Understanding bike infrastructure – roundabouts

vista street bike blvd-85Almost three years ago the City of Long Beach put in two roundabouts and five smaller traffic circles on Vista Street as part of making it a bike boulevard. Since installing the roundabouts and circles overall traffic accidents have fallen by over 50% and accidents at the two major intersections where roundabouts were installed have dropped by 75%.

In spite of this dramatic decrease there are people who argue that the roundabouts are unsafe because of the height of the landscaping (a 6 foot high pampas grass is used for decorative landscaping and to intentionally limit sight distance).  They argue that the landscaping limits sight distances and thus makes the intersections more dangerous.  As is discussed in the letter to the editor shown below, while this argument seems logical, in fact the reverse is true.  The landscaping focuses the drivers attention to the left and right where vehicles, pedestrians and bicyclists are entering the intersection resulting in a safer intersection.

Let us know if you are facing opposition to various types of bike infrastructure and what you are doing to counter those arguments.

Letter to the Editor, Grunion Gazette, Long Beach, CA

Over the past few weeks there have been two letters to the editor suggesting the landscaping of the roundabouts at the intersections of Park and Vista and Ximeno and Vista in Belmont Heights be kept low to improve safety at the intersections.

While this seems logical in fact the reverse is true: higher foliage focuses the vision of the driver to the left and right where vehicles, pedestrians and bicyclists are entering the intersection.  This results in the drivers being more cautious and driving more slowly resulting in a safer intersection.

Prior to installing the roundabouts, according to City records these were two of the more dangerous intersections in the city with several accidents recorded per year.

After installation of the two roundabouts accident rates dropped at the two intersections by 75%. In the three years since installation there have been no recorded accidents at Park and Vista and three at Ximeno, one of which was associated with a DUI and one with intentional speeding.  According to the City’s Traffic Engineer, such a dramatic safety improvement is rarely realized by a single project and thus is significant and notable.

The reason for the dramatic reduction in accidents is two fold.  First the mere presence of the roundabout causes most drivers to slow as they approach and navigate the intersection. But equally important is the foliage.  Here is what the Federal Highway Administration’s roundabout design guide says about the importance of landscaping in how roundabouts help control speed:

Landscaping of roundabouts plays an important role in improving the aesthetics of an area. However, landscaping has a number of functional purposes:

  • It makes the center island more conspicuous;
  • It focuses driver attention on key conflict areas by blocking the view of other areas; and
  • It discourages pedestrian traffic through the center island

What the landscaping does is: (1) alert the driver that there is something ahead in the roadway and (2)  focus the drivers attention to the left and right where vehicles, pedestrians and bicyclists are entering the intersection resulting in a safer intersection.

What is observed at the intersections of both Park and Ximeno is that when the landscaping is higher motorists drive more slowly.  After the roundabouts were installed speeds at the intersection of Park and Vista dropped from nearly 35 mph to under 20 mph. Now that the landscaping is cut way back motorists feel that it is “safe” to drive through the intersection more quickly, thus speeds increase making the intersection less safe for motorists, pedestrians and bicyclists.

For several years the residents that live near the intersections of Park and Vista and Ximeno and Vista fought to reduce traffic speeds through these accident prone intersections.  Now that we have successfully slowed traffic and significantly improved the safety of these intersections please do not take us backwards by increasing traffic speeds and reducing the safety of these intersections or by eliminating the beauty of the landscaping.

Regards

Allan Crawford

Executive Director, BIKEable Communities

 

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The following diagrams and photos from FHWA Documented and the Parkl/Vista roundabout and diagram illustrate the effect of landscaping round about sight distances

 

 

 

 

 

 

 

 

 

 

This illustration above from FHWA Roundabouts shows the important sight lines for roundabouts.  As the diagram illustrates the most important direction is to the left in the direction of oncoming traffic.  Landscaping in the center of the roundabout focuses the drivers attention in the direction.

roundabout sight distance nchrp 672The adjacent quote from NCHRP 672 emphasizes this point as well.  “Excessive intersection sight distance can lead to higher vehicle speed that reducte the safety of the intersection for all road users (motorists, bicyclist, pedestrians).

 

 

 

The following two photos from the Park and Vista intersection show the differences of a fully landscaped versus a significantly cut back roundabout.

vista street round about vegitation vista roundabout with vegitation

 

 

 

 

 

 

 

 

 

 

If you have questions for comments about roundabouts or any other form of bike infrastructure please don’t hesitate to send us an e-mail or better yet add your questions/comments to this blog post.