At 14 feet wide, Chula Lane in the Mission District is one of the narrowest residential streets in San Francisco — barely wide enough for a single car to pass. At the other end of the spectrum is Parker Avenue. Running north and south along the east side of the Richmond District, it has an average width of 93 feet — enough for two car lanes, on-street parking on both sides of the street and sidewalks as wide as the car lanes.
That’s according to data on street widths from Adam Millard-Ball, an associate professor at the University of California, Los Angeles. The data includes primarily residential streets, as categorized by OpenStreetMap, that are at least 100 yards long. Street dimensions are of the entire right-of-way, including the roadway, sidewalks and landscaping.
Millard-Ball’s research suggests that the narrowest and widest streets aren’t just fun trivia. It also matters for how many people can comfortably live in a city.
In his new paper, Millard-Ball compared a street’s width to the value of land used for the street to understand the economic tradeoff between using land for streets versus other purposes, like parks, houses and other infrastructure. In places experiencing housing shortages, like San Francisco, wide streets take up land that could be used to build more homes.
The average residential street in San Francisco is about 50 feet wide, according to Millard-Ball’s research, similar to other U.S. cities. This is in part because of federal regulations established in the 1930s that set a 50-foot minimum-width requirement for residential streets to qualify for Federal Housing Administration mortgage insurance. Since then, local regulations have established minimum-width requirements ranging from 40 to 60 feet.
Similar standards are still in place today. In San Francisco, minor streets excluding alleys must be at least 40 feet wide, with a minimum roadway width of 26 feet. Some exceptions are made based on an area’s topography or conservation plans, but must be approved by the city’s public works department.
According to Millard-Ball, 16 feet is considered the functional minimum width required for access on residential streets. For some city dwellers, that might seem too narrow, and raise concerns over congestion, reduced on-street parking and unsafe conditions for pedestrians and cyclists. But Millard-Ball notes that, on low-volume residential streets, these changes would affect few people, and previous research suggests that narrower streets actually reduce traffic speeds and lead to fewer accidents. Streets like Chula Lane, with segments narrower than 16 feet, show that it’s possible to build such narrow streets.
In contrast, streets in the Richmond and Sunset districts, neighborhoods developed later in the city’s history, are notably wide. Parker Avenue, Jordan Avenue, and Palm Avenue on the east edge of the Richmond District are all wider than 80 feet. That is valuable land, according to Millard-Ball. He estimates that every 25 feet of land along each avenue is worth hundreds of thousands of dollars.
Millard-Ball’s research finds that high-cost West Coast counties, like San Francisco and Santa Clara, are particularly harmed by using land for wide streets that could be devoted to other uses. Although there would be costs to narrowing streets, Millard-Ball thinks it would be worth the investment.
In Santa Clara County, where the average street width is 53 feet, Millard-Ball claims narrowing streets to 16 feet would lead to over $100,000 in additional land value along the average street. This land reclaimed from streets could be used for parks and conservation, or simply given to the homeowners on that street, increasing their wealth.
But the primary lesson is for places that are growing, says Millard-Ball. In new neighborhoods, planners could build narrower streets, saving land for developers to build more housing, such as duplexes instead of single-family homes.
For cities with less growth, like San Francisco, narrowing existing streets may be difficult. But the pandemic has shown that cities can adapt unused street spaces into outdoor dining parklets, slow streets, and other recreational spaces.
