Preventing Unsafe Speeds
A Resource to Support Safe Speeds in Your Community
Why Speed Matters Most
1. Why Speed Matters Most
Managing speeds is the #1 priority to advance Vision Zero
Why? Higher speed increases kinetic energy, which leads to more severe crash impacts, resulting in more injuries and fatalities.
The human body can only tolerate so much force in a crash. And higher speeds are even riskier for people with lower physical tolerance, such as the young and elderly.
“People have physical limits for tolerating crash forces before death or serious injury occurs; therefore, it is critical to design and operate a transportation system that is human-centric and accommodates physical human vulnerabilities.”
Vehicle design has evolved faster than the human body. Wondering how the human body would need to change to tolerate the impacts of a car crash? Meet Graham.
1. Why Speed Matters Most
Likelihood of death for people walking if hit at these speeds
Speed poses an even greater risk to those outside of motor vehicles
Why? When we’re walking, biking, or riding scooters or motorcycles, our bodies are not protected by a vehicle’s hard shell or safety features, such as airbags or seat belts.
“To achieve a truly safe transportation system, road safety practitioners should not only manage speeds but make achieving safe speeds on all roads a cornerstone of their safety policies.”
1. Why Speed Matters Most
Other effects of higher speeds include:
- Worsening a driver’s reaction time and braking distance, making it harder to respond quickly to risks.
- Limiting a driver's field of vision, reducing the ability to perceive and react to changes in the driving environment.
- Increasing risks exponentially as vehicle size and weights increase, compounding the force of impact during crashes.
“Higher vehicle speeds increase both the likelihood of a pedestrian being struck by a car and the injury severity.”
Source: National Highway Traffic Safety Administration (2015)
Source: NACTO Urban Street Design Guide (2013)
1. Why Speed Matters Most
Small shifts in speed = big safety results
Reducing speeds by even relatively modest amounts can significantly improve safety, especially for people who are more physically vulnerable, such as people walking and biking, and kids and seniors.
Research shows that a reduction of 1 mph in average speed is associated with a 5% reduction in crashes. The evidence is clear: crash frequency rises with higher average speeds, and the increase becomes more rapid at higher speeds.
Shifting to Safety Over Speed
2. Shifting to Safety Over Speed
Level of Service prioritizes moving vehicles
VS
Level of Safety prioritizes moving people
We can prioritize safety over speed
The U.S. transportation system is designed to maximize speedy movement of vehicles – often at the expense of the safe movement of people. This issue disproportionately affects communities of color and low-income neighborhoods that are overburdened with high-traffic, high-speed roads with limited sidewalks and safety features.
For decades, roads have been designed and speed limits set to meet “Level of Service” goals to move vehicles “efficiently” and to minimize traffic congestion. This approach overlooks the vulnerability of people in crashes. Our call to prioritize “Level of Safety” is meant to shift the focus in decision-making: from moving vehicles efficiently to moving people safely. It’s time to center safety as the guiding principle in how we design and operate our roads.
“The Department [of Transportation] believes it is important to prioritize safety and moving individuals at safe speeds over focusing exclusively on the throughput of motor vehicles."
2. Shifting to Safety Over Speed
Focus on upstream speed management strategies
From a public health standpoint – as demonstrated by the Safe System Pyramid (shown to the right) – speed management work should prioritize population-level (or upstream, systemic) measures that benefit the greatest number of people with the minimal effort required from individuals.
For example, more people will benefit from investments in traffic calming measures than passive, individual-focused efforts, such as billboard campaigns telling people to “slow down.”
Safe System Pyramid. Adapted from "The Safe System Pyramid: A New Framework for Traffic Safety"
2. Shifting to Safety Over Speed
“A singular focus on speeding ignores the impact that even high, legal speeds can have on safety, since human injury tolerance can be exceeded even when drivers comply with the legal speed limit. Speed management efforts are intended to reduce harmful speeds rather than just control speeding behavior.”
Address unsafe speeds – not only speeding
Speeding – individuals driving above speed limits – has traditionally been considered the biggest problem on our streets. However, this overlooks the critical problem of preventing unsafe speeds – these are unintentionally encouraged by certain street designs, vehicle capabilities and inappropriate posted speed limits.
Advancing Vision Zero will take a focus not only on curbing speeding but also prioritizing an upstream approach, using self-enforcing road designs, appropriate speed limits and technologies to encourage drivers’ safe behavior.
This aligns with the Federal Highway Administration's Safe System Approach for Speed Management, which recommends managing speeds on the system level – not just curbing speeding at the individual level.
Note that managing speeds helps safe drivers and prevents reckless drivers from behaving dangerously. Lower speed limits slow overall traffic, making it harder for reckless drivers to speed or weave, creating a safer environment for everyone.
2. Shifting to Safety Over Speed
Small design changes can make a big difference, for example:
- Narrowing travel lanes, which encourages slower driving speeds.
- Reducing the number of travel lanes, possibly replaced by dedicated left-turn pockets and/or bike lanes.
- Buffered or protected bike lanes, that are physically separated from travel lanes with posts, planters, etc.
- Green-painted “crossbikes” (essentially crosswalks for bicyclists).
- Adding high-visibility painted crosswalks.
- Lowering posted speed limits (from 30 to 20 mph).
- Adding daylighting at intersections.
Before
After
2. Shifting to Safety Over Speed
Make safe speeds the simplest choice
We can design streets to encourage safe travel speeds and reduce the number and severity of crashes. We can make safe travel the easiest and most obvious choice for drivers by physically designing for safe speeds.
Example below: Installing left-turn calming speed bumps at an intersection can reduce drivers’ speeds when making a turn, as well as improving their visibility of pedestrians crossing the street.
“Roadway design strongly influences how people use roads… Design can help to make roads and streets “self-enforcing,” offering drivers contextual encouragement – via lane width, intersection design, pedestrian and bicyclist infrastructure, and other features – to drive at safer speeds.”
2. Shifting to Safety Over Speed
Examples of prioritizing safety over speed
Boulder, CO, reduced speed limits on all residential streets to 20 mph speed. Many cities, such as Atlanta, Austin, Boston, Minneapolis, NYC, Portland, Seattle, Tacoma, Washington, DC and others, are lowering speed limits to enhance safety.
San Francisco, CA’s Safe Streets Neighborhood Traffic Calming program prioritizes street design interventions to curb dangerous speeds, including raised crosswalks and speed humps, leading to an average overall reduction of 5 - 14 mph.
Philadelphia, PA saw a 50% reduction in traffic deaths, 36% decrease in crashes, and 90% reduction in excessive speeding in the first seven months after speed safety cameras were added on high-injury Roosevelt Blvd. (See how to equity can be prioritized in speed safety camera programs).
Top Strategies to Manage Speeds
Using all of these strategies together is most effective
3. Top Strategies to Manage Speed
Set appropriate speed limits
Start with the basics: Speed limits should be set at safe and appropriate speeds. Setting speed limits should consider context, including land use, roadway factors, and who is using the roads (or potentially can use the roads), such as people walking and biking.
Recognizing that the human body can only tolerate so much in a crash, the recommended maximum default citywide speed limit is 20-25 mph, with lower speeds for residential, shared and minor streets. For more details and recommendations, see NACTO’s Speed Limits guide & FHWA Speed Limit Setting Handbook.
Speed limits categories for urban streets. Source: NACTO City Limits
“The basis of any speed management approach should be the setting of speed limits "
3. Top Strategies to Manage Speed
Use modern, updated tools to set speed limits
Communities are shifting away from the outdated 85th percentile method for setting speed limits, especially in urban areas, as it ignores non-motorized users, land use, and road context, while encouraging a dangerous cycle of speed escalation (learn more).
Practitioners can use resources such as USLIMITS2, NACTO City Limits and NCHRP Report 966. For more details, consult the USDOT's Safe System Approach for Speed Management report and FHWA Speed Limit Setting Handbook.
"A 20-mph speed limit for urban roads that have a mix of motorized and non-motorized road users along with the application of additional speed-management countermeasures to achieve the set 20-mph speed limit is an example of the outcome of applying the SSA [Safe System Approach] principles."
3. Top Strategies to Manage Speed
Case study: Seattle
Seattle improved safety by reducing speed limits from 25 to 20 mph on residential streets and from 30 to 25 mph on arterial streets.
Results:
↓ 18% reduction in fatal and injury crashes.
↓ 22% reduction in overall crashes.
↓ 54% reduction in drivers exceeding the speed limit by 40 mph or greater.
Seattle combines speed limit reductions with traffic calming measures like road diets, but even without engineering changes or enforcement, simply lowering speed limits and adding more signs has reduced speeds and crashes.
“It is critical that agencies collect data after the implementation of speed management countermeasures to ensure that the effectiveness of those countermeasures can be evaluated."
3. Top Strategies to Manage Speed
Design streets for safety over speed
Too many U.S. roads are designed to prioritize speed over safety. Roads with multiple, wide, straight lanes encourage high speeds, create a false sense of security for drivers and endanger others, particularly people walking and biking.
Physical design features such as narrower lanes, roundabouts, speed humps, medians and protected bike lanes help deter high speeds, improving safety for everyone on the road.
Self-enforcing, or self-explaining, street design embeds physical cues to encourage safe driving. This is a more effective, long-lasting and equitable way to prevent unsafe speeds. This focus on Complete Streets helps lessen the need for enforcement, which can be cost-prohibitive, fleeting in its safety effects and also raises important equity concerns.
“...safer roadways mean incorporating design elements that offer layers of protection to prevent crashes from occurring and mitigate harm when they do occur... A one-size-fits-all approach to roadway design will not work; instead, context-sensitive designs must be the norm."
3. Top Strategies to Manage Speed
Design matters in preventing unsafe speeds
Specific strategies are well-tested and proven in reducing traffic deaths and severe injuries. FHWA’s important resource, Proven Safety Countermeasures, showcases dozens of strategies to effectively manage speeds for safety. These strategies are “designed for all road users and all kinds of roads — from rural to urban, from high-volume freeways to less traveled two-lane State and county roads, from signalized crossings to horizontal curves, and everything in between.”
Examples include:
↓ 82% reduction in fatal and injury crashes linked to roundabouts.
↓ 53% reduction in bicycle/vehicle crashes by converting unprotected bike lanes into separated bike lanes.
↓ 19-47% reduction in total crashes comes from implementing road diets, or roadway reconfigurations.
Examples of street design measures that can manage speeds for safety
- Chicanes
- Curb extensions
- Daylighting
- Diverters
- Enhanced curve delineation
- Lane shifts
- Left turn traffic calming or “no left turns”
- Medians
- Protected bike lanes
- Raised crosswalks
- Road diets
- Roundabouts and traffic circles
- Slow Streets or slow zones
- Speed feedback signs
- Speed humps, speed tables, and speed cushions
3. Top Strategies to Manage Speed
Leverage technology to manage speeds
Technology alone cannot solve our road safety problems but, if used carefully, can be effective tool to advance safety.
Many technologies are available to help maintain and manage safe speeds: Speed Safety Cameras and Intelligent Speed Assistance (ISA) stand out as particularly promising solutions. Explore their potential in the case studies below.
3. Top Strategies to Manage Speed
Case Studies: Speed Safety Cameras
Speed Safety Cameras — when well designed, operated and monitored — can deter high speeds, reduce crashes and lessen the severity of injuries when crashes do occur. They are widely used internationally and in more than 240 U.S. communities, resulting in reductions of roadway injuries and fatalities ranging from 20% to 37%.
New York City’s program helped reduce speeding in the camera zones by 73% and traffic injuries by 34%. Montgomery County, Maryland’s program reduced the likelihood of vehicles exceeding speed limits by more than 10 mph by 62% and decreased fatal or incapacitating injuries by 39% on residential roads with speed limits of 25 to 35 mph.
Speed safety cameras offer some clear advantages over police-led stops for speeding. Yet their use also poses risks of exacerbating racial and income disparities. So, speed safety cameras – and traffic enforcement in general – should not be the sole nor primary tool to manage speeds. Instead, cameras should be considered temporary components of comprehensive speed management plans which prioritize “upstream” strategies, such as designing safe roadways and vehicles and setting appropriate speed limits.
“In places where roadways require engineering improvements, cameras can serve as a helpful interim measure but are not a replacement for changes to roadway design.”
— Washington, DC. Report on Automated Traffic Enforcement Equity and Safety, 2024
Read our new report – Fair Warnings: Recommendations to Promote Equity in Speed Safety Camera Programs – to learn more about equitable implementation of this technology.
3. Top Strategies to Manage Speed
Case Studies: Intelligent Speed Assistance
Intelligent Speed Assistance (ISA) is a safety technology that alerts drivers when they exceed specific speeds. Already in use and proven to improve safety in other nations, ISA is a prime example of a Safe System approach that manages speeds at a fundamental level, reducing the likelihood and severity of speed-related crashes, injuries and deaths. The National Transportation Safety Board (NTSB) recommends ISA in all vehicles, as is required in the European Union. ISA is among the safety strategies recommended in NHTSA's Countermeasures That Work.
States and local entities are stepping in to address the slow pace of federal action:
- In 2024, Washington, D.C. enacted this law requiring the use of Intelligent Speed Assistance (ISA) technology in vehicles owned by individuals convicted of serious, repeat speeding offenses. Virginia and Washington State have since passed "super-speeder" laws and over 20 states are considering similar policy.
- The American Association of Motor Vehicle Administrators has model legislation to promote uniform adoption. Read updates from the National Conference of State Legislators.
- Many communities are proactively equipping their municipal fleets with ISA technology – with NYC leading the way, recognizing its value in promoting safer speeds.
- Learn about ISA technology in this webinar, about ISA in public fleets in this webinar and about proven benefits in this webinar.
California advocates gathered in front of the State Senate to support an ISA bill in 2024. Photo: WalkSF
“Require as standard equipment in all new vehicles intelligent speed assistance systems that, at a minimum, warn the driver when the vehicle exceeds the speed limit.”
— Recommendation from National Transportation Safety Board (NTSB)
3. Top Strategies to Manage Speed
Additional Strategies to Manage Speeds
Where to Start: Preventing Unsafe Speeds
More Resources to Manage Speeds
- Reducing Speeding-Related Crashes Involving Passenger Vehicles (NTSB)
- Safe System Approach for Speed Management (FHWA)
- Speed Safety Camera Program Planning and Operations Guide (FHWA and NHTSA)
- Speed Management Library (ITE)
- Improving Pedestrian Safety on Urban Arterials: Learning from Australasia (FHWA)
- Vision Zero Network webinars about Safe Speeds