Hazardous materials facility siting optimization and ranking: A transportation risk mitigation framework.

Hazardous material transportation problems have widely been studied in the past especially in the context of routing, scheduling, and network design problems. Yet, the combined hazardous material facility location-routing problem has not been studied adequately. We emphasize that locating a hazardous material facility is a rich process, and a good site can mitigate the potential transportation risk beforehand. A methodological framework is proposed which allows evaluation and ranking of potential sites based on hierarchical relationship utilities. The proposed method attempts to improve the risk functions and applies a stochastic analysis to measure the risk, which relaxes some assumptions in deterministic analysis, and is more realistic while avoiding overestimation of the risk. The study covers multi-objective optimization considering the decision-makers' preferences on network segments and risk to the population and water bodies. Potential hazardous material facility sites' rank is determined by the probability of optimality and one-to-one relationship utilities with the points of interests. Results show that the proposed stochastic analysis offers more flexibility to select and rank the potential sites.

A reliability-based weather-responsive variable speed limit system to improve the safety of rural highways.

Weather-responsive Variable Speed Limit (WRVSL) systems treat speed limits as weather-dependent random variables, as opposed to the conventional static speed limits. This study (i) evaluates drivers' response to a fixed speed limit in different road-weather conditions, and (ii) proposes an effective approach to set WRVSLs, for rural divided highways located in extremely cold regions. Study data: road-weather, and speed data, collected from a rural highway (fixed speed limit = 110 km/h), are used to (i) estimate the 85th percentile speeds of population-level speed distributions, and (ii) develop WRVSLs based on the reliability theory. More specifically, the WRVSLs are set based on reliability: the probability of a speed being (i) likely complied by drivers, and (ii) adequate to avoid a rear-end collision. The study results reveal that merely 73 % of the drivers at the study site comply with the existing posted speed limit under normal road-weather conditions i.e., no precipitation and dry pavements. The reliability of the current speed limit is revealed to be approximately-one under normal road-weather conditions; thus, the current speed limit is perceived credible under such road-weather conditions. Yet, reliability of the current speed limit is substantially reduced in the presence of slight snow, and ice warning pavement conditions. A set of reliability-based WRVSLs ranging from 80 to 110 km/h is proposed. Jurisdictions experiencing extreme road-weather conditions may adapt the proposed methodology to effectively manage speed, particularly in rural highways under adverse road-weather conditions to enhance the probability of speed limits being safe and complied by drivers and as a result reduce crash propensity.

Modelling speed behaviour in rural highways: Safety analysis of driving under adverse road-weather conditions.

This study proposes a methodical approach to model desired speed distributions under different road-weather and traffic conditions followed by identification of road-weather conditions with potentially higher safety risks in rural divided highways located in extremely cold regions. Desired speed distributions encompassing unique combinations of adverse road-weather and traffic conditions are modelled as normal distributions characterized by their means and standard deviations formulated based on two principal statistical theorems and techniques i.e., Central Limit Theorem and Minimum Variance Unbiased Estimation. Combination of the precipitation conditions, road surface conditions, time of the day, temperature, traffic flow and the heavy vehicle percentage at the time of travel were considered in defining the combinations of road-weather and traffic conditions. The findings reveal that simultaneous occurrence of particular precipitation and pavement conditions significantly affect the characteristics of the desired speed distribution and potentially expose drivers to elevated safety risks. Jurisdictions experiencing extreme road-weather conditions may adapt the proposed methodology to assess speed behaviour under different road-weather conditions to establishing and deploying weather-responsive traffic management strategies such as variable speed limit to regulate speeding and improve traffic safety in winter.

A methodology to estimate the number of unsafe vehicle-cyclist passing events on urban arterials.

In this study interactions between motorized vehicles and bicycles were studied by analyzing the overtaking behavior of motorized vehicles when passing bicycles on urban arterials. A methodology is presented to estimate the number of 'unsafe' passing events on 4-lane urban arterials with no on-street bike lanes. A 'critical passing distance' is defined to classify expected passing maneuvers i.e. when a motorized vehicle overtakes a bicycle, into 'safe' and 'unsafe' passing events. The proposed method enables calculation of the expected number of 'unsafe passing' events based on the expected bicycle demand, road segment's length, AADT, speed limit, and traffic signal timing parameters. The 'critical passing distance' is an input parameter and can be set by the planner. Given the number of expected 'unsafe passing' events, and institutional safety objectives and standards in terms of acceptable risk levels for cyclists, transportation planning departments can use the proposed methodology to decide whether provision of a specific cycling facility is necessary for a given road segment.