September 4, 2019
Roundabouts continue to be constructed at a rapid pace in the United States. We have well over 5,000 roundabouts nationwide, and that number is quickly climbing. Click “play” to watch how roundabouts expanded across the U.S. from 2009 to 2018!
There’s no better time to talk about roundabouts than National Roundabouts Week. In honor of this national celebration of traveling in circles, we’ve compiled some of the latest research and tools for evaluating roundabouts.
The latest guidance includes new capacity predictions that account for a broad spectrum of observations across the United States, information about safe crossings for blind pedestrians, and crash prediction models that quantify the expected safety performance of roundabouts. We also look ahead to the next edition of the national Roundabouts: An Informational Guide.
NCHRP Report 888
Summary: Research indicates that roundabouts can provide substantial reductions in crashes, especially of the more severe kind. NCHRP Report 888, “Development of Roundabout Crash Prediction Models and Methods,” provides crash prediction models that quantify the expected safety performance of roundabouts.
How It Can Be Used: The models may help identify and prioritize locations for safety improvements, estimate safety benefits of a proposed project, compare project alternatives, and guide detailed design decisions to optimize safety.
NCHRP Report 834
Summary: Blind pedestrians can face significant impediments when accessing and crossing intersections. NCHRP Report 834, “Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook,” recognizes these challenges at roundabouts and at channelized turn lanes at signalized intersections.
How It Can Be Used: The guidebook is written to provide practitioners with useful information about establishing safe crossings at roundabouts and channelized turn lanes for pedestrians with vision disabilities and assessing their performance within a performance-based design process.
Highway Capacity Manual, 6th Edition
Summary: Since the publication of the Highway Capacity Manual (HCM) 2010 edition, more than $4 million of funded research had been completed on a variety of topics touching every part of the HCM. Roundabouts were no exception. Kittelson led the project team that produced the HCM 6th Edition, as well as the supporting research on roundabout capacities for FHWA.
How It Can Be Used: An operational analysis estimating the capacity of a facility can be used to evaluate the performance of an existing roundabout during a base or future year, or to evaluate new roundabout designs.
On the Horizon: NCHRP Project 03-130
Summary: Since its publication in 2010, the second edition of Roundabouts: An Informational Guide has been a source of national information and guidance for the planning and design of roundabouts. In that time, roundabout implementation in the United States has accelerated, and roundabouts have evolved. The body of roundabout-related research has also grown. Led by Kittelson’s Brian Ray, NCHRP Project 03-130 will produce a new Roundabout Guide that will provide relevant updates based on changes in practice and based on original research conducted by the project team.
How It Can Be Used: As with previous editions of the guide, it will provide principles-based guidance that can underpin local practice rather than being a prescriptive document.
The NW La Center/I-5 interchange in the state of Washington features multiple roundabouts in a design that supports long-term traffic demands and pedestrian/bicycle activities.
Kittelson staff have participated in the development of each of these resources, and we continue to play an active role in each one. We’d be happy to discuss any of this guidance further, so don’t hesitate to reach out to start a conversation!
Did you know that Kittelson is the keeper of one of the most comprehensive inventories of our nation’s roundabouts? Click on the map to see the database maintained by a team led by Lee Rodegerdts, and pinpoint the roundabout closest to where you live!
