What's your angle? Analyzing angled parking via satellite imagery to aid bike-network planning

摘要

U.S. cities prioritize the storage of automobiles over the safe movement of bicycles. While this generally occurs by allocating street curbs for car parking instead of bike lanes, the privileging of the automobile is even more evident in the case of angled parking, in which cars sit roughly perpendicular to the flow of traffic. Such a layout takes up nearly double the space in the right of way as does parallel parking, which leaves even less room for bike lanes. Though angled parking is defended as a traffic-calming measure, numerous studies indicate that this layout is associated with higher rates of collisions than parallel parking. In addition, angled parking also inherently increases the number of cars that can be parked along a given curb, which incentivizes automobile travel generally. However, one challenge of understanding the impact that angled parking has on safety and bicycle infrastructure is that cities do not always maintain accurate records as to where angled parking occurs. For example, San Francisco, CA has ambitious air-quality, climate-mitigation, and active transportation goals, all of which are undermined by angled parking. Yet, its supply of this parking layout is unquantified, given that parking angle was omitted from the city’s parking census. This study uses satellite imagery to resolve this data gap, and calculates that San Francisco dedicates 50 miles of street curbs to angled parking. While some assume angled parking is a planning response to San Francisco’s famed hills, the majority of it occurs on streets with no incline at all. As to angled parking’s traffic-calming effect, this benefit appears to be non-existent in San Francisco; average vehicle speeds differed by less than a half-mile per hour between angled-parking streets and adjacent non-angled streets. The angled parking identified here—particularly the four miles that overlap with the city’s bike-lane network—represents opportunities for conversion to more balanced road layouts. Overall, this methodology can serve as the basis for identifying angled parking in other cities, a configuration that should be re-evaluated by transportation planners given its car-centric effects, debatable ability to calm traffic, and preclusion of separated bicycle facilities.