Panos Michalopoulos, Professor, Civil, Environmental and Geo-Engineering
Freeway ramp control has been successfully implemented since the mid-1960s as an efficient and viable freeway management strategy. However, the effectiveness of any ramp control strategy largely depends on optimum parameter values, which are preferably determined prior to deployment. This is the case with the current stratified zone metering (SZM) strategy deployed in the 260-mile freeway network of the Minneapolis-St. Paul metropolitan area. To improve the performance of the SZM, which depends on the values of more than 20 parameters, this research first proposed a general methodology for site-specific performance optimization of ramp-control strategies using a microscopic simulation environment, as an alternative to trial-and-error field experimentation, and implemented the methodology with the SZM. The testing results showed that the new SZM control with site-specific optimum parameter values significantly improves the performance of the freeway system compared to the original SZM strategy. Second, this research proposed a methodology to explore the common optimum parameter values for the current SZM strategy for the entire Twin Cities freeway system in order to replace the site-specific optimum values, which are difficult to implement and time-consuming to search site-specific optimum values for all freeway sections, and thus have little practical value. The common parameter values were identified applying the response surface methodology (RSM) based on four specific freeway sections that represent all types of freeway sections in the metropolitan area.