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.
This paper evaluates the influence of on-street bike lanes on the lateral separation between motor vehicles and cyclists when the vehicle overtakes the cyclist and investigates the relationship between the passing behavior and traffic conditions. A bicycle was instrumented with a sensor array that consisted of an ultrasonic sensor, a GPS receiver, and a video camera. A total of 5,227 passing events were recorded across different categories of urban arterials. The results showed that the facilities with on-street bike lanes provided greater separation between bicycles and motor vehicles. Passing maneuvers with lateral separation of less than 1,000 mm (3.30 ft) were observed less frequently on the facilities with on-street bike lanes. Further, it was found that, in the absence of a bike lane, a higher proportion of passing vehicles moved laterally to the left and encroached on the adjacent lane. The analysis showed that for arterial roadways without on-street bike lanes, drivers tended to provide increased lateral clearance by either changing lanes or encroaching on the adjacent lane. However, drivers' ability to perform either of these maneuvers may be restricted by surrounding vehicles.
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