UC Irvine

Modeling capacity is an integral component towards multiple traffic engineering objectives such as design and evaluation of control strategies. Traffic dynamics at bottlenecks, both on freeways and on arterial networks, influenced by bounded acceleration and lane-changing, affect the capacity in intriguing ways. This research attempts to capture these impacts of the bounded acceleration behavior and its interplay with lane-changing, by constructing a modeling framework that accurately models traffic dynamics at bottlenecks.

Towards this goal, first a modified Cell Transmission Model (CTM) is proposed, by substituting the traditionally constant demand function with a linearly decreasing function for congested traffic. The jam-density discharge flow-rate is introduced as an additional parameter to characterize the macroscopic bounded acceleration effects. Analytically the new model is shown to reproduce observed features in the discharge flow-rate and headway at signalized intersections. Calibration with observations from existing studies, as well as new observations, further suggests that the model can reasonably capture all traffic queue discharge features.

The demand function is further modified by integrating macroscopic lane-changing effects on capacity. The Lane Changing Bounded Acceleration CTM (LCBA-CTM) thus developed, is shown to realistically model the capacity drop phenomenon at active freeway lane-drop bottlenecks in stationary states. The capacity drop magnitude is determined by macroscopic bounded acceleration and lane-changing characteristics. Constant loading problems are analytically solved to reveal the onset and recession processes of congestion.

An addition to the framework connects microscopic acceleration profiles of vehicles to modified demand functions. This completes the framework presented by offering a mechanism to start from any acceleration model.

Finally, two applications of the modified CTM are presented illustrating the use of the framework: a) to model impacts of improved vehicle acceleration on traffic dynamics at intersections; and b) to create Macroscopic Fundamental Diagrams (MFDs) for arterial networks and compare their accuracy with traditional CTM methods.

This dissertation offers a systematic approach to incorporating bounded acceleration and lane-changing into the CTM demand functions. Such an approach is shown to capture important static and dynamic features at critical bottlenecks, including lost time and queue discharge features at signalized intersections, as well as capacity drop magnitude and the onset of capacity drop at active freeway bottlenecks. The consistency between the modified demand function and microscopic bounded acceleration models is also established.