Filling the Void, Maintaining Sight Lines

When cars park too close to the corner, drivers and pedestrians often cannot see each other well enough to make safe decisions. To correct the problem, parking is frequently prohibited near intersections to improve sight lines, a practice sometimes referred to as "daylighting." Nevertheless, regulations cannot actually prevent the hazardous conditions from continuing. The public and even some enforcement agencies seem to have a low level of awareness or appreciation for the need to keep these locations clear, and the residual nature of these spaces continues to be problematic.


In an effort to improve the situation, enhanced markings are often used to reinforce the regulatory signage. Even with this effort to emphasize the regulations and create some illusion of occupancy, the space continues to feel unused. In an active urban environment, a space marked off for the sole purpose of a sight line really is, in practice, underutilized. The demand to make more intense use of it is probably inevitable.

The solution to these residual spaces is to provide them with uses that do not compromise the sight lines. To be effective and persuasive enough to continue installing them elsewhere, treatments must embrace uses that are appealing to the community.

The classic response is to install a curb extension, sometimes called a "neckdown." These rely on the curb as a physical barrier that effectively discourages parking. They also provide benefits for traffic calming and shortening crossing distances for pedestrians. A curb extension is an expansion of the sidewalk, creating more usable space for pedestrians, although they may recognize relatively little value in the extra panels of concrete. This solution is often complicated, though, by mundane engineering details like drainage or even traffic signal location. Capital costs can discourage or delay construction.

Source: Digital Media Productions
via ITE Intersection Design Guidelines

The enhanced barrier, the physical permanence, and the integration with the sidewalk generally create an effective occupancy of the space, ending the parking problem. Yet the conversion into sidewalk space can at times allow other, new uses that are also detrimental to sight lines. On Columbus Avenue, I recently saw a food cart set up on a neckdown - a regular use that was captured by Google Street View. In that particular case, the impact is minor, since the intersection is controlled by a signal light. At other intersections, a cart at that location could block the view for drivers trying to enter traffic or looking for pedestrians.


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Food carts and other sidewalk activities may occupy sidewalk extensions, creating new obstructions to sight lines

To allow for improvements while containing costs, places like New York City have turned toward lower quality curb extensions. Rather than building out the sidewalk, paint, plastic bollards, and sometimes planters or large stones are added to the repurposed portion of the roadway. This continues to provide more traffic calming effect than merely putting in pavement markings to prohibit parking, since the obstacles require drivers to navigate more carefully through a narrower space than when they can freely cut across a little paint on the ground. This strategy enables installation of traffic calming treatments in many more locations more quickly, but the resulting space is even less attractive to the pedestrians and the broader community as a form of public space.

Another solution gaining in popularity, which I particularly like, is the installation of a bike corral. This is similarly low-cost, but the public benefits may be more substantial. The bike racks physically occupy the space, preventing parking. The small loss in auto parking spaces is replaced in far greater number of bicycle parking spaces. The location of the bicycle parking in the street, rather than on the sidewalk, subtly helps to assert the legitimacy of bicycles on the street while providing an equally subtle discouragement against sidewalk cycling. And by moving the bicycles out into a prime, visible location, it also works to subtly promote growing levels of bicycle activity.