Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
21 Conclusions and Suggested Research 4.1. CONCLUSIONS The Guide developed by the research team exhibits contemporary roundabout planning and design guidance. Roundabout implementation in the United States has increased in the last decade, and practitioners have learned lessons in successfully applying roundabouts in various land use and transportation environments and contexts. The Guide expands performance-based decision making to better account for vulnerable users and adapt roundabouts to all contextual environments. Integrating research findings from state and national guidance, and other sources, the Guide benefits from broad transportation planning and design guidance outside the roundabout practice area. This includes concepts such as project type (new versus reconstruction) and context classification that expands design flexibility beyond focusing on functional classification. Performance-based roundabout planning and design is adaptable to developing and future concepts and themes. This includes integrating equity, equality, and public health considerations in addition to Vision Zero and Toward Zero Deaths programs. A Safe System approach to transportation planning and design is in its infancy in the United States. 4.2. SUGGESTED RESEARCH The research team identified areas of further research that would provide additional benefit to this topic area. The following list provides a summary of suggested future research related to roundabout planning, design, maintenance, and operations. The order in which the topics are presented does not represent a priority or emphasis. ⢠Bicycle and pedestrian design and integration: The Guide provides guidance for bicyclists and pedestrians. There is emerging exploration and investigation of pedestrian guide strips and other means of supporting bicyclists and pedestrians in general. As this topic is investigated and implemented at roundabouts future research could explore the state of the practice and performance findings. ⢠Safety Performance: NCHRP Report 888 Development of Roundabout Crash Prediction Models and Methods presented a needed advancement of expanding beyond crash modification factors to develop crash prediction models (Ferguson et al. 2018). The safety performance information presented could potentially be updated in time to reflect the continued implementation of various roundabout forms presented in the Guide. This could include but not be limited to addressing: o Further development and calibration of safety performance functions and crash modification factors that relate design decisions to safety performance.
22 o Mini and compact roundabouts (reduced footprint roundabouts) to be included in crash prediction models. Given the emergence of reduced footprint roundabouts as retrofit solutions, future research could develop crash prediction methodologies for these mini and compact roundabout forms. o Multilane roundabout design and operations. Multilane roundabouts continue to reveal nuances in operations and safety performance. The Guide includes concepts for integrating turbo-roundabout features. Future research could explore multilane roundabouts, including design factors associated with certain crash types. There is also interest in additional research related to safety performance of multilane versus single lane roundabouts. In the future if there are sufficient sites with appropriate data to assess before and after, research could be conducted to correlate safety performance to project phasing. o Any findings related to safety performance of roundabouts for people biking or walking, as roundabouts continue to proliferate and pedestrian and bicyclist exposure at roundabouts may be quantifiable. ⢠Operational Performance: Operational models could be developed to include other configurations that practitioners desire to evaluate. This could include but not be limited to addressing: o Capacity and operational performance models for mini-roundabouts and compact roundabouts. o Capacity and operational performance models for multilane roundabout design and operations for configurations that have more than two lanes or that have short or flared lanes on one or more approaches. o Capacity attributes of multilane design with turbo features. This could differentiate between European style and conventional roundabouts that include features. o Capacity and operational performance models that are sensitive to truck operation, including distinctions between straddling lanes and staying in lane for multilane roundabouts. o Capacity and operational performance models that fully integrate bicycle and pedestrian performance under the full range of bicycle and pedestrian facility configurations presented in the Guide. This includes models that examine the effects that bicycle and pedestrian crossing treatments and configurations have on each affected mode (nonmotorized and motorized). o Further integration of connected and automated vehicles as technologies continue to develop. ⢠Pedestrian Accessibility: This could include:
23 o Integration of accessibility features into performance models as described previously for operational performance. o Further testing of configurations for tactile surface indicators to assist people who are blind or have low vision with wayfinding in complex intersection environments. These include further testing of applications of tactile directional indicators and tactile warning delineators. ⢠Truck and/or Oversized/Overweight (OSOW) vehicles: Designing for large trucks may continue to be a foundational roundabout consideration. The research for the Guide determined there is not a clear understanding by drivers of their expected operations at roundabouts. Future research might investigate: o A synthesis of truck driver training by commercial training companies or large fleet operations to understand how to support driver comprehension and expectations at roundabouts. o The effects of the various ways drivers of large trucks navigate roundabouts and considerations of the range of and priority of operational and safety performance effects. o The considerations and tradeoffs of various design treatments implemented to serve OSOW vehicles. ⢠Improve existing roundabouts: As more retrofits occur and the more opportunities there are to investigate retrofitted roundabouts, documenting the effectiveness of the retrofits could help support and prioritize recommendations for future guidance. In particular, this could tie with other research topics noted as follow ups to safety and operations performance investigations for enhancing existing two-lane roundabouts building upon findings from the ongoing pooled fund study that is noting considers of how the roadway network and system affects driver behavior. ⢠Traffic control devices. Potential research topics include: o Metering and other explorations that maximize the longevity of single lane roundabouts given the documented safety performance benefits of single lane configurations over their multilane counterparts. o Pedestrian crossing treatment guidance. Future research could document the effectiveness of the guidance provided for people with vision disabilities and other pedestrians. o Traffic control devices and considerations for roundabouts near railroad crossings. The assessments could be applied broadly to consider stop controlled intersections in addition to roundabouts. This would be consistent with intersection control evaluations that investigate stop, yield, and signal control strategies.
24 o Investigating signing and pavement marking for 450-degree right turn or other means of drivers making a right turn by going around the roundabout. This would focus on how to best convey this as possible design options to serve right turning trucks versus making a right turn path extra-large. ⢠Effectiveness of designing for people biking: The Guide provides new direction to support people biking. The guidance is principles-based and upon principles related to designing roundabouts for people biking, specifically people âinterested but concernedâ in biking. Future research could document the effectiveness of the guidance that is based upon these principles: ⢠Economic Impacts of Roundabouts: Intersection lifecycle computations include a variety of costs. Future research findings could potentially lead to documenting economic considerations that could possibly be included in intersection life cycle evaluations as part of intersection control evaluations (ICE). ⢠Illumination: Future research could assess locations with lighting configurations.
