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Recently, speed management practices have shifted away from an historical focus on the 85th percentile speed toward a safe systems approach that is focused on promoting safer speeds in all roadway environments through a combination of thoughtful, equitable, context-appropriate roadway design, appropriate speed-limit setting, targeted education, outreach campaigns, and enforcement. This includes the incorporation of a Complete Streets approach to roadway design, which uses cross-sectional characteristics that reduce speeds and create a more accommodating environment for people biking and walking. This study aims to inform this design process by advancing our understanding of how drivers adjust their speeds based on changes in the posted speed limit and other contextual factors related to the roadway environment. Field data were collected from 19 highway corridors across Minnesota using handheld lidar guns to track drivers' operating speeds as they transitioned from high-speed rural highways to lower-speed rural and suburban communities. The study results in the estimation of a series of speed reduction factors (SRF), which detail the impacts of various site-specific characteristics on travel speeds. Various features are shown to serve as effective speed-control measures, such as single-lane roundabouts, which reduced speeds by about 7 mph. Speeds were also lower on segments that included two-way, left-turn lanes (0.7mph), depressed medians (1.2 mph), and raised medians (3.1 mph). The results also show that drivers typically begin reducing their speeds approximately 800 ft upstream of posted speed limit signs and continue to reduce their speeds to a distance 400 ft beyond the sign location. Ultimately, this study will allow for a more proactive and data-driven approach to highway design that considers the needs of all users.

The purpose of this research was to evaluate the safety and operational characteristics of two-way left-turn lanes (TWLTLs) compared to four-lane undivided roadways in Minnesota. Research tasks to achieve this purpose consisted of a comprehensive literature review, data collection from the identified study sites, and statistical data analysis. Nine study sites were selected, located throughout the state of Minnesota. Operational and crash data were analyzed before and after the conversion from a four-lane undivided roadway to a three-lane roadway with a TWLTL. The results of a yoked/group comparison analysis showed statistically significant reductions in total crashes, PDO crashes and left turn crashes. The percentage reductions in total crashes, PDO crashes and left turn crashes after the conversion were approximately 37 percent, 46 percent and 24 percent, respectively. The reductions in crash rates for total crashes and PDO crashes were found statistically significant and the percentage reductions were 46 percent and 45 percent, respectively. Additionally, the change in the mean speed and 85th percentile speed were found statistically significant, but in both cases the change was less than two miles per hour. The results of this research show that safety characteristics of a roadway are improved when a four-lane undivided roadway is converted to a three-lane roadway with a TWLTL when daily traffic volumes are less than 17,500 vehicles per day.

Bridge-approach guardrail provides protection for vehicles from collision with bridge components, such as the blunt end of the bridge rail or abutment, and other types of run-off-the-road collisions. The primary objective of this research was to determine the average daily traffic (ADT) at which the benefit/cost ratio for the installation of approach guardrail at county-state-aid (CSAH) bridges in Minnesota becomes greater than 1.0. A survey of state transportation agencies found that 26 of 35 responding agencies have policies or guidelines requiring placement of approach guardrail on any bridge if the bridge was built using state funds. Results of the research analyses showed that bridge-approach guardrail was effective at reducing the severity of run-off-the-road crashes occurring on the approach or departure to CSAH bridges. Fatalities and A-injury crashes accounted for only 6 percent of the crashes occurring at bridges with approach guardrail compared to 28.5 percent at bridges without approach guardrail. The subsequent benefit/cost analysis showed that bridge-approach guardrail is cost-effective (i.e., B/C > 1) for CSAH bridges with ADT greater than or equal to 300 vehicles per day (vpd). Overall, approach guardrail has a benefit/cost ratio of approximately 3.5 to 5.5. The researchers recommended that the ADT threshold for approach guardrail on CSAH bridges be set at 400 vpd, which is consistent with previous Mn/DOT standards and AASHTO low-volume local road guidelines. Approach guardrail should be considered on a case-by-case basis for bridges with ADT between 150 and 400 vpd, especially those between 300 and 400 vpd. Placement of approach guardrail at bridges with ADT less than 150 vpd is not cost-effective in most cases.

This research sought to identify best practices for channelized right-turn lanes (CRT) that better accommodate the safety and accessibility needs of all road users. This was accomplished through a comprehensive literature review, a state-of-the-practice survey of state and local roadway agencies (nationwide and within Minnesota), a review of agency policy and guidance materials (nationwide and MnDOT), and a series of focus group meetings focused on vulnerable road users. Feedback received both from the survey of transportation agencies and the focus group sessions performed as a part of this research suggest that roadway agencies throughout the United States are moving toward proactive policies for the use of CRTs that emphasize safety and mobility for vulnerable road users. This movement is generally based on the concerns for the safety of vulnerable road users outlined in the prior section and commonly includes 1.) minimizing the use of CRTs at urban and suburban intersections and/or 2.) designing new CRT facilities or retrofitting existing facilities with mitigation strategies to improve the safety and accessibility for vulnerable road users. This information was synthesized along with the best practices found in the research literature and agency policy/guidance materials to develop implementation guidance, which is organized within the report as follows: 1.) guidance for use of CRTs based on the project scenario; 2.) traffic control recommendations for CRTs; 3.) recommended design features for CRTs; and 4.) recommended mitigation strategies intended to improve CRT safety and/or accessibility for vulnerable road users.