Commentary: Will a Speeding Crackdown in Davis Disproportionately Impact Black and Brown People? History Says It Will


By David M. Greenwald
Executive Editor

Davis, CA – Before the Nextdoor admins removed the discussion there was an interesting engagement on the issue of a supposed police speed trap on Covell and Anderson.  Given that speed traps are not legal in California, I assumed that they simply meant they were cracking down on speeding vehicles.

My concern that I expressed on the site, before it was all removed, was that increased enforcement would mean a disproportionate crackdown on Black and brown populations.

Even in places like Davis—even facing clear and unambiguous stats—you get the same responses when you point this stuff out.

The first is the idea that the people they catch are simply lawbreakers.  If Black and brown people, by extension, are being disproportionately pulled over, that would mean they are speeding disproportionately.

The problem, as I tried to point out, is if you camp yourself out at a location with free-flowing traffic, you will have tons and tons of speeders.  How do you decide whom to pull over?  Many would say the most egregious violators.  To some extent, you will see that.  But most of the drivers pulled over with crackdowns are not being chosen in an objectively reckless manner.  Those are notable and noticeable, but relatively rare.

This is the problem—if half of the traffic is committing a moving violation, and a good proportion is exceeding the speed limit by at least five to ten mph, whom do you stop?

We know the answer to that because we have the data.  We have data in Davis and data that is universal.  In Davis, we know that Black and brown people are about six times more likely to be pulled over than whites.

And, in a lot of these cases, they are not issued tickets.  In fact Blacks, for example, in Davis as elsewhere are more likely to be pulled over and stopped, less likely to be issued a ticket for a moving violation, more likely to be searched and, once searched, less likely to be found in possession of contraband.  (Since I’ve made this point many times, not going to regurgitate the stats, google it though).

So what was the response?

One of the points made in response many times is unless you are right next to the car, it’s hard to tell the race of the driver.

We have data that disproves this as well.

In May of 2020 (before George Floyd and some of the other incidents, by the way), the Stanford School of Engineering released the largest ever study of racial profiling during traffic stops (link).

They analyzed 95 million traffic stops filed by officers with 21 state patrol and 35 municipal police forces (in other words, nearly half the states and 35 cities across the nation), over an eight-year period from 2011 to 2018.

“Researchers concluded that ‘police stops and search decisions suffer from persistent racial bias.’”

But, more than that, they found “blacks, who are pulled over more frequently than whites by day, are much less likely to be stopped after sunset, when ‘a veil of darkness’ masks their race.”

What does that tell you?  It tells you that, contrary to what ordinary residents can tell, the police really can tell the race of the driver when they pull them over.

That doesn’t surprise me because when I have ridden on ride-alongs—many of them over the years—police officers really see things that I don’t or can’t.

I used to think it was probably make and model of the car, and it may be some of that.  But obviously, that difference would not disappear at night.

There really isn’t a good counter-hypothesis here.  The volume of data and the starkness of the difference is overwhelming.

We are talking about hundreds of thousands of data points here.

“Because they had such a massive database, the researchers were able to find 113,000 traffic stops, from all of the locations in their database, that occurred on those days, before or after clocks sprang forward or fell back, when the sky was growing darker or lighter at around 7 p.m. local time.

“This dataset provided a statistically valid sample with two important variables — the race of the driver being stopped, and the darkness of the sky at around 7 p.m. The analysis left no doubt that the darker it got, the less likely it became that a black driver would be stopped. The reverse was true when the sky was lighter.”

The response on Nextdoor was a bit of data denial.  There is a reason you run multiple regressions in studies like this and collect a huge amount of data to avoid the kinds of pitfalls people tend to cite.  Here they use a logit model, modeling for the probability that a stopped driver is Black at a certain time, location and period of year.  (Read the whole study here—but, warning, the math will be obnoxious for the casual reader).

One person argued that they had no agenda here—other than a confessed desire to make streets safer, and that’s undoubtedly true.  Systemic racism does not generally arise from racist motivations, but rather from practices that over time have been shown to produce biased results.

I have no problem with cracking down on speeding.  But if the data show a disproportionate impact on Black and brown people—as the data have shown with police stops—that might suggest that there is a problem here.

We don’t solve this by denying that there was a problem—and unfortunately, Nextdoor didn’t help things by removing it.

About The Author

David Greenwald is the founder, editor, and executive director of the Davis Vanguard. He founded the Vanguard in 2006. David Greenwald moved to Davis in 1996 to attend Graduate School at UC Davis in Political Science. He lives in South Davis with his wife Cecilia Escamilla Greenwald and three children.

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    1. Bill Marshall

      Speed bumps and speed humps don’t discriminate. 

      I hope that was ‘tongue in cheek’…

      Speed bumps are hazardous to vehicles and occupants, particularly over 5 mph, yet ironically, at greater speeds, say 50 mph,, less so… they also work no better than frequent stop signs.  Speed humps a bit less so.

      Problem is, actually recognized by the “85% rule” that is the general method for establishing speed limits… study after study over very many years, indicate that ~85% of drivers drive at a speed equal to or less than what is safe for roadway and other conditions (inherent in the “basic speed law”).

      So, if you ‘artificially’ slow traffic @ a point, the human brain leads folk to ‘make up for lost time’, between them… most studies (going back ~ 50 years) consistently show that too many stop signs (for ex.), actually INCREASE speeds between intersections.  Or, they are ignored and sometimes ‘blown thru’, which decreases safety.  There have been fewer studies re:  speed humps or bumps, but they tend to trend to similar conclusions.

      “Traffic calming”, except for design features like visually (or physically) narrowing lanes, or some other striping schemes, is largely a ‘myth’… except for ‘impaired driving’, there is little correlation between velocity and crashes (if right-of way is clearly established at conflict points), but if someone does a ‘stupid’ or an ‘unwise’ and a crash happens, velocity IS directly related to severity of damage and extent of injuries (basic physics and biology)…

      1. Richard_McCann

        “Traffic calming”, except for design features like visually (or physically) narrowing lanes, or some other striping schemes

        This is precisely what “traffic calming” is. It’s setting up physical features (speed bumps etc are the worst option) that cause drivers to slow, and more importantly, to pay attention to the road because they must navigate a more challenging stretch of road. If speeding on Covell is a problem, the City should be adding features such a chicane to slow drivers.

        Speeding tickets are largely a waste of time to slow speeding because enforcement is so sporadic and really inconsequential in most cases. The cost of effective enforcement is so high that traffic calming is less expensive overall.

        1. Bill Marshall

          Another way of wording it (traffic calming), is making a roadway to either appear to be more dangerous, or physically make it so.

          But, we’re drifting, and admit my partial culpability there… by responding to Don S.

          The topic is crackdown in speeding, and racial overtones/bias.

      2. Bill Marshall

        rather than selective enforcement.

        Missed Don’s good point.

        Selective enforcement is not good nor appropriate.  It needs to be objective, not subjective, and based on reason. That is a true enforcement “issue”… not solvable by physical roadway changes.

        Which brings me to another pet peeve… family member got a new car that has a big display digital speedometer… I’ve always had an analog.  They see a speed limit sign, and speed up when they go below it, then brake if they are 1 mph above it.  Not rational.  But is.  I “drive the road”, aware of the factors that tell my gut what is reasonable and safe, under the driving conditions… if I have the gut feel that I am going too slow or too fast, I glance @ the speedometer… funny thing, is that I have yet to see a ‘speed study’ where the 85%-tile differed from my habits by more than 2 mph.

        Most traffic calming was demanded by “vox populi”, often with little/no objective basis (desire for ‘selective enforcement’?).  I’ve always wanted to do a speed study in neighborhoods demanding “traffic calming” to see what the driver behaviors of the ‘demanders’ is, compared to what they are complaining about, by “others”.  I think it would be illuminative.  Reviewing many of the “complaints”, there often seemed to be a correlation between what one neighborhood “got”, and what another neighborhood claimed to need somewhat thereafter…

        Speed limits are set (generally) by 5 mph increments… 25 MPH means somewhere between 22.5 and 27.5 should be de facto “OK”, unless other factors, such as weather lighting, pedestrian/bicycle activity, construction activity, etc. are present, where a reasonable person would dictate slowing… using those other factors, I have oft driven @ 10 mph in a 25 mph zone.  Duh!


  1. Keith Y Echols

    Maybe instead of not cracking down on speeding; safeguards, policies and procedures need to be put in place to prevent or at least mitigate any racial bias in speeding stops.

    That report isn’t a conclusive mic drop on the subject.  The “Veil of Darkness” is just a theory.  There’s nothing to indicate that pure racial bias is the cause of the racially disproportionate  traffic stops.   Maybe black people drive safer at night (because they have more to fear by being pulled over….the other conclusion of the study is that people of color tend to have their car searched more often) or that maybe non-people of color/white people drive more recklessly at night?   Racial bias probably is the reason is some regions. In other regions that’s the way the numbers shake out for whatever the reason.

    But back to my point that fear malpractice by the police shouldn’t prevent traffic enforcement.  The article states:

    For example, the researchers helped reporters at the Seattle-based non-profit news organization, Investigate West, understand the patterns in the data for stories showing bias in police searches of Native Americans. That reporting prompted the Washington State Patrol to review its practices and boost officer training. Similarly, the researchers helped reporters at the Los Angeles Times analyze data that showed how police searched minority drivers far more often than whites. It resulted in a story that was part of a larger investigative series that prompted changes in Los Angeles Police Department practices.

    This seems to me to be the best kind of use for this study.  Implementing measures to prevent racial bias and not simply avoiding law enforcement that may disproportionately effect a group for whatever the reason.

    1. David Greenwald

      It’s hard to statistically demonstrate motivation.  It’s easy to show comparative statics, which is what this did.  I don’t find your alternative explanation more compelling than the initial hypothesis.

      1. Keith Y Echols

        It’s hard to statistically demonstrate motivation.  I don’t find your alternative explanation more compelling than the initial hypothesis

        You choose to interpret the data the way you want to (Is there need for a study on your possible journalistic bias?).  I’m providing alternative plausible reasons for the data.

        The difficulty in assigning motivation is why decisions on overarching law enforcement strategy based on comparative statistics isn’t a good idea.  Training law enforcement to prevent and mitigate problems on the other hand is a good one reason to use these studies.

        And yes you can get closer to motivation with a more specific and targeted study.

      2. David Greenwald

        Bill criminal standard doesn’t apply here. If we are going to use a civil standard it would be preponderance of the evidence which I think is more than demonstrated with the data.

  2. Dave Hart

    The report that refers to the 113,000 traffic stops doesn’t break this down by how the driver was targeted.  I can definitely understand disparity if a motorist is pulled over after being visually observed.  This is the classic “broken tail light” or “failure to signal” stop that has led to the death of motorists of color.  But what are the data on radar based speeding or cameras?  This is the type of enforcement that would not seem to involve race, gender or any other driver characteristic.  If we are going to use enforcement as a tool to reduce speeding and signal violations, we need to get over the idea that cameras and radar are “bad”.  Technology is great when it runs everyone through the same meat grinder and I will gladly include myself if it can cut down on the nonsense we see on the roads.

    That said, I want to give a BIG second to Richard McCann’s comments about street and road design.  I would rather be held up for a whole minute or “my gawd” two whole minutes crossing town if the streets would simply not allow me to go any faster.  Speed bumps are a lot less expensive than police officers’ time and can eliminate tickets and fines for the rest of us.  And damage to vehicles — puh-leeeze! What is this worship of being able to drive way too fast in the name of “saving” an insignificant amount of time?

    And, finally, while this may be a little off topic, I’d love to see an addition to the vehicle code that requires an exhaust system decibel test as part of the emissions control test for registration.  If it’s too loud when tested specifically for loudness, the car can’t be released to the motorist without returning the exhaust system to factory condition.

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