Concerns have been raised about the HCM6 weaving method’s lack of sensitivity to weaving segment length. This study explores the trends in HCM6 as they relate to lane change estimates and their impact on the segment speed and level of service (LOS). The study also compares HCM6 estimates of lane changes against empirical data from an NGSIM weaving site. Thus, the objectives of this study are twofold: ( a) critically investigate the effect of weaving length on lane change and associated speed model estimates in HCM6, and ( b) analyze trends in lane changes against congestion levels using detailed NGSIM trajectory data, comparing against HCM6 estimates. For ( a) it was found that the lack of sensitivity to weave length is because of the absence of this parameter in the nonweaving lane change and speed models. For ( b), a comparison of HCM6 lane change rates with NGSIM, US-101 data confirmed that the HCM6 estimates for weaving vehicles are fully consistent with those at the NGSIM site, controlling for density. In contrast, nonweaving lane change estimates in HCM6 did not deliver the expected trends, with more discretionary lane changes predicted as congestion increased. Finally, analysis of lane change patterns at the NGSIM site revealed a tendency for early merging for freeway to ramp traffic and uniform merging for ramp to freeway traffic over the length of the weave. Interestingly, a speed analysis showed that in most cases, a higher frequency of discretionary lane changes yielded lower travel times for drivers executing them.
Weigh stations are necessary for safeguarding highway infrastructure by enforcing truck weight limits. However, mandating all trucks to stop at all weigh stations decreases travel time reliability. This decrease in travel time reliability adversely impacts the productivity of the trucking industry and to a lesser degree impacts personal travel reliability as well. This study, conducted at the Lumberton weigh station on Interstate 95 in North Carolina, quantifies the impact of weigh stations on truck travel time reliability. Truck travel times were observed over periods of weigh station operation and weigh station closure. Comparison of these two states sheds light on the variability in travel time caused by weigh station operation. Results show that when the weigh station is operational, truck travel time reliability degrades significantly. VISSIM microsimulation software was used to quantify the expected impact of weigh in motion (WIM) on truck travel time reliability assuming different scenarios of WIM truck bypass. The model results indicate that WIM technology does increase travel time reliability and provides benefits to both trucking companies and enforcement agencies. It was also found that increases in the proportion of WIM bypass result in increases in route travel time reliability. However, this simulation model improvement was not uniform, with the highest marginal improvement occurring in the 30%–40% WIM bypass range.
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