Davenport, Iowa to La Crosse, Wisconsin: Highway Corridor Study, 1974

The proposed Davenport to Lacrosse route corridor includes the Iowa counties of Scott, Clinton, Jackson, and Dubuque. In addition, an influence region has been defined which includes six additional counties. The region is predominantly agricultural, however, following the national trend, movement away from the small farm to large mechanized operations has created an adequate labor force for the two major industrial cities of Davenport and Dubuque. From a total 1971 regional work force of 186,990, only 23,190, or slightly over 12% were engaged in agriculture, 91% of the land area being agricultural notwithstanding. It is forecasted that the urban population of the two counties containing the above cities will increase by 26% between 1970 and 1990, while the population of the remaining region counties can expect only a 3% increase.

VISSIM Calibration for Urban Freeways, 2015

In urban areas, interchange spacing and the adequacy of design for weaving, merge, and diverge areas can significantly influence available capacity. Traffic microsimulation tools allow detailed analyses of these critical areas in complex locations that often yield results that differ from the generalized approach of the Highway Capacity Manual. In order to obtain valid results, various inputs should be calibrated to local conditions. This project investigated basic calibration factors for the simulation of traffic conditions within an urban freeway merge/diverge environment. By collecting and analyzing urban freeway traffic data from multiple sources, specific Iowa-based calibration factors for use in VISSIM were developed. In particular, a repeatable methodology for collecting standstill distance and headway/time gap data on urban freeways was applied to locations throughout the state of Iowa. This collection process relies on the manual processing of video for standstill distances and individual vehicle data from radar detectors to measure the headways/time gaps. By comparing the data collected from different locations, it was found that standstill distances vary by location and lead-follow vehicle types. Headways and time gaps were found to be consistent within the same driver population and across different driver populations when the conditions were similar. Both standstill distance and headway/time gap were found to follow fairly dispersed and skewed distributions. Therefore, it is recommended that microsimulation models be modified to include the option for standstill distance and headway/time gap to follow distributions as well as be set separately for different vehicle classes. In addition, for the driving behavior parameters that cannot be easily collected, a sensitivity analysis was conducted to examine the impact of these parameters on the capacity of the facility. The sensitivity analysis results can be used as a reference to manually adjust parameters to match the simulation results to the observed traffic conditions. A well-calibrated microsimulation model can enable a higher level of fidelity in modeling traffic behavior and serve to improve decision making in balancing need with investment.