Will Recker

A calibration procedure for microscopic traffic simulation

Simulation modeling is an increasingly popular and effective tool for analyzing transportation problems that are not amendable to study by other means. For any simulation study, model calibration is a crucial step to obtaining any results from analysis. This paper presents a systematic, multistage calibration and validation procedure for microscopic simulation models. The procedure is demonstrated in a calibration study with a corridor network in the southern California. The model validation results for the study network are also summarized.

Travel time reliability with risk-sensitive travelers

In recent empirical studies on values of time and reliability, many have suggested that travelers are interested not only in travel time saving but also in reduction in travel time variability. Variability introduces uncertainty for travelers such that they do not know exactly when they will arrive at their destination. Thus, it is considered as a risk (or an added cost) to a traveler making a trip. Continuing research is reported on route choice models and the effect on travel time reliability in an uncertain environment caused by demand and supply variations. The goal is to examine what the aggregate impact of changes in variability might be on network assignment and how travelers with different risk-taking behaviors respond to these changes.

Using Microscopic Simulation to Evaluate Potential Intelligent Transportation System Strategies Under Nonrecurrent Congestion

A microsimulation method is presented for evaluating the effectiveness of potential intelligent transportation system (ITS) strategies under nonrecurrent congestion. The evaluated ITS strategies include incident management, adaptive ramp metering, traveler information systems, arterial management, and a combination of those strategies. These strategies are implemented and evaluated over a road network in Irvine, California, with the microsimulation model PARAMICS. The evaluation results show that all ITS strategies have positive effects on network performance. Because of the network topology (one major freeway with two parallel arterial streets), real-time traveler information has the greatest benefits among all single ITS strategies. However, a combination of ITS strategies can further increase benefits.

Solving the bicriteria traffic equilibrium problem with variable demand and nonlinear path costs

In this paper, we present an algorithm for solving the bicriteria traffic equilibrium problem with variable demand and nonlinear path costs. The path cost function considered is comprised of two attributes, travel time and toll, that are combined into a nonlinear generalized cost. Travel demand is determined endogenously according to a travel disutility function. Travelers choose routes with the minimum overall generalized costs. The algorithm involves two components: a bicriteria shortest path routine to implicitly generate the set of non-dominated paths and a projection and contraction method to solve the nonlinear complementarity problem (NCP) describing the traffic equilibrium problem. Numerical experiments are conducted to demonstrate the feasibility of the algorithm to this class of traffic equilibrium problems.

Strategies for Selecting Additional Traffic Counts for Improving O-D Trip Table Estimation

Traditional traffic counting location (TCL) problem is to determine the number and locations of counting stations that would best cover the network for the purpose of estimating origin-destination (O-D) trip tables. It is well noted that the quality of the estimated O-D trip table depends on the estimation methods, an appropriate set of links with traffic counts, and the quality of the traffic counts. In this paper, we develop strategies in the screen-line-based TCL model for selecting additional traffic counts for improving O-D trip table estimation. Using these selected traffic counts, the O-D trip table is estimated using a modified path flow estimator that is capable of handling traffic count inconsistency internally. To illustrate the impact of the additional number of traffic counts on O-D estimation, we set up a unique experiment in a real world setting to visually observe the evolution of O-D estimation as the number of traffic counting locations increases. By comparing the O-D trip tables in a GIS, we visualize the actual impacts of counting locations on the estimation results. Various spatial properties of O-D trip tables estimated from traffic counts of different locations are identified as results of the study.

Development of a microscopic activity-based framework for analyzing the potential impacts of transportation control measures on vehicle emissions

Abstract The 1990 Clean Air Act Amendments (CAAA) and the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA) have defined a set of transportation control measures to counter the increase in the vehicle emissions and energy consumption due to increased travel. The value of these TCM strategies is unknown as there is limited data available to measure the travel effects of individual TCM strategies and the models are inadequate in forecasting changes in travel behavior resulting from these strategies. The work described in this paper begins to provide an operational methodology to overcome these difficulties so that the impacts of the policy mandates of both CAAA and ISTEA can be assessed. Although the framework, as currently developed, falls well short of actually forecasting changes in traveler behavior relative to policy options designed to encourage emissions reduction, the approach can be useful in estimating upper bounds of certain policy alternatives in reducing vehicle emissions. Subject to this important limitation, the potential of transportation policy options to alleviate vehicle emissions is examined in a comprehensive activity-based approach. Conclusions are drawn relative to the potential emissions savings that can be expected from efficient trip chaining behavior, ridesharing among household members, as well as from technological advances in vehicle emissions control devices represented by replacing all of the vehicles in the fleet by vehicles conforming to present-day emissions technology.

Strategic Hydrogen Refueling Station Locations with Scheduling and Routing Considerations of Individual Vehicles

A hydrogen refueling station siting model that considers scheduling and routing decisions of individual vehicles is presented. By coupling a location strategy of the set covering problem SCP and a routing and scheduling strategy of the household activity pattern problem, this problem falls into the category of location routing problems. It introduces a tour-based approach to refueling station siting, with tour-construction capability within the model. There are multiple decision makers in this problem: the public sector as the service provider and the collection of individual households that make their own routing decisions to perform a given set of out-of-home activities together with a visit to a refueling location. A solution method that does not require the full information of the coverage matrix is developed to reduce the computational burden. Compared to the point-based SCP the results indicate that the minimum infrastructure requirement may be overestimated when vehicle refueling demand-infrastructure refueling supply interactions with daily out-of-home activities are excluded.

Performance evaluation of ITS strategies using microscopic simulation

This work presents a micro-simulation method to evaluate the effectiveness of potential ITS strategies under the incident scenarios. The evaluation is conducted over a corridor network located at the City of Irvine, California. The potential ITS strategies include incident management, local adaptive ramp metering, coordinated ramp metering, traveler information systems, and a combination of the above. Based on the calibrated simulation model, we implement and evaluate these scenarios in the microscopic simulation model, PARAMICS. The evaluation results show that all ITS strategies have positive effects on the network performance. Due to the network topology (one major freeway with two parallel arterial streets), real-time traveler information system has the greatest benefits among all single ITS components. The combination of several ITS components, such as integrated control, can generate better benefits.

Stochastic Preplanned Household Activity Pattern Problem with Uncertain Activity Participation SHAPP

The so-called activity-based approach to analysis of human interaction with the social and physical environments dates back to the original time-space geography works of Hagerstrand and his colleagues at the Lund School in 1970. Despite their obvious theoretical attractiveness, activity-based approaches to understanding and predicting travel behavior have suffered from the absence of an analytical framework that unifies the complex interactions among the resource allocation decisions made by households in conducting their daily affairs outside the home while preserving the utility-maximizing principles presumed to guide such decisions. In this paper, we develop a computationally tractable system, based on an extension and modification of some rather well-known network-based formulations in operations research, to model human dynamics in uncertain environments. The research builds on the mathematical programming formulation of the household activity pattern problem by embedding stochastic elements in the planned household activity schedule decision process that capture the uncertainty of the need for rescheduling.

Policy Implications of Incorporating Hybrid Vehicles into High-Occupancy Vehicle Lanes

Abstract High-occupancy vehicle (HOV) lanes have been regarded as a cost-effective and environmental friendly option to help move people along congested routes. In spite of wide adaptation of policies, the effectiveness of HOV systems has been criticized for its under-utilization. A California statewide policy that allows hybrid vehicles to use HOV lanes was adopted under the expectation that vehicular emissions would be reduced by encouraging drivers to use fuel efficient vehicles as well traffic congestion would be eased through the more efficient use of the reserved capacity on the HOV lanes. To test the validity of this expectation, the impacts of the policy on the freeway network in Orange County, California was investigated using a method that combines a traditional planning model for demand estimation and analysis with a calibrated microscopic simulation model for accurate measures of system performance. The policy was analyzed in terms of overall system performance, corridor level performance and air quality. The key findings from this study are that the policy can be expected to have significant negative impact on HOV lanes that do not have reserve capacity. The maximum number of hybrid vehicles that the Orange County HOV system can absorb without significant degradation is about 50,000, and within this limitation, the policy can be expected to be successful in reducing emissions by allowing hybrid vehicles into HOV lanes.