Two bicyclists have been killed at the intersection of US-36 and Violet Avenue since 2009. The most recent was TJ Doherty, on July 24th, 2012. Both cyclists were headed southeast on US-36, and were hit by cars traveling northwest, making left turns onto Violet. In this area US-36 is just outside of Boulder’s city limits, in the county, but it’s the Colorado Dept. of Transportation (CDOT) that’s responsible for it. Looking at the aerial view below we can explore why this intersection might be particularly dangerous for cyclists.
Northwest bound vehicles on US-36 have a dedicated left turn lane, and no obligation to stop before making their turn. The angle that Violet Ave. makes with the highway is quite oblique, meaning that it can be taken at high speed, and because US-36 has a speed limit of 55 mph in this area, cars often will take it at high speed if they don’t see any oncoming traffic.
From a southeast bound bicycle’s point of view, there’s no obviously correct place to be on the road, if they’re planning to proceed through the intersection. The shoulder on the west side of the road narrows to a few inches, and it’s to the right of a right-turn-only lane. If you ride all the way to the right, you risk a vehicle turning in front of you onto Violet. Your intent to continue through the intersection is also unclear to oncoming traffic. Most cyclists instead take a position that’s well within the right turn lane, to prevent right-turning vehicles from passing them and immediately turning right in front of them. However, this lane position still leaves their intent ambiguous to oncoming traffic. Alternatively, you might choose to straddle the line separating the through travel lane and the right turn lane. This makes the bike relatively visible, and more clearly conveys the intent to continue through the intersection, at the expense of potentially sandwiching the cyclist between right turning vehicles and very fast moving through traffic. If the cyclist instead chooses to behave exactly like a motor vehicle, moving into the through lane of traffic, the very large difference in speed between the bike and the other vehicles in that lane creates a hazard. Thus, there’s no right place for a cyclist to be on this road if they’re planning to continue through the intersection.
When we combine the unavoidable ambiguity of the through cyclist’s intent with the very high left-turning speeds of oncoming traffic, we have a recipe for disaster. A recipe which has killed two people in three years.