Abstract
The truck escape ramp design presented by the Transportation Association of Canada is based on deterministic values of the design variables which include the required stopping distance, design speed, rolling resistance, and grade. Currently, a reliability analysis of the design of truck escape ramps does not exist. This report presents two methods used to analyze the reliability of truck escape ramp design; the first order second moment reliability method and the advanced first order second moment reliability method. These methods do not rely on deterministic values rather the mean and variance (moments) of each random variable’s probability distribution. Each reliability method was used to analyze truck escape ramps with one grade and two grades, for a total of four cases. The results of each case are provided and discussed along with an application to two existing truck escape ramps. The results show that the advanced first order second moment reliability method ensures more accurate results as well as a larger safety margin in comparison to the first order second moment method due to the nature of the methodology itself which considers design points.
Highlights
A truck escape ramp is a type of auxiliary lane used in extreme circumstances and as a final resort by runaway vehicles that are out of control
The First Order Second Moment (FOSM) analysis produces a shorter truck escape ramp (TER) design supply length in comparison to the Advanced First Order Second Moment (AFOSM) analysis. This is because the AFOSM analysis is a more accurate reliability method and uses iterations to reduce error created in the FOSM model
In regards to the reliability analysis, it is clear that shorter TERs yield a higher probability of failure as the runaway vehicle does not have as much available distance to safely stop
Summary
A truck escape ramp is a type of auxiliary lane used in extreme circumstances and as a final resort by runaway vehicles that are out of control. Truck escape ramps are designed based on their capacity to stop a runaway vehicle and are implemented to increase roadway safety. The design of truck escape ramps depends on several factors including the speed the runaway vehicle enters the truck escape ramp, rolling resistance, and the truck escape ramp grade. Two reliability methods are developed which examine and analyze various truck escape ramp designs. The purpose of developing these methods is to limit the probability of failure of a truck escape ramp in order to enhance roadway safety. These models were applied to two existing truck escape ramps to assess the reliability of the design of the existing truck escape ramps. The implementation of TERs results in lower vehicular damage and reduced collision injury
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