2 research outputs found
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A Safety and Emissions Analysis of Continuous Flow Intersections
Increasing travel demand, and challenges associated with high percentages of left-turning vehicles, have encouraged the introduction of significant infrastructure advancements. Certain alternative intersection designs, such as continuous flow intersections, median U-turns, and jughandles, eliminate the traditional protected left-turn, increasing the intersection\u27s optional efficiency. While the design and operations of these intersection types have been studied to varying degrees, their safety and emissions-related impacts are not well-understood.
This project develops a series of microsimulation models for two continuous flow intersections (CFI) located in Missouri and Colorado, and uses the Surrogate Safety Assessment Model (SSAM) to determine the impact of those designs on the location and type of conflicts compared to conventional signalized intersections. Additionally, an emissions model, CMEM, was used in the analysis of the Colorado study site to determine whether CFIs have the potential to reduce emissions compared to conventional signalized intersections.
As hypothesized, the number of total conflicts did decrease upon installation of a CFI for both study sites, despite lane-change conflicts experiencing an insignificant increase at the Loveland, CO study site. While too small of a sample size to provide a definite validation of SSAM, these results show SSAM can accurately predict the types of conflicts likely to occur as well as indicate a reduction in total vehicle conflicts when a conventional signalized intersection is converted into a CFI.
Emission rates per mile at the CFI were lower than those at a conventional signalized intersection, most likely due to fewer total stops and lower delay times for users. The CMEM analysis was repeated for four other volume scenarios, varying left-turn demand. Under all scenarios, the CFI performed better than the conventional signalized intersection. This improvement increased as volume increased, showing that the environmental performance of a CFI is less sensitive to demand than a conventional signalized intersection.
This project set forth to quantify sustainability benefits to the installation of a CFI for practitioners. Ultimately, this research can aid transportation decision-makers by providing quantitative evidence that CFIs can improve the safety impacts for vehicle users and environmental impacts for the general population in both rural and urban applications
Microscopic Simulation and Safety Analysis of Roundabouts
Although circular junctions are usually associated with the British, their presence in the United States dates back to at least 1905. Those early twentieth century circular junctions, called traffic circles, were designed for high-speed entries into the circular area and gave priority to the entering vehicles over the circulating vehicles. The resulting high crash frequency and choked traffic circles associated with these intersections stopped the spread of circular junctions in the United States. In the 1960s, the United Kingdom introduced the mandatory yield-at-entry rule at circular junctions, which led to the birth of the modern roundabout. Safety is the hallmark of modern roundabouts, as they reduce both the frequency and severity of crashes. The first modern roundabout in the United States was built in Nevada in 1990 and their number is steadily rising since then: 38 in 1997, more than 2,000 in 2010, and over 3,500 at present. Initial resistance by the public usually changes to a favorable response upon the completion of roundabouts. As a result, hundreds of roundabouts are expected to be built each year in the United States. This study presents a microscopic simulation modeling and safety analysis of modern roundabouts. Various microscopic simulation modeling tools were explored for traffic analysis of roundabout operation. For safety analysis, researchers looked at simulation-based surrogate safety analysis model (SSAM) as well as guidelines in the Highway Safety Manual. The proposed roundabout at Laporte-Silhavy and 5-points roundabout in Valparaiso will be studied as field cases and modeled using microscopic traffic simulation