Street Smarts note: The following guest post is about roundabouts, by Chris Schneiter, Assistant Director/City Engineer
City of Santa Cruz Public Works
The Santa Cruz Beach and South of Laurel Comprehensive Area Plan recommended that the City consider the development of two modern roundabouts or traffic signals in the Beach Area, one at Pacific Avenue and Center Street (Depot Park intersection) and another at Pacific Avenue and Beach Street (Wharf intersection). The purpose is to improve traffic flow and safety, and mitigate future development generated traffic.
With the recently developed Depot Park, the Monterey Bay Sanctuary Visitor Center currently under construction and a future Natural History Museum, a more attractive beach gateway would also be a plus.
Since approval of the Beach/SOLA plan, Public Works staff and a consultant studied both options and recommended that modern roundabouts be installed instead of traffic signals. The public process resulted in the approval of the roundabouts by City Council in 2006. Since then significant progress has been made resulting in the design, permitting and financing of both roundabouts, with the Depot Park roundabout now under construction. The Depot Park roundabout is funded from federal stimulus funds, traffic impact fees and redevelopment funds. The Wharf intersection roundabout will be constructed after the 2011 tourist season.
Roundabouts have gone through a renaissance since the early rotaries and traffic circles were constructed many years ago. The circle roadway around the Arch de Triomphe in Paris is not a roundabout. The center island on King Street at Baldwin is not a
roundabout. The modern roundabout is a more efficient and safer intersection than the traditional traffic signal or all-way stop. Many people have now encountered them on their travels through North America, the United Kingdom, Europe, China, Australia and other countries. There are currently about 2300 modern roundabouts in the United States and the number is growing fast. The Depot Park roundabout will be the first in Santa Cruz County.
Under many traffic conditions, a roundabout can operate with less delay to users than traffic signal control or all-way stop control. Unlike all-way stop intersections, a roundabout does not require a complete stop by all entering vehicles, which reduces both
individual delay and delays resulting from vehicle queues. A roundabout can also operate much more efficiently than a signalized intersection because drivers are able to proceed without delay when traffic is clear instead of waiting for the signal to change.
Roundabouts can also reduce delays for pedestrians when compared to traffic signals because pedestrians are able to cross during any safe gap rather than waiting for the traffic signal to turn green. During peak hours of congestion when large gaps are infrequent, the very slow speed of traffic entering and leaving the roundabout can compensate for the smaller gaps and facilitate pedestrian crossings.
Roundabouts are safer as there are fewer conflict points for vehicles, cyclists and pedestrians. Vehicle speeds are low, there is a lower speed differential between users and the lower speeds and geometry reduce the number and severity of collisions. Crossing
distances for pedestrians are shorter and require looking in one direction only, therefore making it safer.
Roundabouts are more aesthetically pleasing than a traffic signal or all-way stop, providing a platform for landscaping and public art. The Dept park and Wharf roundabouts will have major public art pieces along with landscaping and quality
Safety and efficiency statistics compared to other intersection control:
- 40% Reduction in all non-injury collisions
- 80% Reduction in injury collisions
- 90% Reduction in fatalities
- 30% Reduction for pedestrian and bicycles
- Excellent capacity and up to a 75% reduction in delay
- Speed through intersection significantly reduced.
- Reduced greenhouse gas emissions with less stop and go.
Not every intersection is right for a roundabout. The traffic volume, traffic characteristics, topography and site characteristics can limit their application. A roundabout varies based on the number of entry and circulating lanes, and also on more subtle geometry elements including entry angle and lane width. Also, like other types of junctions, the operational performance of a roundabout depends heavily on the flow volumes from various approaches. A single-lane roundabout can be expected to handle
approximately 20,000 to 26,000 vehicles per day, while a two-lane roundabout can be expected to handle 40,000 to 50,000 vehicles per day. The Depot intersection will be a one-lane roundabout and the Wharf intersection is a partial two-lane roundabout.