Development of an Optimal Ramp Metering Control Strategy for I-12

This study presents a comprehensive evaluation of various adaptive ramp metering strategies in order to identify the optimum algorithm that can help improve traffic conditions on I-12, Baton Rouge, Louisiana. The evaluated ramp metering strategies included the ALINEA local ramp metering control and mixed strategies case which included HERO coordinated and the local ALINEA control. The coordination was performed between three sets of two on-ramps, one on the eastbound and two on the westbound, while the other on-ramps were operating as ALINEA. The different strategies were compared to the current ramp metering strategy that was fixed-time. Geometric and traffic data were collected to build and calibrate a simulation model to be used to test the different ramp metering strategies. Comparative evaluation was then performed on the simulation results of the three strategies using three performance measures: travel time, speed, and vehicle hours traveled (VHT). The three measures were aggregated for the entire corridor and averaged for different sections on the corridor while each section was representing a ramp metering location. The evaluation was conducted separately for the eastbound and westbound directions. For the eastbound direction, the average travel time reduction was 2 seconds for ALINEA and 6 seconds for the mixed strategy case. For the travel speed, the average increase in speed was 0.2 mph for the ALINEA control and 0.4 mph for the mixed strategy. For the VHT, the average reduction was 2.5 veh.hrs for the ALINEA control and 6.5 veh.hrs for the mixed strategy case. On the other hand, for the westbound direction, the results showed more significant improvements. The average travel time reduction increased to 20 seconds for ALINEA control and 40 seconds for the mixed strategy case. For the travel speed, the average increase in speed was one mph for the ALINEA control and 2 mph for the mixed strategy. For the VHT, the average reduction was 195 veh.hrs for the ALINEA control and went up to 197 veh.hrs for the mixed strategy case. The statistical analysis on these results showed that while the improvements were not significant for the eastbound, they were significant for the westbound direction. Yet, most of the results were not considered practically significant. Therefore, more detailed section-by-section analysis was performed using the calculated performance measures for each section on the corridor. The section-by-section analysis showed that none of the eastbound sections experienced any significant improvements. Whereas, on the westbound direction, three sections experienced significant improvements in the different performance measures: Range-O’neal, O’neal-Millerville, and Millerville Sherwood. The travel time reductions on these sections were as high as 45 seconds and 30 seconds for ALINEA and the mixed strategies, respectively. The increase in speed was 9 mph and 13 mph for ALINEA and the mixed strategies, respectively. For the VHT, both strategies achieved reductions that reached 100 veh.hrs for the three sections. When the ALINEA and mixed strategies where compared to one another, the mixed strategy showed more significant improvements. In summary, the eastbound did not experience any significant improvements in the traffic conditions. This is expected since this direction is operating at free flow conditions with the fixed-time strategy. On the other hand, for the westbound directions, the mixed strategy improved the traffic conditions significantly compared to the other control strategies. Yet, the achieved improvements were not as significant as expected. This was caused by the spillbacks at the off-ramps resulting from the vehicles waiting at the red traffic signals on the surface streets. Therefore, the study recommended investigating the integrated corridor management between the ramp meters and the traffic signals on the surface streets.