To What Extent the Human Being Is So Far Regarded in Modern Highway Geometric Design--An International Review and a Personal Outlook

In general the relationships among geometric design, speed, driving dynamics and safety can be regarded today to a large extent as soundly solved, while the human being (the driver), if at all, is only indirectly considered, although more than 90% of all accident causes are attributed to human error or improper human behavior. To find out to what extent driver performance as part of the road traffic system is regarded as essential for effective road design, operation, and safety, twelve modern highway geometric design guidelines were studied. The results of the in-depth reviews are discussed, analyzed, compared and evaluated. It was found that most of the guidelines only regard directly or indirectly human behavioral modes by simple assessments, for example, about perception and reaction time, eye and obstacle height, recommendations for limiting values of design elements, fatigue considerations for tangents, qualitative advice for three-dimensional alignment and sight distance quantifications. Only a few modern guidelines have begun to incorporate human factors additionally, for example, expressed by qualitative statements about the driving task, vision, driver expectancy, driver reaction, driver error, or driver workload and quantitatively by consistency considerations. Thus, this paper reflects a summary/state-of-information and the analysis is a recommendation of the need for quantitative analysis of the associated human factors considerations. For instance, new research is addressed which reveals that human behavior can be analyzed by using driver workload measures in terms of psychophysiological parameters. It is concluded that the additional introduction of human performance capabilities and behavioral characteristics has to be required as vital input into modern highway geometric design guidelines, since when a design is compatible with human capabilities, the opportunities for errors and accidents decrease.