Technical Resources

Safe System

This webpage was developed in partnership with the Road to Zero Coalition and members of the RTZ Safe System Working Group.

Safe System Explanation

The Safe System approach differs from conventional safety practice by being human-centered, i.e. seeking safety through a more aggressive use of vehicle or roadway design and operational changes rather than relying primarily on behavioral changes – and by fully integrating the needs of all users (pedestrians, bicyclists, older, younger, disabled, etc.) of the transportation system. Safe Systems provide a safety-net for the user by:

1. Anticipating Human Error – A Safe System is designed to anticipate and accommodate errors by drivers and other road users.
Example: Even a momentary distraction can prevent a driver from seeing vulnerable road users or vice-versa. Separating vulnerable road users, such as pedestrians and bicyclists, from traffic wherever possible reduces the likelihood that such predictable errors will lead to a deadly collision.
Example: On rural highways the application of rumble strips can recapture the driver’s attention when they drift out of the lane due to distraction or fatigue. In newer vehicles, lane-keeping technologies can provide similar benefit.

2. Accommodating Human Injury Tolerance – A Safe System is designed to reduce or eliminate opportunities for crashes resulting in forces beyond human endurance.
Example: Where pedestrians and vehicles need to occupy the same space – such as urban crosswalks – reducing vehicle speeds through the use of lower speed limits combined with road design changes can reduce the likelihood of fatal collisions with pedestrians or bicyclists. 
Example: Breakaway designs on traffic control devices installed in the right-of-way can reduce the force of impact when struck by an errant vehicle.

When we take a Safe System approach we may employ some of our current safety practices, but by taking a human-centered approach we will often make different decisions than we would have otherwise.

Safe System Framework

The goal of a Safe System approach is to design and operate our vehicles and infrastructure in a manner that anticipates human error and accommodates human injury tolerances with a goal of reducing fatal and serious injuries.  The following framework is intended to assist the vehicle and infrastructure communities in making decisions in alignment with Safe System principles.  Consistently selecting safe system designs will incrementally improve safety and over time result in the widespread implementation of safe system practices.

Creating a Safe System will involve  both traditional and new approaches.  We must embrace and expand the use of Safe System practices that we know work, while being willing to try and evaluate new or non-traditional approaches, particularly when it comes to protecting vulnerable users.

Adopting a Safe System approach necessarily means adopting a safety culture. Steady progress can be made by putting safety first and following Safe Systems principles in each of the large and small decisions that confront us every day.

Adopting a Safe System approach does not absolve users of responsibility.  Programs such as education and enforcement will remain essential.  Providing effective emergency response when crashes do occur is also a critical element of Safe Systems. However, safe system design choices recognize that road users make mistakes or bad decisions and seeks to reduce the opportunities to do so or mitigate the consequences.

Reducing speed is not a direct prerequisite of a Safe System, but will sometimes be necessary to achieve alignment with Safe System principles.  In locations where vehicles interact with vulnerable road users, speeds should be controlled to a level at which a collision is unlikely to result in a fatal or serious injury.

When we choose a Safe System approach, we must accept that doing so may result a decrease in vehicle throughput and may limit the range of behavioral choices for users. However, such decisions are part of responsible system stewardship.  As transportation professionals we have a moral obligation to protect lives while creating a reliable transportation system.

I. Anticipating Human Error

Recognizing that humans are human and that they will continue to make errors when traveling, one way to implement a Safe System strategy is to reduce the opportunity for error by:

  • Separating Users in Space – This approach segregates the physical space to provide travelers with a dedicated part of the right-of-way.  Typically, travelers moving at different speeds – pedestrians, bicyclists, etc.  (e.g. sidewalks, cycle tracks) – or different directions (e.g. turning vehicles in separate turn lanes) are separated in space to minimize conflicts with other users.
  • Separating Users in Time – This approach assumes that users will need to occupy the same physical space on the roadway, but creates a safer environment by separating the users in time and reducing vehicle interactions with vulnerable road users.  An example is a pedestrian scramble phase at an intersection.  During this phase pedestrians have exclusive access to the intersection without having to worry about vehicle encroachment.

Note: Sometimes a combination of both techniques is used, such as a protected left turn bay where the turning vehicles are physically separated while awaiting the opportunity to turn and separated in time through the use of a protected left turn phase.

  • Increasing Attentiveness and Awareness – This approach seeks to alert users to potential hazards and/or the presence of other users.  These techniques can be vehicle, user or infrastructure-based.  There are a variety of areas to be explored, including:
    • Increasing Visibility
      • “Daylighting” intersections by removing parking at the corners to allow greater visibility between drivers and pedestrians.
      • Street lighting that increases nighttime visibility of users.
      • Vehicle, scooter or bicycle lights or retroreflective clothing that allows users to be visible to one another.
    • Increasing Attentiveness
      • Rumble strips and in-vehicle lane departure systems that alert inattentive or drowsy drivers that they are leaving their lanes.
      • Rectangular Rapid Flashing Beacons that warn drivers of the presence of crossing pedestrians.
    • Reducing Impairment
      • Alcohol detection and ignition interlock systems that help prevent intoxicated drivers from operating a motor vehicle.
      • In-vehicle systems that help prevent use of cell phones while the vehicle is moving to minimize distraction.
      • Applications and programs that incentivize and reward safe behaviors.

II. Accommodating Human Injury Tolerance

The laws of physics dictate that greater harm will occur at higher speeds and that, typically, the greater the mass of a vehicle, the more harm that it will inflict on others.

  • Reduce Speeds - For vulnerable users speed is a determining factor in survivability – a human’s chance of surviving being struck by a vehicle increases from 20% at 40 miles per hour to 60% at 30 miles per hour to 90% at 20 miles per hour.  Reducing speed in the presence of vulnerable users is a key Safe System strategy.  Approaches include:
    • Physical roadway designs (width, horizontal alignment) to limit free flow speeds,
    • Traffic calming treatments that induce slower speeds,
    • Traffic signal timing that minimizes high speed flow,
    • Traditional or automated enforcement that discourages speeding.
  • Reduce Impact Forces – A variety of methods can be used to increase crash survivability by reducing the impact forces.  These include:
    • Intersection Design – alternative intersections, such as roundabouts, reduce the angle and speeds of entering vehicles to limit impact forces.  Designs which limit right-angle conflicts can also achieve this goal.
    • Occupant Protection – this can include interior design of the vehicle, seat belts, air bags, etc.  Much work has been done in this area in recent decades.
    • Exterior Vehicle Design - the aggressiveness of the exterior of the vehicle can affect the consequences of a collision.  Increasing size of vehicles in recent years has worked against this goal, but recent innovations in vehicle front-end design offer the potential to create softer vehicle-to-vulnerable user impacts.
    • Automated Braking - automated braking systems have been introduced to detect other users or objects and slow or stop vehicles prior to a collision.
    • Roadside Crashworthiness – this can include clear zones, breakaway supports, etc.  Much work has been done in this area in recent decades.

Safe System Resources

Sustainable and Safe: A Vision and Guidance for Zero Road Deaths
A report from World Resources Institute published in January 2018 highlights systemic approach that shifts responsibility away from the drivers and pedestrians using the roads to the city planners and officials designing them. This report is international and could be applied in the US since it is not written toward a specific roadway system. The report is available for download:

Speed management: a road safety manual for decision-makers and practitioners. 
The World Health Organization Speed Management Manual highlights the Safe System approach to speeds starting on page 14 of the Manual. This is an international focused document with elements that could be applied to Safe Systems in the US as it is not written toward one countries roadway system.

Road Safety Manual: A Manual for Practitioners and Decision Makers on Implementing Safe System Infrastructure
The World Road Association Road Safety Manual is wholly written around a Safe System as a means for road safety and the manual also provides as specific section on how to apply a Safe System. The Safe System section of the Road Safety Manual covers topics of crash causes, responsibilities, principles, elements and implementation with an international focus but some topics could also be considered for application in the US as we shift our system toward a Safe System.

Speeding - Did you know? Fact Sheet
The New South Wales Centre for Road Safety has a short fact sheet on a Safe System, the key to managing road safety that provides an overview of Safe System principles that may be applied in the US from countries like Australia, the Netherlands and Sweden.

Toward Zero: Ambitious Road Safety Targets and the Safe System Approach
The Transport Research Centre also has an internationally focused report titled “Toward Zero: Ambitious Road Safety Targets and the Safe System Approach” which highlights a Safe System as a means to eliminate road fatalities, but also specifically gets in to Safe System approaches on pages 107 through 133 as a context for developing interventions, Safe System implementation tools, and performance measures to gauge improvement.

How would a Safe System approach to road safety work in the U.S.?
The Collaborative Sciences Center for Road Safety has an evolving web page on “Safe Systems and the role of systems science” with an overview and numerous resources from reports to articles. Most of the resources featured are about general systems based thinking, but some resources are geared toward transportation systems. The page can be found:

A report titled “Implementing Safe Systems in the United States: Guiding Principles and Lessons from International Practice” published by CSCRS in June of 2019. This report identifies Safe System elements and principles from countries that have improved safety through the application of a Safe System approach.

Another report titled “Safe Systems Synthesis: an International Scan for Domestic Application” published by HSRC in late June of 2019 provides an overview of numerous successful international approaches internationally and may apply in the US. Starting on page 31, the synthesis outlines five Safe System trends and three concerns to applying a Safe System in the US.

Webinars and Podcasts on a Safe System Approach

ITE's May Talks Transportation Podcast features Robert Wunderlich, P.E., ITE Fellow and Director of the Center for Transportation Safety at the Texas A&M Transportation Institute, discusses the Safe System approach to reducing serious injuries and fatalities on roadways. He highlights various aspects of the Safe System, including roadway design that reduces user error and lowers impact forces, and explains what transportation professionals can do to help implement a Safe System approach.

ITE Introduction to Safe System webinar provides a summary of a US Safe System Explanation, Framework and provides a connection between US fatal crashes, roadway design and vehicle design.

ITE Safe System and Speed Management webinar outlines the need for speed management to achieve a Safe System and how US cities are thinking about a Safe System approach in speed management work.

Vision Zero Network webinars on a Safe System

National Center for Rural Road Safety Safe Systems for Rural Users webinar.

Shorter Articles on Safe Systems

The Road to Zero: Taking a Safe System Approach

Speed, Kinetic Energy, and the Safe Systems Approach to Safer Roadways