(Ed Note: Most of the information on Bicycle Friendly Street treatments in this post comes from the new Bike Plan’s Technical Design Handbook. Though we are happy to present it in bite-sized pieces, we highly recommend you download it yourself and have a good read. You can download the Technical Design Handbook here. For a refresher on what a Bicycle Friendly Street is – you can read our introductory post here.)

In our ongoing series explaining the elements of a Bicycle Friendly Street, today we will laud the virtues of the Mini Roundabout. The mini-roundabout is related to the traffic circle, which was conceived in 1902 by William Phelps Eno (the “Father of Traffic Safety” and designer of Columbia Circle). The terms tend to get lumped together often and can lead to some confusion. However, in a roundabout:

Yield Control is used at all entries (no stop signs).

Circulating vehicles have the right-of-way.

Pedestrian access is allowed only at the legs of the roundabout, behind the yield line.

All vehicles circulate counter-clockwise and pass to the right of the central island.

Deflection is built into the design in order to slow down motor vehicles upon entry into the roundabout.

The roundabouts being described in this post have a single lane surrounding a raised island in the center of an intersection (they can also be multi-lane). They range in price from $100,000 to $750,000 for installation and are considered to be a Level 5 treatment, which is the highest level of treatment provided for in the 2010 LA Bike Plan‘s Technical Design Handbook (TDH).

Location, Location, Location

While the idea of mini roundabouts seems like a great strategy for traffic calming, there are a variety of concerns that go into the selection of appropriate intersections. The optimal site has level terrain on a local or connector street with low-to-medium usage and good visibility. They are rarely used on arterials. Placement on a low-volume neighborhood street (less than 2,000 ADT) may ensure that cut-through traffic looks for other routes.

Traffic circles are on a street near you (Depending on how close you are to Westholme and Ashton)

A (Near) Perfect Circle

Good design makes a good roundabout. The intent is to create a break in the vehicle path of the driver and create the perception of a narrowed corridor to slow traffic (similar to a bulb-out curb). Some emergency and large vehicles may have difficulty negotiating a right-hand loop around the circle, so they may need to turn left. These vehicles necessitate mountable aprons surrounding the Mini Roundabout to accommodate their larger mass. Despite this, roundabouts are less of a hindrance to emergency vehicles than speed tables or speed bumps.

While they may seem simple, there are a lot of people who aren’t familiar with operating a vehicle in a Mini Roundabout. As mentioned earlier, cars enter the facility and continue in a counter-clockwise direction around the center island. Right-of-way is given to vehicles already occupying the circle. This principle makes the intersection effectively governed by yield signage. Along with less conflict in the immediate center of the intersection and a single direction of traffic flow, implementation of roundabouts reduce conflicts of right-of-way between vehicles.

Out of the Loop

Some criticism comes up when suggesting the usage of roundabouts. As mentioned previously, this usually boils down to placement. As some are concerned about pedestrian and disabled access, this method is best when used in the pedestrian context. Pedestrians cross these intersections as they would any other, but the reduction in speed greatly enhances pedestrian safety (in most studies by as much as 94%). Mini roundabouts serve to control speeds in the intersection, but not necessarily mid block, so effectiveness is enhanced with other mid-block measures, such as pedestrian crossings or chicanes. When taken into account with other measures (such as traffic diverters) on the same street, this could better accommodate bike traffic by eliminating the need for stop signs in between treatments because of the magnitude of the traffic calming effects.

A Cheat Sheet for all your Roundabout designing needs

Now, there is one problem with being innovative in street treatments: Many people may not be all that familiar with how a roundabout works. Sometime the price of progress is a learning curve, and this is no different. For those of you who may be unfamiliar with the rules, we’ve included the basics. While it can be more awkward for less experienced riders, best practices in a roundabout are:

Respect others right-of-way when entering

Assert you right-of-way – It is single-lane and low-speed, so you have the run of the circle once you’re inside.

– It is single-lane and low-speed, so you have the run of the circle once you’re inside. Maintain in the middle of the lane – Riding on the outside edge of the lane opens you to being broad-sided by drivers unaware or unfamiliar with navigating the mini roundabouts.

– Riding on the outside edge of the lane opens you to being broad-sided by drivers unaware or unfamiliar with navigating the mini roundabouts. As always, practice safe biking habits

A Little Something Extra

If you haven’t noticed, roundabouts can look way better than pavement. While upkeep is usually the responsibility of the neighborhood, landscaping greatly enhances the look of the facility and creates a great visual sense of place. Because of this fact, installation requires neighborhood outreach and support for installation and maintenance is essential.

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Guidance for this article was provided by these documents:

• California MUTCD

• Caltrans Highway Design Manual

• FHWA Roundabouts: An Informational Guide

• AASHTO Guide for the Development of Bicycle Facilities

• Berkeley Bicycle Boulevard Design Tools and Guidelines

For more on the history or traffic circles and roundabouts, click here. (Courtesy of the Montana Department of Transportation)

Also of note is the book Traffic: Why We Drive the Way We Do (And What It Says About Us) by Tom Vanderbilt.