City to construct mini-roundabout at Third and Tietan
Analyses found this would be the safest and most efficient traffic-control system at the intersection.
As residential development continues on the south end of Walla Walla, the resulting traffic is increasing delay for Third Avenue traffic at Tietan Street. The intersection also has a history of accidents and near misses, and is difficult for bicycles and pedestrians to cross.
To combat these issues, the City of Walla Walla studied the intersection, and plans to make improvements in 2019 as part of a larger overall project.
The City hired PBS Engineering and Environmental Inc. to perform an alternatives analysis for the Third Avenue/Tietan Street intersection. From the data collected, PBS forecasted traffic volumes to the year 2040 and analyzed four separate intersection alternatives. These included two-way stop control (as it exists today with stop signs on Third); four-way/all-way stop control; a traffic signal; and a mini-roundabout.
Each alternative was evaluated for safety, vehicle delay, pedestrian and bicycle movements, right-of-way impacts and installation/maintenance costs. Based on the evaluation of these alternatives, PBS recommended a mini-roundabout as the best option.
To confirm these findings, the City had the recommendation peer reviewed by a separate traffic expert, who concurred with the mini-roundabout being the best alternative.
What makes the mini-roundabout the best option for this location?
Based on studies conducted throughout the United States, roundabouts have proven to be safer than alternative methods of traffic control:
• Over 90 percent reduction in fatalities
• 76 percent reduction in injury collisions
• 35 percent reduction in total crashes
• Very little reported pedestrian and bicycle crash experience
Of the four intersection alternatives evaluated, the mini-roundabout provided the least amount of delay and the highest level of service for users. More importantly in this case, private-property impacts were also significantly reduced. In addition, by lowering delay at an intersection, vehicle emissions are also reduced.
What is a mini-roundabout?
In contrast to standard roundabouts, mini-roundabouts are much more compact, usually fitting within the existing footprint of an intersection. Passenger vehicles, buses and small trucks can move slowly around the center island, which is designed to be low enough for large vehicles to drive over if they have trouble navigating the curve.
It is important to note that while Tietan Street serves a very low volume of trucks, turning movements through the roundabout will be no more restrictive than currently exist at the intersection today.
What are the project limits, and when will this be built?
After the Walla Walla City Council expressed support for the concept in 2018, design of the mini-roundabout was integrated into the Tietan Infrastructure Repair & Replacement Project (IRRP) slated to start construction early this summer. The Tietan IRRP will replace aging utilities and the roadway surface between Fourth Avenue and Modoc Street.
The City Council on March 27 awarded the construction contract for the Tietan IRRP to Premier Excavation, Inc., in the total amount of $1,825,720.61.
More about roundabouts:
• National Cooperative Highway Research Program’s report on roundabouts in the U.S.
Mike Laughery, P.E., is Capital Projects engineer for the City of Walla Walla.