A multi-lane traffic flow model realistically captures the disruptive effects of lane- changing vehicles by recognizing their limited ability to accelerate. While they accelerate, these vehicles create voids in the traffic stream that affect its character. Bounded acceleration explains two features of freeway traffic streams: the capacity drop of freeway bottlenecks, and the quantitative relation between the discharge rate of moving bottlenecks and bottleneck speed. The model com- bines a multilane kinematic wave module for the traffic stream, with a detailed constrained-motion model to...
According to the duality theory of traffic flow any well-posed kinematic wave (KW) and/or variational theory (VT) problem can be solved with the same methods either on the time-space plane or the time vs vehicle number plane. To achieve this symmetry, the model parameters and the boundary data need to be expressed in a form appropriate for each plane. It turns out, however, that when boundary data that are bounded in one plane are transformed for the other, singular points with infinite density (jumps in vehicle number) sometimes arise. These singularities require a new form of weak...
Various theories have been proposed to describe vehicular traffic movement in cities on an aggregate level. They fall short to create a macroscopic model with variable inputs and outputs that could describe a rush hour dynamically. This dissertation work shows that a macroscopic fundamental diagram (MFD) relating production (the product of average flow and network length) and accumulation (the product of average density and network length) exists for neighborhoods of cities in the order of 5-10km2. It also demonstrates that conditional on accumulation large networks behave predictably and...
This research describes field studies of how on-ramp metering can increase the capacity of freeway merges. Some effects of on-ramp metering have been known for a long time. We have known that on-ramp metering can 1) increase freeway flow and speed upstream of a merge; and 2) reduce system-wide delay by alleviating gridlock-causing queues that have blocked off-ramps. However, past studies have not conclusively shown that on-ramp metering can increase the maximum outflow (capacity) of freeway merges. The experiments conducted in the present study verify that on-ramp metering can increase...
This report gives a comprehensive survey of the theory of highway traffic signals including isolated signals, one-way arterials, two-way arterials, and networks, limited however, to the common right angle junctions. The emphasis is on the logistics of control strategies rather than recipes for implementation. It is anticipated, however, that the implementation of some of the strategies described here will give substantial reductions in delays as compared with existing procedures.
Although we lack a complete theory of the motion of individual cars, there are many simple facts that even the most inexperienced driver knows and there are others which we could determine through experiment if we thought these facts were worth the effort required to find them. The lack of such a theory however, should not deter us from constructing a framework of possible theories consistent with what is known and seeing if such an incomplete theory can give any useful information about the gross aspects of traffic.
A simple symmetric network consisting of two tangent rings on which vehicles obey the Kinematic Wave Theory of traffic flow and can switch rings at the point of tangency is studied. An online adaptive simulation reveals that if there is any turning whatsoever the two-ring system becomes unevenly loaded for densities greater than the optimal density. This reduces flow. Furthermore, the two-ring system jams at significantly lower densities than the maximum density possible.
This paper describes some simplifications allowed by the variational theory of traffic flow (VT). It presents general conditions guaranteeing that the solution of a VT problem with bottlenecks exists, is unique and makes physical sense
Traffic flow theory is used to analyze the spatio-temporal distribution of flow and density on closed loop homogeneous freeways with many ramps, which produce inflows and allow outflows. It is shown that if the on-ramp demand is space-independent then this distribution tends toward uniformity in space if the freeway is either: (i) uncongested; or (ii) congested with queues on its on-ramps and enough inflow to cause the average freeway density to increase with time. In all other cases, including any recovery phase of a rush hour where the freeway's average density declines, the distribution...
A recent study reported that the Macroscopic Fundamental Diagram of a medium size city exhibited a clockwise hysteresis loop on a day in which a major disturbance caused many drivers to switch to unfamiliar routes. This paper shows that clockwise loops are to be expected when there are disturbances, especially if the disturbances cause a significant fraction of the drivers to not change routes adaptively. It is shown that when drivers are not adaptive networks are inherently more unstable as they recover from congestion than as they are loaded. In other words, during recovery congestion...
