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Executive Summary

The U.S. transportation community has placed high emphasis on the need to improve highway safety. The American Association of State Highway and Transportation Officials (AASHTO) and the Federal Highway Administration (FHWA) have adopted a goal to reduce highway fatalities from 1.5 per 100 million vehicle-miles traveled to 1.0 by 2008. AASHTO has established a Strategic Highway Safety Plan to determine the most promising countermeasures that improve safety in a cost-effective manner and are acceptable to the majority of the public. FHWA has focused its Safety Vital Few initiative on reducing intersection, run-off-the-road, and pedestrian fatalities. Human factors issues associated with roadway design and operations are a critical component of these highway safety improvement areas. It is also one of the five critical research needs contained in the highway infrastructure and operations component of the National Highway Research and Technology Partnership's report on highway safety. This study provides methodological and technical insights into how best to incorporate human factors issues in the research, design, and operation of highways.

Panel Composition

The nine scan team members were a cross section of experts from Federal and State government and academia. A great benefit of the study for participants was the opportunity to view information through the eyes of colleagues with different training and experience. For example, human factors experts visiting a construction site gained from the explanations of highway engineers, who, in turn, gained from the human factors experts when the team visited a driving simulator. Team members included cochair Kevin Keith of the Missouri Department of Transportation (DOT), cochair Michael Trentacoste of FHWA, Dr. Leanna Depue of Central Missouri State University, Dr. Thomas Granda of FHWA, Ernest Huckaby of FHWA, Bruce Ibarguen of the Maine DOT, report facilitator Dr. Barry Kantowitz of the University of Michigan, Wesley Lum of the California DOT, and Terecia Wilson of the South Carolina DOT.  

Sites Visited

The team visited public and private institutions in six European countries (Denmark, Finland, France, the Netherlands, Norway, and Sweden) during a two-week period. When the team spent two days in one location, the first day was devoted to lectures and facilities tours, and the second day was spent on a bus touring road sites that illustrated points explained the previous day. The eight institutions visited included the Technical Research Centre of Finland (VTT), the University of Helsinki, the Foundation of Scientific and Industrial Research at the Norwegian Institute of Technology (SINTEF), the Danish Transport Research Institute (DTF), the Netherlands Organization for Applied Scientific Research (TNO), the Netherlands Institute of Road Safety Research (SWOV), the Swedish National Road and Transport Research Institute (VTI), and the French National Institute for Transport and Safety (INRETS). In addition to representatives of those agencies, representatives from the various Ministries of Transport and others involved in human factors safety research for the countries participated in the meetings. All were exceptionally helpful in addressing the concerns of the panel.

Key Findings

The goal of this report is to make researchers, designers, and operators of U.S. highway systems aware of good ideas that are either unknown or unused here. The best practices identified in this report, if used in the United States, could greatly increase the safety and mobility of highway operations. The scanning team was so impressed by these new concepts that it has pledged to do its utmost to facilitate the early adoption of some of these key ideas. While many excellent ideas and practices were observed, the team agreed to focus on seven vital concepts:

These concepts are briefly described and illustrated by successful examples that demonstrate the utility and benefit of each idea. It is important to note that these topics are not mutually exclusive, e.g., self-organizing roads impact speed management.

Self-Organizing Roads

A self-organizing road increases the probability that a driver will automatically select appropriate speed and steering behavior for the roadway without depending on road signs. The geometric features of the road encourage the desired driver behavior, and do not rely on the driver’s ability or willingness to read and obey road signs. A perfect self-organizing road would not require speed limit signs and curve advisory warnings.

While the United States has some examples of self-organizing roads, such as using curved road segments in national parks to limit driver speed, this concept is far more common in Europe. It is easy to understand that geographic topography can create a self-organizing road that limits driver speed selection. It is harder to appreciate intentionally designing a road to be self-organizing in an urban area.

A roundabout is a self-organizing road. The road geometry forces the driver to select a lower speed than used on a tangent. Pavement markings help the driver perceive this lower speed requirement.

In a similar manner, intentionally narrowing the roadway and shoulders also creates self-organizing features that instruct the driver to slow down. When there is a conflict between road features and road signs, drivers may often follow the speed implied by the roadway design rather than the speed instructed by the road sign. For example, building a connecting roadway to interstate design standards and then putting a 30-mile-per-hour (mi/h) (50 kilometer-per-hour (km/h) sign on the side of the road would encourage drivers to ignore the speed limit displayed on the sign.

Another important example of a self-organizing road is the 2+1 roadway design the team observed in Finland and Sweden. This road design also offers significant safety advantages, especially with the cable barrier in a flush divider used in Sweden. The 2+1 roadway is a three-lane road with the passing lane alternating on each side of the road in a regular manner. This organizes the driver’s expectations about being able to pass.

One of the teams’ most impressive observations involved watching Swedish drivers approaching the end of a passing lane. During a 20-minute observation interval, no driver speeded up to pass a slower vehicle before the passing lane ended. Such driver behavior is quite common in the United States. The expectations induced by the 2+1 design reassured drivers that another passing opportunity would occur shortly. Hence, drivers did not feel a need to pass immediately and so did not incur risk by trying to pass just before the passing lane ended.

Even in more congested conditions, traffic flow remained stable, as passing was reduced and drivers maintained more uniform speeds. Early skeptics, such as emergency responders who expected additional delays in going around median cable guardrails to get to crashes, became highly supportive of the 2+1 design because of the vast reduction in crashes they needed to respond to and the ease of removing the cable barrier when necessary.

Swedish experience with this design has been better than expected. Level of service has been equal or better at directional flows of up to 1,400 vehicles per hour, with a capacity of 1,500 to 1,600 vehicles per hour in one direction, some 300 vehicles per hour fewer than for an ordinary 13-meter (m) (14.2-yard (yd) road. Traffic safety effects also have been better than expected. By June 2004, there had been nine fatalities, compared to the normal 60, and an estimated 50 percent reduction in severe injuries.

Median cable barrier crashes are very frequent, but normally without personal injuries. Crashes are often caused by skidding, flat tires, or loss of control of the vehicle. Maintenance problems are fewer than expected, but barrier repairs are major concerns. Maintenance costs have increased almost 100 percent per year, although 70 percent of barrier and car repair costs are paid by insurance companies.

Driving Simulators: Roadway Design and Visualization

The fidelity level of the driving simulators (e.g., degrees of motion, picture size and quality, etc.) at the European agencies visited was comparable to the range of simulators in use in the United States at universities and FHWA’s Turner- Fairbank Highway Research Center. Driving simulators are often used in Europe, however, to help design roadways, an application that is far less common in the United States. It is much simpler and cheaper to reject a design element in a driving simulator than to rebuild a road or tunnel to fix design errors.

Simulators have been used both formally, with controlled experiments to conduct tests of driver behavior and approval of project features, and informally, with highway designers using the simulator to experience alternate roadway plans. At VTI, for example, an informal simulator project was described in which highway designers had planned to visit for one day to view their new designs in the simulator, but stayed for three days and made several design changes based on their simulator experience.

An example of a formal evaluation of alternate designs by drivers was explained to the team at SINTEF in Norway. SINTEF was asked to help design the world’s longest tunnel in western Norway. Results showed that lighting strategies using blue, yellow, and green lights increased driver safety and comfort in the tunnel. Changes in lighting every 2 km (1.2 mi) reduced driver anxiety. These design strategies have been successful, with high ratings of driver comfort in the tunnel and no crashes. In addition, the Laerdal project has won two European lighting awards.

Multidisciplinary Teams

At the University of Helsinki in Finland, the team learned that all fatal crashes in the country are investigated by a multidisciplinary team that includes a police officer, vehicle engineer, traffic engineer, physician, and sometimes a psychologist. The investigation results are documented in an original folder and a database with more than 300 variables using a methodology from the Finnish Motor Insurers’ Centre. Results can vary, depending on the composition of the team. From the examples given, it appeared that the presence or absence of a psychologist on the team could critically alter conclusions and interpretation of data.

No data were presented on the statistical reliability of this method. Since multidisciplinary crash investigation has been criticized in the United States for lacking such reliability, this caveat must be kept in mind when evaluating European results.

Speed Management

The 2+1 roadway design discussed earlier also has worked well for speed management. It has improved throughput and raised speeds on two-lane roadways. In Finland, travel speeds at low flow rates improved 1 to 2 km/h (0.6 to 1.2 mi/h),with gains of 4 to 5 km/h (2.5 to 3.1 mi/h) for higher flow rates. In Sweden, average passenger car spot speeds on two-lane sections are 4 km/h (2.5 mi/h) faster on a 2+1 roadway with a median cable barrier than on a 13-m (14.2-yd) roadway with wide lanes.

In Sweden, France, Norway, and the Netherlands, speed cameras were effective in controlling driver speed. Multiple camera boxes were installed in Sweden with the driver unable to determine which box, if any, contained a speed camera, as is done in the United States with red-light-running cameras. Speeding tickets are sent to the driver of the vehicle.

In Finland, variable speed limits were successful in managing driver speed. Speed limits varied according to the season, with lower limits in winter than in summer.

Human-Centered Roadway Analysis and Design

Human-centered design starts with the limitations and preferences of the driver, and then derives appropriate technology from these human principles. This approach has been extremely successful for aviation and is slowly being incorporated into highway design in both the United States and Europe.

Of course, the general principles of human-centered design apply to many of the topics discussed previously. Self-organizing roads depend on human-centered design. The roundabout is a good example. Instead of blaming the human driver for failing to stop at a signalized intersection, the roundabout removes the need for stopping. People inevitably make errors. Good design anticipates these errors and minimizes their consequences. An error at a signalized intersection can result in a 90-degree crash with drastic consequences to drivers and vehicles. A crash at a roundabout results in an angle much less than 90 degrees with smaller risk and damage to vehicles and occupants.

The cable barrier in a 2+1 roadway also demonstrates human-centered design. Instead of blaming drivers for incorrectly crossing the median, the barrier prevents such a driver error. The Laerdal Tunnel lighting design is human centered because it anticipates and minimizes driver anxiety and boredom inside the tunnel. At TNO in the Netherlands, the team learned about efforts to reduce the number of words on traffic signs because drivers have a limited ability to assimilate language while driving down the highway.

Two excellent examples of human-centered design and analysis were presented at SINTEF in Norway: design for pedestrians and human-based standards for geometric roadway design. The program of active-children pedestrian design derives from the Norwegian preference of having children walk to school instead of being driven by their parents. Observational studies of pedestrian crossings revealed that raised zebra crossings and signalized zebra crossings are best for young children. Studies of human reaction time helped formulate standards for geometric roadway design.

Cognitive Models

The need for cognitive models of the driver was emphasized at the University of Helsinki in Finland, TNO in the Netherlands, and INRETS in France. Such models are useful in several ways. They are part of microscopic traffic models that can be validated by observing traffic flow. Indeed, the driver models used for this purpose at INRETS are so detailed that they are referred to as " nanoscopic" driver models. Cognitive models are also useful when implementing human-centered design and analysis. Instead of having to perform a new experiment to answer each new question, the model itself can generate answers.

This model is written in Smalltalk, a computer language well suited for artificial intelligence applications. INRETS has a considerable financial investment in this model, which was developed over 10 years with a three-year break because of other internal priorities. Only now are validation studies being conducted for the model. This delay in validation illustrates how important continuous funding is for high-risk, high-reward basic research. The team congratulates INRETS for seeking and funding such a long-term goal.

Top-Down Leadership

The team was impressed with the coordination between research goals and the highest levels of government in Europe. The best example of this is Sweden ’s Vision Zero. The Swedish Parliament passed an act specifying that the country’s long-term traffic safety goal is zero fatalities. This provides extremely clear direction to researchers and agencies responsible for highway design and operations. Unlike the road safety guiding philosophy in the United State that tolerates a certain number of fatalities and injuries on highways and mandates only a desired percentage decrease in death and destruction, Sweden has stated that no one should die on a Swedish road. SWOV in the Netherlands expressed similar goals. In France, road safety was a campaign issue in the national elections, and President Jacques Chirac has put major emphasis on road safety as a national priority. In general, Europe appears to be ahead of the United States in directing drastic improvements in roadway safety.


While the team obtained many useful ideas, six specific topics were selected as potential high-reward areas of opportunity:

More details can be found in the scan tour implementation plan.

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Page last modified on November 7, 2014
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