle traffic signals, and colored green bicycle lanes, crosswalks, and conflict zones.
To test hypotheses concerning driver response at LED stop signs, TIM units were set up at a rural location before and after the installation of an LED stop sign. Driver trajectories were extracted from the video and used to compare stop positions, speeds, time and place of deceleration, and magnitude of deceleration for drivers approaching intersections with and without the altered traffic control device. In conjunction with a statistical model relating crash frequency to traffic volume, this study developed a base-case statistical model that estimates the crash reduction effects of LED stop signs.
To examine the gap-selection behavior of drivers at green-ball permitted left turns against those with the flashing yellow arrow indicators, TIM units were deployed to two locations selected for their relatively high speed limits (40-45 mph). The higher speed limits coincide with more difficult driver judgment and increased risk. Trajectories of vehicles using the flashing yellow arrow treatments were extracted from the video and are being analyzed to assess the safety effects of this new traffic control device.
Trailers containing custom recording systems based on the same devices used within the other TIM observation stations have been deployed for several studies, notably two relevant to roundabouts. The most recent iteration of these recording systems utilizes a 360 degree high-resolution camera which captured the entire roundabout in one continuous image.
With benefits such as improved safety, minimized delays, and reduced vehicle emissions, roundabouts have become an increasingly popular design solution for intersections throughout the United States. Despite this increase, drivers throughout the country continue to misunderstand the rules of the roundabout, resulting in improper use and avoidable collisions. National design guidelines pertaining to roundabout signing and striping are in their infancy, but could be the key to improving driver understanding of proper roundabout use. To assess the effectiveness of two different designs, the MTO deployed a custom recording system based on the same system used within other TIM stations prior to and following the implementation of changes to the signing and striping of a subject roundabout in Richfield, Minnesota. The associated before-and-after study utilized the collected video to extract and compare the frequency of instances of vehicular violations including improper turns, yielding failures, traffic impedances, as well as traffic volumes.
Pedestrian and Bicyclist Safety at Roundabout Crossings
Addressing the lack of existing research pertaining to pedestrian safety at roundabouts, a study was developed to investigate pedestrian and bicyclist accessibility using two subject urban roundabouts located in Minneapolis. Using the video collected from the MTO’s custom recording system, thousands of pedestrian and cyclist crossings were extracted and cross-referenced with the conditions experienced by drivers within the roundabout. A regression analysis was performed for both sites, producing resulting regarding driver yielding rates and pedestrian and cyclist delay and safety.