Poster Session Abstracts
A Quadratic Linear Control Approach to Managing Network-level Performance Goals of Pavement Infrastructure Systems
Aristeidis Pantelias, Ph.D. Candidate and Graduate Research Assistant and Zhanmin Zhang, Ph.D., Associate Professor, Cockrell School of Engineering
This paper presents a new formulation and solution to the problem of managing infrastructure-specific, network-level performance goals through the planning of maintenance and rehabilitation (M&R) activities for the case of pavement infrastructure systems. The proposed approach is based on tracking agency-set targets with the use of optimal control theory. In particular, the problem is formulated as a discrete time, continuous state space quadratic linear tracking control problem considering M&R actions for a finite planning horizon. The formulation builds on previous research efforts using deterministic yet realistic empirical deterioration models. The problem is subsequently solved by using a standard non-linear mathematical programming solver. The obtained results are realistic and the formulation provides ample modeling flexibility, allowing the decision-maker to obtain target-specific optimal solutions.
Evaluation Of Airfield Pavements At Denver International Airport Using The Rolling Dynamic Deflectometer And Second-Generation Rolling Sensors
Boo Nam, M.S. Candidate and Graduate Research Assistant
The Rolling Dynamic Deflectometer (RDD) is a nondestructive, deflection-based device that is used to evaluate structural conditions of pavements. The RDD has previously been used to evaluate pavements at airfields of all sizes, such as Dallas-Fort Worth, Atlanta Hartsfield-Jackson, Seattle-Tacoma, Fort Worth Mecham, Fort Worth Alliance, Greenville (Texas) and Grayson County (Texas). The RDD is a powerful tool that provides continuous deflection profiles. RDD testing had been previously limited to a testing speed of 1.6 km/h. This limiting speed is controlled by the rolling sensors used to measure the deflections from the applied dynamic loading. Second-generation RDD rolling sensors were developed to increase the limiting speed. The second-generation rolling sensors use larger-diameter wheels that are less sensitive to rough surfaces and an additional hold-down force which ensures the sensors maintain contact with the pavement at higher testing speeds of 2.4 to 4.8 km/h, depending on the pavement type. In this paper, the development of the second-generation rolling sensors is discussed and their application at the Denver International Airport (DIA) is presented. At DIA, the RDD deflection data were used to assess the overall stiffness of the runway pavements and evaluate the load-transfer characteristics at every joint and crack along the testing paths. RDD deflection profiles were also used to identify both typical and critical areas for additional investigation at discrete location using a Heavy Weight Deflectometer (HWD). The HWD data allowed an additional comparison between the RDD and HWD and verification of the performance of the second-generation rolling sensors.
Intercity variation in the relationship between urban form and travel mode choice: Case study of Boston, Portland, and Houston
Transportation Research Record: Journal of the Transportation Research Board of the National Academies 1902:55-62, 2005.
Ming Zhang, Ph.D., Assistant Professor, School of Architecture
This study is motivated by the need for more empirical research on the urban form-travel connection. There is a two-tiered travel effect expected from strengthening the urban form-travel connection to reduce automobile dependence: 1) the enhancement of access to choices and 2) a shift in travel mode choice from driving to nondriving. Existing studies have primarily focused on the second-tier effect, but have largely omitted the first. This study attempted to fill that gap. Through joint-logit modeling of choice set formation and travel mode choice in Boston, Massachusetts, Portland, Oregon, and Houston, Texas, the study measures the degree of automobile dependence in the three cities and estimates elasticities of automobile dependence and of mode choice probabilities with respect to land use densification, transit access improvement, and control of motorization. There are large variations in the levels of automobile dependence and their elasticity estimates among the three cities. Public policies aimed at reducing automobile dependence should be formulated and evaluated based not just on the final outcome of modal split, but also on the provision of travel options to travelers. As cities differ in their existing urban forms, currently available transportation services, and prevailing preferences of travel, it is important to recognize that the same set of policy strategies implemented in different cities are not likely to generate the same amount effects on the reduction of automobile dependence.
Bus vs. Rail: A Meta-Analysis of Cost Characteristics, Carrying Capacities, and Land Use Impacts
Transportation Research Record: Journal of the Transportation Research Board of the National Academies, 2009 (forthcoming).
Ming Zhang, Ph.D., Assistant Professor, School of Architecture
Bus or rail? It has long been a public debate on the choice of transit systems for urban transportation. Recent developments in bus rapid transit (BRT) and light rail transit (LRT) throughout the world spur further heated discussions on the comparative advantages of bus- vs. rail-based mass transit. This paper presents a meta-study that synthesizes current understanding of the cost and operational characteristics as well as land use impacts of bus vs. rail mass transit in the framework of land use/transit integration. Its main purpose is to provide a balanced view that will help identify conditions under which a particular transit mode, bus or rail, is most appropriate. Here conditions refer to such factors as demand for and supply of transit uses, availability of public resources, performance features of transit technologies, and potential land use impacts of the system.
Thickness Distribution of Asphalt & Granular Layers Based on GPR Data and Its Effect on M-E PDG
Jose P. Aguiar, Graduate Research Assistant, and Jorge Prozzi, Ph.D., Associate Professor, Cockrell School of Engineering
It is widely accepted that a change in thickness of one of the pavement layers has a considerable impact on the performance that the pavement will exhibit during its life. It is therefore important to characterize the variability of pavement layer thickness so that the pavement structure will perform adequately throughout its design life. This study makes use of Long Term Pavement Performance (LTPP) SPS-1 sections located in the State of Texas for the purpose of determining the thickness distribution associated with the hot-mix asphalt (HMA) surface layer, the HMA binder course, and the granular base layer, as determined by Ground Penetrating Radar (GPR). Results from previous research and visual analysis indicate that pavement layers are normally distributed. Therefore, tests for determining normal goodness-of-fit were used for assessing the hypothesis that the thickness data for each individual analyzed layer has the normal distribution. The results indicate that 86.1% of the analyzed pavement layers have normally distributed thicknesses. An analysis of the thickness changes that occur within a given section, as measured along the lane centerline and under the right wheel-path, was also performed. Finally, based on the coefficient of variation identified for the HMA surface and granular base layers, sensitivity analyses were performed using the Mechanistic-Empirical Pavement Design Guide (M-E PDG). The results show a considerable change in distress, mainly fatigue cracking, as the layer thicknesses change within a range of ±3 standard deviations from the mean thickness.
Routine Maintenance Contract Management System (RMCMS)
This system has been developed and designed specifically for use by TxDOT to manage Strategy 144 funded Routine Maintenance Contracts (RMC).
It provides various maintenance contract management tools for contract planning, budget projections and monitoring, letting schedule management, contract time monitoring and general RMC reporting functions. Currently this system relies on Microsoft Access based front-end (for user inputs and reports) and an SQL server 2000 database in the back-end. The system uses the updated CMCS data from the mainframes and transforms it for use in a relational database automatically. In addition, the system develops various projections about contract budgets and charge-days using historical data for each contract CSJ. Individual contract CSJ data is aggregated to provide Maintenance Office or District Office level projections through various reports.
The system is currently in use in the Dallas District of TxDOT with approximately 70 users. In addition, it is being upgraded to provide a web-based interface to enhance the features of the user-interface. Phase II of this work will enhance its capabilities to provide similar functionality for Strategy 105 funds category.