Real-time Travel Time Estimation Using Macroscopic Traffic Flow Models

This paper presents the estimation of travel time on highways based on macroscopic modelling. The focus is on real-time values as compared to average or static values. The macroscopic models are used for distributed and time/space lumped settings and corresponding travel time estimation functions and algorithms are developed. The implications of these algorithms for the implementation of various incident management and traffic control strategies are also discussed

Assessment of red light running cameras in Fairfax County

A study was conducted to assess the Red Light Running (RLR

Want to Make Your Website Better? Ask a Librarian.

Raise your hand if you have served on a committee in your library. If your hand isn’t raised, just give it some time … libraries definitely like committee work. For instance, I recently had the opportunity to work with a committee consisting mostly of librarians. When the committee’s goals were accomplished, my non-librarian coworker commented that “Librarians sure have a lot of opinions.” Since this article is about usability testing, and is written by and for librarians, let’s test his hypothesis. Let’s also test a few other hypotheses about librarians while we’re at it. (Disclaimer: In this article, “librarians” include staff who work in libraries, and has nothing to do with degrees or job classifications.) Washington County Cooperative Library Services (WCCLS) is a Cooperative of 13 member libraries and two special libraries, each uniquely governed and operated. WCCLS is a primary funding source for member libraries, and our WCCLS “Office” provides other support such as daily courier deliveries, cataloging coordination, and e-book collections. The WCCLS website and Extranet are two other ways the WCCLS Office supports member libraries in Washington County. The WCCLS Extranet is a repository of policies, procedures, and committee meeting documents. It also includes training and promotional materials for WCCLS resources, as well as opportunities for sharing ideas

Comparison of TRANSIMS' Light Duty Vehicle Emissions with On-Road Emission Measurements

The Transportation Analysis and Simulation System, TRANSIMS, contains a vehicle emissions module that estimates tailpipe emissions for light and heavy-duty vehicles and evaporative emissions for light-duty vehicles. This paper describes and validates the TRANSIMS emission module and compares its emission estimates to on-road emission-measurements and other state-of-the-art emission models. The trend of the emissions estimated in thirteen different runs in each model are compared. The results indicate that the TRANSIMS model provides consistent trends of estimated carbon monoxide (CO) and hydrocarbons (HC) with field data trends and inconsistent trends of estimated nitrogen lxides (NOx). However, the magnitude of the emission estimated in TRANSIMS is closer to the field data than for other models

A linear programming approach for synthesizing origin-destination trip tables from link traffic volumes

We present a nonproportional-assignment, user-equilibrium motivated, linear programming model for estimating origin-destination (O-D) trip tables from available data on link traffic volumes. The model is designed to determine a traffic equilibrium network flow solution that reproduces the link volume data, if such a solution exists. However, it recognizes that due to incomplete information, the traffic may not conform to an equilibrium flow pattern, and moreover, there might be inconsistencies in the observed link flow data. Accordingly, the model permits violations in the equilibrium conditions as well as deviations from the observed link flows but at suitable incurred penalties in the objective function. A column generation solution technique is presented to optimally solve the problem. This methodology is extended to the situation in which a specified prior target trip table is available and one is required to find a solution that also has a tendency to match this table as closely as possible. Implementation strategies are discussed and the proposed method is illustrated using some sample test networks from the literature.

Parameter optimization methods for estimating dynamic origin-destination trip-tables

Dynamic origin-destination tables help in on-line control of traffic facilities and, consequently, are of significant use in alleviating traffic congestion. Such tables find useful applications in the contexts of Advanced Traffic Management Systems and Advanced Traveler Information Systems. This paper considers the estimation of split parameters that prescribe an origin-destination trip-table based on dynamic information regarding entering and exiting traffic volumes through an intersection or a small freeway segment. Two models are developed and motivated for this problem, one based on a least-squares estimation approach and the other based on a least absolute norm approach. Both models enhance existing dynamic origin-destination trip-table estimation models in that they also consider freeway segments having differing time-dependent transfer lags between different pairs of entrances and exits. A projected conjugate gradient scheme is employed for solving the constrained least-squares problem and is compared against a standard commercial software. The least absolute norm estimation problem is posed as a linear programming problem and is also solved using a commercial software for the sake of comparison. Computational results are presented on a set of test problems using synthetic as well as realistic simulated data, involving the determination of origin-destination trip tables for both intersection and freeway scenarios, in order to demonstrate the viability of the proposed methods. These results exhibit that, unlike as reported in the literature based on previous efforts, properly designed parameter optimization methods can indeed provide accurate estimates in a real-time implementation framework. Hence, these methods provide competitive alternatives to the iterative statistical techniques that have been heretofore used because of their real-time processing capabilities, despite their inherent inaccuracies.

A location-allocation model and algorithm for evacuation planning under hurricane/flood conditions

The location of shelters in a region threatened by a hurricane can greatly influence the highway network clearance time, i.e. the time needed by evacuees to escape from origin points to safe areas. The studies conducted to date for developing hurricane plans have not implicitly considered the impact of shelter locations on evacuation times. The purpose of this research is to develop both a planning and an operational computer-based tool through a particular location-allocation model. This model selects a set of candidate shelters from among a given set of admissible alternatives in a manner feasible to available resources, and prescribes an evacuation plan which minimizes the total congestion-related evacuation time. An extraneous flow is also superimposed on the network in order to represent the traffic of evacuees not using the designated shelters as destinations. The model formulated is a nonlinear mixed-integer programming problem, for which we develop a heuristic and (two versions of) an exact implicit enumeration algorithm based on the generalized Benders' decomposition method. Computational experience is provided against a set of realistic test problems formulated on the Virginia Beach network. Potential avenues for future research are also explored.

Comparison of TRANSIMS’ Light Duty Vehicle Emissions with On-road Emission Measurements

The Transportation Analysis and Simulation System (TRANSIMS) contains a vehicle emissions module that estimates tailpipe emissions for light and heavy duty vehicles and evaporative emissions for light duty vehicles. It uses as inputs the emissions arrays obtained from the CMEM model. This paper describes and validates the TRANSIMS emission module and compares its emission estimates to on-road emission measurements and other state-of-the-art emission models including the VT-Micro, CMEM, and MOBILE6 models. Thirteen different runs were conducted to compare emissions from field measurements to the trends in emissions obtained form the above-mentioned four models. The results indicate that the TRANSIMS model provides consistent trends of estimated Carbon Monoxide (CO) and Hydrocarbons (HC) with field data, while inconsistent trends of estimated Nitrogen Oxides (NOx). However, the magnitude of emissions estimated by TRANSIMS is closer to the field data than those obtained form the other models; MOBILE6, CMEM, and VT-Micro

Comparison of TRANSIMS' Light Duty Vehicle Emissions with On-Road Emission Measurements

The Transportation Analysis and Simulation System, TRANSIMS, contains a vehicle emissions module that estimates tailpipe emissions for light and heavy-duty vehicles and evaporative emissions for light-duty vehicles. This paper describes and validates the TRANSIMS emission module and compares its emission estimates to on-road emission-measurements and other state-of-the-art emission models. The trend of the emissions estimated in thirteen different runs in each model are compared. The results indicate that the TRANSIMS model provides consistent trends of estimated carbon monoxide (CO) and hydrocarbons (HC) with field data trends and inconsistent trends of estimated nitrogen lxides (NOx). However, the magnitude of the emission estimated in TRANSIMS is closer to the field data than for other models

Comparison of TRANSIMS’ Light Duty Vehicle Emissions with On-Road Emission Measurements

The Transportation Analysis and Simulation System, TRANSIMS, contains a vehicle emissions module that estimates tailpipe emissions for light and heavy-duty vehicles and evaporative emissions for light-duty vehicles. This paper describes and validates the TRANSIMS emission module and compares its emission estimates to on-road emission-measurements and other state-of-the-art emission models. The trend of the emissions estimated in thirteen different runs in each model are compared. The results indicate that the TRANSIMS model provides consistent trends of estimated carbon monoxide (CO) and hydrocarbons (HC) with field data trends and inconsistent trends of estimated nitrogen lxides (NOx). However, the magnitude of the emission estimated in TRANSIMS is closer to the field data than for other models