Tactics to Reduce Urban Vehicle Speeds
MIT Mobility Initiative Research Briefing
David Zipper
MIT Mobility Initiative Senior Fellow 2025
Executive Summary & Key Findings
This briefing examines ways in which American city leaders can reduce excessive motor vehicle speeds within their jurisdictions. Speed is a key contributing factor in crash deaths, particularly among “vulnerable road users” such as pedestrians and cyclists who are more numerous within urban areas. As a result, many cities have sought to manage speed as part of Vision Zero strategies intended to reduce roadway fatalities. Their tactics can include street-calming infrastructure, enhanced enforcement, and measures to slow traffic flows.
Although academic research regarding the efficacy of various speed-mitigating tactics is well-established, less scholarly attention has been paid to the politics of implementation. This briefing summarizes available research about public acceptance of speed-mitigating measures and shares insights drawn from interviews with 11 urban transportation leaders from across the United States.
Respondents agreed that speed humps and automatic traffic enforcement are particularly popular among residents, while road diets are controversial. In general, tactics designed to limit speed are broadly popular, especially after residents have had a chance to experience their benefits, and are less divisive than could be inferred from rhetoric in the media or during public hearings.
Background & Motivation
Vehicle velocity is one of the most important determinants of crash deaths. In 2023, speeding played a contributing role in crashes that killed 11,775 people in the US, representing 29 percent of total traffic fatalities, and injured over 330,000 (NHTSA, 2025). Those figures may understate speed’s danger because they are limited to collisions in which drivers exceeded the posted speed limit and do not include those involving vehicles moving quickly but legally. (Principles like the controversial 85th percentile rule may lead to speed limits being set higher than they would be if safety were considered alongside vehicle throughput.)
Speed is particularly lethal for people walking and biking. According to a study by AAA, only one in four pedestrians dies after colliding with a vehicle going 23 mph, but half or three-quarters will be killed if that vehicle is moving at 31 mph or 39 mph, respectively (Tefft, 2011). A 2025 report by the Centers for Disease Control concluded that the US has the highest pedestrian crash death rate among 28 high-income countries, and that the US pedestrian death rate had risen 50% between 2013 and 2022 (Naumann et al., 2025). Cyclist deaths are also increasing, hitting 1,166 in 2023, the most since at least 1980 (Shepardson, 2025).
Federal, state, and local governments deploy various tools to mitigate speed. At the federal level, the National Highway Traffic Safety Administration runs public awareness campaigns and has the power to mandate speed governors or Intelligent Speed Assist, an emergent technology that mechanically prevents or deters drivers from driving above the posted speed limit. The Federal Highway Administration manages the Manual on Uniform Traffic Control Devices (MUTCD), which includes guidance about establishing speed limits.
States, for their part, design and control many urban roadways themselves, including some that are among the deadliest. According to one analysis, two-thirds of crash deaths in the 101 largest urban areas occurred on state-controlled roads, even though state roads represented just 14 percent of total urban road miles (Transportation for America, 2024). States also determine the legality of installing automatic traffic cameras that penalize speeders, and they have the authority to confiscate the drivers licenses of habitually reckless drivers. In the last year, states including Virginia and Washington have adopted laws that allow judges to require the installation of Intelligent Speed Assist within cars owned by speeding drivers (Zipper, 2025).
Leaders of municipalities, the focus of this research briefing, are particularly motivated to temper speeding because urban residents are more likely to travel by bike, on foot, or via transit (which generally requires walking the “first/last mile”). Protecting them – and reducing the severity of crashes – is the central tenet of Vision Zero, a commitment made by dozens of cities to eliminate traffic deaths.
City tactics
Anti-speeding tactics available to urban leaders can be grouped into three categories: Infrastructure, Enforcement, and Traffic. Several such tactics can be and often are implemented concurrently, such as lower speed limits applied to newly narrowed lanes.
Infrastructure-based tactics include road diets and lane narrowings, both of which have been found to reliably reduce vehicle speed. For instance, road diets installed on five Los Angeles corridors reduced speeds by 6.7% during peak times and 7.9% during offpeak times, while a 2023 Johns Hopkins report found that lanes nine and ten feet wide had lower speeds (and fewer crashes) than those twelve and thirteen feet wide (Venegas et al., 2023 & Hamidi, 2023). Vertical traffic calming devices such as speed humps and speed tables can consistently slow vehicles, such as during a 2023 pilot in Arlington, VA in which speed humps reduced speeds by over 40% (County of Arlington, 2024). An additional speed mitigation tactic entails limiting clear zones, such as by planting roadside trees, which can compel drivers to slow down (Fitzpatrick et al., 2016).
Enforcement-based tactics can include reducing the speed limit, with the caveat that s ome jurisdictions are restricted by state policy mandating the legal maximum reflect the 85th percentile speed. Even in the absence of infrastructure revisions, speed limit adjustments do affect vehicle velocity: When Boston reduced its default speed limit from 30 mph to 25 mph in 2017, the city experienced a relative 29% drop in vehicles that exceeded 35 mph compared to Providence, RI, a nearby city where speed limits did not change (Hu and Cicchino, 2020).
Automatic enforcement cameras, which are restricted or banned in many states, have been found to reliably reduce illegal speeding, including a 94% drop at school-adjacent New York City sites (NYCDOT, 2024). Deployment of police issuing tickets may also deter speeding, although the effect is likely to be temporary. One study found an eight-week “time-halo” of lower speeds following the conclusion of an enforcement action (Vaa, 1997). A lighter-touch enforcement tactic involves creating and distributing media, such as signage or videos, that implores drivers to slow down. Although most such campaigns are pursued at the national and state levels, cities sometimes adopt them as well, such as New York City’s “Speeding Ruins Lives” program (NYCDOT, 2023).
Traffic-related tactics include signal adjustments to reduce the speed at which a driver will encounter a series of green lights. A research project testing this strategy in Danvers, MA found that shifted signal timing reduced the number of vehicles breaking the speed limit by 78% (Furth, 2024). An emergent approach involves installing Intelligent Speed Assist on city-owned fleet vehicles. A relatively small number of ISA-equipped vehicles could have an outsized impact on traffic speeds, since they constrain the velocity of vehicles behind them on the roadway. Over the last two years, New York City and the District of Columbia have launched ISA pilots involving municipal fleets.
Comparative Efficacy
Several studies have summarized and compared the efficacy of various anti-speed tactics that cities can deploy. In a 2023 report, the World Health Organization deemed speed humps and lane narrowings “proven” speed management interventions, while Intelligent Speed Assist is “promising” and PSA education campaigns are “ineffective” (WHO, 2023). Drawing from numerous academic studies, NHTSA’s encyclopedic Countermeasures that Work assigns its maximum five stars of effectiveness to Lower Speed Limits and Speed Safety Camera Enforcement, while issuing four stars to High-Visibility Enforcement and three stars to Intelligent Speed Assist (NHTSA, 2023). A 25-year-old meta-analysis by Reid Ewing examined hundreds of before-and-after studies of traffic calming interventions, concluding that installing speed humps, speed tables, lane narrowings and traffic circles generally reduce vehicle speeds, but with wide variations in outcomes that complicate efforts to draw more nuanced conclusions (Ewing, 2000).
Indeed, quantitative comparisons of anti-speed tactics are inherently challenging if not impossible. Implementation costs vary widely; while speed bumps can be installed for around $5,000 each, road diets can cost millions depending on the nature of the infrastructure replaced and installed. The universe of potential treatments of a given roadway are also context-specific. As Jeffrey Tumlin, the recent leader of San Francisco’s MTA, said, “The challenge with speed mitigation is there are 800 things that you can do, and so much of their efficacy varies primarily according to pre-existing geographic context. It's not like medicine, where you can ascribe specific efficacy factors.”
Many more studies explore the capacity of anti-speed approaches to reduce vehicle velocities than the popular support and opposition observed when pursuing them. Those tactics that are effective and popular could be particularly appealing to local leaders seeking to save lives without sacrificing citizen support.
Data, Research Work and Methods
The first stage of research consisted of reviewing academic studies examining the political support or opposition to particular speed mitigation tactics. The second stage involved interviews conducted during the summer of 2025 with eleven individuals who are currently or were recently senior transportation leaders of US municipalities. The cities represented include three in the Midwest, three in the West, three in the Northeast, and two in the South. All have over 100,000 and fewer than 1,000,000 residents.
Interviewees were asked about the nature, efficacy, and public acceptance of the speed countermeasures their city had implemented in recent years. Some were granted anonymity because they were not authorized to be quoted.
A caveat: The research focused specifically on speed countermeasures that could be pursued by local governments. Tactics for state and federal policymakers were not a focus; nor were city strategies to reduce crashes through measures not directly related to speed (i.e., daylighting intersections).
Key Results and Takeaway Messages
Overview of studies examining the acceptance of anti-speed measures
Although few researchers have considered the popularity of speed countermeasures, those who have generally found moderate-to-strong support that rises over time as residents experience the benefits of slower streets. One study examining acceptance of road safety policies across the US (in rural areas, rather than cities) noted that “strong support exists across all major demographic, geographic, gender, and ideological groups” (Munrich et al., 2011).
A few examples: A 2002 evaluation of speed humps installed in Iowa found that a majority of nearby residents supported them (Hallmark et. Al, 2002). A 2015 briefing by Rice University noted that road diets are often more popular than they appear to casual observers because “public hearings will always skew towards those who oppose something new” (Kinder, 2015).
A 2011 NHTSA survey found that well over half of Americans support the use of automatic speed enforcement in high crash locations and construction zones (Schroeder et al., 2013). Researchers also found that more than three-quarters of and five-eighths of those residing in the District of Columbia and Montgomery County, MD, respectively, approve of their use (Cicchino et al., 2014 & Hu and McCartt, 2016). Another study found that framing automatic speed enforcement around racial justice benefits (since cameras negate the need for officer-citizen interactions) boosts popular acceptance further beyond 50% (Ralph et al., 2022).
Perspectives of city transportation leaders
With few exceptions, the city transportation leaders provided consistent feedback about the popularity of anti-speed measures they have pursued. Several noted that public support for reducing vehicle speed has risen over the last twenty years due to growing awareness of increasing pedestrian and cyclist deaths as well as an influx of new residents seeking an “urban” lifestyle in contrast to a suburban and car-centric one.
“Politics around speed management have changed completely from 2010 to today,” said the transportation operations director of a large Western city. “There's been a shift and a general acceptance for slowing people down – but sure, there's still people that aren't really pleased when you force them.”
All but one interviewee said that safety was the main argument they used when discussing speed mitigation efforts with the public. “I used to focus on other benefits of vehicle speed reduction, like noise, better public health, and streets that feel more welcoming,” said Brandi Peacher, the Complete Streets Coordinator for the city of Lexington, KY. “People told me, ‘that’s nice, but not essential.’ What we’re leading with now is safety, because everyone says that the roads need to be safe – especially if it involves children.” [The exception was a leader in the South who said she preferred to note the negative economic effects of fast vehicles, such as “if a motorist is driving by your business at 45 miles an hour, they probably aren't noticing your sign or business.”]
Feedback on individual tactics are summarized below.
Infrastructure
A majority of city leaders said that speed humps are the most requested speed countermeasure. “Speed humps are the thing that we hear most from community members, because that's what they know,” said Lauren Grove, the Vision Zero Coordinator for Durham, NC. “Everyone starts the conversation with ‘can we put a speed hump there,’” said Kevin Muhs, Milwaukee’s city engineer with oversight over transportation. In Portland, OR, speed humps are requested so often that the budget-limited transportation agency is considering allowing neighborhoods to request and pay for installation themselves. Beyond their documented effectiveness, speed humps’ popularity can be attributed to widespread familiarity as well as a NIMBY-esque perception among residents that they will force “other drivers” to slow down while using “our” streets. Pushback to speed humps is minor, often limited to the occasional homeowner complaining about noise from vehicles traversing the speed hump in front of their property.
Road diets that reduce travel lanes or parking to add a bike lane and/or widen pedestrian infrastructure were seen as the most controversial of all anti-speed tactics. Still, every leader surveyed deemed them essential. “Road diets are just about the only tool that I have in my toolbox for arterials and collector roadways,” said one leader of a mid-sized Southern city. Another transportation executive from a small Northeastern city said she avoids the term “road diet”: “I'm not a huge fan of the terminology, because I think people immediately jump to the removal of traffic lanes.” Muhs, in Milwaukee, said that his team is focused on “aesthetic improvements with traffic calming, like green infrastructure and trees, because we’ve gotten pushback over just pouring concrete or using delineators.”
All city representatives said that public communication about the reasons for installing road diets can reduce opposition. Several noted that they sometimes seek to mitigate pushback by starting with “quick build” installations that can later be removed, if necessary. Since many road diets gain popularity after installation, presenting their establishment as temporary can sidestep opposition that later dissipates. However, residents’ resistance is not the only obstacle to adjusting street design: A majority of city officials said that emergency responders presented the biggest challenge because they worried that their vehicles would struggle to navigate the “new” streets quickly (“The fire department is our number one roadblock,” said one leader of a large Midwestern city). A common compromise entails installing speed cushions with cut-outs that permit wide-axled vehicles like fire trucks to proceed without slowing down.
Few cities surveyed have strategically reduced clear zones to mitigate speeding. The two that had agreed that they are relatively uncontroversial, particularly if the project involves planting trees or other beautification elements that nearby residents enjoy.
Enforcement
Enforcement actions were seen as being broadly popular among urban residents, and typically less controversial than road diets. “Whether it from cameras or police officers, people generally want enforcement,” said Stefanie Seskin, the head of policy for the National Association of City Transportation Officials who previously worked on street safety for the city of Boston. “They see others as the problem, not themselves, and so they want accountability.”
City leaders agreed that that automatic speed cameras are highly effective at reducing speeding, and that most residents support their installation. “People really like them,” said Tumlin. “By San Francisco standards, we’ve had virtually no pushback.” Officials in another large Western city said that traffic cameras are the most requested countermeasure among residents, and a street safety leader in the Mid-Atlantic said that such requests disproportionately come from low-income, minority neighborhoods. Privacy concerns about speed cameras raised by advocacy groups seem to seldom be voiced by residents themselves.
Indeed, speed cameras appear to be a tactic whose popularity is higher than commonly perceived, perhaps due to media stories amplifying a narrative of controversy. Such discrepancies matter, because they could compel elected leaders to be unnecessarily wary of using automatic enforcement. “The opposition to cameras generally comes from reporters and politicians,” said one transportation leader in the Mid-Atlantic. Despite speed cameras’ popularity and efficacy, most states place strict limitations on cities’ ability to deploy them. In some states, such as Massachusetts, Texas, and Wisconsin, they are banned (Zipper, 2025).
Similarly, local public officials said that a strong majority of their constituents, including in low-income areas, support bursts of police enforcement on high-speed thoroughfares. Several transportation leaders noted that activists who decry traffic police deployments within minority communities may not reflect the views of most residents.
Reducing speed limits was universally seen as an uncontroversial tactic, although one Western city leader said some residents’ indifference may arise from a belief that the limits “really don’t matter because no one is getting ticketed for breaking them.”
None of the city leaders surveyed spent public money on “education campaigns” such as Public Service Announcements requesting that drivers slow down. They agreed that such efforts are accepted by the public, but that they have no effect on speeding. As one Midwestern official bluntly put it, “they don’t work.”
Traffic
Not all cities possess the infrastructure necessary to adjust traffic signals so that only those drivers obeying the speed limit come upon a series of green lights. But the consensus was that such modifications can reliably induce speed reductions (“99% effective,” said the street safety leader of a large Northeastern city) and are highly unlikely to spur popular pushback. Most drivers, they said, do not even notice them.
Only one city surveyed had installed Intelligent Speed Assist on fleet vehicles, and in that case the deployment was too limited to affect velocities on the overall street network. However, several city officials shared optimism that ISA on public fleets could in the future dramatically reduce speeding while eliciting virtually no pushback from the public.
Conclusion
Even in the absence of action at the state or federal levels, municipalities still possess myriad tools to control speeding. The research around speed-related countermeasures concludes that, with the exception of PSA campaigns, speed countermeasures at the local level reliably reduce vehicle speeds and that some of them, such as speed humps, road diets, and automatic speed enforcement, are particularly powerful. Based on interviews, speed countermeasures are notably popular among residents, particularly after they have been able to experience the benefits firsthand.
A question, then, is why cities that are officially committed to Vision Zero are not moving faster to control vehicle speed. One explanation is that a gulf exists between the popular acceptance of such measures and exaggerated perceptions of residential pushback. Such gaps could be due to a vocally loud minority of community members sharing disapproval of tactics such as road diets and speed cameras, as well as the media’s intrinsic interest in presenting stories portraying conflict. Either way, it appears that those leaders who take forceful steps to reduce speeding are likely find robust community support for their lifesaving efforts.
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