Abstract
Diverging segments are potential bottlenecks because of frequent lane change and deceleration maneuvers. Speed study has been proven to be an effective way to understand the safety performance of diverging segments. This paper addresses the safety level of diverging segments in terms of speed consistency. Speed data is extracted by Tracker based on aerial video imager collected at the diverging segment of MaQun interchange of G42 in Nanjing, China. The operating speed of vehicles is assumed to follow the Linear Regression Model with two explanatory variables—initial velocity and running distance, and the estimated operating speed is amended un der actual traffic conditions. Furthermore, average speed, speed difference and the coefficient of variation are used as safety indicators to establish the speed evaluation criteria. Last but not the least, based on vague set of material-units, the safety level of diverging segments in terms of the velocity arrives at level III, which means that consideration must be given about the safety of diverging segments. The proposed methodology can be used to estimate the safety of diverging segments.
Highlights
Freeways play a v ital ro le in serving mega-cities, which could significantly raise the speed for mid and long distance traffic
Operating speed of vehicles is influenced by all these factors
Three indicators are used to evaluate the safety level for vehicles according to Specifications for Highway safety audit [19] and the speed safety criteria of highway [20], the criteria of vehicles developed with the consideration of traffic circu mstances, which is shown as Table 5
Summary
Freeways play a v ital ro le in serving mega-cities, which could significantly raise the speed for mid and long distance traffic. The efficiency and safety of freeways has been dramatically constrained by bottlenecks. Diverging segments may become bottlenecks because of frequent lane change and deceleration maneuvers. Understanding the efficiency and safety of d iverging segments are important and necessary. Freeway diverg ing segments occur primarily at offramp junctions with the freeway main line [1]. There are two movements in diverging segments, na mely mainline-to-mainline and mainline-to-ramp , which can affect the operations of each other. Influence area of diverging segments is defined as the deceleration lane(s) and Lanes 1 and Lanes 2 of the freeway for a distance of 450m upstream of the diverge point [1].
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