How to Use Optical Narrowing to Make a Street Safer
An example of how a street can be visually narrowed using street trees. (Source: Google Maps, with illustration by Edward Erfurt.)
We all perceive the world around us through visual reference points. As we look around, we are next to the wall, or across the street from the bank—in other words, we position ourselves relative to what we see. This is even more apparent when we are driving: you may perceive yourself as behind another car, or between the lines on the road.
Drivers make decisions based on these visual cues. If things are further away, we are more inclined to speed up. The auto industry has marketed this as the “freedom of the open road,” and the visual of a wide open road is paired with the acceleration of the car. If no one is near and all the fixed objects, such as curbs and buildings, are far away, then the perception is that we have less risk and we throw caution to the wind.
If things are closer, we are more inclined to slow down. Our natural inclination is caution and possibly a little bit a fear that we may hit something. When you drive on a street where the lanes are a little narrower, or the buildings are at the back of the sidewalk, our reference points become closer. We have to focus, and in an abundance of caution we drive slower. The perspective is that we have more risk, and we pay more attention to counter that risk.
There is a direct relationship between spatial distancing and speed in road design. Transportation engineers use wider lane widths on highways. They also push back any vertical elements, such as signs, far away from the travel lanes. The next time you go on a highway, pay attention to the highway bridge. When you are on the bridge, you will see a really wide shoulder on each side of the bridge. This space is not provided for a disabled vehicle; rather, it is provided to keep the visual width open. These cues are provided as a subliminal signal that you are on the open road and that it is ok to accelerate. Compare this to your experience in a street located in an urban city where the buildings are built close to the street. As a driver, this street feels more restrictive.
Streets in too many places have been designed with the buildings and any potential obstacles pushed back from the street. The roadway feels wide and unobstructed, which results in a natural inclination to drive faster. I may be on Main Street in name only where the speed is posted at 25 mph but I am instinctively driving at 45 mph.
Understanding this little bit of psychology, we can apply this knowledge to the design of our streets. These overly wide local streets need visual cues to inform drivers of the intended and appropriate speed of the street. Using a technique called optical narrowing, we can introduce these cues.
Optical narrowing is when you add design elements and visual cues that make the street feel narrower. Simple vertical elements, like street trees or landscaping, bring the street edge closer to the driver. Lanes can be narrowed with painted edge lines, bike lanes, or on-street parking. Intersections can be visually narrowed by painting tighter turn radii or wider and more brilliant crosswalks. All of these elements are easy to implement and bring spatial reference points closer to the driver.
One of my favorite optical narrowing projects was done on an overly wide street constructed in a new residential subdivision in Ranson, West Virginia. The street’s posted speed limit was 25 mph, but in reality drivers were going at an average of 45 mph—something I know because the HOA added a very expensive speed clock in a failed attempt to slow the cars.
North Fairfax Boulevard as a visually wide street. (Source: Google Maps.)
We looked at the street and it was obvious the street was too wide, and we also observed that there was a need for more on-street parking. After a meeting with the residents and the public works department, we decided to try striping a single line to delineate the parallel parking along the curb and the additional parking adjacent to the center median. A quick 15-minute field meeting and $100 of paint resulted in double the on-street parking and a visually narrower roadway.
The public works department completed two blocks of striping, and we stood by the HOA’s speed clock. The first car, and every subsequent car, drove at 25 mph as a result of a single stripe of paint. The next morning I returned and observed that several cars parked in the new median parking. The addition of parked cars on both sides of the street increased the visual cues for drivers, and further reduced the speed.
North Fairfax Boulevard after the parking lanes were painted and street visually narrowed. (Source: Google Maps.)
Optical narrowing is an approach that can be applied through a lot of low-risk ideas in a location where speed is an issue. A first smallest step could be adding a couple of benches or straw bales adjacent to the street. You may try planting street trees, which provide additional community benefits, or add some paint to the street for parking or bike lanes. These low-risk responses can be implemented by both the city and the citizen. If they fail to slow the cars, try something else. However, if they result in lower speed, share and repeat.
Edward Erfurt is the Director of Community Action at Strong Towns. He is a trained architect and passionate urban designer with over 20 years of public- and private-sector experience focused on the management, design, and successful implementation of development and placemaking projects that enrich the tapestry of place. He believes in community-focused processes that are founded on diverse viewpoints, a concern for equity, and guided through time-tested, traditional town-planning principles and development patterns that result in sustainable growth with the community character embraced by the communities which he serves.