Importance of Good Design
Article by Leif Ourston, September 2003.
Shown below is a drawing of the final design of the Clearwater Entryway roundabout in Clearwater, Florida. Barry Crown re-designed the roundabout in response to numerous crashes since it opened in December 1999. You may download his report here.
This roundabout replaced several former signalized intersections near Clearwater Beach, and during Spring Break handles as much as 58,000 vehicles and 4,000 pedestrians per day. In the 6 months before Barry Crown’s re-design there were 262 crashes in the roundabout, mostly at two of the exits.
With minor geometric and pavement marking alterations, he achieved the following remarkable results (all crashes before and after were property damage only):
- 6 months before, 262 crashes = 524 per year
- 18 months after, 3 crashes = 2 per year
- Reduction = 522 per year
- Percent reduction = 99.6%
I am an old highway engineer who started working as a grademan on a paving crew before my nineteenth birthday. In my 44 years of highway engineering, I have never heard of a remedial measure that reduced crashes by 99.6%.
I believe Barry Crown is the best roundabout engineer in the world. He converted one of the worst roundabouts in the world to one of the best by making subtle changes.
There are good lessons to be learned from Clearwater.
- Trust Barry Crown and his methods. He has learned roundabout design the most powerful way, by redesigning hundreds of roundabouts in England and watching his results.
- Signing, striping, and little things mean a lot. Often our clients think, "I may not know roundabouts, but I surely know signs and stripes," and they replace our signing and striping designs with their own. Sometimes the results are disastrous. Barry's improvements were almost all signs and stripes. In addition, he realigned a few outer curbs by just a few feet. Small adjustments have powerful effects.
- Roundabouts cause few injuries. Even the original Clearwater roundabout hadn’t caused any injuries before its re-design.
- British roundabout design methods transfer well to North America. Barry has extended the outstanding roundabout science of his country with his deep experience and expert skill. What he learned on the other side of the Atlantic works reliably on this side.
- Design guidelines are not enough. Spiral striping, which so helped Clearwater, is not covered in British, Australian, or North American guidelines. The concentric striping originally dividing lanes 1 and 2 in the circulatory roadway at Clearwater was common if not standard practice in France and Germany for many years. Exit blisters, which worsen exit path overlap similarly to the sharp exits originally at Clearwater, have been recommended in Australia's guidelines. Guidelines are not created equal. Roundabout design is a skill learned by experience and attention to good science. It is not a cookbook branch of engineering.
It is always the design – always, always, always. When I first began advocating roundabouts in California in 1984, the prevailing view was, "Of course it works in Britain, but it would never work here." "Our people are not used to them." "We have too many trucks." "Our drivers are too aggressive." In Florida, one engineer really said, "Our drivers are too dumb."
It wasn't the drivers. It was the design. It always is. We designers deserve full blame and full credit for the performance of our work.
The Wall Street Journal should run a prominent story correcting their previous story in which drivers were blamed for the disaster of the original Clearwater roundabout, and all roundabouts, good and bad, were wrongly given a bad name.
The most important lesson to be learned from Clearwater is that we have nothing to fear with regard to roundabouts built in North America except bad design. It is never the driver. It is never inexperienced drivers. Otherwise Vail and Avon and Clearwater would not be such successes today. It is always the design.
Most importantly, this lesson applies to those British types of roundabout which North American states and provinces are loath to try, namely: high-capacity roundabouts, with three or four lanes; roundabouts on high-speed highways and at the ends of freeways; and two- and three-lane mini-roundabouts, with overrunable central islands. These are commonplace in Britain. We need them too. Hopefully one day they will be standard all over our continent.
If you are a roundabout policy setter, remember Clearwater. Remember that good roundabout design works as well in North America as in the United Kingdom. And do everything you can to push the envelope, advocating more roundabouts, more roundabouts at high-flow sites, more roundabouts at high-speed sites, and more medium-capacity mini-roundabouts to relieve congestion on downtown main streets with speed limits of 25 or 30 miles per hour. When you advocate these advances, respect the need for good design.
Remember Clearwater. It is always the design, not the drivers, and not the country. It is always the design.