Search

Traditionally, the impacts of traffic and earthquake loading have been considered independently when assessing bridge reliability. This paper presents a framework for joint seismic and live-load fragility assessment of highway bridges. Full probabilistic analyses accounting for variation in bridge parameters, ground motion, and truck load and position are proposed to develop bridge system fragility curves and to identify the critical truck position that renders the bridge most vulnerable to earthquakes. A fragility surface is derived for the critical truck position at which the failure probability is conditioned on the governing vehicle weight in addition to ground motion intensity, thus depicting the impact of truck load on bridge seismic fragility. This fragility surface is convolved with the governing vehicle weight distribution (obtained from weigh-in-motion data) and probability of truck occurrence (function of truck flow rate) to determine traffic-informed conditional seismic reliability estimates. The proposed methodology is demonstrated on a case study of a multispan continuous steel girder bridge in the central and southeastern United States. The framework can find ready extensions to assess the joint impact of earthquake and live loads for other bridges and hazard conditions and can offer a basis for deriving reliability-based load combinations consistent with emerging trends in bridge design. [ABSTRACT FROM AUTHOR]

This paper explores the relationship between sight distance parameters, crash rates, and operating speeds at low-volume single-lane roundabouts in the United States. The understanding of the interaction of design, operations, and crash performance is a step forward in the development and application of performance-based standards for roundabouts. The specific objective of this paper is to quantify the relationship between crash rates, sight distance parameters, and operating speeds to present an approach to establishing performance-based standards that highway practitioners can adopt in roundabout design. Geometric, traffic, and crash data were collected on 72 approaches to 19 low-volume single-lane roundabouts in six states. The data for these sites were broken into two groups based on the posted speed limit (at and greater than ). In addition, the associations between different sight distance parameters, crash parameters, and operating speed data were investigated. The research findings provided insight into relating the operational and safety effects of sight distance geometry at roundabouts. This research also identified a methodology that provides guidance as to the development of performance-based standards that rely on a better understanding of these relationships. In general, the research findings were consistent with previously conducted studies and indicated that exceeding sight distance thresholds increases the risk of crashes occurring. It was also found that exceeding sight distance thresholds yielded greater speed differentials between the approach and the entry to these roundabouts. The results of this research can advance the state of practice in understanding the relationships of sight distance design attributes, operational characteristics, and safety metrics for low-volume single-lane roundabouts, which is necessary to the creation of performance-based standards. [ABSTRACT FROM AUTHOR]

This paper analyzes driver behavior when alerted to the impending end of green while they travel on high-speed signalized intersection approaches that are equipped with actuated advance warning (AAW) systems. These systems are widely deployed in Nebraska and provide a more than 90% likelihood of improving safety. They consist of one detector placed in advance of the intersection and active warning signs with the legend, 'prepare to stop when flashing.' The overall goal is to reduce, if not eliminate, the number of drivers who are caught in the dilemma zone. A nonintrusive mobile data collection system was used to monitor traffic and collect a continuous stream of traffic data up to 304.8 m (1,000 ft) upstream of the stop line on two high-speed signalized intersection approaches that were equipped with AAW systems. The results indicate that the system is effective at alerting drivers to the impending end of the green light; approximately 78% of the drivers observed in this study either maintained their speeds or slowed down when the active warning signs began to flash. The number of vehicles in their dilemma zones was statistically significantly lower than would be expected if the AAW system was not used. [ABSTRACT FROM AUTHOR]

Vehicle emissions from mobile sources are major contributors to air pollution and air quality degradation in the United States. The inventory of these emissions is a key component in ambient air quality assessment and air pollution abatement strategies. Procedures for preparing the mobile source emission inventory require complex data processing and calculations. This paper presents a simplified methodology for estimating vehicle emissions based on key parameters of vehicle model year, average vehicle speed, and air temperature, which have major effects on emission rates. Simplified multiple linear regression equations are developed from a database of the EPA’s MOBILE6 computations to calculate emission factors. The coefficient of determination (R2) values of the models range from 0.82 to 0.99. The methodology has been implemented in Mississippi and validated for rural areas in Ohio. The methodology is applicable to other areas in comparable geographical regions with similar traffic volume and fleet mix. The results of vehicle emissions show good correlation with daily ground-level ozone variations and can be effectively used for ozone modeling and air quality assessment. [ABSTRACT FROM AUTHOR]