Date of Award
Master of Science
Civil, Construction, and Environmental Engineering
Microsimulation models have been growing in popularity in traffic engineering in recent years, and are often used as an important tool in the decision making process on large roadway design projects. In order to get valid results, it is necessary to calibrate such microsimulation models to local conditions. This is frequently achieved through a trial and error process of adjusting model parameters to get simulation results to match real world calibration data. Rarely is data collected on the model parameters themselves to provide a physical basis for the selection of their value. Two of the most important microsimulation model parameters for freeway models are standstill distance (the distance between stopped vehicles) and preferred time headway or time gap (the time between successive vehicles). Many simulation models treat these values as constants for all drivers and do not allow them to be set separately for different vehicle classes. This study presents a repeatable methodology for collecting standstill distance and headway/time gap values on freeways (mostly urban, with one rural location). It applies that methodology to locations throughout the state of Iowa. It continues by analyzing that data and comparing it for different locations and conditions. It finds that standstill distances vary by location and vehicle pair type. Headways/time gaps are found to be consistent within the same driver population and across different driver populations when the conditions are similar. An initial comparison between headways/time gaps at three urban areas to one rural location indicates a potential difference in driver behavior between those two conditions. Both standstill distance and headway/time gap are found to follow fairly disperse and skewed distributions. As a result of these findings, it is recommended that microsimulation models are 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. Additionally, the standstill distances and headway/time gaps found in this study may be used as a starting point for future microsimulation calibration efforts on urban freeways in Iowa.
Andrew Jeremy Houchin
Houchin, Andrew Jeremy, "An investigation of freeway standstill distance, headway, and time gap data in heterogeneous traffic in Iowa" (2015). Graduate Theses and Dissertations. 14817.