On April 26th, Reid Our Blog posted a report on roundabout design at East Lake Sammamish Parkway in Issaquah. We received the comment referenced below, and found that our answer was too long to fit in the comment reply section, so we’ve devoted an entire post to answering our reader’s question. Below is the original comment and a further explanation of roundabout design along with some specifics about the East Lake Sammamish Parkway roundabout. We love talking about good roundabout design. Check out the “roundabout” section of our website for further reading: http://www.reidmiddleton.com/services/transportation-engineering/roundabouts/.
Comment: I’m not sure that your statement “shows several examples of bicyclists comfortably claiming the lane in line with motor vehicles during the evening peak hour” is highly accurate. I ride north onE L Sammamish Parkwayand that is one of the most dangerous intersections because cars will not slowdown until they get into the circle. I’ve had so many close calls at that intersection from cars that are trying to pass me while I get into the travelling lane that I’m considering hopping onto the gravel trail for that section. Firstly, there should be a painted bicycle lane all along that section ofE Lake Samm Pkwy.Second, it would be beneficial to both cyclist and motorists if there was a painted bicycle lane that leads onto the travelling lane (just like the one that heads south on E L Sammamish Pkway that goes east onto Inglewood.
Response: Good speed control is a characteristic of good roundabout design. One characteristic of a well-designed roundabout is that motor vehicle speeds are reduced to bicycle speeds. We have done a speed study at the ELSP/SE 43rd Way roundabout to quantify how well the geometry dictates motor vehicle speed. You mentioned that you ride the northbound movement through the roundabout on your bicycle. Below is the data collected for that movement (click on either image for an enlarged view).
The figure shows where the speed data was collected and the 85th percentile speeds at each location. The northbound motor vehicle speeds were reduce from a free-flowing approach speed of 44 mph to 18 mph at the entry crosswalk. The greatest reduction of speed is between the midpoint of the splitter island and the entry crosswalk (30 mph reduced to 18 mph). This is the area where the motor vehicles are reaching bicycle speed and where the video shows the northbound bicycles move into the northbound through lane.
The northbound bicycle approach to the SE 43rd Way intersection and the southbound bicycle approach to the NE Inglewood Hill Road both require the bicyclist to weave across the right-turn lane in order to enter through lane. When you enter the northbound through lane at the SE 43rd Way intersection, it is important that the bicyclist claims the lane and position himself in the center of the through lane—not on the edge of the through lane. Note in the video how the bicyclists position themselves in the center of the through lane.
If you are uncomfortable making this maneuver, you may indeed use the gravel trail for that section of ELSP, or you may approach the intersection on the sidewalk and use the NE 43rd Way crosswalk as a bicyclist does at the end of the video.
The only designated bicycle lane on this portion of ELSP is what was added on the north side of the intersection. We agree that it would be nice to have designated bicycle lanes along ELSP—if the lane widths would accommodate them and if funding was available.
One thing we absolutely do not want to do is paint a bicycle lane up to the YIELD line or in the circulating lane of the roundabout. This has been done in Belgium and has resulted in many motor vehicle/bicycle collisions. The collisions occurred when a motor vehicle turning right crossed the path of a bicyclists that was continuing through the roundabout. This is of course very dangerous.
Thank you again for your question. We are always happy to talk about the components of good roundabout design.