/pdf/safety-in-geometric-design-standards-3oewyco64x.pdf

Safety in Geometric Design Standards.

Stopping sight distance is an important design parameter in that it defines the minimum sight distance that must be provided at all points along the highway. Thus, it influences geometric design values, construction costs, and highway safety. Stopping sight distance is defined as the sum of two components - brake reaction distance and the braking distance. The basic model for calculating stopping sight distances was formalized in 1940, and the model's parameters have been altered to compensate for changes in eye height, object height, and driver behavior over the past 50 years. Recent studies, however, question whether the model's parameters and assumptions represent real-world conditions. This paper presents a new model for determining stopping sight distance requirements for geometric design of highways. The new model is based on parameters describing driver and vehicle capabilities that can be validated with field data and defended as safe driving behavior. More than 50 drivers, 3,000 braking maneuvers, 1,000 driver eye heights, and 1,000 accident narratives were used in developing the recommended parameter values for the new model. The recommended values are attainable by most drivers, vehicles, and roadways. The new model results in stopping sight distances, sag vertical curve lengths, and lateral clearances that are between the current minimum and desirable requirements, and crest vertical curve lengths that are shorter than current minimum requirements.

A new stopping sight distance model for use in highway geometric design

An exemplum and its road safety morals.

Stopping sight distance is an important design parameter in that it defines the minimum sight distance that must be provided at all points along the highway. Thus, it influences geometric design values, construction costs, and highway safety. Stopping sight distance is defined as the sum of two components—brake reaction distance and braking distance. The basic model for calculating stopping sight distances was formalized in 1940, and the model's parameters have been altered to compensate for changes in eye height, object height, and driver behavior over the past 50 years. Recent studies, however, question whether the model's parameters and assumptions represent real-world conditions. A new model for determining stopping sight distance requirements for geometric design of highways is presented. This model is based on parameters describing driver and vehicle capabilities that can be validated with field data and defended as safe driving behavior. More than 50 drivers, 3,000 braking maneuvers, 1,000 driver e...

New Stopping Sight Distance Model for Use in Highway Geometric Design

Road safety is a serious public health issue throughout the world, with more than one million people killed in traffic accidents each year. Despite the severity of its health impacts, the World Health Organization says that traffic safety is a neglected topic. Perhaps this is the case in the US, where traffic accidents are the leading cause of death for people up to age 34, and where the traffic safety record is one of the worst among high-income countries. Other high income countries such as Sweden have much better road safety performance. Differences in road safety between countries could be explained by the quality of infrastructure, driving conditions, the culture of driving, or the power of enforcement. Each of these elements is shaped by institutional contexts such as design, planning, and policy making processes. Moreover, research about other technical systems has shown the powerful effect of organization, norms, and communication on safety. This led me to ask: How do our cultural and professional interpretations of safety influence the way we plan, design, and manage streets? Based on field studies, statistical analysis of crash and injury data, and interviews with practitioners, I found that professionals in California and Sweden share similar ideas about road safety, such as the roles of driver behavior, the road environment, and the vehicle in producing hazards. Professionals in both cases also face similar conflicts in road safety planning, such as whether to provide greater mobility for cars, or to reduce the speed of traffic to prevent injury. These similarities reflect shared professional and disciplinary backgrounds and sources of information, as well as similarities in the issues that municipalities and regions face. The main differences are in the interaction between road safety ideas and larger institutional contexts such as suburban land development. For instance, in the middle of the 20th century, Sweden created a multi-modal transportation system that accommodated cars as well as transit, pedestrians, and bicyclists—even in the suburbs. A combination of architects, city planners, and transportation engineers supported this development. Multi-disciplinary policy communities in Sweden found traction for their safety-oriented designs in the relatively integrated transportation and land use planning system. In the US, such integration was not the norm, and efforts to use design and land use controls to create a safe transportation system often meet resistance from the established institutions of the car-oriented road transportation system. Improving road safety in California and the US requires addressing not only the dominance of automobiles, but also recognizing that sectors outside of, but related to transportation, such as housing, public health, and land use planning, need to be key participants in creating a safe road transportation system.

/pdf/road-safety-in-the-context-of-urban-development-in-sweden-3igqi8jeyc.pdf

Road safety in the context of urban development in Sweden and California

What civil engineers do has a major effect on road safety. However, contrary to appearances, the level of safety built into roads is largely unpremeditated. Standards and practices have evolved without a foundation knowledge. At times the safety consequences of engineering decisions are not known, at others some knowledge exists but is not used. In this paper I attempt to describe the current, unsatisfactory, state of affairs. I explore some of its root causes and speculate what needs to be done to change course.

E Hauer

Papers

A case for science-based road safety design and management