FOR PUBLICATION

UNITED STATES COURT OF APPEALS

FOR THE NINTH CIRCUIT

SUSAN PORTER, 

Plaintiff-Appellant,

 v. 

KELLY MARTINEZ, in her official 

capacity as Sheriff of San Diego 

County; AMANDA RAY, as 

successor to Warren Stanley, in her 

official capacity as Commissioner of 

California Highway Patrol, 

Defendants-Appellees,

and 

WARREN STANLEY, 

Defendant.

No. 21-55149 

D.C. No. 

3:18-cv-01221-

GPC-LL 

ORDER AND 

AMENDED 

OPINION

Appeal from the United States District Court

for the Southern District of California

Gonzalo P. Curiel, District Judge, Presiding
2 PORTER V. MARTINEZ

Argued and Submitted March 7, 2022

Submission Vacated March 17, 2022

Resubmitted March 31, 2023

Pasadena, California

Filed April 7, 2023

Amended May 22, 2023

Before: Marsha S. Berzon and Michelle T. Friedland, 

Circuit Judges, and Edward R. Korman,* District Judge.

Order;

Opinion by Judge Friedland;

Dissent by Judge Berzon

SUMMARY**

Civil Rights

The panel affirmed the district court’s summary 

judgment in favor of the State of California in an action 

challenging a California law that prohibits honking a 

vehicle’s horn except when reasonably necessary to warn of 

a safety hazard. Cal. Veh. Code § 27001.

Plaintiff was cited for misuse of a vehicle horn under 

Section 27001 after she honked in support of protestors 

* The Honorable Edward R. Korman, United States District Judge for the 

Eastern District of New York, sitting by designation.

** This summary constitutes no part of the opinion of the court. It has 

been prepared by court staff for the convenience of the reader.
PORTER V. MARTINEZ 3

gathered outside a government official’s office. Although 

the citation was dismissed, Porter filed suit to block future 

enforcement of 27001 against any expressive horn 

use―including honks not only to “support candidates or 

causes” but also to “greet friends or neighbors, summon 

children or co-workers, or celebrate weddings or 

victories.” She asserted that Section 27001 violates the First 

and Fourteenth Amendments as a content-based regulation 

that is not narrowly tailored to further a compelling 

government interest. Alternatively, she argued that even if 

the law is not content based, it burdens substantially more 

speech than necessary to protect legitimate government 

interests.

The panel first held that plaintiff had standing to 

challenge the law because, ever since she received a citation 

for impermissible horn use, she has refrained from honking 

in support of political protests to avoid being cited again.

Addressing the merits, the panel determined that at least 

in some circumstances, a honk can carry a message that is 

intended to be communicative and that, in context, would 

reasonably be understood by the listener to be 

communicative. The panel next held that because section

27001 applies evenhandedly to all who wish to use a horn 

when a safety hazard is not present, it draws a line based on 

the surrounding factual situation, not based on the content of 

expression. The panel therefore evaluated Section 27001 as 

a content-neutral law and applied intermediate scrutiny. The 

panel concluded that Section 27001 was narrowly tailored to 

further California’s substantial interest in traffic safety, and 

therefore that it passed intermediate scrutiny. The panel 

noted that plaintiff had not alleged that the State has a policy 

or practice of improper selective enforcement of Section 
4 PORTER V. MARTINEZ

27001, so the panel had no occasion to address that 

possibility here.

Dissenting, Judge Berzon would hold that Section 27001 

does not withstand intermediate scrutiny insofar as it 

prohibits core expressive conduct, and is therefore 

unconstitutional in that respect. The majority’s fundamental 

error was that it failed to sufficiently focus on the specific 

type of enforcement at the core of this case—enforcement 

against honking in response to a political protest. Honking 

at a political protest is a core form of expressive conduct that 

merits the most stringent constitutional protection, and is, in 

that respect, qualitatively different from warning honks and 

other forms of vehicle horn use. Section 27001 violates the 

First Amendment because defendants have not shown that 

the statute furthers a significant government interest as 

applied to political protest honking, and because the statute 

is not narrowly tailored to exclude such honking. Judge 

Berzon would grant an injunction prohibiting the 

enforcement of Section 27001 against political protest 

honking.

COUNSEL

John David Loy (argued), First Amendment Coalition, San 

Rafael, California; J. Mark Waxman, Mikle S. Jew, Lindsey 

L. Pierce, and Benjamin J. Morris, Foley & Lardner LLP, 

San Diego, California; for Plaintiff-Appellant.

Jeffrey P. Michalowski (argued), Quarles & Brady LLP, San 

Diego, California; Timothy M. White, Senior Deputy, Office 

of County Counsel, County of San Diego, San Diego, 
PORTER V. MARTINEZ 5

California; for Defendant-Appellee Kelly Martinez, Sheriff 

of San Diego County.

Sharon L. O’Grady (argued), Deputy Attorney General; Paul 

E. Stein, Supervising Deputy Attorney General; Thomas S. 

Patterson, Senior Assistant Attorney General; Rob Bonta, 

Attorney General of California; Office of the California 

Attorney General; San Francisco, California; for DefendantAppellee Amanda Ray, commissioner of California 

Highway Patrol.

David Snyder, First Amendment Coalition, San Rafael, 

California; G.S. Hans, Cornell Law School, Ithaca, New 

York; for Amicus Curiae First Amendment Coalition.

ORDER

The opinion filed on April 7, 2023, from which Judge 

Berzon dissented, is amended as follows, with Judge Berzon 

dissenting from the amendment as well:

Page 18, Footnote 6: Change <Indeed, when pressed at 

oral argument on whether she sought to enjoin the statute as 

applied only to political honking, she expressly disavowed 

any such limitation of her argument, firmly replying that she 

sought to enjoin enforcement against “all expressive conduct 

through use of a vehicle horn.”> to <Indeed, when pressed 

at oral argument on whether she sought to enjoin the statute 

as applied only to political honking or as applied to all 

expressive conduct, Porter’s counsel expressly disavowed 

any such limitation of Porter’s argument: “We would ask 

ultimately for an injunction that prohibited enforcement 

against all expressive conduct through use of a vehicle horn. 
6 PORTER V. MARTINEZ

If the district court chose to limit it more narrowly, for 

concerns about workability or enforcement, we would 

address that in the briefs and the district court would decide 

that in its discretion based on the record and evidence. Our 

position as plaintiff is that yes, the First Amendment would 

prohibit enforcement of the statute against all expressive 

horn use, be it personal or political.” Oral Arg. at 00:07:50-

00:08:51. At other times in the oral argument, Porter’s 

counsel again said that the district court would have 

discretion in crafting an injunction, but never backed away 

from the notion that Porter’s challenge was to Section 

27001’s prohibition on all expressive honking.>

With that amendment, Judge Friedland has voted to deny 

the petition for rehearing en banc, and Judge Korman so 

recommends. Judge Berzon recommends granting the 

petition for rehearing en banc.

The full court has been advised of the petition for 

rehearing en banc, and no judge has requested a vote on 

whether to rehear the matter en banc. Fed. R. App. P. 35.

The petition for rehearing en banc is DENIED. No 

future petitions for rehearing or rehearing en banc will be 

entertained. 
PORTER V. MARTINEZ 7

OPINION

FRIEDLAND, Circuit Judge:

Appellant Susan Porter brings a First Amendment 

challenge to a California law that prohibits honking a 

vehicle’s horn except when reasonably necessary to warn of 

a safety hazard. We hold that Porter has standing to 

challenge that law because, ever since she received a citation 

for impermissible horn use, she has refrained from honking 

in support of political protests to avoid being cited again. 

Applying intermediate scrutiny, we affirm the district court’s 

rejection of Porter’s constitutional challenge.

I.

A.

California has regulated the use of automobile warning 

devices such as horns since the dawn of the automobile. In 

1913, five years after the introduction of the Model T Ford, 

California adopted the first version of the law challenged 

here: 

Every motor vehicle shall be equipped with a 

bell, gong, horn, whistle or other device in 

good working order, capable of emitting an 

abrupt sound adequate in quality and volume 

to give warning of the approach of such 

vehicle to pedestrians and to the riders or 

drivers of animals or of other vehicles and to 

persons entering or leaving street, interurban 

and railroad cars. No person shall sound such 

bell, gong, horn, whistle or other device for 

any purpose except as a warning of danger.
8 PORTER V. MARTINEZ

Act of May 31, 1913, ch. 326, § 12, 1913 Cal. Stat. 639, 645; 

see Robert Casey, The Model T: A Centennial History 1 

(2008). Today, the relevant provision of the California 

Vehicle Code provides:

(a) The driver of a motor vehicle when 

reasonably necessary to insure safe 

operation shall give audible warning with 

his horn.

(b) The horn shall not otherwise be used, 

except as a theft alarm system.

Cal. Veh. Code § 27001 (“Section 27001”). Section 27001 

“applies to all vehicles whether publicly or privately owned 

when upon the highways.” Id. § 24001. “Highway” is

defined as “a way or place of whatever nature, publicly 

maintained and open to the use of the public for purposes of 

vehicular travel”—in other words, “[h]ighway includes 

street.” Id. § 360. Forty other states and the Uniform 

Vehicle Code provide similar limitations on the use of 

vehicle horns. See Appendix. 

Section 27001 is in a division of the California Vehicle 

Code regulating the required equipment for vehicles in 

California. See id. div. 12 (“Equipment of Vehicles”). That 

division of the Code contains various other limitations on the 

use of equipment for safety purposes. See, e.g., id. § 25268 

(“No person shall display a flashing amber warning light on 

a vehicle as permitted by this code except when an unusual 

traffic hazard exists.”); id. § 25269 (“No person shall display 

a flashing or steady burning red warning light on a vehicle 

except as permitted by Section 21055 or when an extreme 

hazard exists.”). The Vehicle Code is enforced by the 
PORTER V. MARTINEZ 9

California Highway Patrol and by local law enforcement 

agencies. 

B.

In 2017, Susan Porter drove her car past a group of 

protesters gathered outside a government official’s office—

a protest that, minutes earlier, she herself had been attending. 

As she drove down the street, which was located between a 

residential area and a six-lane freeway, Porter honked in 

support of the protesters. A sheriff’s deputy pulled her over 

and gave her a citation for misuse of a vehicle horn under 

Section 27001. Porter’s citation was later dismissed when 

the sheriff’s deputy failed to attend Porter’s traffic court 

hearing. Porter subsequently brought this action challenging 

the constitutionality of Section 27001. 

Porter’s Complaint seeks declaratory and injunctive 

relief against the Sheriff of San Diego County (“the Sheriff”)

and the Commissioner of the California Highway Patrol 

(“CHP”) in their official capacities (collectively, “the 

State”1). She contends that Section 27001 violates the First 

and Fourteenth Amendments as a content-based regulation 

that is not narrowly tailored to a compelling government 

interest. Alternatively, she argues that even if the law is not 

content based, it is a content-neutral regulation that burdens 

substantially more speech than necessary to protect 

legitimate government interests. Porter alleges that she

drives by rallies, protests, and demonstrations in San Diego 

1 The Sheriff joins all of CHP’s arguments about the constitutionality of 

Section 27001. Those arguments address all the issues we need to reach 

to affirm, so we do not consider any arguments that are specific to the 

Sheriff, including her argument that she is not liable under Monell v. 

Department of Social Services, 436 U.S. 658 (1978).
10 PORTER V. MARTINEZ

County and elsewhere in California and would like to 

express her support for these events by honking. She alleges

that she now refrains from using her horn for such purposes

because she fears enforcement of Section 27001. Porter 

seeks to block enforcement of Section 27001 against what 

she calls “expressive” honking. In Porter’s view, expressive 

horn use includes honks not only to “support candidates or 

causes” but also to “greet friends or neighbors, summon 

children or co-workers, or celebrate weddings or victories.” 

The State moved to dismiss Porter’s First Amendment 

claim. The State argued that even if Section 27001 governs 

expressive activity, the law is content neutral and reasonably 

furthers California’s interests in promoting traffic safety and 

reducing noise pollution. Applying intermediate scrutiny, 

the district court concluded that, on the pleadings at least, the 

State had “defaulted on [its] burden of showing that honks 

such as Plaintiff’s undermine the government’s interest in 

traffic safety and noise control.” Accordingly, the district 

court refused to dismiss the First Amendment claim.

The parties proceeded to discovery and eventually filed 

cross-motions for summary judgment. In support of the

noise-control rationale for Section 27001, the State 

submitted numerous government reports and scientific 

articles discussing the contributions honking and other 

traffic sounds can make to noise pollution, and the dangers 

noise pollution poses to human health. 

In support of the traffic-safety rationale, the State relied 

heavily on the expert testimony of Sergeant William Beck, a

twenty-four-year veteran of CHP. Sergeant Beck opined 

that “when a vehicle horn is used improperly, it can create a 

dangerous situation by startling or distracting drivers and 

others,” and that “the vehicle horn’s usefulness as a warning 
PORTER V. MARTINEZ 11

device would be diminished if law enforcement officers 

were unable to enforce Vehicle Code section 27001.” He 

explained: 

Absent Vehicle Code section 27001, people 

would be free to, and could be expected to, 

use the horn for purposes unrelated to traffic 

safety. That would, in turn, diminish the 

usefulness of the vehicle horn for its intended 

purpose, which is to be used as a warning or 

for other purposes related to the safe 

operation of a vehicle. 

When asked in a deposition, Sergeant Beck admitted that he

was unaware of any “specific accident or collision that was 

caused by the use of a vehicle horn.” Porter’s rebuttal expert, 

Dr. Peter Hancock, criticized Sergeant Beck’s opinions 

about the link between Section 27001 and traffic safety as 

unsupported by scientific studies; relying in part on these 

criticisms, Porter moved unsuccessfully to exclude Sergeant 

Beck’s expert testimony under Federal Rule of Evidence 

702. 

The district court entered summary judgment in favor of

the State. After holding that Porter had standing to bring a 

pre-enforcement challenge based on self-censorship, the 

district court repeated its earlier conclusion that Section 

27001 is content neutral and subject to intermediate scrutiny. 

The court excluded the State’s government and scientific 

reports as hearsay but held that, although the State “ha[d] 

offered little in the way of scientific studies that [wa]s not 

hearsay, . . . history, consensus, common sense, and the 

declaration of Sergeant Beck support[] the [State’s] 

proffered justification[s].” The court concluded that 
12 PORTER V. MARTINEZ

California’s interests in maintaining traffic safety and 

reducing noise pollution are significant, and that Section 

27001 is narrowly tailored to serve those interests. 

Porter timely appealed. 

II.

We evaluate standing de novo. California v. Azar, 911 

F.3d 558, 568 (9th Cir. 2018). We also review de novo an 

order granting summary judgment. Italian Colors Rest. v. 

Becerra, 878 F.3d 1165, 1171 (9th Cir. 2018). 

III.

To establish Article III standing, a plaintiff must show 

that she suffered an injury in fact, the injury is fairly 

traceable to the challenged conduct of the defendant, and it 

is likely that her injury will be redressed by a favorable 

judicial decision. Italian Colors Rest. v. Becerra, 878 F.3d 

1165, 1171 (9th Cir. 2018). “First Amendment challenges 

‘present unique standing considerations’ because of the 

‘chilling effect of sweeping restrictions’ on speech.” Id. at 

1171 (quoting Ariz. Right to Life Pol. Action Comm. v. 

Bayless, 320 F.3d 1002, 1006 (9th Cir. 2003)). “[W]here a 

plaintiff has refrained from engaging in expressive activity 

for fear of prosecution under the challenged statute, such 

self-censorship is a constitutionally sufficient injury as long 

as it is based on an actual and well-founded fear that the 

challenged statute will be enforced.” Libertarian Party of 

L.A. v. Bowen, 709 F.3d 867, 870 (9th Cir. 2013) (alteration 

in original) (quoting Human Life of Wash. Inc. v. 

Brumsickle, 624 F.3d 990, 1001 (9th Cir. 2010)). To assess 

the credibility of a claimed threat of enforcement, we have

looked to factors such as “(1) whether the plaintiffs have 

articulated a ‘concrete plan’ to violate the law in question, 
PORTER V. MARTINEZ 13

(2) whether the prosecuting authorities have communicated 

a specific warning or threat to initiate [enforcement] 

proceedings, and (3) the history of past prosecution or 

enforcement under the challenged statute.”2 Id. (quoting 

McCormack v. Hiedeman, 694 F.3d 1004, 1021 (9th Cir.

2012)).

The State argues that Porter has not established a wellfounded fear because she has not shown a concrete plan for 

expressive honking and she previously “honked only at the 

single protest at which she was cited.” The State’s argument

is unpersuasive. Porter testified: “[I]f I was driving down 

the freeway and there was a banner that said ‘Support Our 

Veterans,’ I now would not honk my horn because the CHP 

could pull me over.” She also described driving by specific 

political protests where she had wished to honk to show her 

support but refrained from doing so to avoid receiving 

another citation. Porter’s testimony is specific enough to 

show that her expressive activity is being chilled. 

The State next argues that the odds of anyone being cited 

for honking are “vanishingly small.” For example, CHP 

points out that it issues an average of eighty citations per year 

for Section 27001 violations. Similarly, evidence in the 

record shows that in recent years the Sheriff’s Department

has issued approximately eight citations per year under 

Section 27001. But both CHP and the Sheriff nevertheless 

do enforce Section 27001, and they do not disclaim their 

ability to do so in cases of expressive honking. That Porter

was cited the one time she honked in support of a protest is 

“good evidence that the threat of enforcement is not 

2 As discussed below, we conclude that honking can constitute 

expressive activity.
14 PORTER V. MARTINEZ

‘chimerical.’” Susan B. Anthony List v. Driehaus, 573 U.S. 

149, 164 (2014) (quoting Steffel v. Thompson, 415 U.S. 452, 

459 (1974)). Whatever the statistical likelihood of any 

driver’s receiving a Section 27001 citation, Porter’s own 

experience supports “an actual and well-founded fear that 

the challenged statute will be enforced” against her. Bowen, 

709 F.3d at 870 (quoting Human Life, 624 F.3d at 1001).

Porter has thus shown a concrete injury in the form of selfcensorship caused by Section 27001. 

The State further arguesthat Porter’s alleged injury is not 

redressable, contending that a statewide injunction to protect 

expressive honking would be unconstitutionally vague and 

would raise concerns about federalism. But those concerns 

go to the proper scope of any remedy, not the “constitutional 

minimum” of redressability, which “depend[s] on the relief 

that federal courts are capable of granting.” Kirola v. City 

& County of San Francisco, 860 F.3d 1164, 1176 (9th Cir. 

2017). Because the district court could declare Section 

27001 unconstitutional and unenforceable in its entirety, 

thereby redressing Porter’s alleged injury, we conclude that 

the redressability requirement is satisfied. We therefore 

proceed to the merits of Porter’s First Amendment 

challenge.

IV.

The First Amendment “literally forbids the abridgment 

only of ‘speech,’” but its protections “do[] not end at the 

spoken or written word.” Texas v. Johnson, 491 U.S. 397, 

404 (1989). Conduct—such as burning a flag, wearing a 

black armband, or staging a sit-in—“may be ‘sufficiently 

imbued with elements of communication to fall within the 

scope of the First and Fourteenth Amendments.’” Id. 

(quoting Spence v. Washington, 418 U.S. 405, 409 (1974)
PORTER V. MARTINEZ 15

(per curiam)); see also id. at 406 (holding that burning an 

American flag at a political protest was protected 

expression); Tinker v. Des Moines Indep. Cmty. Sch. Dist., 

393 U.S. 503, 505-06 (1969) (holding that wearing black 

armbands to protest the war in Vietnam was protected 

expression); Brown v. Louisiana, 383 U.S. 131, 141-42 

(1966) (holding that a silent sit-in to protest racial 

segregation in a public library was protected expression). 

“Non-verbal conduct implicates the First Amendment when 

it is intended to convey a ‘particularized message’ and the 

likelihood is great that the message would be so understood.” 

Nunez v. Davis, 169 F.3d 1222, 1226 (9th Cir. 1999) 

(quoting Johnson, 491 U.S. at 404)). That said, “a narrow, 

succinctly articulable message is not a condition of 

constitutional protection” for expressive conduct. Hurley v. 

Irish-Am. Gay, Lesbian & Bisexual Grp. of Bos., 515 U.S. 

557, 569 (1995). 

In “quintessential public forums” such as streets, parks,

and other “places which by long tradition . . . have been 

devoted to assembly and debate, the rights of the state to 

limit expressive activity are sharply circumscribed.” Perry 

Educ. Ass’n v. Perry Loc. Educators’ Ass’n, 460 U.S. 37, 45 

(1983). “The government bears the burden of justifying the 

regulation of expressive activity in a public forum.” Berger 

v. City of Seattle, 569 F.3d 1029, 1035 (9th Cir. 2009) (en 

banc). 

When considering a First Amendment challenge to a law 

regulating expression in a public forum, we ask first whether 

the law is content based or content neutral. United States v. 

Swisher, 811 F.3d 299, 311 (9th Cir. 2016) (en banc). 

“Government regulation of speech is content based if a law 

applies to particular speech because of the topic discussed or 

the idea or message expressed.” Reed v. Town of Gilbert, 
16 PORTER V. MARTINEZ

576 U.S. 155, 163 (2015). The “crucial first step in the 

content-neutrality analysis,” the Supreme Court has 

instructed, is “determining whether the law is content neutral

on its face”—that is, whether it “draws distinctions based on 

the message a speaker conveys.” Id. at 163, 165. “A law 

that is content based on its face is subject to strict scrutiny 

regardless of the government’s benign motive, contentneutral justification, or lack of ‘animus toward the ideas 

contained’ in the regulated speech.” Id. at 165 (quoting 

Cincinnati v. Discovery Network, Inc., 507 U.S. 410, 429 

(1993)). The second step in the content-neutrality analysis 

is to ask whether the law is content based in its justification. 

Even “facially content neutral” regulations will be 

considered content based if they “cannot be ‘justified 

without reference to the content of the regulated speech’” or 

“were adopted by the government ‘because of disagreement 

with the message [the speech] conveys.’” Id. at 164

(alteration in original) (quoting Ward v. Rock Against 

Racism, 491 U.S. 781, 791 (1989)). 

The threshold content-neutrality question is often 

critical. “It is rare that a regulation restricting speech 

because of its content will ever be permissible,” United 

States v. Playboy Ent. Grp., Inc., 529 U.S. 803, 818 (2000), 

because such a regulation must satisfy strict scrutiny—that 

is, “the regulation is valid only if it is the least restrictive 

means available to further a compelling government 

interest,” Berger, 569 F.3d at 1050. By contrast, a contentneutral regulation of expression must meet the less exacting 

standard of intermediate scrutiny. Turner Broad. Sys., Inc. 

v. FCC, 512 U.S. 622, 642 (1994). For content-neutral rules 

governing expressive conduct, then, a regulation is 

constitutional “if it furthers an important or substantial 

governmental interest; if the governmental interest is 
PORTER V. MARTINEZ 17

unrelated to the suppression of free expression; and if the 

incidental restriction on alleged First Amendment freedoms 

is no greater than is essential to the furtherance of that 

interest.” United States v. O’Brien, 391 U.S. 367, 377

(1968); see Swisher, 811 F.3d at 312.

3

A.

The parties do not dispute that Section 27001 effectively 

forbids drivers from honking in public forums unless there

is a traffic-safety reason to do so. That makes sense, because 

Section 27001 applies on public streets, which are “the 

archetype of a traditional public forum.” Comite de 

Jornaleros de Redondo Beach v. City of Redondo Beach, 657 

F.3d 936, 945 (9th Cir. 2011) (en banc) (quoting Snyder v. 

Phelps, 562 U.S. 443, 456 (2011)).

4

The parties also do not dispute that at least some of the 

honking prohibited by Section 27001 is expressive for First 

Amendment purposes. We agree. Whether conduct such as 

honking is “sufficiently imbued with elements of 

communication” to be protected expression depends on “the 

3 The O’Brien test is substantively equivalent to the requirement that a 

content-neutral time, place, or manner restriction on speech be “narrowly 

tailored to serve a significant governmental interest” and “leave open 

ample alternative channels for communication of the information.” 

Clark v. Cmty. for Creative Non-Violence, 468 U.S. 288, 293, 298 & n.8

(1984); see Swisher, 811 F.3d at 312 & n.7 (explaining that the two tests 

are equivalent). In the analysis that follows, we therefore rely on cases 

applying either test.

4 Presumably because Section 27001 applies in some public forums, the 

State concedes that intermediate scrutiny applies to our evaluation of the 

statute’s constitutionality. Given that concession, and because we 

conclude that the law survives intermediate scrutiny, we need not decide 

whether all the places in which Section 27001 applies are public forums.
18 PORTER V. MARTINEZ

nature of [the] activity, combined with the factual context 

and environment in which it was undertaken.” Spence, 418 

U.S. at 409-10. The protest at which Porter received a 

Section 27001 citation provides an example. Porter attended 

the protest and, while departing in her car, honked her horn 

in three clusters of short beeps, for a total of fourteen beeps. 

She later testified that her intent was to show support for the 

protest. The crowd cheered, suggesting that the group with 

which she had just been protesting understood her intended 

message. Porter’s experience shows that, at least in some 

circumstances, a honk can carry a message that “is intended 

to be communicative and that, in context, would reasonably 

be understood by the [listener] to be communicative.” Clark 

v. Cmty. for Creative Non-Violence, 468 U.S. 288, 294 

(1984). Of course, a honk is just a noise, so it may not 

always be understood—indeed, it may be particularly 

susceptible to being misunderstood given the inflexibility of 

the medium. A driver honking while passing by a protest 

might be expressing support, expressing disagreement, or 

signaling to another driver that continuing to change lanes 

could cause an accident. But the nature and circumstances 

of the honk will sometimes provide the necessary context for 

the message intended by the honk to be understood. 

Although we do not define today the full scope of expressive 

honking, we hold that enough honks will be understood in 

context to treat Section 27001 as prohibiting some 

expressive conduct.5 

5 Porter’s Complaint purported to challenge Section 27001 both (1) on 

its face and (2) as applied to expressive horn use, though at times in the 

litigation she has seemed to use these phrases interchangeably. Those 

challenges are probably not entirely equivalent, because some horn use 
PORTER V. MARTINEZ 19

B.

We next consider whether Section 27001 is a contentbased regulation of expressive honking.

6

 Again, Section 

seems neither safety-related nor expressive. For example, a driver might 

honk along to the beat of music, or a child might reach over the driver to 

honk the horn for fun. Ultimately, however, we need not decide whether 

Porter’s claim is best described as an as-applied or facial challenge (or 

both). Our constitutional analysis will be the same either way because 

“the substantive legal tests used in [facial and as-applied] challenges are 

‘invariant.’” Hoye v. City of Oakland, 653 F.3d 835, 857 (9th Cir. 2011)

(quoting Legal Aid Servs. of Or. v. Legal Servs. Corp., 608 F.3d 1084, 

1096 (9th Cir. 2010)). 

6 The dissent argues that Section 27001 is unconstitutional as applied to 

political honking—specifically, “honking in response to a political 

protest.” But Porter herself has not advanced that argument, contending 

instead that the statute is unconstitutional as applied to all expressive 

honking, which under her definition includes honking to communicate 

greetings and celebratory sentiments, among other things. Indeed, when 

pressed at oral argument on whether she sought to enjoin the statute as 

applied only to political honking or as applied to all expressive conduct, 

Porter’s counsel expressly disavowed any such limitation of Porter’s 

argument:

“We would ask ultimately for an injunction that 

prohibited enforcement against all expressive conduct 

through use of a vehicle horn. If the district court 

chose to limit it more narrowly, for concerns about 

workability or enforcement, we would address that in 

the briefs and the district court would decide that in its 

discretion based on the record and evidence. Our 

position as plaintiff is that yes, the First Amendment 

would prohibit enforcement of the statute against all 

expressive horn use, be it personal or political.” 

Oral Arg. at 00:07:50-00:08:51. At other times in the oral argument, 

Porter’s counsel again said that the district court would have discretion 
20 PORTER V. MARTINEZ

27001 provides that “[t]he driver of a motor vehicle when 

reasonably necessary to [e]nsure safe operation shall give 

audible warning with his horn,” but that “[t]he horn shall not 

otherwise be used, except as a theft alarm system.”7 Cal. 

Veh. Code § 27001. Porter argues that Section 27001 is 

content based “on its face” because it “draws distinctions 

based on the message a speaker conveys.” Reed, 576 U.S. 

at 163. 

We disagree. Even if we were to accept Porter’s 

questionable assertion that honking to give a warning is a 

form of expression, the relevant distinction Section 27001 

makes is not, as Porter suggests, between honks intended to 

convey warnings and honks intended to convey other 

messages. Rather, the law prohibits all driver-initiated horn 

use except when such use is “reasonably necessary to 

[e]nsure safe operation” of the vehicle. Thus, while it may 

be that Section 27001 prohibits some expressive conduct, the 

in crafting an injunction, but never backed away from the notion that 

Porter’s challenge was to Section 27001’s prohibition on all expressive 

honking. Taking Porter at her word, we decide only whether the statute 

is unconstitutional on its face or as applied to all expressive honking. See 

Bell v. Wilmott Storage Servs., LLC, 12 F.4th 1065, 1071 n.8 (9th Cir. 

2021) (declining to consider certain arguments where the defendant 

failed to make the relevant arguments in its briefing and disclaimed such 

arguments at oral argument); cf. Greenlaw v. United States, 554 U.S. 

237, 243 (2008) (“[W]e rely on the parties to frame the issues for 

decision and assign to courts the role of neutral arbiter of matters the 

parties present.”). We emphasize that although Porter’s Article III 

standing stems from the citation she received after honking at a protest, 

that citation was dismissed, and no aspect of her current arguments or 

our analysis of them turns on the particular facts of that incident.

7 Use of a horn as a theft alarm is part of an automatic system, not a honk 

initiated by the driver. See Cal. Veh. Code. § 28085. Porter does not 

argue that the exception for theft alarms is a content-based distinction. 
PORTER V. MARTINEZ 21

primary distinction the statute makes does not depend on the 

message that might be conveyed. Section 27001 does not 

single out for differential treatment, for example, political 

honking, ideological honking, celebratory honking, or 

honking to summon a carpool rider. Instead, the law 

“applies evenhandedly to all who wish to” use the horn when 

a safety hazard is not present. Heffron v. Int’l Soc’y for 

Krishna Consciousness, Inc., 452 U.S. 640, 649 (1981). 

Section 27001 draws a line based on the surrounding factual 

situation, not based on the content of expression.8

Porter contends that Section 27001 is content based on 

its face because an officer must “‘examine the content of the 

message that is conveyed to determine whether’ a violation 

has occurred.” McCullen v. Coakley, 573 U.S. 464, 479 

(2014) (quoting FCC v. League of Women Voters of Cal., 

468 U.S. 364, 383 (1984)). But to conclude that a honk 

complies with the statute, an officer need not examine the 

“content” of the honk the way one might read a sign or 

evaluate a spoken statement—he need only observe the 

traffic circumstances and determine if a safety risk is present. 

For instance, the sheriff’s deputy who cited Porter explained

that he “was watching the traffic” and “didn’t see an 

8

It is true that, in those safety-related situations where honking is 

permitted, Section 27001 permits the driver to honk only to “give audible 

warning.” But Porter has not argued that it violates the First Amendment 

to allow only warning, but not other, honks when a warning honk is 

“reasonably necessary to [e]nsure safe operation” of the vehicle. 

Moreover, Porter likely would not have standing to challenge an alleged 

content-based distinction in the context of a scenario where honking is 

“reasonably necessary to [e]nsure safe operation” of the vehicle. After 

all, the honk she was cited for did not occur in such a situation, and she 

never has claimed to want to give non-warning honks when a safety 

concern is present. 
22 PORTER V. MARTINEZ

emergency” when Porter honked, so he decided to pull her 

over. 

In any event, even if evaluating the traffic-related context 

of a honk involves listening to the sound of the horn—and 

thus could be seen as analogous to reading a sign to evaluate 

its content—the Supreme Court recently rejected as “too 

extreme an interpretation of [its] precedent” a rule “that a 

[sign] regulation cannot be content neutral if it requires 

reading the sign at issue.” City of Austin v. Reagan Nat’l 

Advert. of Austin, LLC, 142 S. Ct. 1464, 1471 (2022). In 

City of Austin, the Court considered a challenge to a city 

ordinance that distinguished between “off-premises” and 

“on-premises” signs—that is, “between signs (such as 

billboards) that promote ideas, products, or services located 

elsewhere and those that promote or identify things located 

onsite.” Id. at 1469. The Court explained that the most 

recent case in which it had held a sign ordinance to be 

content based, Reed v. Town of Gilbert, had involved “a 

comprehensive sign code that ‘single[d] out specific subject 

matter for differential treatment.’” Id. at 1471 (alteration in 

original) (quoting Reed, 576 U.S. at 169); see also Reed, 576 

U.S. at 160-61 (discussing an ordinance with different rules 

for “ideological” signs, “political” signs, and “temporary 

directional” signs relating to events “sponsored, arranged, or 

promoted by a religious, charitable, community service, 

educational, or other similar non-profit organization”). In 

City of Austin, by contrast, the Court held that the sign 

ordinance was content neutral because “the City’s offpremises distinction require[d] an examination of speech 

only in service of drawing neutral, location-based lines. It 

[was] agnostic as to content.” 142 S. Ct. at 1471.

Indeed, the Supreme Court has “consistently recognized 

that restrictions on speech may require some evaluation of 
PORTER V. MARTINEZ 23

the speech and nonetheless remain content neutral.” Id. at 

1473. As the Court emphasized in City of Austin, it has 

treated as content neutral regulations of solicitation—“that 

is, speech ‘requesting or seeking to obtain something’ or 

‘[a]n attempt or effort to gain business,’” Id. (alteration in 

original) (quoting Solicitation, Black’s Law Dictionary 

(11th ed. 2019))—even though enforcement requires an 

examination of the speaker’s message. The Court explained:

To identify whether speech entails 

solicitation, one must read or hear it first. 

Even so, the Court has reasoned that 

restrictions on solicitation are not content 

based and do not inherently present “the 

potential for becoming a means of 

suppressing a particular point of view,” so 

long as they do not discriminate based on 

topic, subject matter, or viewpoint.

Id. (quoting Heffron, 452 U.S. at 649). 

Under these cases, the fact that an officer, after hearing 

the sound of a honk, would need to look at the surroundings 

for a traffic hazard before deciding if the honk was

“reasonably necessary to [e]nsure safe operation” of the 

vehicle, does not render the limitation on honking a contentbased regulation of expression. Such an examination—like

evaluating a message to determine if it is solicitation, or

reading a sign to see if it is on-premises or off-premises

advertising—“do[es] not inherently present ‘the potential for 

becoming a means of suppressing a particular point of 

view.’” Id. (quoting Heffron, 452 U.S. at 649).

Turning to the final step of the content-neutrality inquiry,

we have no concern that Section 27001 “cannot be ‘justified 
24 PORTER V. MARTINEZ

without reference to the content of the regulated speech’” or

was “adopted by the government ‘because of disagreement 

with the message [the speech] conveys.’” Reed, 576 U.S. at

164 (alteration in original) (quoting Ward, 491 U.S. at 791). 

Porter does not argue that Section 27001 is justified by

anything other than the safe operation of motor vehicles and 

noise reduction, nor does she argue that the California 

legislature was motivated by disagreement with any 

particular expressive use of the vehicle horn. Aware of no 

evidence that would have supported such arguments, we 

proceed to evaluate Section 27001 as a content-neutral law, 

applying intermediate scrutiny. 

C.

To survive intermediate scrutiny, a content-neutral 

regulation of expressive conduct must “further[] an 

important or substantial governmental interest,” that interest 

must be “unrelated to the suppression of free expression,” 

and the “incidental restriction on alleged First Amendment 

freedoms [must be] no greater than is essential to the 

furtherance of that interest.” O’Brien, 391 U.S. at 377. To 

be no more burdensome “than is essential to the furtherance 

of” the government’s interest, id., a regulation “need not be 

the least restrictive or least intrusive means” of serving that 

interest. Ward, 491 U.S. at 798. But the “[g]overnment may 

not regulate expression in such a manner that a substantial 

portion of the burden on speech does not serve to advance its 

goals.” Id. at 799. The regulation must also “leave open 

ample alternative channels for communication of the 

information.” Clark, 468 U.S. at 293.

1.

We first consider whether Section 27001 furthers a 

substantial government interest that is unrelated to the 
PORTER V. MARTINEZ 25

suppression of free expression. The State asserts that 

Section 27001 furthersits interest in traffic safety. There can 

be no doubt that this interest is substantial. See Metromedia, 

Inc. v. City of San Diego, 453 U.S. 490, 507-08 (1981) 

(holding that traffic safety is a “substantial governmental

goal[]”). And California’s interest in traffic safety is

unrelated to the suppression of free expression; Porter does 

not contend otherwise. But our inquiry does not end there, 

because when the government seeks to regulate expression, 

even incidentally, to address anticipated harms, it must 

“demonstrate that the recited harms are real, not merely 

conjectural, and that the regulation will in fact alleviate these 

harms in a direct and material way.” Turner, 512 U.S. at

664. That is, we must be persuaded that the law actually

furthers the State’s asserted interests. 

The asserted interest in traffic safety appears on the face 

of the statute itself. Section 27001’s first subsection

provides that the driver of a motor vehicle shall, “when 

reasonably necessary to [e]nsure safe operation,” “give 

audible warning with his horn.” Cal. Veh. Code § 27001(a)

(emphasis added). The second subsection then dictates that

“[t]he horn shall not otherwise be used, except as a theft 

alarm system.” Id. § 27001(b). These twin commands make 

logical sense: For the horn to serve its intended purpose as a 

warning device, it must not be used indiscriminately.9

9 The dissent contends that this justification for Section 27001 is 

undercut by the statute’s lack of enforcement. There is no evidence in 

the record, however, indicating that the statute is indeed rampantly 

underenforced. The State acknowledges that citations for violations of 

the statute are rare, but this says nothing about how frequently the statute 

is violated―citations could be rare for the simple reason that violations 
26 PORTER V. MARTINEZ

The State’s expert testimony supports that logic.

Drawing on his decades of experience working for the CHP, 

Sergeant Beck explained that “the horn itself is a great 

warning device for traffic safety” because it allows drivers 

to “communicate if there’s a hazardous situation.” He went 

on to opine that indiscriminate horn use could dilute the 

potency of the horn as a warning device, testifying that if law 

enforcement officers were unable to enforce Section 27001, 

“the public in general would . . . [think it was] okay to use 

your horn whenever you want for whatever purpose.” He 

said that, as a result, “people would not recognize the horn 

as something that’s used for safety or to warn them of a 

hazard” and “the effectiveness of the horn would be 

diminished.” In other words, the more drivers honk in 

protest, or in greeting, or for no reason at all, the less likely 

people are to be alerted to danger by the sound of a horn. 

Sergeant Beck also explained that indiscriminate horn 

use can distract other drivers and pedestrians. He opined

that, “when a vehicle horn is used improperly, it can create a 

dangerous situation by startling or distracting drivers and 

others.” Sergeant Beck explained that, in his own 

experience, the sound of a horn “makes me look up, take my 

eyes off what I’m doing, which could affect my safety.” He 

also explained that honking can startle pedestrians in hightraffic areas, potentially putting them in harm’s way.

Porter argues that the State has not met its burden to 

show that Section 27001 furthers traffic safety because it 

relied primarily on Sergeant Beck’s testimony, which Porter 

are rare. To the extent that the dissent relies on Lieutenant Munsey’s 

comment to Deputy Klein as evidence of underenforcement, that 

comment’s meaning is too hard to decipher to support the dissent’s claim 

that “Section 27001 is pretty much a dead letter.” 
PORTER V. MARTINEZ 27

contends was pure speculation and should not have been 

admitted. We disagree. 

As an initial matter, the district court did not abuse its 

discretion in admitting Sergeant Beck’s testimony under 

Federal Rule of Evidence 702. “The inquiry envisioned by 

Rule 702 is . . . a flexible one.” Daubert v. Merrell Dow 

Pharms., 509 U.S. 579, 594 (1993). In evaluating expert 

testimony, the district court need not follow a “definitive 

checklist or test.” Kumho Tire Co. v. Carmichael, 526 U.S. 

137, 150 (1999) (quoting Daubert, 509 U.S. at 593). Where 

an expert offers non-scientific testimony, “reliability 

depends heavily on the knowledge and experience of the 

expert, rather than the methodology or theory behind” the 

testimony. Hangarter v. Provident Life & Acc. Ins. Co., 373 

F.3d 998, 1017 (9th Cir. 2004) (quoting United States v. 

Hankey, 203 F.3d 1160, 1169 (9th Cir. 2000)); see also 

Kumho Tire, 526 U.S. at 150 (explaining that the reliability 

inquiry “may focus upon personal knowledge or experience” 

of the witness). 

The district court carefully considered Sergeant Beck’s 

knowledge and experience before concluding that his 

opinions were relevant, reliable, and helpful to the court. 

The court pointed, for example, to Beck’s “extensive 

experience working for the CHP, responding to car 

accidents, and training CHP cadets.” To be sure, “reliability 

becomes more, not less, important when the ‘experiencebased’ expert opinion is perhaps not subject to routine 

testing, error rate, or peer review type analysis, like sciencebased expert testimony.” United States v. Valencia-Lopez, 

971 F.3d 891, 898 (9th Cir. 2020). But “the trial judge must 

have considerable leeway in deciding in a particular case 

how to go about determining whether particular expert 

testimony is reliable.” Kumho Tire, 526 U.S. at 152. The 
28 PORTER V. MARTINEZ

district court appropriately exercised that discretion here in 

concluding that Sergeant Beck’s opinions were relevant, 

reliably grounded in his training and experience, and helpful 

to the court. 

Sergeant Beck’s decades of experience in highway patrol 

allowed him to elucidate “the practical realities” of Section 

27001’s relationship to traffic safety. Given that Sergeant 

Beck’s experience comes from a world in which Section 

27001 does exist, he could not reasonably be expected to 

opine authoritatively―contrary to what the dissent seems to 

suggest―on what traffic safety would be like in the absence 

of that statute.10 He could, however, help the court assess 

the current relationship between Section 27001 and traffic 

safety. 

Although Porter’s expert criticized Sergeant Beck’s 

opinions about the impact of enjoining Section 27001 

enforcement against expressive activity, averring that they 

were “founded upon insufficiently representative 

observations” to be “scientifically reliable,” he did not 

contend that Sergeant Beck’s explanations were wrong—

rather, he merely opined that “we don’t have the science to 

support or deny” those explanations. In other words, studies 

on the issue simply do not exist. And Porter’s own expert 

10 The dissent seems to assume that Section 27001 is effectively 

nonexistent. But Section 27001 does exist, and we take judicial notice 

of the fact that California’s driver education materials, provided for 

anyone taking the test for a state driver’s license, instruct that the horn 

should be used only “to let other drivers know you are there,” “warn 

others of a hazard,” “avoid collisions,” or “alert oncoming traffic on 

narrow mountain roads where you cannot see at least 200 feet 

ahead”―all safety-related functions. See State of Cal. Dep’t of Motor 

Vehicles, California Driver’s Handbook 13 (2023), 

https://www.dmv.ca.gov/portal/file/california-driver-handbook-pdf. 
PORTER V. MARTINEZ 29

acknowledged that conducting a study to obtain such 

evidence would be both “very expensive” and 

“exceptionally difficult.” Given the infeasibility of scientific 

studies on the topic, it was not inappropriate to treat Sergeant 

Beck as having gained expertise from his decades of 

experience enforcing traffic safety.

Once properly admitted, Sergeant Beck’s testimony 

assisted the State in meeting its burden under intermediate 

scrutiny. The Supreme Court has instructed that courts must 

“never accept[] mere conjecture as adequate to carry a First 

Amendment burden.” Nixon v. Shrink Mo. Gov’t PAC, 528 

U.S. 377, 392 (2000). But “the quantum of empirical 

evidence needed to satisfy heightened judicial scrutiny of 

legislative judgments will vary up or down with the novelty 

and plausibility of the [law’s] justification.” Id. at 391. In a 

case applying strict scrutiny to content-based restrictions 

around polling places, for instance, the Supreme Court has 

considered “[a] long history, a substantial consensus, and 

simple common sense” to be sufficient evidence to support 

the justification of protecting the fundamental right to vote. 

Burson v. Freeman, 504 U.S. 191, 211 (1992).

There is nothing novel about Section 27001’s trafficsafety justification—in fact, it seems the California 

legislature had traffic safety in mind when it first enacted a 

version of Section 27001 in 1913. That early version of the 

law prohibited honking “for any purpose except as a warning 

of danger.” Act of May 31, 1913, ch. 326, § 12, 1913 Cal. 

Stat. 639, 645. The traffic-safety justification for restricting 

the use of the horn can also be seen in the vehicle codes of 

at least forty other states, indicating a near-nationwide 

consensus on the need for such laws. See Appendix; see

also, e.g., Del. Code Ann. tit. 21, § 4306(b) (“The driver of 

a vehicle shall, when reasonably necessary to insure safe 
30 PORTER V. MARTINEZ

operation, give audible warning with the horn but shall not 

otherwise use the horn for any other purpose.”). This long 

history and consensus, coupled with the common-sense 

inference that the horn’s usefulness as a warning tool will 

decrease the more drivers use it for any other function, 

support the State’s asserted interest in traffic safety.

“Sound policymaking often requires legislators to 

forecast future events and to anticipate the likely impact of 

these events based on deductions and inferences for which 

complete empirical support may be unavailable.” Turner, 

512 U.S. at 665. Here—where the law has existed since the 

dawn of the automobile, forty other states have similar laws, 

the law’s justification is so logical, and conducting the 

relevant studies would be prohibitively difficult and 

expensive—California does not need to produce new 

empirical evidence to justify Section 27001. “There might, 

of course, be [a] need for a more extensive evidentiary 

documentation” if Porter “had made any showing of [her] 

own to cast doubt” on the State’s justifications. Nixon, 528 

U.S. at 394. But Porter has done nothing to cast doubt on 

Sergeant Beck’s testimony that Section 27001 helps guard 

against distracting honking, or the entirely common-sense 

inference that, the more drivers honk for non-warning 

purposes, the less people can rely on the sound of a honk as 

an alert of imminent danger. See Aesop, The Shepherd Boy 

and the Wolf, in Aesop’s Fables 74, 74 (Boris Artzybasheff

ed., Viking Press 1947) (1933) (telling the tale of a boy who 

cried “Wolf!” to trick local villagers so many times that later, 

when a wolf actually arrived and the boy “cried out in 
PORTER V. MARTINEZ 31

earnest,” the “neighbors, supposing him to be at his old 

sport, paid no heed to his cries”).11

Accordingly, we conclude that Section 27001 “furthers 

an important or substantial governmental interest” that is 

“unrelated to the suppression of free expression.” O’Brien, 

391 U.S. at 377. 

2.

We are also persuaded that Section 27001 is narrowly 

tailored to further California’s interest in traffic safety. The 

statute encourages the use of a vehicle’s horn “when 

reasonably necessary to [e]nsure safe operation” and 

prohibits honking in all other circumstances—because, as 

explained above, honking when there is no hazard both 

dilutes the horn’s usefulness as a safety device and creates 

dangers of its own. To be sure, most non-warning honks do 

not create distractions resulting in accidents, but we discern 

no plausible means by which California could permit nondistracting honks while prohibiting distracting honks.

12

 

11 Contrary to Porter’s suggestion, the exception for theft alarms does not 

undermine California’s anti-dilution justification for Section 27001. 

Theft alarms sound very different from honking initiated by the driver, 

so they are unlikely to be mistaken for warning honks. 

12 Porter points to a local ordinance in Rio Rancho, New Mexico, which 

provides: “No person shall . . . operate a motor vehicle’s equipment, 

including but not limited to the vehicle horn or lights, in such manner as 

to distract other motorists on the public way or in such a manner as to 

disturb the peace.” Rio Rancho Mun. Code § 12-6-12.18(5). She argues 

that such a law would be more narrowly tailored to promoting traffic 

safety. Although “the existence of obvious, less burdensome alternatives 

is ‘a relevant consideration in determining whether the fit between ends 

and means is reasonable,’” the State need not adopt “‘the least restrictive 

or least intrusive means’ available to achieve [its] legitimate interests.” 
32 PORTER V. MARTINEZ

And, regardless, any honking other than “when reasonably 

necessary to [e]nsure safe operation” of the vehicle

undermines the effectiveness of the horn when used for its 

intended purpose of alerting others to danger. Thus, by 

banning horn use in all other circumstances, the State “did 

no more than eliminate the exact source of the evil it sought 

to remedy.” Members of City Council of Los Angeles v. 

Taxpayers for Vincent, 466 U.S. 789, 808 (1984). 

Finally, Section 27001 plainly leaves open ample 

alternative channels for people to communicate their ideas 

and messages, including from their cars. Porter argues that 

Section 27001 prevents spontaneous communication by 

drivers about protests or other events, but common sense and 

Berger, 569 F.3d at 1041 (first quoting Cincinnati, 507 U.S. at 417 n.13, 

then quoting Ward, 491 U.S. at 798). In any event, we are not persuaded 

that this sort of alternative law would achieve California’s interest in 

traffic safety. A law against distracting honking might be 

counterproductive if it discouraged honking to warn others of danger. 

And, as the State notes, New Mexico has a statewide law similar to 

California’s that instructs drivers to honk only when reasonably 

necessary to ensure traffic safety, but not otherwise—suggesting that the 

local ordinance does not need to achieve the same traffic safety goals as 

Section 27001, because a statewide law already has those goals covered. 

N.M. Stat. Ann. § 66-3-843(A).

The dissent also contends that local noise ordinances or California Penal 

Code § 415(2), which prohibits “maliciously and willfully disturb[ing] 

another person by loud and unreasonable noise,” could allow the State 

more narrowly to achieve its interests in traffic safety and noise control. 

But Porter has offered no argument that such noise control provisions 

would achieve the State’s goal of ensuring traffic safety. In any event, 

our holding rests on the state’s interest in traffic safety alone. Because 

we conclude that Section 27001 is narrowly tailored to advancing 

California’s substantial interest in traffic safety, we do not address the 

parties’ arguments about the State’s separate interest in noise control.
PORTER V. MARTINEZ 33

Porter’s own testimony indicate otherwise. As Porter herself 

has done on numerous occasions, drivers can park their cars 

and attend political demonstrations on foot. They can also 

express agreement with protestors from their cars by waving, 

giving a thumbs up, or raising a fist as they drive by.13 They 

can put bumper stickers on their cars. Although some people 

may find it more satisfying to honk in certain circumstances, 

“[w]e will not invalidate a regulation merely because it 

restricts the speaker’s preferred method of communication.” 

United Bhd. of Carpenters & Joiners v. NLRB, 540 F.3d 957, 

969 (9th Cir. 2008); see also Taxpayers for Vincent, 466 

U.S. at 812 (“[T]he First Amendment does not guarantee the 

right to employ every conceivable method of 

communication at all times and in all places.”). 

We hold that Section 27001 is narrowly tailored to

advancing California’s substantial interest in traffic safety, 

and therefore that it passes intermediate scrutiny. 

* * *

We make one final observation: It appears that Section 

27001 citations are not common, and officers are taught to 

use “sound professional judgment” in deciding whether to 

give a warning or a citation for a violation of Section 27001. 

As the dissent aptly observes in footnote 6, such broad 

discretion could open the door to selective enforcement. 

Porter does not allege, however, that the State has a policy 

or practice of improper selective enforcement of Section 

13 The dissent theorizes that these options “would surely pose a greater 

threat to traffic safety than a honk.” But there is no basis for the 

conclusion that briefly taking a hand off the wheel is more dangerous 

than startling others by honking. 
34 PORTER V. MARTINEZ

27001, so we have no occasion to address that possibility

here. 

V.

For the foregoing reasons, we affirm the district court’s 

summary judgment in favor of the State.

BERZON, Circuit Judge, dissenting:

The majority today upholds a ban on a popular form of 

political expressive conduct—honking horns to support 

protests or rallies. Political protest “has always rested on the 

highest rung of the hierarchy of First Amendment values.” 

Carey v. Brown, 447 U.S. 455, 467 (1980). Defendants’ 

enforcement of California Vehicle Code Section 27001 

prohibited Susan Porter from exercising her right to 

participate in political protest by honking in support of a 

demonstration against an elected official.1 Yet, there is no

evidence in the record (or elsewhere, as far as I can 

determine) that such political expressive horn use 

jeopardizes traffic safety or frustrates noise control. 

I therefore respectfully dissent. I would hold that Section 

27001 does not withstand intermediate scrutiny insofar as it 

prohibits core expressive conduct, and is therefore 

unconstitutional in that respect. 

1 The majority refers to the defendants, the Sheriff of San Diego County 

and the Commissioner of the California Highway Patrol, collectively as 

“the State.” See Majority Op. 9. I use the term “Defendants” instead.
PORTER V. MARTINEZ 35

I.

As a preliminary matter, but one critical to my larger 

concerns, I would hold—contrary to the majority’s 

conclusion—that the district court’s admission of the expert 

testimony of California Highway Patrol (CHP) officer 

Sergeant William Beck in support of Defendants’ motion for 

summary judgment was an abuse of discretion. 

“Before admitting expert testimony into evidence, the 

district court must perform a ‘gatekeeping role’ of ensuring 

that the testimony is both ‘relevant’ and ‘reliable’” under 

Federal Rule of Evidence 702. United States v. RuvalcabaGarcia, 923 F.3d 1183, 1188 (9th Cir. 2019) (quoting 

Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579, 597 

(1993)). The majority assumes that Beck’s experience 

working for the CHP provided a reliable basis for his 

opinions as to Section 27001’s impact on road safety. See 

Majority Op. 26–28. But “reliability becomes more, not less, 

important when the ‘experience-based’ expert opinion 

is . . . not subject to routine testing, error rate, or peer review 

type analysis, like science-based expert testimony.” United 

States v. Valencia-Lopez, 971 F.3d 891, 898 (9th Cir. 2020). 

An examination of the record reveals that Beck utterly failed 

to explain how his general law enforcement experience 

supported the specific opinions he enunciated regarding the 

impact of Section 27001—especially with regard to political 

protest honking—on traffic safety. 

Beck declared that his opinions were based on his “24 

years of experience working for the California Highway 

Patrol.” Based on that experience alone, he opined that the 

improper use of a vehicle horn can create danger by startling 

or distracting others. But when asked during his deposition 

for the basis of this opinion, Beck couldn’t articulate a 
36 PORTER V. MARTINEZ

reasoned explanation for the connection between his 

experience and that opinion. He did not provide a single 

example of an accident caused by any type of horn honking, 

let alone honking in support of a political protest. 

Of the three examples he was able to give in which he 

was personally distracted by horn honking, two of the 

examples were safety-related honks, permissible under 

Section 27001, used to notify drivers “backing out” who 

“don’t see other people that are behind them.” In reciting the 

third example, Beck explained that he has been briefly 

startled “when I’m writing a citation” or “working a traffic 

collision” and “somebody blasts their horn for a reason.” In 

none of these examples did Beck report any actual danger 

created by the honk. And, in any case, those examples were 

based on Beck’s personal experience, no different from 

anyone else’s experience with horn honking and so unrelated 

to any “scientific, technical, or other specialized knowledge” 

or experience. Compare Fed. R. Evid. 701(c), with 702(a). 

The examples are therefore not admissible as a basis for 

expert opinion. 

Beck also conjectured that a horn’s usefulness as a 

warning device would be diminished if law enforcement 

officers were unable to enforce Section 27001. People, he 

supposed, would think it “okay to use your horn whenever 

you want for whatever purpose and I feel that people would 

not recognize the horn as something that’s used for safety.” 

He analogized the enforcement of Section 27001 to speeding 

laws and bicycle helmet laws, opining that “more people 

break [the] law if we’re not out enforcing it.” 

One problem with this speculative testimony is that 

nothing in Beck’s specific experiences as a CHP officer 

provides a basis for determining the effect of non-
PORTER V. MARTINEZ 37

enforcement of traffic laws. He did not suggest that he has 

done, or read, any studies demonstrating a correlation 

between the degree of enforcement of speeding or bike 

helmet laws and the prevalence of violations of those laws. 

Nor did he aver, even anecdotally, that he had observed in 

his experience that fewer people speed or more people wear 

bike helmets in areas where the relevant statutes are 

enforced.

Moreover, and more importantly, Beck reported that, in 

his twenty-four-year career, he had stopped people for a 

Section 27001 violation only “four or five times” and the last 

time he wrote a citation was “several years ago . . . probably 

around 2013, 2014.” Thus, his opinion as to the salutary 

effect of actually enforcing Section 27001’s ban on nonsafety-related horn honking has no grounding in his own 

experience, as he has exceedingly rarely enforced the statute. 

Finally, Beck opined that other laws, including local 

noise ordinances and California Penal Code Section 415(2), 

are inadequate alternatives to Section 27001.2 But he stated 

that “I have not generally enforced local ordinances,” that he 

was not aware of any local noise ordinances, and that he was 

not aware of any specific situation where enforcement of a 

local noise ordinance was an inadequate substitute for the 

absolute prohibition contained in Section 27001. He also 

stated that he had never personally enforced, nor seen an 

officer enforce, Section 415(2) against horn honking, nor 

was he aware of any specific problems that would arise were 

an officer to attempt to do so. 

2 Penal Code Section 415(2) provides that “[a]ny person who maliciously 

and willfully disturbs another person by loud and unreasonable noise . . . 

shall be punished” by imprisonment or fine.
38 PORTER V. MARTINEZ

When an expert witness “is relying solely or primarily 

on experience, then the witness must explain how that 

experience leads to the conclusion reached, why that 

experience is a sufficient basis for the opinion, and how that 

experience is reliably applied to the facts.” Fed. R. Evid. 702 

advisory committee’s note to 2000 amendment. Although 

Beck’s “qualifications and experience are relevant . . . the 

record contains no evidence as to why that experience, by 

itself, equals reliability for his testimony.” Valencia-Lopez, 

971 F.3d at 898, 900. An expert “must establish that reliable 

principles and methods underlie the particular conclusions 

offered.” United States v. Hermanek, 289 F.3d 1076, 1094 

(9th Cir. 2002). Beck could point to nothing specific in his 

experience as a CHP officer to substantiate his general 

speculations about the effect of horn honking on traffic 

safety, or any basis for supposing that the inclusion of 

political protest honking in Section 27001 enhances traffic 

safety. As a result, that testimony does not satisfy the 

reliability requirement of Rule 702. 

The district court thus abused its discretion when it 

admitted Beck’s expert testimony. That error was far from 

harmless. As discussed later, Beck’s testimony was the only

evidence upon which the district court relied, and which the 

majority opinion emphasizes, to conclude that Section 

27001 passes intermediate scrutiny as applied to horn 

honking as a medium for political protest. 

II.

Turning now to the merits of Porter’s First Amendment 

challenge, I would hold that Section 27001 is 

unconstitutional as applied to political expressive conduct 

such as Porter’s. The majority’s fundamental error, in my 

view, in concluding otherwise is that it does not sufficiently 
PORTER V. MARTINEZ 39

focus on the specific type of enforcement at the core of this 

case—enforcement against honking in response to a political 

protest. 

Generally, when a statute has both constitutional and 

unconstitutional applications, we “enjoin only the 

unconstitutional applications . . . while leaving other 

applications in force.” Ayotte v. Planned Parenthood of N. 

New England, 546 U.S. 320, 329 (2006). Porter was cited for 

honking in support of a political protest, and she asserted in 

her deposition that the threat of enforcement has chilled her 

future plans only for such political honking; she did not aver 

an intent to engage in any other honking she characterizes as 

“expressive.” So the particular “subset of the statute’s 

applications” cognizably challenged here is the enforcement 

of Section 27001 against political protest honking. Hoye v. 

City of Oakland, 653 F.3d 835, 857 (9th Cir. 2011).

The requested relief in Porter’s complaint does include 

enjoining Defendants from enforcing Section 27001 against 

“protected speech or expression.” The complaint and her 

briefs on appeal assert that “expressive” honking can include 

using a vehicle horn to “express support or approval of 

parades, protests, rallies, demonstrations, or fundraising or 

for other expressive purposes such as greeting a relative, 

friend, or acquaintance.” Relying on this expansion of the 

requested relief beyond Porter’s own past experience and 

desired future actions, the majority states that, because 

Porter seeks to enjoin enforcement against all expressive 

honking, “we decide only whether the statute is 

unconstitutional on its face or as applied to all expressive 

honking.” Majority Op. 20 n.6. 

But we are not bound by the scope of a party’s requested 

remedy. See, e.g., Hoye, 653 F.3d at 856–57 (crafting narrow 
40 PORTER V. MARTINEZ

declaratory relief despite plaintiff’s broad facial challenge to 

ordinance); N. Cheyenne Tribe v. Norton, 503 F.3d 836, 

842–44 (9th Cir. 2007) (affirming partial rather than blanket 

injunction requested by parties). Porter’s actual injury, past 

and future, which provides her Article III standing, is 

narrower than the scope of the injunctive relief she 

requested. See Majority Op. 12–14. Moreover, as will 

appear, I would conclude that “expressive horn use” is a 

fairly narrow subset of horn beeping, of which political 

protest honking is the most obvious example. 

For these reasons, I concentrate this dissent on the 

application of Section 27001 to political protest honking. 

A.

I agree with the majority that “at least some of the 

honking prohibited by Section 27001 is expressive for First 

Amendment purposes,” Majority Op. 17, and that Section 

27001 is content neutral, id. at 19–24. It is important to 

clarify, however, that honking at a political protest is a core

form of expressive conduct that merits the most stringent 

constitutional protection, and is, in that respect, qualitatively 

different from warning honks and other forms of vehicle 

horn use.

Expressive conduct that merits protection under the First 

Amendment is “characterized by two requirements: (1) an 

intent to convey a particularized message and (2) a great 

likelihood that the message would be understood by those 

who viewed it.” Edge v. City of Everett, 929 F.3d 657, 668 

(9th Cir. 2019) (cleaned up). Porter’s political protest 

honking meets both criteria.

The incident that gave rise to this lawsuit is illustrative. 

Porter honked “in three clusters of short beeps” while 
PORTER V. MARTINEZ 41

driving by a political protest, and “her intent was to show 

support for the protest.” Majority Op. 18. The crowd 

cheered, suggesting that her intended message was 

understood. Id. The officers’ body-worn camera footage 

shows that many other drivers honked as they drove by the 

protest that day, with protesters cheering in response. More 

generally, honking is a widespread, long-established form of 

political protest.3

Political honking is thus “imbued with elements of 

communication.” Spence v. State of Wash., 418 U.S. 405, 

409 (1974). As the majority explains, such honking 

“carr[ies] a message that ‘is intended to be communicative 

and that, in context would reasonably be understood by the 

[listener] to be communicative.’” Majority Op. 18 (quoting 

Clark v. Cmty. For Creative Non-Violence, 468 U.S. 288, 

294 (1984)). “The expressive, overtly political nature of 

[Porter’s] conduct was both intentional and overwhelmingly 

apparent.” Texas v. Johnson, 491 U.S. 397, 406 (1989).

But most other honking is not equally expressive. As the 

majority notes, ordinarily, “a honk is just a noise.” Majority 

Op. 18. Thus, whether any given honk is “sufficiently 

imbued with elements of communication” to constitute 

protected expression depends on “the nature of [the] activity, 

combined with the factual context and environment in which 

it was undertaken.” Id. at 17–18 (quoting Spence, 418 U.S. 

at 409–10). “It is possible to find some kernel of expression 

3 See, e.g., Kirk Johnson, Honk if You Agree There Is a Difference 

Between Free Speech and Noise, N.Y. Times, Nov. 18, 2011, 

https://www.nytimes.com/2011/11/19/us/is-honking-free-speech-orjust-noise-pollution.html; Honk for Peace Cases, ACLU of Minnesota, 

https://www.aclu-mn.org/en/cases/honk-peace-cases; Honk for Justice 

Chicago, https://honkforjusticechicago.com/.
42 PORTER V. MARTINEZ

in almost every activity a person undertakes . . . but such a 

kernel is not sufficient to bring the activity within the 

protection of the First Amendment.” Barnes v. Glen Theatre, 

Inc., 501 U.S. 560, 570, (1991) (quoting Dallas v. Stanglin, 

490 U.S. 19, 25 (1989)).

Warning honks, for example, are, in my view, not 

expressive conduct.4 A person’s reaction to hearing a warning

honk is to look up or toward the source of the noise. But 

“given the inflexibility of the medium,” Majority Op. 18, the 

hearer cannot tell if the honk conveys some specific traffic 

direction—for example, whether it means “slow down” or 

“speed up.” Instead, a warning honk is just a loud noise that 

grabs the attention of the hearer. Once engaged, the hearer 

can notice the traffic situation and determine an appropriate 

course of action. This attention-grabbing function is why the 

Vehicle Code requires vehicle horns to be loud, “capable of 

emitting sound audible under normal conditions from a 

distance of not less than 200 feet.” Cal. Veh. Code 

§ 27000(a). And it is also why a warning honk does not carry 

a “great” likelihood of conveying a “particularized 

message,” Johnson, 491 U.S. at 404—it is just a noise.

Because of the attention-alerting nature of a warning 

honk, determining whether a honk qualifies as a warning 

honk does not require evaluating and differentiating honks 

based on their content. A law enforcement officer seeking to 

determine whether a beep on the horn was a warning honk, 

as the majority explains, “need only observe the traffic 

circumstances and determine if a safety risk is present.” 

4 The majority leaves this issue (slightly) open, simply noting that 

Porter’s “assertion that honking to give a warning is a form of 

expression” is “questionable.” Majority Op. 20.
PORTER V. MARTINEZ 43

Majority Op. 21. I therefore agree that “Section 27001 draws 

a line based on the surrounding factual situation, not based 

on the content of expression.” Id. at 21.

I would go further: In many contexts, a honk conveys no 

comprehensible expressive message. Porter asserts that 

honks to “greet friends or neighbors” or “summon children 

or co-workers” are expressive honks. But even in those 

instances, honks are used to grab the hearer’s attention, not 

to convey any articulable message. A greeting honk, for 

example, emits a loud noise that causes the listener to look 

up; the honk itself is not a greeting message, but it causes the 

listener to look up, notice, and identify the honker as a friend. 

Similarly, a honk to summon a child does not itself convey 

a message; it grabs the child’s attention, so she notices that 

her parent is waiting for her. 

Honking at a political protest, on the other hand, is a use 

of a vehicle horn that definitely does constitute messageconveying expressive conduct and so merits First 

Amendment protection. When Susan Porter honked while 

passing a protest against U.S. Representative Darrell Issa, 

she was not just making noise to attract attention. She was 

conveying a distinct message—agreement with the 

protesters’ objections to Darrell Issa’s stance on gun control.

And that message was understood, as the protesters cheered 

when she beeped. The protesters did not have to be startled 

into looking up to understand what Porter was honking 

about; in the context, they understood the message 

immediately.

Because political protest honking conveys a distinct 

message, one that implicates core First Amendment values, 

it is the banning of this message that should be—but in the 

majority opinion is not—the focus of the First Amendment 
44 PORTER V. MARTINEZ

analysis. The constitutionality of Section 27001 must be 

weighed specifically in light of the restrictions it places on 

political expression. See, e.g., Johnson, 491 U.S. at 402–20 

(analyzing constitutionality of a statute prohibiting flag 

burning based on its restriction of an individual’s political 

protest regarding the renomination of Ronald Reagan for 

president).

B.

Beginning from that premise, I cannot agree with the 

majority’s conclusion that Defendants have sufficiently 

demonstrated that Section 27001’s restriction on political 

protest honking furthers a significant government interest.5

The asserted government interests in traffic safety and 

noise control are substantial. However, the fact “[t]hat the 

Government’s asserted interests are important in the abstract 

does not mean . . . that [a challenged statute] will in fact 

advance those interests.” Turner Broad. Sys., Inc. v. F.C.C.,

512 U.S. 622, 664 (1994). “When the Government defends 

a regulation on speech as a means to redress past harms or 

prevent anticipated harms,” the government has the burden 

to “demonstrate that the recited harms are real, not merely 

conjectural, and that the regulation will in fact alleviate these 

harms in a direct and material way.” Id. “[M]erely invoking 

interests in regulating traffic” or noise control “is 

5

I assume for purposes of this dissent that intermediate scrutiny applies.

But I am not certain that categorization is correct. As Section 27001, in 

my view, mostly applies to non-expressive conduct, the content 

neutrality rubric adopted by the majority, see Majority Op. 14–17, seems 

inapplicable. Rather, once again, the focus should be on the ban of 

political protest honking—a ban that viewed discretely would surely 

trigger strict scrutiny. See, e.g., Meyer v. Grant, 486 U.S. 414, 420 

(1988).
PORTER V. MARTINEZ 45

insufficient.” Kuba v. 1-A Agric. Ass’n, 387 F.3d 850, 859 

(9th Cir. 2004). 

I would hold that Defendants have not met their burden 

to show that the asserted harms caused by political honking 

are real. Sergeant Beck’s testimony is the only evidence 

upon which the district court relied. As I have explained, I 

would hold that evidence inadmissible as not meeting the 

standards for competent expert testimony. With that 

evidence out of the case, there is no basis whatever in the 

record for concluding that the asserted governmental 

interests supporting a ban on political horn honking are 

substantial. 

Even if Beck’s testimony were admissible, my 

conclusion would be the same. Beck hypothesized that 

without Section 27001, “the public in general would . . . 

[think it was] okay to use your horn whenever you want” and 

“the effectiveness of the horn would be diminished.” Yet, as 

discussed above, in his twenty-four-year career with the 

CHP, Beck did not know of a single accident caused by any 

type of horn honking, let alone the political honking at issue 

here. And he did not purport to offer any opinions as to the 

impact of horn honking on noise control concerns.

Defendants offered no other evidence deemed 

admissible by the district court to demonstrate that political 

horn honking endangers its asserted interests. For example, 

no evidence was introduced about the frequency of political 

honking, the relationship between political honking and 

increased traffic danger, or its geographic scope. Where 

“[t]here is no record of harm or safety concerns caused by

such activity,” this “void in the record belies” the 

significance of the state interest. Kuba, 387 F.3d at 860. 
46 PORTER V. MARTINEZ

Despite this lack of evidence, the majority asserts that 

the relationship between Section 27001 and a governmental 

interest in traffic safety makes “logical sense: For the horn 

to serve its intended purpose as a warning device, it must not 

be used indiscriminately.” Majority Op. 25. This conclusion 

is too glib. Common sense also indicates that people do honk 

their horns for non-safety reasons all the time, and that they 

are not cited for it. 

This lack of enforcement is borne out by the record and 

undermines the purported importance of Section 27001 in 

furthering the asserted governmental interests. Any 

enforcement of Section 27001 is left to the broad discretion 

of peace officers. The result of that discretion? Section 

27001 is almost never enforced, even though violations are 

legion. Defendants assert, for example, that of the nearly 4.3 

million citations issued by CHP between 2016 and 2018, 

only 180 were for a Section 27001 violation, and that “the 

odds of anyone being cited by CHP for violating Section 

27001 under any circumstances—much less at a protest—

are de minimis.”

The facts of this case bear out what everyone who drives 

in California knows: Section 27001 is pretty much a dead 

letter. The honking of horns for non-safety reasons is 

rampant and hardly ever sanctioned. As Deputy Klein was 

issuing the citation to Porter, his supervisor, Lieutenant 

Munsey, told him, “Oh illegally honking the horn? If you 

want to um, because everybody does it, if you feel like it and 

don’t have any cites, warn them, if you don’t, well, it’s up to 

you.” Klein only wrote one citation for a Section 27001 

violation that day, even though he heard many people 
PORTER V. MARTINEZ 47

honking their horns.6 Were there really a substantial state 

interest in curbing non-safety-related beeping of car horns—

let alone the protest or political honking protected by the 

First Amendment—surely there would be some serious 

attempt to sanction noncompliance. 

C.

Even if we assume Defendants did provide sufficient 

support for their asserted interests in traffic safety and noise 

control, Section 27001’s near-complete ban on honking is 

unconstitutional because it is not narrowly tailored to serve 

those interests. Clark, 468 U.S. at 293.

1.

To satisfy the narrow tailoring requirement, Defendants 

must show that the statute “does not ‘burden substantially 

more speech than is necessary’” to further the asserted 

governmental interests. Comite de Jornaleros de Redondo 

6

Jaywalking is a salient illustration that, where a generic traffic law is 

on the books but not enforced, it may well be because there’s no real 

government interest underlying it. Jaywalking was, until recently, illegal 

in California, but also “endemic” and “rarely result[ed] in arrest.” Nieves 

v. Bartlett, 139 S. Ct. 1715, 1727 (2019); see Cal. Stats. 2022, ch. 957 

(A.B. 2147). Based in part on evidence that people of color and lowincome individuals are disproportionately cited for jaywalking 

violations, a selective enforcement danger that arises where officers have 

probable cause to make arrests but typically exercise their discretion not 

to do so, the California legislature recently amended its jaywalking laws 

to permit a peace officer to stop a jaywalker only if “a reasonably careful 

person would realize there is an immediate danger of a collision with a 

moving vehicle.” See, e.g., Cal. Stats. 2022, ch. 957 (A.B. 2147), § 

11(b)(1); Cal. Veh. Code § 21955 (2023); see Colleen Shalby, 

Jaywalking Is Decriminalized in California Under New Law, L.A. 

Times, Oct. 1, 2022, https://www.latimes.com/california/story/2022-10-

01/jaywalking-decriminalized-in-california-under-new-law.
48 PORTER V. MARTINEZ

Beach v. City of Redondo Beach, 657 F.3d 936, 948 (9th Cir. 

2011) (quoting Turner, 512 U.S. at 665). “In particular, [a 

statute’s] expansive language can signal that the 

[government] has burdened substantially more speech than 

effectively advances its goals.” Cuviello v. City of Vallejo, 

944 F.3d 816, 829 (9th Cir. 2019). 

Downplaying the broad sweep of the statute, the majority 

asserts that Defendants “did no more than eliminate the exact 

source of the evil it sought to remedy.” Majority Op. 32

(quoting Members of the City Council v. Taxpayers for 

Vincent, 466 U.S. 789, 808 (1984)). I would hold that 

Section 27001’s ban on almost all honking burdens 

substantially more speech than necessary, because it 

prohibits political honking that does not implicate traffic 

safety or noise control concerns.

At a basic level, Section 27001—if enforced—could 

contribute to noise control and driver distraction; prohibiting 

drivers from honking in nearly all circumstances does 

reduces noise levels, and noise may be distracting. But a 

sweeping ban on nearly all honking prohibits political 

expression—“the core of speech protected by the First 

Amendment”—without regard to whether such expression 

actually jeopardizes the asserted governmental interests. 

Sanders Cnty. Republican Cent. Comm. v. Bullock, 698 F.3d 

741, 745 (9th Cir. 2012).

The facts of this case show why this is so. Porter was 

cited for honking at a political protest on the sidewalk in 

front of a politician’s office. The protest was a weekly, 

organized event; on this particular day, it had a sign-in table, 

and volunteers in vests helped pedestrians cross the street. 

Deputy Klein perceived that a “couple hundred” protesters 

were present. The protesters had a megaphone and a drum, 
PORTER V. MARTINEZ 49

and they held picket signs, chanted, and sang. A counterprotester stood across the street and played amplified music 

through big speakers to drown out the protesters. Porter 

honked her horn in support of the protest as she drove by—

as many others did—and Deputy Klein heard “people 

cheering . . . someone on a loud speaker, a microphone.”

Whatever the governmental interests may be in noise 

control or curbing driver distraction, there’s just no record 

evidence that Porter’s political honking at an already noisy 

event endangered those interests. A political protest is 

designed to be noticed. As Deputy Klein testified, “it was 

loud.” Political honking was hardly a significant source of 

noise or distraction in that environment. There is no basis for 

supposing that anyone was confused or distracted by the 

honking. Instead, Porter’s honking was understood as 

political expression by the protesters, who cheered in 

response. 

A statute is overinclusive when it prohibits expression, 

especially core political expression, “without any 

specifications or limitations that may tailor [the statute] to 

situations involving the most serious risk to public peace or 

traffic safety.” Cuviello, 944 F.3d at 830. Cuviello held, for 

example, that a permitting requirement for using soundamplifying devices was likely not narrowly tailored, noting 

that it applied to a public sidewalk next to a Six Flags theme 

park, an “already [] noisy area, where patrons flock in 

droves.” Id. “Amidst all the noise, the sound of one bullhorn 

likely would not cause an additional disturbance to traffic 

safety or public peace.” Id.

So here. Porter’s honking was in response to an already 

noisy—and undoubtedly distracting to passersby and 

drivers—political protest. The point of such protests is to 
50 PORTER V. MARTINEZ

draw attention to the cause supported. As in Cuviello, 

Section 27001’s broad ban on noisy, distracting political 

expression serves no governmental purpose where there is 

already cacophony and flurry. The statute therefore is not 

narrowly tailored to the circumstances in which such 

purposes could be served. 

The minimal enforcement of Section 27001 is further 

evidence that the statute sweeps too broadly. When police 

officers exercise their discretion not to enforce a statute, the 

fair inference is that they have concluded that no 

governmental interest would be served by doing so. And 

where, as here, the statute is almost never enforced, one can 

only conclude that it is vastly overbroad, and that a narrower, 

targeted ban would suffice. 

2.

The majority recognizes that “most non-warning honks 

do not create distractions resulting in accidents,” but holds 

that Section 27001 is narrowly tailored because “we discern 

no plausible means by which California could permit nondistracting honks while prohibiting distracting honks.” 

Majority Op. 31. I disagree with the take-off point of this 

analysis, as well as with its conclusion. 

As I’ve explained, much honking is just noise, not First 

Amendment-protected communication. See supra Part II.A. 

The obvious way to eliminate the statutory overbreadth as 

applied to First Amendment-protected honking is to except 

such beeping from the statute’s reach. As Section 27001 has 

no such exception, an injunction against enforcement of the 

statute against political protest honking is an appropriate 

remedy for Porter’s injury here. See Ayotte, 546 U.S. at 328–

29.
PORTER V. MARTINEZ 51

Contrary to Defendants’ submission, law enforcement 

officers should have no difficulty differentiating between 

non-expressive honks and political protest honks. Again, 

conduct is expressive only if an “intent to convey a 

particularized message [is] present, and in the surrounding 

circumstances the likelihood [is] great that the message 

would be understood by those who view[] it.” Spence, 418 

U.S. at 410–11. Many honks do not communicate a 

particularized message and so, as I have explained, do not 

meet this standard. Honking in response to a political protest, 

in contrast, is generally understood by listeners—including 

law enforcement officers—as communicating a message.

i.

To the extent Defendants maintain that political protest 

honking itself must be regulated because such honking can 

be disruptive, there are alternate methods for doing so. To 

satisfy the narrow tailoring requirement, a statute “need not 

be the least restrictive or least intrusive means” of furthering 

legitimate governmental interests, Ward v. Rock Against 

Racism, 491 U.S. 781, 798 (1989), but “an assessment of 

alternatives can still bear on the reasonableness of the 

tailoring,” Long Beach Area Peace Network v. City of Long 

Beach, 574 F.3d 1011, 1025 (9th Cir. 2009) (quoting Menotti 

v. City of Seattle, 409 F.3d 1113, 1131 n.31 (9th Cir. 2005)). 

“Even under the intermediate scrutiny ‘time, place, and 

manner’ analysis, we cannot ignore the existence 

of . . . readily available alternatives.” Comite de Jornaleros, 

657 F.3d at 950. 

Porter has identified various other laws that would allow 

Defendants to achieve the asserted governmental interests in 

traffic safety and noise control. Local noise ordinances are 

designed to regulate “[d]isturbing, excessive or offensive 
52 PORTER V. MARTINEZ

noise.” San Diego, Cal., Code of Regulatory Ordinances ch. 

4, § 36.401; see, e.g., id. § 36.410 (sound level limitations 

on impulsive noise); Vista, Cal., Municipal Code § 8.32.040 

(general noise limits). California Penal Code § 415(2) is 

another tool, prohibiting “maliciously and willfully 

disturb[ing] another person by loud and unreasonable 

noise.”

Porter also points to a local ordinance in Rio Rancho, 

New Mexico, as a viable alternative formulation for Section 

27001. Rather than prohibiting all honking except in certain 

instances, as Section 27001 does, the Rio Rancho ordinance 

permits honking except when it is used “in such manner as 

to distract other motorists on the public way or in such a 

manner as to disturb the peace.” Martinez v. City of Rio 

Rancho, 197 F. Supp. 3d 1294, 1300 (D.N.M. 2016) (quoting 

Rio Rancho Mun. Code § 12-6-12.18(5)). By narrowing the 

category of prohibited honking to actually disruptive honks, 

Rio Rancho’s ordinance better targets honks that implicate 

the asserted governmental interests.

To be sure, Section 27001, which provides officers with 

broad discretion to cite the drivers of their choosing, may be 

easier and more efficient to enforce than those alternatives. 

But “the prime objective of the First Amendment is not 

efficiency.” McCullen v. Coakley, 573 U.S. 464, 495 (2014). 

“To meet the requirement of narrow tailoring, the 

government must demonstrate that alternative measures that 

burden substantially less speech would fail to achieve the 

government's interests, not simply that the chosen route is 

easier.” Id. 

Defendants have not made that showing. Protest honking 

is geographically predictable because it occurs in response 

to events at fixed locations. Thus, the practical difficulties of 
PORTER V. MARTINEZ 53

discerning and enforcing the appropriate local noise 

ordinance in the vicinity of any protest are few. The record 

here indicates that the Sheriff and the City had received 

multiple noise complaints about the weekly protest, so both 

the jurisdiction and the relevant noise ordinances were 

obvious. The geographic predictability of political honking 

can also facilitate the enforcement of the Penal Code or a 

statute like the Rio Rancho ordinance, as law enforcement 

resources purposefully can be dedicated to monitoring 

protest sites for willfully malicious and disruptive honks. In 

any event, any substantive difficulty in enforcing one of 

these ordinances or statutes would be an indication that the 

protest honking at issue was not disruptive or did not 

appreciably increase noise levels. 

ii.

The majority also asserts that Section 27001 is narrowly 

tailored because it “plainly leaves open ample alternative 

channels for people to communicate their ideas and 

messages, including from their cars.” Majority Op. 32. On 

this point, the facts underlying this case are again 

informative, as they demonstrate that Porter had no 

alternative to political honking on that day. 

On October 17, 2017, Porter drove to the crowded 

protest, parked along the street, and participated in the 

protest for about half an hour. She then noticed that law 

enforcement officers were affixing parking citations on 

protesters’ parked cars. Porter’s car was parked close to a 

fire hydrant, so she decided to leave the protest to move her 

car and avoid a possible citation. By the time she found 

parking elsewhere and returned, she was unable to rejoin the 

protest because it was over.
54 PORTER V. MARTINEZ

Thus, the only opportunity Porter had to continue 

protesting was by honking her horn as she drove by. The 

alternative methods of communication the majority suggests 

were possible from the car—including “waving, giving a 

thumbs up, or raising a fist as they drive by”, Majority Op. 

33—would require the driver to take her hand off the wheel. 

Doing that would surely pose a greater threat to traffic safety 

than a honk easily understood as conveying a message of 

support for an already noisy, crowded protest.

“[D]ebate on public issues should be uninhibited, robust, 

and wide-open.” New York Times Co. v. Sullivan, 376 U.S. 

254, 270 (1964). Here, Defendants insist that they can 

continue to ban Porter’s political expressive conduct, but 

offer no cognizable argument that the conduct actually 

endangered either traffic safety or noise control in a manner

that could not be sanctioned if those dangers actually arose. 

III.

In sum, Section 27001 violates the First Amendment 

because Defendants have not shown that the statute furthers 

a significant government interest as applied to political 

protest honking, and because the statute is not narrowly 

tailored to exclude such honking. I would grant an injunction 

prohibiting the enforcement of Section 27001 against 

political protest honking.7

7

I would not extend the injunction to all “expressive” honking, as the 

term is too vague to be enforceable, see Fed. R. Civ. P. 65(d), and an 

injunction limited to political honking would cure the injury-in-fact 

Porter identifies. As discussed, Porter has stated that, in the future, she 

wishes to engage specifically in political protest honking. Others who 

wish to beep their horns to convey a specific message may seek similar 

relief, and an injunction could be tailored to cover their communication 

if the communication were determined to constitute expressive conduct. 
PORTER V. MARTINEZ 55

APPENDIX
56 PORTER V. MARTINEZ

Alabama: “It shall be unlawful . . . for any person to use 

upon a vehicle any siren or for any person at any time to use 

a horn otherwise than as a reasonable warning.” Ala. Code 

§ 32-5-213(a). 

Alaska: “The driver of a motor vehicle shall, when 

reasonably necessary to insure safe operation, give audible 

warning with his horn, but may not otherwise use the horn 

when upon a highway or other vehicular way or area.” 

Alaska Admin. Code tit. 13, § 04.210(a). 

Arizona: “If reasonably necessary to ensure the safe 

operation of a motor vehicle, the driver shall give an audible 

warning with the driver’s horn but shall not otherwise use 

the horn when on a highway.” Ariz. Rev. Stat. § 28-954(B).

Arkansas: “When reasonably necessary to ensure safe 

operation, the driver of a motor vehicle shall give audible 

warning with his or her horn but shall not otherwise use the 

horn when upon a public street or highway.” Ark. Code 

Ann. § 27-37-202(a)(2). 

California: “The driver of a motor vehicle when reasonably 

necessary to insure safe operation shall give audible warning 

with his horn. . . . The horn shall not otherwise be used, 

except as a theft alarm system.” Cal. Veh. Code § 27001(a)-

(b). 

Colorado: “The driver of a motor vehicle, when reasonably 

necessary to ensure safe operation, shall give audible 

warning with the horn but shall not otherwise use such horn 

when upon a highway.” Colo. Rev. Stat. § 42-4-224(1). 

Delaware: “The driver of a vehicle shall, when reasonably 

necessary to insure safe operation, give audible warning with 

the horn but shall not otherwise use the horn for any other 

purpose.” Del. Code Ann. tit. 21, § 4306(b).
PORTER V. MARTINEZ 57

Georgia: “The driver of a motor vehicle shall, when it is 

reasonably necessary to ensure safe operation, give audible 

warning with his or her horn but shall not otherwise use such 

horn when upon a highway.” Ga. Code Ann. § 40-8-70(a). 

Idaho: “The driver of a motor vehicle shall when reasonably 

necessary to insure safe operation give audible warning with 

his horn, but shall not otherwise use the horn when upon a 

highway.” Idaho Code § 49-956(1). 

Illinois: “The driver of a motor vehicle shall when 

reasonably necessary to insure safe operation give audible 

warning with his horn but shall not otherwise use such horn 

when upon a highway.” 625 Ill. Comp. Stat. 5 / 12-601(a). 

Indiana: “The driver of a motor vehicle shall, when 

reasonably necessary to ensure safe operation, give audible 

warning with the horn on the motor vehicle but may not 

otherwise use the horn when upon a highway.” Ind. Code 

§ 9-19-5-2.

Iowa: “The driver of a motor vehicle shall when reasonably 

necessary to insure safe operation give audible warning with 

the horn but shall not otherwise use such horn when upon a 

highway.” Iowa Code § 321.432.

Kansas: “The driver of a motor vehicle when reasonably 

necessary to insure safe operation shall give audible warning 

with his horn but shall not otherwise use such horn when 

upon a highway.” Kan. Stat. Ann. § 8-1738(a).

Kentucky: “Every person operating an automobile or 

bicycle shall sound the horn or sound device whenever 

necessary as a warning of the approach of such vehicle to 

pedestrians or other vehicles, but shall not sound the horn or 

sound device unnecessarily.” Ky. Rev. Stat. Ann. § 189.080.
58 PORTER V. MARTINEZ

Louisiana: “The driver of a motor vehicle shall, when 

reasonably necessary to ensure safe operation, give audible 

warning with his horn, but shall not otherwise use such horn 

when upon a highway of this state.” La. Stat. Ann. 

§ 32:351(A)(1). 

Maine: “A person may not unnecessarily sound a signaling 

device or horn.” Me. Rev. Stat. tit. 29-A, § 1903(2).

Maryland: “The driver of a motor vehicle shall, when 

reasonably necessary to insure safe operation, give audible 

warning with his horn, but may not otherwise use the horn 

when on a highway.” Md. Code Ann., Transp. § 22-401(b).

Michigan: “The driver of a motor vehicle shall when 

reasonably necessary to insure safe operation give audible 

warning with his horn but shall not otherwise use the horn 

when upon a highway.” Mich. Comp. Laws § 257.706(a). 

Minnesota: “The driver of a motor vehicle shall, when 

reasonably necessary to insure safe operation, give audible 

warning with the horn, but shall not otherwise use the horn 

when upon a highway.” Minn. Stat. § 169.68(a).

Mississippi: “The driver of a motor vehicle shall, when 

reasonably necessary to insure safe operation, give audible 

warning with his horn but shall not otherwise use such horn 

upon a highway.” Miss. Code Ann. § 63-7-65(1). 

Missouri: “Such signaling device shall be used for warning 

purposes only and shall not be used for making any 

unnecessary noise, and no other sound-producing signaling 

device shall be used at any time.” Mo. Rev. Stat. 

§ 307.170(1). 

Montana: “The driver of a motor vehicle shall when 

reasonably necessary to ensure safe operation give audible 
PORTER V. MARTINEZ 59

warning with the horn but may not otherwise use the horn 

when upon a highway.” Mont. Code Ann. § 61-9-401(1).

Nebraska: “[I]t shall be unlawful . . . for any person at any 

time to use a horn, otherwise than as a reasonable warning.” 

Neb. Rev. Stat. § 60-6,285. 

Nevada: “A person driving a motor vehicle shall, when 

reasonably necessary to ensure safe operation, give audible 

warning with the horn, but shall not otherwise use the horn 

when upon a highway.” Nev. Rev. Stat. § 484D.400(2).

New Jersey: “The driver of a motor vehicle shall, when 

reasonably necessary to insure safe operation, give audible 

warning with his horn but shall not otherwise use such horn 

when upon a highway.” N.J. Stat. Ann. § 39:3-69. 

New Mexico: “The driver of a motor vehicle shall when 

reasonably necessary to ensure safe operation give audible 

warning with his horn but shall not otherwise use such horn 

when upon a highway.” N.M. Stat. Ann. § 66-3-843(A). 

New York: “[The] horn or device shall produce a sound 

sufficiently loud to serve as a danger warning but shall not 

be used other than as a reasonable warning nor be 

unnecessarily loud or harsh.” N.Y. Veh. & Traf. Law 

§ 375(1)(a).

North Carolina: “[I]t shall be unlawful . . . for any person 

at any time to use a horn otherwise than as a reasonable 

warning.” N.C. Gen. Stat. § 20-125(a). 

North Dakota: “Whenever reasonably necessary for safe 

operation, the driver of a motor vehicle upon a highway shall 

give audible warning with the vehicle’s horn, but may not 

otherwise use the vehicle’s horn while upon a highway.” 

N.D. Cent. Code § 39-21-36(1).
60 PORTER V. MARTINEZ

Oregon: “A person commits the offense of violation of use 

limits on sound equipment if the person . . . [u]ses a horn 

otherwise than as a reasonable warning.” Or. Rev. Stat. 

§ 815.225(1)(b). 

Rhode Island: “The driver of a motor vehicle shall when 

reasonably necessary to insure safe operation give audible 

warning with his or her horn but shall not otherwise use the 

horn when upon a highway.” R.I. Gen. Laws § 31-23-8.

South Carolina: “The driver of a motor vehicle shall, when 

reasonably necessary to insure safe operation, give audible 

warning with his horn but shall not otherwise use such horn 

when upon a highway.” S.C. Code Ann. § 56-5-4960. 

Tennessee: “[I]t is unlawful . . . for any person at any time 

to use a horn otherwise than as a reasonable warning.” Tenn. 

Code Ann. § 55-9-201(a).

Texas: “A motor vehicle operator shall use a horn to provide 

audible warning only when necessary to insure safe 

operation.” Tex. Transp. Code Ann. § 547.501(c). 

Utah: “The operator of a motor vehicle . . . when reasonably 

necessary to insure safe operation, shall give audible 

warning with the horn; and . . . except as provided [herein], 

may not use the horn on a highway.” Utah Code Ann. § 41-

6a-1625(1)(c)(i)-(ii). 

Vermont: “The operator of a motor vehicle, whenever 

reasonably necessary to ensure safe operation, shall give an 

audible warning with the horn of his or her vehicle but shall 

not otherwise use the horn when upon a highway.” Vt. Stat. 

Ann. tit. 23, § 1131. 
PORTER V. MARTINEZ 61

Virginia: “It shall . . . be unlawful for any person at any time 

to use a horn otherwise than as a reasonable warning.” Va. 

Code Ann. § 46.2-1060.

Washington: “The driver of a motor vehicle shall when

reasonably necessary to insure safe operation give audible 

warning with his or her horn but shall not otherwise use such 

horn when upon a highway.” Wash. Rev. Code 

§ 46.37.380(1). 

West Virginia: “The driver of a motor vehicle shall when 

reasonably necessary to insure safe operation give audible 

warning with his horn but shall not otherwise use such horn 

when upon a highway.” W. Va. Code § 17C-15-33(a). 

Wisconsin: “[N]o person shall at any time use a horn 

otherwise than as a reasonable warning.” Wis. Stat. 

§ 347.38(1).

Wyoming: “The driver of a motor vehicle shall when 

reasonably necessary to insure safe operation give audible 

warning with his horn but shall not otherwise use the horn 

when upon a highway.” Wyo. Stat. Ann § 31-5-952(a). 

Uniform Vehicle Code: “The driver of a motor vehicle shall 

when reasonably necessary to insure safe operation give 

audible warning with the horn but shall not otherwise use it.” 

Unif. Veh. Code § 12-401(a) (Nat’l Comm. on Unif. Traffic 

Laws & Ordinances 2000).