Development of Prototype Driver Models for Highway Design: Research Update

NHTSA · 1999 · ROSA P / United States. Federal Highway Administration

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Summary

This 1999 research update from the Federal Highway Administration (FHWA) outlines the development of the Interactive Highway Safety Design Model (IHSDM), a suite of tools designed to help highway designers explicitly evaluate the safety implications of geometric design decisions. The project addresses the limitations of current design processes, which assume that compliance with policy ensures safety, a method deemed insufficient given modern demands for context-sensitive design and concerns regarding tort liability. The IHSDM aims to improve the safety cost-effectiveness of highway projects, contributing to the FHWA’s strategic goal of reducing highway fatalities and serious injuries by 20 percent within ten years. Initial development focuses on two-lane rural highways, which constitute approximately two-thirds of Federal-aid highways, with a full model release scheduled for 2002. The IHSDM comprises five modules: Policy Review, Accident Analysis, Design Consistency, Traffic Analysis, and Driver/Vehicle. This update specifically details the Driver/Vehicle Module, which integrates a Driver Performance Model (DPM) with a Vehicle Dynamics Model. The DPM simulates human performance by modeling six functional components: Perception, Speed Decision, Path Decision, Speed Control, Path Control, and Attention. The Perception component translates environmental data into vehicle state estimates, while decision components compute desired speed and path profiles. Control components generate accelerator, brake, and steering inputs to regulate these profiles. The Attention component manages the distribution of limited mental capacity among these tasks, accounting for potential performance degradation when demand exceeds capacity. Concurrently, the research involves modifying TWOPAS, a microscopic traffic simulation model used in the Traffic Analysis Module, to better represent driver behavior. Initial efforts in 1995 established specifications for the DPM, including hardware requirements and algorithm candidates. Current objectives include developing a functioning prototype Driver/Vehicle Module that allows designers to model drivers operating AASHTO design vehicles under various control strategies to identify conditions leading to loss of vehicle control. Modifications to TWOPAS aim to incorporate effects of narrow lanes and shoulders on speed selection, the use of paved shoulders by slower vehicles, continuous two-way left-turn lanes, and automatic determination of reduced-speed zones and truck downgrades. These candidate improvements are being prioritized by the IHSDM development team and a group of 30 engineers familiar with similar design tools. The significance of this work lies in its shift toward a systematic, human-centered approach to highway design. By integrating empirical human performance data with vehicle dynamics and traffic simulation, the IHSDM provides designers with tools to maximize safety benefits within cost and environmental constraints. The ability to model specific driver characteristics and traffic interactions allows for more precise safety evaluations than traditional policy compliance checks, ultimately supporting more effective and safer highway infrastructure development.

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Topics

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• mental model of traffic
• perceptual countermeasures
• situational awareness
• rail grade crossings
• road geometry

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• Methodological Resource: tool software, dataset resource
• Theoretical Contribution: computational model