Table of Contents
Highway safety represents one of the most critical challenges facing transportation professionals, policymakers, and communities across the nation. Traffic fatalities have fallen for 10 straight quarters, with an estimated 29,135 people dying in traffic crashes in the first nine months of 2025, representing a decrease of about 4.4% compared to 30,490 fatalities projected for the same period in 2023. While this trend is encouraging, the ongoing toll of roadway deaths and serious injuries demands continued vigilance and innovation in highway design and safety practices. Effective highway safety design requires a comprehensive, data-driven approach that considers all road users, incorporates proven countermeasures, and adapts to evolving challenges in our transportation system.
Understanding the Foundation of Highway Safety Design
Highway safety design has evolved significantly over recent decades, moving from reactive approaches based solely on crash history to proactive, systematic methodologies that prevent crashes before they occur. The Highway Safety Manual (HSM), published by the American Association of State Highway Transportation Officials (AASHTO), is the recognized source of information and methods for quantitatively evaluating traffic safety performance on existing or proposed roadways, providing a science-based, technical approach that helps State and local agencies take the guesswork out of safety analysis.
Modern highway safety design is grounded in the Safe System Approach, which recognizes that humans make mistakes and that the transportation system should be designed to accommodate these errors while minimizing their consequences. This philosophy represents a fundamental shift from traditional approaches that placed primary responsibility on road users to avoid crashes. Instead, the Safe System Approach distributes responsibility across multiple elements: safer roads, safer vehicles, safer speeds, safer people, and effective post-crash care.
Effective traffic safety relies on a balanced approach where engineering, enforcement, education, and equipment all play interconnected roles. This integrated framework ensures that improvements in one area complement and reinforce progress in others, creating a comprehensive safety ecosystem that addresses the complex nature of roadway crashes.
The Role of Data in Safety Planning
Data-driven decision-making forms the cornerstone of effective highway safety improvement programs. Transportation agencies must collect, analyze, and apply multiple types of data to identify safety problems, prioritize interventions, and measure the effectiveness of implemented countermeasures. This includes crash data, traffic volume information, roadway characteristics, environmental factors, and behavioral observations.
A wave of new, innovative technologies is addressing core safety challenges like speeding, impaired driving and distracted driving, while data and advanced analytics are helping shine a light on trends and opportunities that were unseen with traditional methods. Advanced analytics capabilities now allow agencies to identify patterns and risk factors that would have remained hidden using conventional analysis methods, enabling more targeted and effective interventions.
The development of comprehensive traffic records systems that integrate data from multiple sources—including law enforcement crash reports, emergency medical services, hospital records, and roadway inventory databases—provides a more complete picture of safety challenges. This integrated approach supports more accurate problem identification and enables agencies to track outcomes across the entire spectrum of crash severity, from property damage only crashes to fatalities.
Comprehensive Assessment of Highway Safety Conditions
Before implementing safety improvements, transportation agencies must thoroughly assess existing conditions to identify specific problems, understand their causes, and prioritize interventions based on potential safety benefits. This assessment process involves multiple complementary approaches that together provide a comprehensive understanding of safety performance and opportunities for improvement.
Crash Data Analysis and Pattern Recognition
Analyzing historical crash data remains a fundamental component of highway safety assessment. This process involves examining crash frequency, severity, type, and contributing factors to identify locations and conditions associated with elevated crash risk. Effective crash analysis goes beyond simple frequency counts to examine crash rates that account for exposure (typically measured in vehicle-miles traveled), allowing for meaningful comparisons between locations with different traffic volumes.
Pattern recognition within crash data helps identify systemic issues that may affect multiple locations across a roadway network. For example, analysis might reveal that certain intersection configurations, roadway cross-sections, or environmental conditions are consistently associated with specific crash types. This systemic perspective enables agencies to implement proven countermeasures at multiple similar locations, even those without extensive crash histories, preventing crashes before they occur.
Advanced analytical techniques, including predictive modeling and spatial analysis, enhance traditional crash analysis methods. These approaches can identify emerging safety problems, predict future crash patterns based on roadway and traffic characteristics, and prioritize locations for intervention based on potential for safety improvement rather than solely on historical crash frequency.
Road Safety Audits: A Proactive Approach
A Road Safety Audit (RSA) is the formal safety performance examination of an existing or future road or intersection by an independent, multidisciplinary team that qualitatively estimates and reports on potential road safety issues and identifies opportunities for improvements in safety for all road users. Road safety audits represent a critical tool for proactively identifying safety concerns before crashes occur, complementing reactive approaches based on crash history.
RSAs both identify potential hazards by looking at roads in-service from the perspectives of different road users and offer suggestions for improvement that do not rely on a crash history for validation. This proactive characteristic makes RSAs particularly valuable for new construction projects, major reconstruction efforts, and locations where crash history may not yet reflect underlying safety problems.
The RSA process involves several essential elements that distinguish it from conventional design reviews. RSAs are performed by a multidisciplinary team independent of the project, consider all road users, account for human factors and road user capabilities, are documented in a formal report, and require a formal response from the road owner. This independence ensures objectivity and brings fresh perspectives to safety evaluation.
RSAs are performed by a team of at least three auditors who represent a variety of experience and expertise specifically tailored to the project, with audit team members being independent of the design team charged with the development of the original plans. Team composition typically includes professionals with backgrounds in highway design, traffic operations, safety engineering, human factors, maintenance, law enforcement, and other relevant disciplines depending on project characteristics.
RSAs applied early in the planning and preliminary design of roads offer the greatest opportunity for beneficial influence, as changes that may improve safety performance typically become more difficult, costly, and time-consuming to implement as a design progresses into detailed design and construction. This timing consideration emphasizes the importance of integrating safety evaluation throughout the project development process rather than treating it as a final check before construction.
Field Reviews and Operational Analysis
Direct observation of roadway conditions and traffic operations provides insights that cannot be obtained through data analysis alone. Field reviews allow safety professionals to experience roadways from the perspective of various users, identifying potential confusion points, visibility limitations, maintenance issues, and other factors that may contribute to crash risk.
Operational analysis examines how traffic actually behaves on existing facilities, including vehicle speeds, lane utilization, gap acceptance at intersections, pedestrian crossing behavior, and other observable characteristics. Discrepancies between intended design performance and actual operational behavior often reveal safety concerns that require attention. For example, if drivers consistently exceed posted speed limits or make unexpected maneuvers, this may indicate that roadway design elements are sending conflicting messages or that design assumptions do not match real-world conditions.
Conducting field reviews under various conditions—including different times of day, weather conditions, and traffic volumes—ensures comprehensive understanding of safety challenges. Nighttime reviews are particularly important for evaluating visibility, lighting adequacy, and retroreflectivity of signs and pavement markings. Reviews during peak traffic periods reveal congestion-related safety issues, while off-peak observations may identify speeding concerns or other problems that emerge under light traffic conditions.
Community Engagement and User Feedback
Engaging with community members and road users provides valuable qualitative information about safety concerns, near-miss events, and locations where people feel unsafe. This input often identifies problems that may not yet be reflected in crash data or that affect vulnerable populations whose safety concerns might otherwise be overlooked.
Public input processes should be designed to reach diverse populations, including pedestrians, bicyclists, transit users, older adults, people with disabilities, and residents of underserved communities. Multiple engagement methods—such as public meetings, online surveys, walking audits, and targeted outreach to specific groups—help ensure broad participation and comprehensive feedback.
Near-miss data collection represents an emerging approach to understanding safety problems before crashes occur. By systematically collecting information about close calls and dangerous situations, agencies can identify locations and conditions that pose elevated risk even if crashes have not yet occurred. This proactive data source complements traditional crash analysis and supports earlier intervention.
Fundamental Design Principles for Highway Safety
Effective highway safety design incorporates multiple principles that work together to create roadway environments that are intuitive, forgiving of human error, and protective of all users. These principles should guide decision-making throughout the project development process, from initial planning through final design and construction.
Self-Explaining Roads and Positive Guidance
Self-explaining roads are designed so that their intended use is immediately obvious to all users without requiring extensive signage or prior knowledge. This principle recognizes that drivers make rapid decisions based on visual cues from the roadway environment. When roadway characteristics clearly communicate appropriate speeds, expected maneuvers, and potential conflicts, drivers are more likely to behave in safe, predictable ways.
Positive guidance involves providing clear, consistent information to road users through the roadway’s geometric design, traffic control devices, and delineation. This includes ensuring adequate sight distance, providing clear lane delineation, using consistent signing and marking practices, and designing transitions between different roadway types to allow drivers time to adjust their expectations and behavior.
Consistency in design elements across a roadway network reinforces positive guidance. When similar situations are treated similarly, drivers develop accurate expectations about how to navigate various roadway features. Conversely, unexpected changes in design standards or traffic control practices can lead to confusion and increased crash risk.
Designing for Human Capabilities and Limitations
Highway design must account for the capabilities and limitations of human perception, cognition, and physical abilities. This includes considering reaction times, visual acuity, information processing capacity, and the effects of aging on driving performance. Design decisions should accommodate the full range of user capabilities rather than assuming ideal conditions and perfect performance.
Visual complexity and information load significantly affect driver performance. Roadway environments that present too much information simultaneously, require rapid decision-making without adequate time or distance, or include conflicting cues increase the likelihood of driver error. Effective design manages information load by presenting information in logical sequences, eliminating unnecessary visual clutter, and ensuring that critical information stands out from the background environment.
Age-related changes in vision, cognition, and physical abilities require special consideration in highway design. Older drivers may need additional time to perceive and process information, greater letter heights on signs for adequate legibility, and longer gaps to safely complete maneuvers. Design accommodations that support older drivers—such as larger signs, enhanced lighting, and simplified decision points—generally benefit all users by creating more forgiving roadway environments.
Complete Streets and Multimodal Design
Creating a “culture of safety” requires prioritizing the needs of all users in roadway planning, design, and maintenance, as well as expanding Complete Streets principles into everyday practice. Complete Streets are designed and operated to enable safe access for all users, including pedestrians, bicyclists, motorists, and transit riders of all ages and abilities.
Implementing Complete Streets principles requires moving beyond vehicle-centric design to consider the needs of all potential users from the earliest stages of project development. This includes providing appropriate facilities for each mode, ensuring safe crossings and transitions between modes, and creating environments where vulnerable road users are protected from high-speed motor vehicle traffic.
Context-sensitive design recognizes that appropriate roadway design varies based on surrounding land use, community character, and user needs. Urban streets serving adjacent development require different design approaches than rural highways, and design solutions should reflect these contextual differences. Flexibility in applying design standards allows for solutions that balance mobility, safety, and community objectives.
Forgiving Roadside Design
Forgiving roadside design recognizes that vehicles will occasionally leave the traveled way and seeks to minimize the consequences when this occurs. This principle involves providing clear zones free of fixed objects, using traversable slopes that allow drivers to maintain control, and installing roadside barriers only where necessary to shield more severe hazards.
Clear zone width depends on traffic volume, speed, and roadside geometry. Higher-speed, higher-volume roadways require wider clear zones to accommodate the greater distances that errant vehicles may travel. Where adequate clear zones cannot be provided due to physical or economic constraints, roadside barriers protect motorists from more severe hazards such as steep slopes, bodies of water, or rigid obstacles.
Roadside hardware design has evolved significantly to reduce injury severity in crashes. Breakaway supports for signs and luminaires collapse upon impact rather than acting as fixed objects. Modern guardrail end treatments redirect or capture vehicles rather than spearing through the passenger compartment. Median barriers prevent cross-median crashes while minimizing injury severity when struck. Selection and installation of appropriate roadside hardware requires careful consideration of site-specific conditions and potential crash scenarios.
Proven Safety Countermeasures and Design Features
Transportation agencies have access to a robust toolkit of proven safety countermeasures—treatments that have been demonstrated through research and field implementation to reduce crashes and improve safety. Selecting and implementing appropriate countermeasures based on specific safety problems and site conditions forms the core of effective highway safety improvement programs.
Intersection Safety Improvements
Intersections represent locations of elevated crash risk due to the complexity of vehicle interactions, decision-making requirements, and potential conflicts between different movements. Comprehensive intersection safety improvements address geometric design, traffic control, and visibility to reduce both crash frequency and severity.
Roundabouts represent one of the most effective intersection safety treatments, particularly for reducing severe crashes. Modern roundabouts use geometric design to control speeds and simplify conflict points, resulting in dramatic reductions in fatal and serious injury crashes compared to conventional intersections. Single-lane roundabouts are particularly effective, while multi-lane roundabouts require careful design to maintain safety benefits.
Intersection lighting improves nighttime visibility and has been shown to reduce nighttime crashes, particularly those involving pedestrians and bicyclists. Effective intersection lighting provides adequate illumination of the conflict area, approaches, and crossing pedestrians while minimizing glare and light pollution. LED technology has improved the energy efficiency and maintenance characteristics of roadway lighting systems.
Advanced intersection design features include protected left-turn phasing to separate conflicting movements, leading pedestrian intervals that give pedestrians a head start before vehicles receive a green signal, and restricted crossing U-turn (RCUT) designs that eliminate direct left turns and U-turns from minor approaches. Each of these treatments addresses specific crash patterns and requires careful analysis to ensure appropriateness for site conditions.
Sight distance improvements at intersections ensure that drivers can see conflicting traffic and make safe gap acceptance decisions. This may involve removing or relocating visual obstructions, adjusting vertical and horizontal geometry, or installing traffic control devices to assign right-of-way when adequate sight distance cannot be provided. Intersection sight distance requirements vary based on approach speeds and intersection configuration.
Roadway Departure Countermeasures
Roadway departure crashes—those in which vehicles leave the traveled way and strike fixed objects, overturn, or cross the centerline—represent a significant portion of fatal and serious injury crashes, particularly on rural highways. Effective roadway departure countermeasures address both crash prevention and severity reduction.
Rumble strips and rumble stripes provide tactile and audible warning to drivers who are drifting from their intended path. Centerline rumble strips alert drivers who are crossing into opposing traffic lanes, while edge line rumble strips warn of departure toward the roadside. Rumble stripes combine the alerting function of rumble strips with the visual guidance of pavement markings. Proper design and installation of rumble strips considers noise impacts on adjacent properties and accommodation of bicyclists.
High-friction surface treatments improve pavement friction at locations where wet-weather crashes or crashes on curves indicate inadequate skid resistance. These treatments apply a thin layer of high-friction aggregate to the pavement surface, significantly increasing available friction and reducing wet-weather and curve-related crashes. Applications include horizontal curves, approaches to intersections and traffic signals, and other locations where vehicles must brake or change direction.
Median barriers prevent cross-median crashes on divided highways. Cable median barriers offer a cost-effective solution for relatively wide medians, while concrete barriers are appropriate for narrow medians or locations requiring greater containment. Proper barrier selection considers median width, traffic volume and speed, and maintenance requirements. Median barrier installation must include appropriate end treatments and transitions to ensure effectiveness.
Enhanced delineation and curve warning systems help drivers navigate horizontal curves, particularly at night or in adverse weather. Chevrons, larger curve warning signs, dynamic curve warning systems that activate when vehicles approach at excessive speeds, and enhanced pavement markings all contribute to improved curve negotiation. The appropriate combination of treatments depends on curve geometry, crash history, and operating speeds.
Pedestrian and Bicycle Safety Features
The Vulnerable Road User Safety Assessment is aimed at addressing the safety of pedestrians and bicyclists through a data-driven analysis to identify high-risk areas and vulnerable populations. Protecting vulnerable road users requires dedicated infrastructure, traffic calming measures, and design features that separate or protect these users from motor vehicle traffic.
Crosswalk enhancements improve pedestrian visibility and driver yielding behavior. High-visibility crosswalk markings, pedestrian crossing signs and warning devices, pedestrian hybrid beacons (also known as HAWK signals), and rectangular rapid flashing beacons (RRFBs) all increase driver awareness of pedestrian crossings and improve yielding rates. Selection of appropriate treatments depends on roadway characteristics, traffic volumes and speeds, and pedestrian demand.
Pedestrian refuge islands provide a protected space for pedestrians crossing wide roadways, allowing them to cross one direction of traffic at a time. This is particularly beneficial for older pedestrians and others who may need additional time to cross. Refuge islands also narrow the roadway from a driver’s perspective, encouraging lower speeds and increased awareness of pedestrians.
Separated bicycle facilities provide physical separation between bicyclists and motor vehicle traffic, significantly improving both actual and perceived safety for bicyclists. Protected bike lanes use vertical elements such as bollards, planters, or parked cars to separate the bike lane from adjacent traffic lanes. Shared-use paths provide completely separated facilities for bicyclists and pedestrians. The appropriate level of separation depends on motor vehicle speeds and volumes, with higher-speed, higher-volume roadways requiring greater separation.
Bicycle detection and accommodation at traffic signals ensures that bicyclists can actuate signals and receive adequate green time to clear intersections. This includes properly positioned and marked detection zones, bicycle signal heads that provide clear indication to bicyclists, and signal timing that accounts for bicycle speeds. Leading bicycle intervals, similar to leading pedestrian intervals, give bicyclists a head start before vehicles receive a green signal.
Speed Management Strategies
Speed management represents a critical component of highway safety, as crash severity increases dramatically with impact speed. Effective speed management involves setting appropriate speed limits based on roadway characteristics and context, designing roadways to encourage appropriate speeds, and using enforcement and automated speed enforcement where appropriate.
Traffic calming measures use physical design features to reduce vehicle speeds, particularly in residential areas and other contexts where lower speeds are desired. Speed humps, speed tables, raised crosswalks, chicanes, and other vertical and horizontal deflections encourage lower speeds through geometric design rather than relying solely on posted speed limits and enforcement. Proper design of traffic calming features considers emergency vehicle access, noise impacts, and effects on bicyclists.
Road diets involve reducing the number of travel lanes, typically converting a four-lane undivided roadway to a three-lane cross-section with a center two-way left-turn lane and bicycle lanes. This treatment reduces speeds, simplifies crossing for pedestrians, provides dedicated left-turn lanes to reduce rear-end crashes, and creates space for bicycle facilities. Road diets are most appropriate for roadways carrying less than 20,000 vehicles per day, though specific capacity depends on intersection spacing and turning volumes.
Dynamic speed feedback signs display approaching vehicle speeds, alerting drivers when they are exceeding the speed limit. These devices have been shown to reduce speeds, particularly when first installed, though effects may diminish over time. They are most effective when combined with enforcement and when placed at locations where drivers may not be aware of speed limits or where speed reduction is particularly important for safety.
Signing, Marking, and Delineation
Traffic control devices provide essential information, warning, and guidance to road users. Effective signing, marking, and delineation requires careful attention to visibility, placement, consistency, and maintenance to ensure that devices serve their intended functions throughout their service lives.
Retroreflectivity of signs and pavement markings directly affects nighttime visibility and driver ability to perceive and respond to information. Minimum retroreflectivity standards ensure that signs and markings remain visible under nighttime conditions throughout their service lives. Agencies must implement management systems to maintain retroreflectivity, either through scheduled replacement, condition assessment, or use of control signs to trigger replacement.
Sign size and letter height affect legibility distance, which must be adequate to allow drivers time to perceive, process, and respond to information. Larger signs with greater letter heights are required on higher-speed roadways to provide adequate legibility distance. Oversized signs may be appropriate at complex locations or where additional emphasis is needed.
Pavement marking width and pattern affect visibility and driver response. Wider markings are more visible, particularly in wet conditions and at night. Skip patterns for lane lines and centerlines are designed to provide adequate guidance while allowing for passing or lane changing where appropriate. Solid markings indicate that crossing is prohibited or discouraged. Consistency in marking patterns across a roadway network reinforces driver understanding and appropriate behavior.
Raised pavement markers supplement painted markings to provide enhanced guidance, particularly in wet conditions when painted markings may be difficult to see. Different colors serve different functions: white for lane lines, yellow for centerlines and left edge lines, and red for wrong-way indication. Proper placement and maintenance of raised pavement markers ensures continued effectiveness.
Integrating Safety into Project Development
FHWA has developed supporting implementation tools including the Interactive Highway Safety Design Model (IHSDM), the Crash Modification Factors (CMF) Clearinghouse, and the Systemic Safety Project Selection Tool, which will greatly advance state and local highway agencies’ ability to incorporate explicit, quantitative consideration of safety into their planning and project development decision making.
Safety Performance Prediction and Evaluation
Quantitative safety analysis allows agencies to predict the safety performance of proposed designs and compare alternatives based on expected crash frequency and severity. This capability supports data-driven decision-making and helps ensure that safety receives appropriate consideration alongside other project objectives such as mobility, cost, and environmental impacts.
The Highway Safety Manual provides predictive methods for estimating expected crash frequency for various facility types based on traffic volume, geometric characteristics, and other factors. These predictions can be compared to observed crash frequencies to identify locations with higher-than-expected crash rates, or used to estimate the safety performance of proposed designs before construction. Calibration of predictive models to local conditions improves accuracy and ensures that predictions reflect regional crash patterns and reporting practices.
Crash Modification Factors (CMFs) quantify the expected change in crashes associated with specific design features or treatments. The Crash Modification Factors Clearinghouse houses a web-based database of CMFs along with supporting documentation to help transportation engineers identify the most appropriate countermeasure for their safety needs. CMFs allow agencies to estimate the safety effects of proposed improvements and compare the effectiveness of alternative treatments.
Benefit-cost analysis provides a framework for comparing the economic value of safety improvements to their costs. By monetizing the value of crash reductions based on comprehensive crash costs that include medical expenses, lost productivity, property damage, and quality-of-life impacts, agencies can prioritize investments to achieve the greatest safety benefit per dollar spent. This economic analysis supports resource allocation decisions and demonstrates the value of safety investments to decision-makers and the public.
Design Exception and Variance Processes
Design standards provide important guidance for achieving safe roadway design, but site-specific constraints sometimes make full compliance with standards impractical or impossible. Design exception and variance processes allow agencies to approve designs that do not meet all applicable standards while ensuring that safety implications are carefully considered and documented.
Effective design exception processes require documentation of the specific standards that cannot be met, the reasons why compliance is not feasible, the safety implications of the proposed design, and any mitigation measures that will be implemented to address safety concerns. This documentation ensures that decisions are made with full understanding of safety tradeoffs and creates a record for future reference.
Safety analysis should be a central component of design exception decisions. Quantitative evaluation of expected safety performance, comparison to alternative designs, and consideration of crash history at similar locations all inform the decision-making process. In some cases, innovative designs that do not strictly comply with standards may actually provide superior safety performance compared to standard designs.
Value Engineering and Safety Integration
Past experience indicates that RSAs can be integrated with the value engineering method and the results of RSAs can be used in value engineering studies, however, a Value Engineering study that does not integrate an RSA is not a viable substitute for an RSA. Value engineering seeks to optimize project value by examining functions and identifying opportunities to reduce costs while maintaining or improving performance.
Safety must be explicitly considered in value engineering studies to ensure that cost reduction measures do not compromise safety performance. This requires including safety professionals on value engineering teams, conducting safety analysis of proposed alternatives, and establishing clear criteria for evaluating safety implications. In many cases, value engineering can identify opportunities to improve both cost-effectiveness and safety through innovative design solutions.
Life-cycle cost analysis provides a more complete picture of project economics by considering not only initial construction costs but also maintenance, operation, and crash costs over the facility’s service life. Safety improvements that reduce crash frequency and severity generate ongoing benefits that may justify higher initial costs. This long-term perspective supports investment in safety features that provide positive returns over time.
Work Zone Safety and Temporary Traffic Control
Work zone safety remained a major focus as federally funded infrastructure projects moved deeper into active construction phases, with guidance from the Federal Highway Administration emphasizing proper work zone setup, device spacing, and visibility. Work zones present unique safety challenges due to changed conditions, reduced speeds, lane shifts, and the presence of workers and equipment in close proximity to traffic.
Work Zone Design and Layout
Effective work zone design balances the need to provide adequate workspace for construction activities with the imperative to maintain safe traffic operations. This involves careful consideration of lane closures, work zone length, traffic control device placement, and transitions between normal roadway conditions and the work zone.
Positive protection of workers through the use of temporary barriers separates workers from active traffic lanes where feasible. Portable concrete barriers, water-filled barriers, and truck-mounted attenuators all provide physical protection that can prevent or mitigate intrusion crashes. The decision to use positive protection depends on factors including traffic speeds and volumes, proximity of work to traffic, duration of work, and available space.
Work zone speed management seeks to reduce speeds through work zones to levels appropriate for changed conditions. This may involve regulatory speed limits, speed feedback signs, enforcement, and geometric design features that encourage speed reduction. Research indicates that simply posting lower speed limits without supporting enforcement or design features often has limited effectiveness, while comprehensive approaches that combine multiple strategies achieve better results.
Temporary Traffic Control Devices
Temporary traffic control devices guide motorists through work zones and provide warning of changed conditions. The Manual on Uniform Traffic Control Devices (MUTCD) establishes standards for work zone traffic control, including device selection, placement, and maintenance requirements.
Advance warning signs alert drivers to upcoming work zones and provide information about changed conditions. A series of warning signs placed at increasing distances from the work zone gives drivers adequate time to reduce speed and prepare for changed conditions. Sign spacing depends on roadway speed, with greater spacing required on higher-speed facilities.
Channelizing devices such as cones, drums, and vertical panels delineate the path through the work zone and separate traffic from the work area. Proper spacing and alignment of channelizing devices provides clear guidance while allowing adequate reaction time for drivers. Retroreflective materials ensure nighttime visibility.
Temporary pavement markings guide drivers through work zones where permanent markings are obscured or no longer applicable. Removal or obliteration of conflicting permanent markings prevents confusion. Temporary markings must meet the same retroreflectivity standards as permanent markings to ensure adequate nighttime visibility.
Intelligent Transportation Systems in Work Zones
Intelligent Transportation Systems (ITS) applications in work zones provide real-time information to drivers and help manage traffic flow. Portable changeable message signs display current conditions, delays, and alternative routes. Queue detection systems identify the back of queues and provide advance warning to approaching drivers, reducing the risk of rear-end crashes.
Speed monitoring and feedback systems measure vehicle speeds and provide feedback to drivers through dynamic message signs or speed display trailers. Some systems include automated enforcement capabilities that issue citations to speeding drivers. These systems have been shown to reduce speeds and improve compliance with work zone speed limits.
Travel time estimation systems provide drivers with information about expected delays, allowing them to make informed decisions about route selection. This information can be displayed on changeable message signs upstream of the work zone or disseminated through connected vehicle applications and smartphone apps.
Maintenance and Asset Management for Safety
Ongoing maintenance of roadway infrastructure and traffic control devices is essential to sustaining safety performance over time. Deferred maintenance can lead to deteriorating safety conditions as pavement quality declines, signs and markings become less visible, and roadside hardware becomes damaged or ineffective.
Pavement Condition and Safety
Pavement condition affects safety through multiple mechanisms. Adequate surface friction prevents skidding and loss of control, particularly in wet conditions. Smooth, well-maintained pavement allows drivers to maintain control and reduces the likelihood of crashes caused by potholes or other surface irregularities. Proper drainage prevents hydroplaning and maintains visibility by reducing spray from vehicle tires.
Friction testing identifies locations where pavement friction has degraded to levels that may contribute to wet-weather crashes. High-friction surface treatments or pavement rehabilitation can restore adequate friction. Prioritizing friction improvements at locations with documented wet-weather crash problems ensures that limited resources address the most critical needs.
Pavement markings deteriorate over time due to traffic wear and environmental exposure. Regular inspection and maintenance of pavement markings ensures continued visibility and guidance. Retroreflectivity measurement provides objective assessment of marking condition and supports data-driven replacement decisions.
Sign and Signal Maintenance
Traffic signs must remain visible and legible throughout their service lives to effectively communicate information to drivers. Retroreflectivity degradation, physical damage, and vegetation growth can all compromise sign effectiveness. Regular inspection identifies signs requiring replacement or maintenance.
Traffic signal maintenance ensures reliable operation and appropriate timing. Signal failures can lead to crashes if drivers are uncertain about right-of-way or if signals display conflicting indications. Backup power systems maintain signal operation during power outages. Regular timing reviews ensure that signal timing remains appropriate as traffic patterns change over time.
Vegetation management maintains sight distance at intersections and along roadways, ensures visibility of signs, and prevents encroachment into clear zones. Regular mowing, trimming, and removal of vegetation is necessary to maintain safe conditions. Vegetation management must balance safety needs with environmental considerations and aesthetic objectives.
Roadside Hardware Inspection and Repair
Guardrails, barriers, and other roadside hardware must be maintained in proper condition to function as intended when struck. Damaged hardware should be repaired promptly, as compromised systems may not provide adequate protection in subsequent crashes. Regular inspection identifies damage and deterioration requiring attention.
End treatment integrity is particularly critical, as damaged or improperly functioning end treatments can lead to severe crashes. Inspection should specifically evaluate end treatment condition and ensure that all components are present and properly aligned. Older end treatment designs that do not meet current standards should be upgraded during routine maintenance or as part of safety improvement projects.
Barrier height and offset must be maintained within acceptable tolerances to ensure proper performance. Settlement, erosion, or changes in pavement elevation can affect barrier geometry and compromise effectiveness. Periodic surveys verify that barriers remain within acceptable parameters.
Emerging Technologies and Future Directions
Rapid technological advancement is creating new opportunities to improve highway safety through connected and automated vehicles, advanced data collection and analysis, and innovative design approaches. While many of these technologies are still emerging, they have significant potential to transform highway safety in coming years.
Connected and Automated Vehicles
Connected vehicle technology enables vehicles to communicate with each other and with roadside infrastructure, providing warnings of potential conflicts, hazardous conditions, and other safety-relevant information. Vehicle-to-vehicle (V2V) communication can warn drivers of vehicles in blind spots, approaching emergency vehicles, or sudden braking ahead. Vehicle-to-infrastructure (V2I) communication can provide information about signal timing, curve speeds, work zones, and other roadway conditions.
Automated vehicle technology has the potential to dramatically reduce crashes caused by human error, which contributes to the vast majority of crashes. However, the transition period during which automated and conventional vehicles share roadways presents unique challenges. Highway design may need to evolve to support both human drivers and automated systems, potentially including enhanced pavement markings for machine vision, dedicated lanes for automated vehicles, or other infrastructure modifications.
The interaction between automated vehicles and vulnerable road users requires careful consideration. Automated vehicles must be able to detect and appropriately respond to pedestrians, bicyclists, and other road users whose behavior may be less predictable than that of other vehicles. Infrastructure design can support these interactions through clear delineation of pedestrian and bicycle facilities, well-defined crossing locations, and consistent design treatments.
Advanced Data Collection and Analysis
New data sources and analytical capabilities are enhancing understanding of safety problems and enabling more targeted interventions. Video analytics can automatically detect near-misses, traffic conflicts, and unsafe behaviors, providing insights into safety problems before crashes occur. This proactive data source complements traditional crash analysis and supports earlier intervention.
Mobile data collection using vehicles equipped with cameras, lidar, and other sensors enables efficient inventory of roadway characteristics, sign and marking condition, and other features relevant to safety. This data supports network-level safety analysis, identification of systemic issues, and prioritization of maintenance activities. Machine learning algorithms can automatically extract relevant information from mobile data collection, reducing the time and cost of data processing.
Predictive analytics using machine learning and artificial intelligence can identify complex patterns in crash data and roadway characteristics that may not be apparent through traditional analysis methods. These techniques can improve crash prediction accuracy, identify emerging safety problems, and support more effective resource allocation. However, care must be taken to ensure that predictive models are transparent, interpretable, and free from bias.
Performance-Based Design and Evaluation
Performance-based approaches to highway design focus on achieving desired outcomes rather than prescribing specific design features. This flexibility allows for innovative solutions that may provide superior performance compared to conventional designs while ensuring that safety objectives are met. Performance-based design requires clear performance metrics, validated analytical methods, and processes for evaluating whether proposed designs will achieve desired performance.
Surrogate safety measures provide intermediate indicators of safety performance that can be evaluated without waiting for crash data to accumulate. Measures such as traffic conflicts, speed variance, and post-encroachment time can be observed or simulated and used to compare design alternatives. While surrogate measures do not directly measure crashes, research has established relationships between certain surrogate measures and crash frequency, allowing them to inform design decisions.
Simulation and modeling tools enable evaluation of design alternatives before construction, supporting informed decision-making and optimization of safety performance. Microsimulation models can evaluate traffic operations and identify potential conflicts or operational issues. Crash prediction models estimate expected crash frequency for different design alternatives. Driving simulators allow testing of driver response to design features in controlled environments.
Organizational Capacity and Institutional Framework
Effective highway safety improvement requires not only technical knowledge and proven countermeasures but also organizational capacity, institutional commitment, and collaborative partnerships. Building and sustaining this capacity involves training, policy development, resource allocation, and coordination across multiple agencies and disciplines.
Training and Professional Development
Highway safety is a specialized field requiring knowledge of crash causation, human factors, geometric design, traffic operations, and countermeasure effectiveness. Ongoing training ensures that professionals have current knowledge of best practices, emerging technologies, and analytical methods. Training should be available to diverse audiences including engineers, planners, maintenance personnel, law enforcement, and decision-makers.
Formal training programs such as those offered by the National Highway Institute provide structured curricula on topics including road safety audits, Highway Safety Manual application, intersection design, and pedestrian and bicycle safety. These programs combine classroom instruction with practical exercises and case studies to develop applied skills.
Peer exchange and knowledge sharing allow agencies to learn from each other’s experiences, successes, and challenges. Site visits to locations where innovative treatments have been implemented, participation in professional organizations, and attendance at conferences and workshops all facilitate knowledge transfer and professional networking.
Policy and Procedure Development
Using experience gained in conducting RSA pilot projects, agencies will be able to develop a formal RSA policy that is suited to local conditions. Formal policies and procedures institutionalize safety practices and ensure consistent application across projects and over time. Written policies provide clear direction to staff, establish accountability, and demonstrate organizational commitment to safety.
Safety policies should address multiple aspects of the project development process, including when and how safety analysis will be conducted, criteria for selecting projects for road safety audits, procedures for documenting and responding to safety concerns, and requirements for safety performance evaluation. Policies should be integrated with other agency procedures to ensure that safety receives appropriate consideration alongside other project objectives.
Design manuals and standard drawings should incorporate safety principles and proven countermeasures, making it easier for designers to implement safe designs. Regular updates to design guidance ensure that current best practices are reflected in agency standards. Flexibility provisions allow for context-sensitive solutions and innovative designs while maintaining safety performance.
Collaboration and Partnerships
The National Roadway Safety Strategy offers a comprehensive approach to address the crisis of deaths on our nation’s roadways, calling upon leaders across the Department and its operating administrations, as well as state and local leadership, safety and health advocates, the private sector, nonprofit organizations, and other external partners to take action.
Effective highway safety improvement requires coordination among multiple agencies and stakeholders. State departments of transportation, metropolitan planning organizations, local governments, law enforcement, emergency medical services, public health agencies, and advocacy organizations all play important roles in improving roadway safety. Regular communication, shared goals, and collaborative planning processes ensure that efforts are coordinated and mutually reinforcing.
Multidisciplinary teams bring diverse perspectives and expertise to safety problem-solving. Engineers, planners, law enforcement officers, public health professionals, and community representatives each contribute unique insights that lead to more comprehensive and effective solutions. Formal structures such as safety task forces or technical committees provide venues for ongoing collaboration.
Public-private partnerships can leverage resources and expertise from both sectors to advance safety objectives. Private sector partners may contribute technology, data, or funding for safety improvements. Partnerships with employers, insurance companies, and other private entities can support education and outreach efforts that complement infrastructure improvements.
Funding and Resource Allocation
Adequate and sustained funding is essential to implementing comprehensive highway safety improvement programs. Multiple funding sources support safety improvements, each with specific eligibility requirements, application processes, and performance expectations.
Federal Highway Safety Programs
The overall purpose of the Highway Safety Improvement Programs is to achieve a significant reduction in fatalities and serious injuries on all public roads through the implementation of highway safety improvement projects, including infrastructure-related projects, selected and justified by proven data-driven approaches. The Highway Safety Improvement Program (HSIP) represents the primary federal funding source for infrastructure-based safety improvements.
HSIP funds are allocated to states based on formulas that consider factors including lane miles and vehicle miles traveled. States must develop Strategic Highway Safety Plans that establish goals, identify emphasis areas, and guide investment decisions. Projects funded through HSIP must be consistent with the Strategic Highway Safety Plan and selected based on data-driven processes that identify locations or systemic issues with safety problems.
Other federal programs also support safety improvements. The Surface Transportation Block Grant Program provides flexible funding that can be used for safety projects. The Transportation Alternatives Program funds pedestrian and bicycle facilities. The National Highway Performance Program includes safety as one of several performance areas. Coordinating across these programs maximizes available resources for safety improvements.
Performance Management and Accountability
Federal transportation legislation establishes performance management requirements that include safety targets and performance measures. States must set annual targets for fatalities, fatality rate, serious injuries, serious injury rate, and non-motorized fatalities and serious injuries. Metropolitan planning organizations set coordinated targets and track progress toward achieving them.
Performance measurement provides accountability for safety investments and enables evaluation of program effectiveness. By tracking outcomes and comparing them to targets, agencies can assess whether their safety programs are achieving desired results and make adjustments as needed. Transparent reporting of safety performance builds public confidence and demonstrates the value of safety investments.
Benefit-cost analysis supports resource allocation by quantifying the expected return on investment for safety improvements. Projects with higher benefit-cost ratios provide greater safety benefit per dollar invested, though other factors such as equity, community priorities, and systemic risk may also influence project selection. Comprehensive economic analysis considers not only crash reduction benefits but also other impacts such as travel time, emissions, and quality of life.
Innovative Financing and Delivery
Traditional project delivery methods may not always be optimal for safety improvements, particularly those that are relatively small in scale or distributed across a network. Innovative delivery approaches can improve efficiency and accelerate implementation of safety improvements.
Systemic safety improvement programs address safety issues that occur at multiple locations across a roadway network by implementing proven countermeasures at all similar locations, regardless of crash history. This proactive approach prevents crashes rather than waiting for crash histories to develop. Systemic programs are particularly effective for low-cost treatments such as signing, marking, and minor geometric improvements that can be implemented at many locations.
Bundling multiple small safety projects into larger contracts can reduce administrative costs and improve contractor efficiency. Rather than advertising and administering dozens of small contracts, agencies can combine similar projects into packages that are more attractive to contractors and easier to manage. This approach is particularly effective for systemic safety improvements and routine safety upgrades.
Alternative project delivery methods such as design-build or construction manager/general contractor may offer advantages for certain safety projects. These methods can accelerate project delivery, improve coordination between design and construction, and leverage contractor expertise in developing cost-effective solutions. However, care must be taken to ensure that safety performance is not compromised in pursuit of cost or schedule objectives.
Equity Considerations in Highway Safety
The Department hosted an Equity in Roadway Safety Webinar Series to highlight innovative practices and tools to integrate equity into roadway safety programs and projects, with more than 1,000 attendees participating in sessions on equity and project delivery and roadway safety for people experiencing homelessness. Ensuring that all communities benefit from safety improvements and that safety investments address the needs of vulnerable and underserved populations represents an important dimension of highway safety planning and implementation.
Identifying Disparities in Safety Outcomes
Safety outcomes vary across different populations and communities. Pedestrian and bicycle fatality rates are higher in some demographic groups and geographic areas. Lower-income communities and communities of color often experience disproportionate safety burdens. Understanding these disparities requires disaggregated analysis of crash data by location, demographics, and other relevant factors.
Spatial analysis can identify geographic areas with elevated crash rates or specific crash types. Mapping crash locations and calculating rates based on population or exposure reveals patterns that may not be apparent from aggregate statistics. This geographic perspective supports targeted interventions in areas with the greatest need.
Demographic analysis examines whether certain populations experience disproportionate crash involvement or severity. This may reveal that older adults, children, people with disabilities, or other groups face elevated risks that require specific countermeasures or design accommodations. Understanding these patterns ensures that safety improvements address the needs of all road users.
Inclusive Planning and Community Engagement
Meaningful community engagement ensures that safety planning reflects the priorities and concerns of affected communities, particularly those that have been historically underserved or excluded from decision-making processes. This requires going beyond traditional public involvement methods to actively reach out to diverse communities and create opportunities for authentic participation.
Engagement methods should be tailored to the communities being served, considering factors such as language, cultural norms, accessibility, and trust in government institutions. This may involve partnering with community-based organizations, holding meetings in community venues rather than government offices, providing translation and interpretation services, and using multiple communication channels to reach diverse audiences.
Community input should inform not only specific project decisions but also broader safety planning priorities and resource allocation. Residents often have detailed knowledge of local safety problems, near-miss locations, and barriers to safe travel that may not be reflected in crash data. Incorporating this local knowledge leads to more effective and community-supported solutions.
Equitable Resource Allocation
Ensuring equitable distribution of safety resources requires examining how funding is allocated across communities and whether investment patterns address disparities in safety outcomes. This may involve developing explicit equity criteria for project prioritization, setting aside funding for improvements in underserved communities, or adjusting benefit-cost analysis methods to account for equity considerations.
Complete Streets and Vision Zero approaches often emphasize equity as a core principle, recognizing that vulnerable road users and residents of lower-income communities are disproportionately affected by traffic crashes. Prioritizing improvements that serve these populations helps address historical inequities and ensures that all communities benefit from safety investments.
Accessibility for people with disabilities must be integrated into all safety improvements. This includes providing accessible pedestrian signals, ensuring that sidewalks and crossings meet accessibility standards, and considering the needs of people with various types of disabilities in design decisions. Universal design principles that create environments usable by people of all abilities benefit everyone.
Measuring Success and Continuous Improvement
Effective highway safety programs require ongoing evaluation to assess whether implemented improvements are achieving desired outcomes, identify opportunities for refinement, and demonstrate accountability for public investments. This evaluation should occur at multiple levels, from individual project effectiveness to overall program performance.
Before-After Evaluation Studies
Before-after studies compare crash experience before and after implementation of safety improvements to quantify effectiveness. Rigorous evaluation methods account for regression to the mean, changes in traffic volume, and general trends in crash rates to isolate the effects of specific treatments. Empirical Bayes methods provide statistically sound approaches to before-after evaluation that address these challenges.
Evaluation results contribute to the body of knowledge about countermeasure effectiveness and inform future project selection. Documenting local experience with various treatments helps agencies refine their safety programs and provides evidence to support continued investment. Sharing evaluation results with the broader transportation community through the Crash Modification Factors Clearinghouse and other venues advances the state of practice.
Long-term monitoring extends evaluation beyond the immediate post-implementation period to assess whether safety benefits are sustained over time. Some treatments may show initial effectiveness that diminishes as drivers become accustomed to changed conditions or as physical elements deteriorate. Understanding these long-term patterns informs maintenance requirements and treatment selection.
Program-Level Performance Assessment
Evaluating overall safety program performance requires examining aggregate outcomes across all projects and investments. This includes tracking progress toward safety targets, analyzing trends in fatalities and serious injuries, and assessing whether the program is achieving desired reductions in crashes and severity.
Performance dashboards and reporting systems provide regular updates on safety metrics and progress toward goals. These tools support data-driven management by making performance information readily available to decision-makers and staff. Public reporting of safety performance builds transparency and accountability.
Periodic program reviews examine whether safety programs are structured and resourced appropriately to achieve goals. This may involve assessing organizational capacity, evaluating project selection processes, reviewing funding allocation patterns, and identifying opportunities to improve program effectiveness. External peer reviews can provide valuable perspectives and identify best practices from other agencies.
Adaptive Management and Learning
Highway safety practice continues to evolve as new research findings emerge, technologies develop, and experience accumulates. Adaptive management approaches embrace this evolution by systematically incorporating new knowledge into practice, experimenting with innovative approaches, and learning from both successes and failures.
Pilot projects and demonstration programs provide opportunities to test new treatments or approaches on a limited scale before broader implementation. Careful evaluation of pilot projects generates evidence about effectiveness and identifies implementation challenges that can be addressed before wider deployment. This staged approach reduces risk while enabling innovation.
Knowledge management systems capture and share lessons learned from safety projects and programs. Documenting what worked well, what challenges were encountered, and how problems were solved creates institutional memory that informs future efforts. Regular knowledge sharing sessions, case studies, and best practice guides facilitate organizational learning.
Research partnerships with universities, research institutions, and other agencies advance understanding of safety problems and solutions. Collaborative research projects can address questions specific to local conditions while contributing to broader knowledge. Participating in national research programs such as the Transportation Research Board provides access to cutting-edge research and opportunities to influence research agendas.
Conclusion: A Comprehensive Approach to Highway Safety
Improving highway safety through design requires a comprehensive, sustained commitment that integrates proven practices, innovative approaches, and collaborative partnerships. Success depends on multiple elements working together: rigorous data collection and analysis to identify problems and prioritize solutions; application of proven countermeasures tailored to specific safety challenges; integration of safety considerations throughout the project development process; adequate and sustained funding; organizational capacity and institutional commitment; meaningful community engagement; and ongoing evaluation and continuous improvement.
As 2026 approaches, continued focus on visibility, consistency, and compliance will remain essential, and while no single year can solve roadway safety challenges, data-informed policy decisions and well-executed traffic control can make a measurable difference. The encouraging trend of declining fatalities demonstrates that comprehensive safety efforts can achieve results, but continued progress requires sustained attention and investment.
Highway design professionals have access to an extensive toolkit of proven safety countermeasures, sophisticated analytical methods, and implementation guidance. The challenge lies in systematically applying this knowledge across the roadway network, ensuring that all communities benefit from safety improvements, and adapting to emerging technologies and changing conditions. By maintaining focus on the ultimate goal—eliminating deaths and serious injuries on our roadways—and working collaboratively across disciplines and organizations, the transportation community can continue to make progress toward safer roads for all users.
For additional resources on highway safety design and implementation, visit the Federal Highway Administration Office of Safety, explore the National Roadway Safety Strategy, access tools and guidance through the FHWA Safety Program, review proven countermeasures at the FHWA Proven Safety Countermeasures page, and consult the Crash Modification Factors Clearinghouse for evidence-based treatment effectiveness information.