Support for LAist comes from
We Explain L.A.
Stay Connected

Share This

Transportation and Mobility

There's A New Push To Put The Brakes On LA's Rising Speed Limits

(Courtesy Los Angeles Department of Transportation)
Before you read this story...
Dear reader, we're asking for your help to keep local reporting available for all. Your financial support keeps stories like this one free to read, instead of hidden behind paywalls. We believe when reliable local reporting is widely available, the entire community benefits. Thank you for investing in your neighborhood.

Years of research, the rules of physics and common sense all point to an established fact about street safety: the faster people drive, the more dangerous and deadly our roads become.

Despite that fact, Los Angeles and other cities across California are regularly raising speed limits on their streets. They're doing that in order to enforce speeding laws in accordance with something called the 85th percentile rule, which roughly says if enough people are driving a certain speed, that should be the speed limit.

If that seems like a counterintuitive and incredibly flawed process to make streets safer, a broad coalition of public safety agencies, advocates and lawmakers across the state agrees. And now a new bill introduced in Sacramento aims to give cities more control over how they set and manage speed limits.


Support for LAist comes from

Here's a more detailed hypothetical of how the 85th percentile rule works on public roadways: say the posted speed limit on a city street is 35 mph. In order for police to enforce that speed limit using radar or laser, the city has to conduct surveys every seven to 10 years to determine how fast people are driving on that street. If the results show that at least 85% of drivers are going at or below 38 mph in that 35 mph zone, the 85th percentile rule requires the city to round the speed limit to the nearest interval of five, meaning the new posted speed limit will be 40 mph.

Fast-forward to the next survey of that street seven to 10 years later (if the city has the money to conduct it); if at least 85% of drivers are clocked at or below 43 mph, the speed limit would go up again, to 45 mph.

That "speed creep," as the task force report calls it, has been happening on hundreds of miles of streets in L.A. and across California.

And decades of research shows that even a 5-mph difference in speed can make all the difference in driver's ability to hit the brakes and avoid hitting a person, cyclist or other motorist.

A human body struck by a vehicle going 35 mph had a 68% chance of survival, according to researchers. That survival rate plummets to 35% if the vehicle is going 40 mph.


Just last month, the Zero Traffic Fatalities Task Force released a report examining the 85th percentile rule's methodology.

The 60-plus-page report outlines major limitations to that method, including that:

  • It is "not supported by scientific research," instead relying on a set of historical assumptions
  • It "privileges driver behavior" and assumes those drivers will act safely and responsibly
  • It does not consider different road types and road users like pedestrians and bicyclists

Those findings aren't new, though. A 2017 report from the National Transportation Safety Board found that "there is not strong evidence that the 85th percentile speed within a given traffic flow equates to the speed with the lowest crash involvement rate for all road types."

In other words, the rule hasn't been proven to reduce crash rates and make streets safer. That federal report also recommended that the Federal Highway Administration stop using the method to set speed limits.

Support for LAist comes from

The rule was originally intended to protect drivers from arbitrary speed traps, usually in rural areas where jurisdictions sometimes set dramatically low speed limits to ticket drivers and raise revenue. But, according to the task force's findings, the state's policy for calculating speed limits has remained "essentially static" even as the population, vehicle technology and road usage has evolved over the past several decades.


According to researchers: decades of misassumptions about a rule-of-thumb method that doesn't require city engineers to account for the complexities of different types of streets.

"It really is drivers voting with their feet," said Yu Hong Hwang, a graduate student researcher from UCLA's Institute of Transportation Studies, whose research into the history of the 85th percentile rule was cited in the state task force's report.

Hwang found evidence of the rule first being floated as far back as the 1930s, when the National Safety Council recommended it be applied to open highways in rural places where fewer car crashes were happening.

But then "like a game of telephone," Hwang said those particulars about what kind of roads and crash incidence rates were lost in the conversations.

"We sort of evolved to where we are today, which is that the 85th percentile is used for a wide variety of roads, even when there are sometimes plenty of other road users," he said. "I thought that there would be a little more scientific backing to it... but, as one of the people I talked to told me, 'it's very scientific, but it's not got a whole lot of science behind it.'"

(Courtesy Chad Elliott via Flickr)


New policy, according to the task force, which is comprised of dozens of state and municipal transportation, health and safety officials, pedestrian and cyclist advocates, auto industry representatives, engineers and consultants.

The group was created through Assembly Bill 2363, authored by state Assemblywoman Laura Friedman.

"This was the first time that we were able to bring all of the different stakeholders together from across the state," Friedman told LAist on Thursday. "I'm hoping that with that consensus, we will be able to go and change some of these laws that have handicapped cities [ability] to implement changes to make streets safer -- primarily for pedestrians and cyclists, [and] everybody who uses the road."

The task force's report calls for the state to adopt a policy that would revise the way traffic surveys are conducted "to specifically require consideration be given to bicyclist and pedestrian safety."

The task force also recommends changing state law to allow cities to reduce speeds below the 85th percentile allowance along High-Injury Networks, and post speed limits below 25 mph when supported by a traffic survey.


The next step just happened on Thursday, as Friedman introduced a new bill in the state Assembly.

AB 2121 calls for a committee of outside street design experts to work on revisions to the state's Highway Design Manual, which mandates the 85th percentile method.

The bill would essentially pause the 85th percentile rule and allow local governments to keep speed limits at the "prima facie" speed -- default speed limits set by the city for specific zones, like school zones, business districts and residential areas -- if road surveys show more traffic crashes are happening on those roads.

Friedman said the bill and future legislation will be amended over time to include more of the recommendations laid out in the task force report.


(Courtesy LADOT)

L.A. representation on the task force includes the city's Department of Transportation Director Seleta Reynolds, who has long maintained that speeding is the single biggest factor in deadly crashes. Reynolds told us the current method for setting speeds creates "a vicious cycle where speed limits increase because drivers are speeding."

"It would be like increasing a person's daily recommended calories because their neighbors overeat," Reynolds said in a statement to LAist. "Cities like Los Angeles need the flexibility to set speed limits that fit. We were grateful for the opportunity to participate in this groundbreaking work and look forward to championing these recommendations that, if implemented, will save lives."

L.A. City Councilman Mike Bonin said he was grateful for the report, which "properly diagnosed the problem," but hoped it had included stronger recommendations moving forward. Bonin has long been critical of the 85th percentile rule, calling it "absurd" and "one of the stupidest pieces of legislation" he's dealt with.

"Not only is it a stupid law, it's also a dangerous law because we know that the faster people are going, the more likely someone who gets hit by a car is going to die," he said. "It actually has deadly consequences."

Bonin, who chairs the council's transportation committee, said he'd like to see a speed limit system based on street type that also accounts for vulnerability and risk to all road users, rather than the current method that relies solely on how drivers behave.

Asked for comment about the possible changes to the 85th percentile rule, Mayor Eric Garcetti's spokesman Harrison Wollman told LAist the mayor "supports state reforms that will grant us more autonomy to set speed limits at the local level."

"Doing that will give us critical tools to keep Los Angeles safe for everyone who walks or bikes in our neighborhoods and drives on our roads," Wollman said.


A growing number of U.S. cities with Vision Zero programs -- an international initiative to eliminate all traffic deaths and serious injuries -- have made reducing speed limits an integral part of their work to reduce traffic deaths.

Seattle is lowering speeds on the vast majority of its streets to 25 mph. In 2017, Portland reduced the speed limit of its residential streets to 20 mph and lowered the limits on dozens of other roadways in the past few years.

New York City launched its Vision Zero program in 2014. That same year, city officials received authorization from the state to lower the speed limit from 30 mph to 25 mph on the majority of its streets. From 2014 through 2018, overall traffic deaths declined about 22% in NYC, and pedestrian deaths dropped nearly 18%. Traffic deaths were up in NYC last year, due in large part to a dramatic increase in cyclist deaths (from 10 in 2018 to 28 in 2019).

Looking at L.A. from 2015 (the year Mayor Garcetti launched Vision Zero) through 2019, overall traffic deaths jumped more than 30%, and pedestrian deaths have soared. An estimated 134 people walking L.A.'s streets were killed by drivers last year, an increase of about 52% from 2015.


The task force's report made several recommendations focused on improving enforcement of speeding laws, including automated speed enforcement (ASE), as in cameras that are triggered when a vehicle is measured going a set speed over the legal limit. California is not currently authorized to use them, but the task force suggested ways to consider them.

The report cites studies that found speed cameras to be an effective tactic to reduce speeding and increase safety. In New York City, which added speed cameras to about 140 school zones in recent years, speeding dropped 60% in those zones, according to city data.

New York City installed automated speed cameras in about 140 school zones and saw speeding drop by 60%, while injuries dropped by 17%, according to city data. (Courtesy New York City Department of Transportation via Twitter)

The task force acknowledges some limitations of speed cameras, including that drivers may continue to speed after encountering a camera and the fact that speed cameras have been challenged in court on constitutional grounds. The report also notes a negative public perception of the cameras as a means to make more money for an agency or city as opposed to a tool to make streets safer.

The report suggests several strategies to make speed cameras successful policy, like ensuring that ASE "supplement, not supplant, existing law enforcement personnel," and mandating that money generated an ASE program only be used to fund that program and other road safety initiatives so it doesn't become a money-making scheme for cities or law enforcement.

Assemblywoman Friedman said she isn't putting forward any legislation involving speed cameras right now, calling them "very controversial" and something that might warrant a larger conversation.


Just reducing speed limits won't fix the epidemic of traffic deaths L.A. and other cities are experiencing. Experts, advocates and some city officials agree that significantly reducing traffic deaths depends on a comprehensive shift on whose travel is prioritized. That means a concerted citywide effort to invest in education, enforcement and street improvements to reduce vehicle speeds.

But, as Los Angeles enters the midpoint year in its 2015-2025 Vision Zero initiative, that's simply not happening, Councilman Bonin told LAist this week.

"We approved the plan, and we talked about the plan, but we have not moved forward with it particularly aggressively," he said, adding that the city is "funding Vision Zero, almost as if it were a pilot [program] as opposed to a real thing."

You can read the full report from the Zero Traffic Fatalities Task Force below: