Last Thursday [3/31/22], I encountered new lane markings on freshly resurfaced Evergreen St, part of my daily commute in Pt Loma. Surprised, I looked up details of the design now referred to as edge lanes, and started following news reports and associated discussion. Rather than a center stripe down the middle of the road to designate two way car traffic, they designate a center car lane with dashed bike lanes on either side. The idea is that cars travel down the middle of the road, and when approaching an oncoming vehicle, merge into the bike lane when safe to do so, or slow to fall behind a cyclist – a very similar maneuver to how cars regularly interact with me on Evergreen st.

One of the common fears voiced at community meetings or news interviews are of a head-on collision between cars. The roads generally selected for this treatment are residential, and carry a 25 mph speed limit. These are speeds chosen such that a driver has sufficient reaction time and braking distance if a child runs into the street, or a car blindly backs out of a driveway. If you were to encounter a car heading straight at you, what would be your reaction? Most likely to get out of the way, and/or slow towards zero mph. A collision between cars traveling at zero and 25 mph is not something anyone wants to experience, but thanks to decades of crash testing, a vehicle occupant would likely fare far better than the roughly 10% of pedestrians or cyclists that die when struck by a motor vehicle at 25 mph.

Does this fear reveal something we know about our residential roads but don’t explicitly mention? That people drive too fast and make it unsafe? We have a national epidemic, with pedestrian and bicyclist deaths rising approximately 40-50% over the last decade. Rather than ignore the underlying problem and hope that it will go away, or attempt to fix it through education or enforcement of speed limits, city engineers decided to try a new solution. They changed our perception of traffic flow using paint. Many people who are upset, in their calls to restore the previous road design, may miss the larger picture. Or if they don’t, perhaps they have different ideas on what could be done to address it. And this is where we should center our discussion – on how to best reduce motor vehicle speeds on our residential roads, and incidentally, roads like Gold Coast and Evergreen that service schools. 

It is clear that business as usual has not solved the problem, so we need to try something different. A review of edge lane roads in other communities in the US and in Australia, have concluded that this treatment reduced crashes by 44%. And this doesn’t include additional examples we can draw from Denmark, or The Netherlands, which developed their cycling culture through decades of policy decisions

As a cognitive scientist, I study perception, attention, and how we plan our actions. We smoothly navigate our environment by subconsciously predicting the future, hundreds of milliseconds at a time. We monitor how incoming sensory information matches our predictions, and adjust our movements as necessary, like an outfielder chasing a fly ball. It is startling and upsetting when we encounter a familiar scene that provides conflicting information: paint markings suggesting a one lane road where previously two lanes coexisted. This forces us to recalibrate our predictions and our driving behavior. Knowing we have to share space with other vehicles demands more attention. And humans are notorious for choosing to endure pain rather than perform a difficult mental task. But maybe a residential road demanding more attention is a good thing. 

So while the city pauses its rollout of the new street design, and we have time to learn about navigating edge lanes, let’s think about how we can make our streets safer for everyone, rather than rush to restore the previous street design. As I commented in the Mira Mesa Town Council meeting, if the changes lead to drivers slowing down, some of the desired effects may have already been achieved.