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Roundabouts in California and Rohnert Park

By: Irene Hilsendager
April 13, 2018

What is a roundabout? Do they have benefits? A roundabout is an intersection where traffic travels around a central island in a counterclockwise direction. Vehicles entering or exiting the roundabout must yield to vehicles, bicyclists and pedestrians.

Roundabouts can have many advantages over any traffic signal when constructed in the proper location. They will provide a calm traffic situation, which results in reduced speeds. They require less maintenance and it reduces the yearly operational costs and have a so called longer service life. Greenhouse gases would be reduced due to less idling time. The median island would provide refuge for pedestrians and would allow them to cross one direction of traffic at a time and they also provide a better opportunity for landscaping in the community. With landscaping each island, it would give residents and clubs an opportunity to get their hands in the dirt and the city could be a co-partner in beautifying the community.

There are rules for vehicles, pedestrians and bicyclists on how to guide your way through a roundabout. Those will be discussed later.

There are about five basic roundabout types: mini, compact, single-lane, multilane and teardrop. General roundabouts are near-circular intersections at grade level. they have fewer conflict points and lower speeds and it requires less maintenance. Mini-Roundabouts are just small single-lane roundabouts just generally used in a 25 mph or less. These mini-roundabouts are not suitable for use on higher-volume state routes. Compact roundabouts are similar to mini-roundabout in that it is used on a single-lane road in regards to design vehicle assumptions. Single-lane roundabouts typically have mountable raised splitter islands, a mountable truck apron and a landscaped central island. Multi-lane roundabouts have at least one entry or exit with two or more lanes and more than one circulating lane. The practice for trucks negotiating roundabouts is to straddle adjacent lanes. Teardrop roundabouts are usually associated with ramp terminals at interchanges. Modern roundabouts are commonplace throughout the world with half of the roundabouts in France although England has more as a proportion of the road than any other country. 

A truck apron is the mountable portion of the central island used to accommodate the turning path of a vehicle larger than a passenger vehicle such as busses, fire engines, etc. Poorly-designed walkways do increase the risks for the vision-impaired as it is more difficult than being at a signalized intersection to audibly detect whether there is a sufficient gap in traffic to cross safely. At a traffic signal intersection, traffic comes to a stop and an audible sound can be generated to indicate that it is the right time to cross. This issue has led to a conflict in the United States between the vision-impaired and roundabout communities. Should a manually-operated pedestrian crossing signal be provided at each entry? This will increase construction and operation costs and there has to be a way to disrupt traffic long enough for the pedestrian to cross such as a sound beacon and that defeats the purpose of the roundabout. Signalized pedestrian crossings are normally used on large-diameter roundabout interchanges rather than a small-diameter roundabout.

Have roundabouts found their place in California? 

For nearly 30 years, transportation agencies at the state and local level have invested in more than 3,500 roundabouts, including over 300 in California and 24 currently on the California State Highway system. Caltrans has 31 roundabouts in the project delivery pipeline.

Roundabouts have been gaining popularity throughout the United States over the past several years and California which is usually a leader in art, technologies and innovation has been slow to embrace roundabouts. Roundabouts have found their place in California and probably the closest one to Rohnert Park is located in Petaluma. Cotati is one place where roundabouts will never show up. It was voted down several years ago when the town was nearly divided due to discussions of roundabouts. The first modern roundabout in the United States was constructed in Summerlin, Nevada in 1990. 

With the scuttlebutt going around about the crazy roundabouts that are coming to Rohnert Park, Mary Grace Pawson, Director of Developmental Services, sent a long list of when the RP City Council commissioned a preliminary review of roundabouts at various locations with the city. On June 14, 2016, the city council authorized a traffic flow improvement study. The purpose was to identify locations where roundabouts could provide an equal or better solution to traffic congestion and safety than traffic signals. The study is a preliminary overview, not a conclusive pre-design report. In all cases where roundabouts appear feasible, additional traffic modeling, pre-design work and public outreach will be needed prior to implementation. 

Does this mean it will go out on a vote to the public? 

The study looked at the five corridors and 14 intersections and the following has been looked at:

On Bodway Parkway: Bodway and E. Cotati, Bodway and Mag

‘Round’ see page 14

‘Round’ see page 3

nolia, Bodway and Middlebrook, Bodway and Camino Colegio and Bodway and Valley House Dr.

Camino Colegio: Camino Colegio and E. Cotati, Camino Colegio and Magnolia and Camino Colegio and Mitchell.

Snyder Lane: Snyder and Keiser.

Commerce Boulevard.: Commerce and Southwest, Commerce and No Name and Commerce and Adrian.

State Farm Drive: State Farm and Commerce and State Farm and Enterprise.


The city’s study generally reviewed single lane, single roundabouts with sidewalks and bike lanes and compared the signalized intersections along with sidewalks and bike lanes. The study assumed that all designs, whether roundabouts or traffic signal it would need to comply with Americans with Disabilities Act, which means they will include features to support visually impaired pedestrians. The one exception to this is the intersection of Snyder Lane and Keiser Avenue, where a double roundabout is needed to accommodate the nearby middle school entrance which will include sidewalks, bike lanes and all ADA compliance features.

The study demonstrated that the construction cost of the roundabout is often higher but long term costs can be lower especially when the cost of collisions is taken into account. The preliminary estimates indicate $2.5 to $3 million for a roundabout compared to $0.5 million for signal improvements.

Roundabout rules:

Slow down and obey traffic signs.

Yield to pedestrians and bicyclists.

Yield to traffic on your left already in the roundabout.

Enter the roundabout when there is a safe gap in traffic.

Keep your speed low within the roundabout.

As you approach your exit, turn on your right turn signal.

Yield to pedestrians and bicycles as you exit.

Emergency vehicles in the roundabout:

 If you have not entered the roundabout, pull over and allow emergency vehicles to pass.

If you have entered the roundabout, continue to your exit, then pull over and allow emergency vehicles to pass.

Avoid stopping in the roundabout.

4.   And always look to your left to see if traffic is next to you.