When are roundabouts indicated?

Strange intersection north of Coe College campus. Is a roundabout the solution?

Construction of roundabouts is "exploding" around the State of Iowa, according to Steve Gent, who is director of traffic and safety for the Iowa Department of Transportation (Morelli 2017). Cedar Rapids recently got into the game with a redesigned intersection of Kirkwood Boulevard and 76th Avenue SW, and will soon get two more on Johnson Avenue SW. All these roundabouts come with many promises of improved traffic performance, and much public angst about the introduction of this unfamiliar traffic feature. Our task today is to decide when roundabouts might be a positive addition, and where they might be overdone.

Roundabout schematic (Source: U.S. Dept of Transportation)

A roundabout is a circular intersection characterized by small diameters (relative to traffic circles like Columbus Circle and DuPont Circle in Washington, D.C.); curvature designed to slow speeds; a center island around which traffic turns; and the requirement for entering drivers to yield to those already in the circle (USDOT 2000: 5). Conceptual or real operation can be seen in the videos listed below. Benefits of roundabouts include:

• improved traffic flow despite slower traffic speeds, because vehicles are moving at a slow steady pace instead of alternating stopping and going fast;
• less pollution, at least at the intersection site, because the cars keep moving;
• improved safety because there are fewer contact points and all cars are going in the same direction; 
• lower year-to-year costs than a traditional signal because those require electricity and maintenance (though construction costs are higher).

St. Paul, MN: Intersection of Charles and Albert Sts is more properly called a "neighborhood traffic circle"

The disadvantages of roundabouts stem from their unfamiliarity in much of this country, outside of the Northeast. Drivers' uncertainty can create more problems than the feature is designed to solve, particularly in a two-lane roundabout where the required lane changes seem to guarantee mass confusion (see second diagram here). Tom Vanderbilt argues that's a feature, not a bug:

With a roundabout, only a fool would blindly sail into the scrum at full speed [as opposed to the common maneuver of speeding through a yellow light]. Drivers [entering a roundabout] must adjust their speed, scan for openings, negotiate the merge. This requires more workload, which increases stress, which heightens the feeling of danger. This is not in itself a bad thing, because intersections are, after all, dangerous places. [From the previous page: 50 percent of all road crashes occur at intersections.] The system that makes us more aware of this is actually the safer one. (2008: 179)

Cultural hostility to change, whether it involves sidewalks or LED light bulbs or the metric system, gets magnified when it hits us where we live, and a lot of us live in our cars. Elected officials are understandably chary of triggering this hostility. Additionally, there is the cost of conversion, estimated at $1.2 million (Morelli 2017), which is about four times the cost of installing a set of traffic signals, and way more expensive than a four-way stop. Finally, there is disagreement over whether bicyclists and pedestrians benefit from this design.

Newly-built intersection of 5th St and 16th Av SW includes a roundabout:
anticipation of future traffic, or vanity feature?

Roundabouts and traffic circles are commended as traffic calming measures in David Sucher's manual for city-building. He explains:

[Roundabouts are] not so much to slow down traffic but to allow movement through intersections without having to stop.... A slow but steady pace would achieve the same overall time from origin to destination but without the mental aggravation of continual acceleration, braking, stopping, and then accelerating again. (2003: 79; see also Vanderbilt 2008: 124)

He cautions, however:

The traffic circle is not manna. Some drivers loathe them and will change their route to avoid them, which may serve to decrease traffic on one block, only to divert it to another, increasing traffic there. (2003: 78)

The main trick with roundabouts is to keep traffic flowing without creating disconnection between the parts of the city on either side. From this we might conclude that roundabouts are indicated where traffic volume is great enough to overwhelm a four-way stop; the volume of turning traffic would require a separate turning light, making the overall light cycle painfully long; and pedestrian and bicycle traffic is manageable. There should be regular breaks in the traffic, so that new entrants can merge easily--unlike Chevy Chase's experience in "National Lampoon's European Vacation!"--pedestrians can get through the intersection in a timely fashion, and cyclists can cycle.

[The Iowa Drivers Manual (cited below) recommends "Generally, cyclists should walk their bicycles across the pedestrian crosswalk using the same rules as pedestrians," though it allows that "Experienced cyclists may navigate roundabouts like motorists." If the traffic feature in an area with significant bicycle traffic depends on cyclists getting out of the way, it is doomed to failure. The idea of urban design is that it accommodates and channels normal human behavior, rather than presuming that one set of travelers is voluntarily going to withdraw from the scene.]

Pair of roundabouts on U.S. 30 south of Mt. Vernon (Google maps)

On roads roundabouts can be focused on traffic flow. One successful roundabout near Cedar Rapids is at the intersection of U.S. 30 and S.R. 1 in Mt. Vernon. It used to be a four-way stop, featuring long backups at most times of the day. With the roundabout we sail right through, though I confess I haven't tried it during rush hour. There's another roundabout to the west where U.S. 30 intersects 10th Street. When I drive through, it seems unnecessary because of the lack of traffic off 10th Street. I understand that traffic occurs mainly at school drop-off and pick-up times, and that there had been a substantial number of crashes there. I don't know that the roundabout was the best solution--maybe cars needing to go east on U.S. 30 could have been guided to S.R. 1--but I don't know that it wasn't. A student from Mt. Vernon reports that every member of the City Council who voted for the roundabouts was defeated at the next election, which speaks to the fraught political climate around this issue. The American Society of Civil Engineers reports the outcome eventually got happy; they quote Justin Campbell, a transportation engineer on the project: Now that the roundabouts are finished and working, people are happy. The cars are moving (Wilcox 2016).

Other than the ones on U.S. 30, the Linn County roundabout that gets the most use is unquestionably the one west of downtown ("Uptown") Marion, at the intersection of 7th Avenue, 7th Street, and 6th Avenues. (An indication of the current rage for roundabouts is that an Internet search for "Marion roundabout" finds stories from Illinois, Indiana and Kansas as well as Iowa.) It opened November 2016 as part of Marion's Central Corridor Project, intended to divert through traffic off 7th Avenue onto 6th and allow 7th to become the hub of a walkable urban district (Kasparie 2016). It is no longer possible to go through the intersection southbound on 7th Street, or westbound on 6th Avenue, though it's not clear how many people were previously doing this.

Traffic moved briskly through the roundabout this morning while I observed it from 7:45-8:30 a.m. Most people drove with confidence, even though the feature is barely a year and a half old. There occasionally appeared to me to be hesitation entering the circle, but nothing that delayed traffic more than a few seconds. Only one driver was yielding to traffic entering the circle, and two drivers--both talking on phones--were observably erratic.

Most traffic this morning was headed west along 7th Avenue i.e. towards Cedar Rapids, and I saw the only mild backups on westbound 7th approaching the roundabout, a string of six and a string of seven cars behind semi-trucks that had had to stop before entering the circle. There was more traffic on 7th Avenue than on 8th Avenue, so no evidence that traffic was diverting away from the roundabout. I'd heard reports from a local student that backups occasionally occurred when a line of cars proceeded north on 7th Street and had to stop at 8th Avenue...

...but I never saw more than one car going in that direction this morning. Country Kitchen Cafe was doing a brisk business on the southwest edge of the circle...

...though I'd be interested to compare their before-and-after numbers. Very few pedestrians or cyclists came through while I was observing. The cyclist used the sidewalks and surprised a driver when he turned left across 7th Street. Few eastbound cars bypassed the commercial area on 7th Avenue by diverting to 6th Avenue, but 6th isn't yet complete around Uptown. Overall, I'd say traffic was moving, quite likely better than it did when the intersection was governed by a set of traffic lights.

So, bottom line: Should the complex intersection north of Coe (pictured at top) be redone as a roundabout? It would certainly facilitate conversion of the streets to two-way, and would seem not to stand in the way either of better development of the area, or of increased pedestrian activity. Here would be something that's broken, and a roundabout would be one, perhaps the best, way to fix it.

VIDEOS
Bicycle Dutch, "A Bicycle Roundabout in Boxtel (Netherlands)," (YouTube, 3:16)
City of Cedar Rapids IA, "Simulation Video of Johnson Avenue NW Roundabouts" (YouTube, 1:29)
Insurance Institute for Highway Safety, "How Roundabouts Work" (YouTube, 2:00)
Charles Marohn, "Pimped Out Roundabout" (YouTube, 2:51)
Thorsten Peters, "Laweplein 02" (Vimeo, 1:47)

SOURCES
"Hans Monderman's People-Friendly Dutch 'Squareabout,'" ThinkBicycling, 13 June 2013
David Hembrow, "Where the Crashes Are: Shared Spaces and Other Poor Junction Designs Which Don't Protect Cyclists Lead to Crashes and Injuries," A View from the Cycle Path, 7 April 2014
Jill Kasparie, "Marion Prepares for Work to Begin on Roundabout Projects," KCRG.com, 15 March 2016
B.A. Morelli, "Cedar Rapids Gets Its First Roundabout as Traffic Tool 'Explodes' Around Iowa," Cedar Rapids Gazette, 9 June 2017
David Sucher, City Comforts: How to Build an Urban Village (City Comforts, rev. ed., 2003)
U.S. Department of Transportation, Roundabouts: An Informational Guide (USGPO, 2000)
Tom Vanderbilt, Traffic: Why We Drive the Way We Do (and What It Says About Us) (Alfred A. Knopf, 2009)
Kevin Wilcox, "Iowa Roundabouts Go with the Flow," Civil Engineering, 12 April 2016

And finally...

...because I've been humming it the whole time I've been writing!