|Roundabout signs and markings from the 2013 FDOT Intersection Design Guide.|
The Florida Department of Transportation released its 2013 Intersection Design Guide on March 1, adding a new chapter on roundabouts. The opening paragraphs are striking:
Due to substantial safety, operational, and capacity characteristics, roundabouts are an equivalent or better intersection configuration for any new roadway or reconstruction project. Roundabouts shall be evaluated on new construction, reconstruction and safety improvement projects, as well as anytime there are proposed changes in intersection control that will be more restrictive than the existing conditions.
An initial screening shall be conducted at the Preliminary Engineering (PD&E) stage of every project to determine which of the intersections within the project limits will be constructed as roundabouts. The initial screening for applicability of roundabouts is based on traffic volumes. Roundabouts shall be considered the preferred option at intersections where the total projected (design year) entering traffic volumes are up to 25,000 vehicles per day (vpd) for a single-lane, and up to 45,000 vpd for a two lane roundabout.
FDOT is specifying that it does not intend high speed traffic circles:
"On State roads or at intersections with State roads, only modern roundabouts as defined in NCHRP 672 will be allowed."
The recommended design speed is slightly more than I would want, but a huge improvement over the 45 mph default speed on the State Highway System:
Roundabouts should be designed for operating speeds between 20 and 25 mph. The approaches to the roundabout must be carefully designed to provide enough deflection to cause motorists to reduce speeds prior to entry. .... At a minimum, roundabouts should accommodate school buses, moving vans, garbage trucks, fire trucks, and other emergency vehicles.
FDOT now prefers roundabouts because:
Roundabouts by nature encourage lower speeds on the approach to, and within the circulatory roadway, thereby enhancing safety characteristics. The numbers of vehicles that are required to come to a complete stop at a roundabout are significantly less than at a conventional intersection, thereby reducing delay.
FDOT notes that "Roundabouts may be especially useful as a practical solution to skewed intersections." Roundabouts should be considered where a history exists of "fatal and injury crashes" as well as a "pedestrian or bicycle crashes." Roundabouts should also be considered when signalization becomes warranted and as a "context sensitive solution."
The new Intersection Control Guide gives new prominence to protecting pedestrians. In the Roundabout chapter:
Pedestrian features (where applicable) shall be plainly obvious through the use of crosswalks and supplementary signs, and shall include splitter islands sufficiently sized to harbor anticipated pedestrian group sizes (6’ minimum at the crosswalk). Night time illumination is mandatory to increase the visibility of the roundabout and improve sight distance during dark hours.
The treatment for bicyclists is interesting, too, in acknowledging the safety of "taking the lane" as advocated by vehicular cyclists: "At the end of the bicycle lane, the cyclist may either “command the lane” and pass through the circulatory roadway, or divert onto the sidewalk and cross at pedestrian crossings. No bicycle lane markings shall be placed within the circulatory roadway."
The new Roundabout chapter is a welcome addition to the Intersection Design Guide. The chapter is timely given that the Federal Highway Administration recently approved two roundabouts on U.S. 41 in the City of Sarasota. Link HERE to a conceptual drawing. Over the coming decade, we should see roundabouts spread throughout Florida and a much safer transportation network.
ADDITIONAL COMMENT (May 8, 2013)--Here's the language set forth in the Design Guide establishing the steps for priority status for roundabouts:
An initial screening shall be conducted at the Preliminary Engineering (PD&E) stage of every project to determine which of the intersections within the project limits will be constructed as roundabouts. The initial screening for applicability of roundabouts is based on traffic volumes. Roundabouts shall be considered the preferred option at intersections where the total projected (design year) entering traffic volumes are up to 25,000 vehicles per day (vpd) for a single lane, and up to 45,000 vpd for a two-lane roundabout. Minor street volumes should not be less than 1,500 vpd nor more than 12,000 vpd for a single-lane, and between 1,500 and 27,000 vpd for a two lane roundabout. Intersections exhibiting volumes outside these limits may be candidates for roundabouts subject to an operational analysis.
If an intersection passes the initial screening, an individual isolated operational analysis of each roundabout shall be performed in compliance with the Highway Capacity Manual (TRB 2010). A series of roundabouts shall be analyzed using corridor simulation. .... If a roundabout exhibits equal or better operating and safety characteristics than a conventional intersection, a roundabout must be completely advanced through the public involvement (CAP) stage.
The cost/benefit analysis shall consider the benefits of crash and delay reduction of a roundabout in comparison to...a proposed conventional intersection. The analysis shall also account for the savings in right-of-way costs...due to the elimination of additional turn and/or auxiliary lanes and their transitions. If the benefit/cost ratio of a roundabout is greater than that for a conventional intersection, a roundabout becomes the preferred alternative.