Duhn, Melissa

In 2009, the FHWA’s Manual on Uniform Traffic Control Devices (MUTCD) introduced the flashing yellow arrow (FYA) traffic signal as an alternative to circular green (CG) to indicate permitted left turns. The FYA is arguably a more intuitive indication that left turns are permitted but not protected and, in addition, the FYA signal heads can support time-of-day changes between protective and permissive left -turn phasing. In 2019, a Research Needs Statement stated that “Research is needed to examine driver comprehension of flashing yellow arrows in different light arrangements and the role of signage.” Our objective in this project was to assess drivers’ understanding of FYA signal indications and to see if the presence or absence of “Left Turn Yield” signs affect gap acceptance. This was accomplished by conducting an online survey of drivers regarding their understanding of FYA signals and by carrying out a field study of drivers’ gap acceptance at a set of Twin Cities intersections.

Separated bicycle lanes (SBLs) are bicycle facilities that employ both paint and a vertical element as a buffer between vehicle traffic and bicycle traffic. In recent years, the installation of SBLs has increased in the U.S. as planners and engineers seek to reduce crash risk, increase safety and foster demand. In turn, public demand for these facilities has continued to grow. This project conducted a thorough literature search to identify knowledge gaps and aspects of design not addressed in depth in existing guides. In collaboration with the Local Road Research Board and MnDOT, the study identified which design elements were of the greatest local interest or missing from the guidance altogether. The identified subject areas were explored with the help of three major knowledge gathering approaches: interviews of industry professionals from local agencies currently operating SBLs, interviews with leading bicycle advocates representing the local cycling community, and an ambitious and lengthy online survey of people who cycle in Minnesota. As noted by several existing guidance documents and corroborated by the information collected and analyzed in this project, the SBL is one of the highest quality bikeway facilities available. This report adds to the existing guidance regarding the planning and operation of SBLs by refining the discussion and taking into account individual aspects of separate design elements and their implementation alternatives, as well as their influence and limitations on maintenance needs, especially in winter. The guidance identifies multiple considerations for each of the selected structural elements and maintenance considerations to inform the choices made during the design process.

Basic Safety Message (BSM) containing data about the vehicle's position, speed, and acceleration. Roadside receivers, RSUs, can capture BSM broadcasts and translate them into information about traffic conditions. If every vehicle is equipped with awareness, BSMs can be combined to calculate traffic flows, speeds, and densities. These three key parameters will be post-processed to obtain queue lengths and travel time estimates. The project team proposed a traffic state estimation algorithm using BSMs based on the Kalman filter technique. The algorithm's performance was tested with BSMs generated from several arterial in a microscopic simulation model and BSMs generated with radar data collected on freeway sections. Then the project team developed a traffic monitoring system to apply the algorithm to a large-scale network with different types of roads. In the system, computers could remotely access the online server to acquire BSMs and estimate traffic states in real-time.

The Minnesota Department of Transportation (MnDOT) has identified Native American as one of six priority populations in the state that face disproportionate risks as pedestrians. This report summarizes results from observations of pedestrian crossing behaviors on four Anishinaabe reservations in northern Minnesota. The University of Minnesota Traffic Observatory (MTO) video-taped and classified pedestrian crossings at 10 intersections identified by Tribal transportation managers as high priority because of perceived risks. Across the intersections; pedestrian crossing volumes during daylight hours ranged from 3 per day to 136 per day. The percent of pedestrian crossings that involved interactions with vehicles ranged from 9% to 54%. Tribal transportation managers from the Bois Forte; Fond du Lac; Grand Portage; and Mille Lacs Bands; MnDOT; county engineers; and the investigators collaborated to identify countermeasures to address risks to pedestrians. Proposed countermeasures varied by intersection and included vegetation removal and line-of-sight improvements; new lighting; crosswalk improvements; Rectangular Rapid Flashing Beacons with advanced warning signs; ADA-compliant ramps; pedestrian education programs; realignment of intersections; and at one intersection a Pedestrian Hybrid Beacon. Prospects for implementation of countermeasures vary by intersection and reservation and are contingent on Tribal and transportation agency budgets; state and county plans for roadway improvements; and categorical grant programs such as Minnesota's Transportation Alternatives Program. Some countermeasures are being implemented; and MnDOT is extending the approach to additional reservations.

Stop lines are ubiquitous; but do they really impact intersection safety? Prior to this project; no long-term studies on intersection safety with stop lines had been completed. This project was developed with two parallel research efforts: a safety study and an observational study. The safety study was developed to address stop lines' effects over the long term and used crash data from five cities' stop-controlled intersections to perform regression and see if stop lines actually influenced safety. The observational study was developed to determine if stop lines have an effect on driver behavior at intersections and to look at where drivers were stopping. Video was collected at 16 different intersections before and after a stop line was painted. The safety study and observational study showed that stop lines did not have a significant impact on driver behavior or intersection safety; but other factors like speed limits and sight distance did. Implications for practice include carefully examining sight distance at the intended stopping point to ensure drivers have adequate sight distance in both directions. If sight distance is not adequate; moving the intended stop location or reconsidering whether the intersection should have signage -- stop or yield -- or be uncontrolled could yield better driver compliance and safety.

Connected and Automated Vehicles (CAVs) are expected to affect the foundations of transportation operations and roadway maintenance as they become more prevalent on the roadways. This report is an effort to address this complex subject for the various owners; agencies and stakeholders involved in traffic operations. It discusses the connected vehicle ecosystem and its background; potential CAV applications; types of communication and hardware required for CAV systems; and recommendations to local road owners. The report also includes a survey sent to local road owners to assess the current readiness of the transportation system for CAVs. Although it is too early to give specific recommendations; general guidance is provided for road owners to begin preparing for the future of CAVs.

Engineers need information about interactions between vehicles and bicyclists to design efficient; safe transportation systems. This study involved a review of design guidelines for bicycle facilities; observation of bicycle-vehicle interactions at nine roadways with different types of bicycle facilities; analysis of results; and description of design implications. Facilities observed included buffered and striped bicycle lanes; sharrows; signed shared lanes; and shoulders of various widths. Driver behaviors were categorized as no change in trajectory; deviation within lane; encroachment into adjacent lane; completion of a passing maneuver; and queuing behind cyclists. Drivers on roadways with bicycle lanes were less likely to encroach into adjacent lanes; pass; or queue when interacting with cyclists than drivers on roadways with sharrows; signs designating shared lanes; or no bicycle facilities. Queueing behind cyclists; the most significant impact on vehicular traffic flows; generally was highest on roads with no facilities or shared facilities without marked lanes. Statistical modeling confirmed the descriptive results. Given an objective of increasing predictability of driver behavior; buffered or striped bicycle lanes offer advantages over other facilities. Sharrows may alert drivers to the presence of cyclists; but traffic impacts on roadways with sharrows may not differ significantly from roadways with no facilities. Signs indicating bicyclists may occupy lanes also may alert drivers to the presence of cyclists; but this study provided no evidence that interactions on roadways marked only with signs differ from roadways with no facilities. From the perspective of reducing potential traffic impacts; bicycle lanes are to be preferred over sharrows or signage.