Jiang et al. (Transportation Research Part B, 2011, 45(2), 343-363) proposed a predictive continuum dynamic user-optimal (PDUO-C) model to investigate the dynamic characteristics of traffic flow and the corresponding route-choice behavior of travelers. Their modeled region is a dense urban city that is arbitrary in shape and has a single central business district (CBD). However, we argue that the model is not well posed due to an inconsistency in the route-choice strategy under certain conditions. To overcome this inconsistency, we revisit the PDUO-C problem, and construct an improved path-choice strategy. The improved model consists of a conservation law to govern the density, in which the flow direction is determined by the improved path-choice strategy, and a Hamilton-Jacobi equation to compute the total travel cost. The simultaneous satisfaction of both equations can be treated as a fixed-point problem. A self-adaptive method of successive averages (MSA) is proposed to solve this fixed-point problem. This method can automatically determine the optimal MSA step size using the least squares approach. Numerical examples are used to demonstrate the effectiveness of the model and the solution algorithm.
On freeways with multiple on-ramps, it is a common practice to design a ramp metering strategy so as to regulate the entering rates from ramps and minimize the disruptions on the mainline. Most of the existing studies examine the performance of ramp metering on mobility and safety, rather than their impacts on the environment. This paper focuses on the estimates of vehicle emissions along mainline freeways under various ramp metering strategies. Vehicle speed and acceleration rates were measured during a field test along Interstate Freeway I-45 with five on-ramps in Houston, Texas, USA, while the instant vehicle emissions were estimated accordingly. The test was carried out in three scenarios: (1) no ramp metering, (2) isolated ramp metering, and (3) integrated ramp metering. Results show that, the isolated ramp metering strategy yields the highest emissions on freeway mainline among the scenarios. The mobility is significantly improved for the integrated ramp metering strategy, which also significantly contribute to the reduction in total emissions due to the reduced travel time and well-managed queue length on on-ramps. As a conclusion, the integrated ramp metering is with better mobility and environmental effects than the isolated and no metering strategies.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.