New Stopping Sight Distance Model for Use in Highway Geometric Design

Abstract

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 eye heights, and 1,000 accident narratives were used to develop the recommended parameter values for the new model. The recommended values are attainable by most drivers, vehicles, and roadways. This 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 farewell to brake reaction times? Kinematics-dependent brake response in naturalistic rear-end emergencies

“…Conclusive answers to these questions have been a long-standing objective of traffic safety research, and have a range of implications: In the design of roads, vehicles, or vehicle support systems for safety and automation, quantitative models of driver behavior can be very directly applied, for example in system algorithms or in computer simulations of crashes (e.g., Perel, 1982;Fambro et al 2000a;MacAdam, 2001;Brännström et al, 2010;Markkula, 2015). In the broader study of traffic safety, the way one thinks about drivers' emergency responses can also be important in more subtle ways, for example by shaping design of experiments and subsequent interpretations of results, or by guiding one's analysis of actual crashes to understand their causation (e.g., Naing et al, 2009;Engström et al, 2013b), sometimes for purposes of litigation (e.g., Maddox and Kiefer, 2012).…”

Vehicle automation and freeway ‘pipeline’ capacity in the context of legal standards of care

“…The scenarios were selected to expose various properties of the simulation system, and are intended to be representative rather than exhaustive. In the Baseline 'Weak' Scenario, a ) is the maximum observed sustained rate of human-driver deceleration of passenger cars on dry pavement reported in (Fambro et al 1997). The Baseline 'Strong' Scenario represents the 'strong' interpretation of the ACDA rule: veh f selects its gap for following veh l such that it ðveh f ) is able to stop in the case of a stationary object in its path that only becomes visible once it has been passed by veh l (i.e.…”

“…This Scenario uses -28.3 ft/s 2 (8.6 m/s 2 ) as the value of a À f . Scenario #1 is identical to the Baseline 'Weak' Scenario, with the exception that a À l is specified to be -21.3 ft/s 2 (6.5 m/s 2 ), which is the maximum sustained braking rate reported by Fambro et al (1997) for a passenger car on wet pavement. Comparing this scenario to the Baseline 'Weak' scenario tests the difference between capacity under conditions of dry and wet pavement.…”

A Novel Surrogate Safety Indicator Based on Constant Initial Acceleration and Reaction Time Assumption

“…Besides the area of surrogate safety analysis the PRT has been also the focus of other research fields including the planning of roads [13], the associated traffic light systems, and their switching times [14,15].…”