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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.

At-grade trail crossings have frequently been the sites of bicycle, pedestrian, and snowmobile crashes in Minnesota and throughout the nation. To date, many resources exist for use in the design of trails and intersections, such as the MnDOT Bikeway Facility Design Manual, while guidelines of traffic control at roadway-trail crossings are covered in the MN MUTCD. Resources on comprehensive guidance for safety treatments at roadway-trail crossings, however, are limited. The goal of this document is to synthesize best practices observed statewide in Minnesota and nationally in order to provide engineers and other transportation professionals with guidance on safety treatment applications at trail crossings. Following discussion of principles of user-friendly trail-crossing designs, this document provides a toolbox of categorized treatments which are widely used in the U.S. with discussion on each treatment. Importantly, a decision tree-based treatment selection methodology is developed for fast look-up and selection of appropriate treatments based on the conditions at a particular trail crossing. These conditions include urban/rural setting of the crossing, number of lanes of the crossed roadway, whether the crossed roadway is divided or undivided, the speed limit and average daily traffic (ADT) of the crossed roadway, and whether the crossing is a midblock or parallel path crossing. Each end node of the decision tree leads to a specific toolbox in table form containing all appropriate treatments for the conditions of the study trail crossing. Final treatments for the study site can be simply chosen from the table, combined with site-specific requirements and engineering judgment.

The degree of modal split in the United States has continued to change with increased use of non-motorized modes. To accommodate a variety of users, context-sensitive solutions are being pursued. Such solutions call for the sharing of right-of-way by multiple user groups with different and often competing demands. Traditionally, the needs of vehicular traffic have been prioritized as evident in many current design standards. This research focuses on developing guidance for design decisions to best balance the competing needs and accommodate all expected roadway users. Non-standard design solutions, often associated with complete streets, were investigated in two major contexts. The first involved a comprehensive review of the current-state-of-the-practice in design standards, complete streets, and associated legislation in Minnesota and nationally. Second, a detailed analysis of 11 'complete street' study sites was conducted. The study primarily focused on evaluating changes in safety and operations between the periods before and after implementation. Differences in the characteristics of the study sites and varying degrees of changes and improvements conducted at each site prevented an aggregate quantification of the implications of complete street improvements across all sites, and specific recommendations for changes in design standards. Nevertheless, the analysis of complete street designs implemented at the 11 study sites suggest that changes made to these study sites did not result in adverse safety or operational impacts. Therefore, providing flexibility and modification to the State Aid Design Standards in the context of complete streets and conditions specified in this research appears to be a reasonable consideration.

Past research has clearly shown that obstructed sight lines at intersections lead to greater possibilities of collisions between left-turning vehicles and opposing oncoming vehicles. Evaluations of the effects of left-turn lane offsets; reported that positive left-turn lane offsets were more effective in reducing intersection left-turn crashes than zero and negative left-turn offsets. Several researchers have developed guidelines for geometric design elements of left-turn offset. The majority of states provide only a limited discussion on this topic. Florida DOT provides the most comprehensive policies and guidance for assuring unobstructed sight lines at left-turn lanes. Recommendations developed in this project center on general policies and guidance for designing offset left-turn lanes for a new edition of MnDOT's Road Design Manual. Recommendations are organized to provide standards; policies; and guidance for new/reconstruction projects and for preservation projects. Topics covered include definition of left-turn lane offset; design factors impacting offset; suggested designs for urban and rural multilane roadways and expressways; accommodating U-turns; pedestrian and bicyclist considerations as well as winter maintenance considerations. Additional recommendations are offered to improve consistency among all MnDOT manuals and guides used for intersection design and operation.