INSIDE THE DOT
South Dakota Department of Transportation
WESTA Evaluation of the Interstate 29 McCook Port of Entry
Rick Glassco, Mitretek
3/1/1998 - 4/30/1999
The Westa (Weigh Station) model is a detailed simulation of truck, car and bus traffic around inspection stations. This study used Westa to model current operations at the McCook Port of Entry inspection station on Interstate I-29 in South Dakota and a proposed replacement for the station. The project was funded by the Federal Highways Administration (FHWA) Joint Program Office (JPO) for Intelligent TransportationSystems (ITS), with support from the FHWA office of Motor Carriers (OMC) Size and Weight team. The study was performed for the South Dakota Department of Transportation (SDDOT) and the South Dakota Highway Patrol (SDHP) as a pilot test of the accuracy and applicability of the Westa model. The measures of effectiveness for the current truck traffic confirm congestion (simulated by Westa) at the McCook weigh station. The high arrival rate for trucks relative to the average rate for weighing a truck causes the queue on the entrance ramp to fill up, causing the station operator to close the scale and wave traffic by without weighing. Overweight trucks and trucks with safety or credential problems may be missed when that happens The weigh-in-motion (WIM) scale in the proposed replacement station (simulated by Westa) is very effective in reducing the number of trucks that must be weighed at the static scale. If only trucks measured over 70,000 lbs gross weight are directed to the static scales, the reduction in the number of trucks that have to wait in the queue leads to significant reductions in the average queue length,the time spent in line by trucks, and the frequency of queue overflow. The proposed operating policy of weighing only a portion of the trucks weighing over the threshold leads to even greater reduction in queue lengths and station transit time, and completely eliminates station closings. The scenarios were repeated with the traffic load increased by 20% and by 30% in accord with a forecast of growth in the number of trucks from the trucking industry. As expected , the results showed increasing congestion for each scenario as the traffic levels increased. However, the proposed replacement station with the (WIM) scale was able to handle the increased traffic loads with few problems, both for the scenario where 20 percent of the trucks over the (WIM) threshold were weighed and the scenario where all trucks over the (WIM) threshold were weighed.
1 To develop and evaluate software that can realistically simulate traffic flows at border crossings, ports of entry, and weigh stations.
2 To validate the simulation software against observed traffic behavior at the present McCook Port of Entry.
3 To evaluate the performance of a proposed replacement for the McCook Port of Entry, using the simulation software.
1 Meet with the project=s technical panel to review project scope and work plan.
2 Develop and refine software to simulate traffic flows at border crossings, ports of entry, and weigh stations.
3 Validate the simulation software against actual observations taken at the McCook Port of Entry on Interstate 29.
4 Simulate the performance of a proposed replacement facility for the McCook Port of Entry.
5 Prepare a final report and executive summary of the literature review, research methodology, findings, conclusions, and recommendations.
6 Make an executive presentation to the SDDOT Research Review Board at the conclusion of the project.
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