Freeway Operations

Ramp Metering Strategies

The Federal Highway Administration and several state DOTs have identified ramp metering as one of the key congestion mitigation strategies. According to the Texas Transportation Institute’s 2009 Mobility Report, ramp metering in the 25 cities reduced delay by 39.8 million person hours in 2007. However, the potential of ramp metering is currently under-utilized with metering rates based on local conditions, limited consideration to linking all the on-ramps along a corridor, and no consideration for the type of bottlenecks such as merge, diverge, etc. Thus, sub-optimal operation results in excessively long queues on the entrance ramps, and insufficient reduction in system delay. 

This project is developing a data collection element of an HOV to HOT lane conversion project in Atlanta.  The Commute Atlanta research project is one of the most comprehensive instrumented vehicle projects deployed in the US. The dataset from this project includes second-by-second speed and position data for more than 1.8 million trips over a three year period.  The dataset also includes household demographics, vehicle data, and trip purpose data.  Given the richness of the dataset and the desire to protect participant anonymity, researchers are developing processed instrumented vehicle data sets that retain the detailed trip information, but eliminate the details about the trip ends to prevent identification of the home location.

Travel-Time Estimation

We will incorporate recent advances in traffic flow theory and simulation to build a framework able to provide short-term (up to ~30 min) travel time forecasts across the metropolitan Atlanta freeway network. This would allow us to predict the onset and propagation of congestion trough the network, and to improve current “real-time” travel time esti-mates in NaviGAtor (which are usually displayed with a ~10 min delay). Because off-the-shelf commercial simulation packages do not perform well in saturated freeways, we will use a traffic simulation model being developed at Georgia Tech, which is able to predict realistic traffic dynamics on congested freeways.

The effects of weaving are some of the least understood aspects of traffic flow. Along the I-85 corridor, weaving regularly occurs between the HOV (or HOT) lane and general purpose lanes, and between interchanges. Because vehicles typically accelerate/decelerate when weaving, the capacity of a freeway network is reduced. Not only does weaving affect capacity, it affects the safety of motorists. Due to safety concerns, attention will be given to weaving zones where there is a high speed differential between weaving lanes. It is important to note that illegal weaving along managed lanes also has the potential to affect safety and capacity.