Entrance ramp metering in freeway work zones was investigated to develop a set of guidelines for entrance ramp control strategies in freeway work zones considering the freeway mainline throughput and local traffic access to freeways and hourly traffic volumes for the freeway mainline and freeway entrance ramp in this study.
The basis for this investigation were the historical hourly traffic volume data and the cumulative interarrival time (IAT) data for signalized and non-signalized freeway entrance ramps and the freeway mainline, which were measured at different freeway work zones in Ohio using microwave radar trailers. The cumulative IAT distributions for signalized entrance ramps were developed and the cumulative IAT distributions for freeway mainline and signalized entrance ramps were extrapolated in order to be able to determine IATs for a few vehicles up to 2500 vehicles/hour (vph).
Two separate Arena simulation models, ran on a PC, were used to investigate spill back queues from entrance ramp metering signal back to the local (arterial) road and to investigate merging of the entrance ramp traffic and determine queue lengths from the freeway mainline merge area back to the ramp metering signals for different entrance ramp and freeway mainline rightmost lane hourly traffic volumes, truck percentages, and ramp metering signal intervals at signalized and non-signalized freeway entrance ramps. Arena simulation models were validated using Pollazcek-Khintchine formula and IATs based on negative exponential distribution and number of vehicles merging into the freeway mainline rightmost lane.
The analysis of the maximum queues determined using Arena simulation models showed that the use of ramp metering signal interval, which is 90% of the metering signal interval that would be equal to process ramp demand in an hour (100%), will result in smaller maximum queues for signalized and non-signalized freeway entrance ramps, while on the other hand not increase the maximum queue from freeway mainline merge area back to ramp metering signal considerably.
A set of guidelines for temporary entrance ramp control strategies in freeway work zones for traffic engineers to design and implement an entrance ramp control strategy including ramp metering was established based on the freeway mainline traffic throughput and local traffic access to freeway importance levels and hourly traffic volume levels for freeway mainline and entrance ramp. These guidelines may also be applied to regular freeway/entrance ramp situations without work zones.