Last December, San Diego released a draft update of its "Street Design Manual," a handbook that guides traffic engineers in the design of city streets.
The highly technical document, which was last overhauled in 2002 ,and tweaked slightly in 2017, includes standards for things like street lighting, crosswalks, bike lanes, bus lanes, medians, tree planting and public seating.
The city says its goal with this update is to support safe and sustainable transportation and to streamline infrastructure projects, some of which have suffered delays and cost overruns due to outdated and inconsistent street design standards. City staffers are seeking public comment on the draft document before presenting it to the city council sometime later this year.
Gianella Ghiglino, spokesperson for the Automobile Club of Southern California, says street design is a critical component of traffic safety because it can reduce reliance on police writing tickets to enforce traffic laws.
"Enforcement isn't always possible for everything that happens," Ghiglino said. "It is very important that all these things align — so that's infrastructure, that's people being mindful and aware of the hazards as well, and people also having the desire to protect one another."
Below are five elements of street design that research shows have an impact on safety, along with an explanation of how they're dealt with in the city's draft Street Design Manual update.
Lane width
Historically, traffic engineers have considered wide lanes to be safer than narrow lanes because they can give drivers more of a buffer zone to react and avoid collisions. But recent research suggests that wider lanes are actually less safe.
A 2023 study from the Bloomberg School of Public Health at Johns Hopkins University, analyzed collision data on more than 1,100 street segments in seven American cities. It found that 12-foot wide lanes see significantly more collisions than 9-foot wide lanes.
Shima Hamidi, the professor who led the study, said wider lanes are more "relaxing" for drivers and can lead to a sense that it's safe and okay to speed.
"Drivers drive faster, and that's the speed that actually leads to crashes," Hamidi said. "When lanes are narrower, drivers tend to be more precautious of their environment and drive more carefully, and that leads to fewer crashes."
San Diego's draft Street Design Manual sets a preference of 10-foot wide lanes in some cases, and 11-foot wide lanes in other cases. It also allows lanes as wide as 12 feet with no additional scrutiny or review.
For lanes that are 9 feet wide, however, the manual requires additional review from the San Diego Fire-Rescue Department. Hamidi said this approach is backwards, and that cities should make narrower lanes the default while requiring extra review and justification for wider lanes.
Hamidi said narrowing lanes can be the fastest and cheapest way to improve street safety while also providing more space for things like wider sidewalks, bike lanes and tree planting.
"We are not making any changes on the traffic volume, the capacity — all of those remain the same," Hamidi said. "It's just about making those lanes that are unnecessarily wide — and unsafe as a result — safer."
Crosswalks
All across San Diego, you can find "no pedestrian crossing" signs. They're typically placed at locations where pedestrians want to cross the street, but where the city wants to discourage it. They can force pedestrians into long detours just to get from one side of the street to the other.
The draft Street Design Manual includes new guidance on crosswalk design, allowing features such as raised crosswalks. These can double as speed humps and force drivers to slow down.
But the manual makes no changes to the city's policy on where to install new crosswalks. The current policy uses a complex point system that can require costly and time consuming traffic studies before installing crosswalks. The policy does not consider collision data, meaning even if a location has a history of drivers hitting pedestrians, the city may still determine that safer crossing infrastructure is not warranted.
Laura Keenan, founder of the San Diego chapter of Families for Safe Streets, said the city should be removing "no pedestrian crossing" signs and making it easier to install safe crossing infrastructure based on the most direct and convenient pathways of travel.
"People are going to cross where it's convenient for them, and the street design should reflect where people are going to cross," Keenan said. "Pedestrians have just as much right to our streets and sidewalks as everybody else, and we want to make sure that they're staying safe."
Eric Dumbaugh, a professor at Florida Atlantic University and associate director of the Collaborative Sciences Center for Road Safety, agreed that cities should not try and prohibit pedestrians from crossing where it's easiest and fastest.
"Whenever we try to design around what we think people should do, and not what people are actually doing, we create situations where they're going to die," said Dumbaugh. "If the pedestrian is showing you what they want to do, then the designer needs to be sensitive to that information. That is critical data for safe design."
Slip lanes
Slip lanes allow drivers to make right turns without having to stop and queue behind other vehicles at an intersection, similar to a freeway exit. Dumbaugh said they can benefit drivers by reducing wait times — but they also lengthen the crossing distance for pedestrians and create new opportunities for collisions.
"In auto-priority zones where there's not a lot of pedestrian activity, it may be helpful to expedite traffic through an intersection," Dumbaugh said. "It's generally an undesirable feature if there's some pedestrian activity because it doesn't cause a vehicle approaching the intersection to stop."
San Diego's draft Street Design Manual does not mention slip lanes and provides no guidance on where they are appropriate or where they should be closed. It does, however, provide guidance around reducing the "turn radius" at intersections.
A large turn radius allows vehicles to make turns at higher speeds. Reducing the turn radius by extending the curb further into the roadway forces drivers into tighter turns that require slower speeds and more precaution.
Dumbaugh said slip lanes are a legacy of decades of auto-oriented planning and street design, and that only recently have cities begun to question their usefulness.
"Most of the stuff that makes it into our design manuals has never been substantially evaluated for its safety impacts," Dumbaugh said. "It's often stuff that was guessed on by folks 30, 40, 50 years ago, put into a manual and has never been substantively evaluated."
Protected bike lanes
Protected bike lanes, also called cycle tracks, include barriers that separate cyclists from moving cars. San Diego has installed them on a handful of streets, often sparking opposition from residents and businesses, especially when the bike lanes require the removal of street parking.
One study published in 2019 examined 13 years of data from 12 large American cities, finding that cities with more protected bike lanes see fewer traffic injuries and deaths. A study from 2022 involved surveys and on-road experiments with cyclists in New Zealand, finding that cyclists feel safer in protected bike lanes, and that parents were more likely to allow their kids to bike in them compared to unprotected bike lanes. Another study in 2022 found protected bike lanes in New York City led to an increase in biking overall, especially among women.
San Diego's draft Street Design Manual includes multiple options for both protected and unprotected bike lanes, along with general guidance on which designs are preferable depending on the context. It encourages — but does not require — buffer zones to protect from biking hazards, such as drivers opening doors into bike lanes without watching for oncoming cyclists. It does not offer design solutions for bike lanes that are frequently blocked by parked vehicles.
Laura Keenan founded Families for Safe Streets San Diego after her husband, Matt, was fatally struck by a driver while biking in an unprotected bike lane in 2021. She said her husband would still be alive today if that bike lane had physical protection, and that concerns over parking or traffic impacts should be secondary to safety.
"Sometimes the city will prioritize people's convenience, parking, people's ability to get places quickly … over someone's life, which is more important," Keenan said. "I don't think they think of it in those terms when they're making the decisions, but ultimately, that's what is happening. And today, the Street Design Manual does not dictate they must prioritize safety over convenience."
Liz Saba owns a jewelry store on 30th Street in North Park, where the city installed protected bike lanes in 2021. She opposed the project because it required the removal of street parking, which she said has led to a drop in foot traffic.
"I used to stay open until eight o'clock on Fridays and Saturdays because this was booming with people walking, waiting for restaurants and stuff," Saba said. "But now people just get dropped off by the Uber, and then they leave."
Even still, Saba said she thinks San Diego can balance the need for both bike lanes and parking by installing more meters in areas where parking is scarce.
"People are willing to pay to park," Saba said. "I think they will come if there's more parking meters in place, and I think that would be a good solution for everyone."
Right turn on red
For most of the 20th Century, it was generally illegal for drivers in the United States to make right turns on red lights. The maneuver was legalized across the country in the late '70s and early '80s in an effort to conserve gasoline by reducing idling at intersections.
Last December, researchers from several California universities published a study that concluded the gasoline savings are negligible, especially with the growth of electric and hybrid vehicles that don't burn fuel while idling. The study also analyzed collision data and found that right turn on red is "generally unsafe for pedestrians, bicyclists and drivers."
"The driver is looking left at oncoming traffic and failing to see the pedestrian right in front of them, or the cyclist right in front of them," said Bruce Appleyard, an SDSU city planning professor who co-authored the study. "The right turn on red policy actually encourages people to just cruise through the intersection."
Appleyard is also the author of Livable Streets 2.0, an updated version of a book his father published in 1981. One year later, his father was killed by a speeding drunk driver.
The book examines research into how good street design can foster not just safety but also greater happiness and stronger social connections among neighbors. Appleyard said these benefits are often overlooked by traffic engineers.
"It's not just about safety, but it's also about comfort and livability for pedestrians and cyclists," Appleyard said. "Rather than just looking at the safety calculations and the quantitative side of things, look at the qualitative side of things. Look at how places are much more comfortable and livable."
San Diego's draft Street Design Manual includes guidance on when "right turn on red" should be prohibited — particularly when walk signals are timed to give pedestrians a head start crossing the street before a traffic light turns green.
