Roundabouts and Urbandale
The City of Urbandale has a number of public roundabouts. While most of these are small roundabouts in neighborhoods, the two-lane roundabout at Douglas Parkway and 142nd Street was one of the first multi-lane roundabouts constructed in the Des Moines Metro area. Although less familiar for American drivers, roundabouts have long been recognized world-wide as an intersection design with benefits for safety and efficient vehicle flow. Roundabouts provide a traffic calming effect which allows vehicles to keep moving but encourages reduced speeds. The configuration of a roundabout offers safety benefits by reducing the severity of crashes; when crashes do occur, they tend to be rear-end or sideswipe rather than broadside collisions. It also offers improved safety for pedestrians, by providing a staggered crossing offset from the main intersection, allowing drivers to focus on the pedestrians separately from the intersection navigation.
- Visit the Iowa DOT Roundabout Page for more information, including Roundabout Safety and Efficiency and How to Drive a Roundabout.
- Watch Navigating a Multi-Lane Roundabout from the Minnesota Local Roads Research Agency.
Remember, choose your lane at a multi-lane roundabout just as you would at a multi-lane traditional intersection. Yield to vehicles already in the intersection, then proceed through.
Image courtesy of Minnesota Local Roads Research Agency
Image courtesy of Wisconsin DOT
The City of Urbandale completed a project in 2018 to improve the Douglas Parkway and 142nd Street Roundabout. The project re-constructed the approaches to better align with the circulatory lanes of the Roundabout. This improved safety by providing a better vehicle path through the intersection, and improved efficiency by maximizing the use of both lanes.
The changes made in 2018 improve both safety and efficiency based on recent design guidelines. Today's guidelines for Roundabout Design recommend a layout similar to a pinwheel. The previous intersection was shaped more like a plus sign.
Changes to the approaches ease the angle of the entry into and exit from the roundabout. This reduces the risk of broadside collisions, and improves efficiency by aligning the entering vehicles with the roundabout lanes.
Since the Roundabout was constructed in 2004, national standards have been updated. The City of Urbandale received Traffic Safety Improvement Program (TSIP) funds from the State of Iowa in order to modify the roundabout to comply with current best design standards. The new approaches provide a deflection prior to reaching the roundabout, so that vehicles are aligned with the proper lane when they enter the intersection. There are five ways the new geometry will improve the intersection:
- By placing the vehicle deflection ahead of the roundabout instead of at the yield line, the chance of a broadside collision is reduced.
- The revised approach angle promotes better paths for vehicles to enter and reduces potential path overlap of adjacent vehicle paths.
- Better guidance through the intersection allows motorists to focus more on surrounding traffic and proper lane assignment and less on navigating the roundabout.
- Vehicle speeds will be gently slowed to more consistent speed. Reducing the speed differential makes it easier to find a good gap in circulating traffic to enter the roundabout.
- The above items will make it easier to enter and navigate the roundabout, which in turn reduces wait times and traffic queues for approaching vehicles.
The improvements were designed to result in a safer roundabout, a reduced frequency of crashes, and more efficient vehicle movement through the intersection.