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COVER PAGE Project Title Investigating Implementation Potentials of Turbo Roundabouts in Nevada Principal Investigator Matthew Vechione, Ph.D. Assistant Professor Department of Civil Engineering The University of Texas at Tyler 3900 University Blvd. Tyler, TX 75799 Telephone: (903) 565-5711 Email: [email protected] Additional Investigators Okan Gurbuz, Ph.D. Assistant Research Scientist Texas A&M Transportation Institute 4050 Rio Bravo Dr., Suite 212 El Paso, TX 79902 Telephone: (915) 521-8117 Email: [email protected] Ruey (Kelvin) Cheu, Ph.D., P.E. Professor Department of Civil Engineering The University of Texas at El Paso 500 W. University Ave. El Paso, TX 70068-0516 Telephone: (915) 747-5717 Email: [email protected] Business Contact Carla Reichard, Ph.D., CPRA Office of Research and Scholarship The University of Texas at Tyler 3900 University Blvd. Tyler, TX 75799 Telephone: (903) 565-5670 Email: [email protected] 1. TITLE Investigating Implementation Potentials of Turbo Roundabouts in Nevada 2. PRINCIPAL INVESTIGATOR Matthew Vechione, Ph.D., Assistant Professor, Department of Civil Engineering, The University of Texas at Tyler. 3. PROBLEM DESCRIPTION Modern roundabouts have been gaining popularity in the United States in the past decade due to the safety benefits as well as other positive impacts (such as reduction in delay) that they bring to the communities. The safety benefits are contributed by the geometric design of the entry approach and circulatory roadway, which reduce vehicle speed and shifting right-angle crashes to angle or sideswipe collisions. A new variant of the modern roundabout, known as the turbo roundabout, has potential to further reduce angle and sideswipe crashes. Turbo roundabouts are so far only in operation in Europe. No turbo roundabout has been constructed in the United States. Since the turbo roundabout is a recent innovation, the design guidelines are very limited. Additional research efforts are necessary to understand the safety benefits and operational implications prior to developing design recommendations, both of which consider the behavior of all type of users in the United States. State and local transportation agencies are in need of guidelines to determine intersections that are potential implementation sites so as to prioritize turbo roundabout implementation projects. 4. BACKGROUND SUMMARY Modern roundabouts began in the United Kingdom and spread to France and Norway in the 1970’s. In the United States, the first modern roundabout was constructed in Summerlin, Nevada in 1990; and since then, around 100 more roundabouts have been constructed in Nevada, and more than 8,400 nationwide (Kittelson, 2020). After the implementation of roundabouts in the United States, the number of fatalities and serious injuries resulting from intersection-related crashes have reduced significantly. Still, more than one-third of all crashes, fatalities, and serious injuries occurred at intersections. The Fatality Analysis Reporting System (NHTSA, 2020) reported a total of 104 fatalities that occurred at intersections in Nevada in 2019. Modern roundabouts are known to be safer than stop-control and signalized intersections. Single- lane modern roundabouts have limited capacity. Multilane modern roundabouts, which provide higher capacity, create issues such as higher speed, more conflict points compared to single-lane modern roundabouts, and allowing lane changing in the roundabout, which all contribute to the risk of crashes. Fortuijn (2009a) addressed those issues by limiting lane changing in the circulatory roadway and removing the need for entering vehicles to yield to traffic on the far side of the circulatory lane (i.e., the inner lane). Turbo roundabouts were first built in 2000 in the Netherlands. This was followed by their adoptions in Poland, Germany, and other European countries. There have been 603 turbo roundabouts in operation in Europe (DeBaan, 2020). There are different types and design features of turbo roundabouts: (i) basic; (ii) egg; (iii) knee; (iv) spiral; and (v) rotor (FHWA, 2020). They differ in capacity and number of approach lanes. A diagram of a basic turbo roundabout is 1 presented in Figure 1. Dabiri et al. (2020) studied the effect of geometric characteristics on operational performances of the turbo roundabouts and found that basic turbo roundabouts have smaller delay, higher capacity, and better level of service compared to rotor turbo roundabouts. Safety is the main benefit of the turbo roundabout. It is basically explained by the reduction of number and type of conflict points. In turbo roundabouts, the reduction of conflict points varies between 38% – 66%. Compared to a typical multilane (two-lane) roundabout, a turbo roundabout reduces the number of potential conflict points from 16 to 10 (Fortuijn, 2009a). The study reported that, when seven intersections in the Netherlands were converted into turbo roundabouts, the reduction in crash rate was 76.1%. In a more recent simulation study, Mauro et al. (2015) found that the number of total potential crashes was reduced by up to 50% and the number of accidents with injuries was Figure 1. Basic turbo roundabout. decreased by up to 30%. Other studies in Source: FHWA (2020). Europe (Macioszek, 2015), which all compared turbo roundabouts with other types of intersections found that turbo roundabouts are the safest option, which provided 30% to 60% reduction in crashes, 40% to 90% reduction in injuries, and 70% to 95% reduction in fatalities. Another factor that contributes to the safety benefits of turbo roundabouts is the lane dividers. The turbo roundabouts with raised lane dividers have fewer sideswipe crashes than the turbo roundabouts with regular pavement markings (Macioszek, 2015). The choices of circulatory lane dividers differ in different European countries. Macioszek (2015) showed that the drivers in turbo roundabouts in Poland without raised lane dividers continued illegal lane changes, while the turbo roundabouts with raised lane dividers were safer. Chodur and Bak (2016) conducted another study in Poland and showed that raised lane dividers reduced the number of crashes between 10% to 17% compared to the regular pavement markings. Besides the safety benefits, another advantage of the turbo roundabout is the ability to handle higher capacity and allow equal entry lane utilization. Drivers approaching a turbo roundabout are expected to decide on their lane choices before entering the roundabout and then keep to the same lane until they exit the turbo roundabout. Therefore, unlike the multilane modern roundabouts, which generally have an underutilized inner circulatory lane, turbo roundabouts promote equal utilization of the entry lanes at the same approach and the circulatory lanes (Homola and Chan, 2014). European studies revealed that the entry capacity of a turbo roundabout is 25% to 35% higher than a multilane modern roundabout (Fortuijn, 2009b). However, as stated by FHWA (2020), the roundabout capacity in Europe is likely to be higher than in the United States mainly because of the driver familiarity with roundabouts. Although some European researchers (Brilon et al., 2014) recommended turbo roundabouts only in suburban areas or in urbanized areas without cyclists and pedestrians, FHWA (2020) reserved 2 a subsection for all type of potential users of turbo roundabouts including motorists, pedestrians, cyclists, and motorcyclists. Generally, the footprint of a turbo roundabout covers a smaller area than a multilane modern roundabout of the same number of lanes because of nesting the spiral lanes to the inner side of the roundabout. This benefit is important especially in densely urbanized areas with limited space and right-of-way (Fortuijn, 2009a). Internationally, the entry radii of the turbo roundabouts vary between 39 to 50 ft, whereas the multilane modern roundabouts in the United States are designed with entry radii between 50 to 100 ft (Rodergerdts et al., 2010). Roundabouts should always be designed for the largest vehicle (i.e., the design vehicle). Since heavy vehicles occupy a greater area when executing their turning movements, the European design standards should be updated to accommodate the larger vehicle sizes in the United States (Rodegerdts et al, 2010). 5. PROPOSED RESEARCH The objective of this research is to investigate the implementation potentials of turbo roundabouts in Nevada through evaluations of applicable conditions, safety benefits, operational performances and costs. This project will be carried out over 12 months. The research team will: (1) Review the current usage of turbo roundabouts, particularly in the Netherlands; (2) Collect intersection data in Nevada; (3) Develop Turbo roundabout Implementation Metric (TIM), with feedback provided by NDOT engineers, in the form of a worksheet for identification and ranking of suitable intersections for turbo roundabout implementation; (4) Develop Turbo roundabout Implementation tool for NevadA (TINA), a user-friendly plug- and-play interactive software application that runs on Microsoft Excel for NDOT to implement TIM with ease; (5) Apply TINA to selected intersections of interest in Nevada; and (6) Develop multilingual, easy-to-understand outreach material for NDOT to use on educating the public and K-12 on turbo roundabouts. A more detailed description of each task, including deliverables, is described below: 1. Literature and Technology Review. [Months 1-2] In this task, the research team will review existing literature

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