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Research Digest FORWARD ALL REQUESTS TO: The University of Texas at Austin Center for Transportation Research LIBRARY 1616 Guadalupe St. | Suite 4.202 | Austin, Texas 78701 Phones: (512) 232-3126 and (512) 232-3138 Email: ctrlib@austin.utexas.edu In this Issue:

TxDOT Reports

Table of Contents Item 1.

Impact of Overhang Construction on Girder Design (CTR 5706-1) 1

Item 2.

Emerging Trade Corridors and Texas Transportation Planning (CTR 5973-2) 

Item 3.

Potential Use of Longer Combination Vehicles in Texas : First Year Report (CTR 6095-1) 

Item 4.

Synthesis of Innovative Contracting Strategies for Routine and Preventive Maintenance Contracts (CTR 6388-1) 

Item 5.

Synthesis of Innovative Contracting Strategies Used for Routine and Preventive Maintenance Contracts (CTR 6388-P1)

Item 6.

The Texas Perpetual Pavements : Experience Overview and the Way Forward (TTI 4822-3) 

Item 7.

Texas Perpetual Pavements : New Design Guidelines (TTI 4822-P6) 

Item 8.

Field and Laboratory Investigation of Warm Mix Asphalt in Texas (TTI 5597-2)

Item 9.

Development, Calibration, and Validation of Performance Prediction Models for the Texas M E Flexible Pavement Design System (TTI 5798-2)

Item 10.

Evaluation of Potential Benefits of Wider and Brighter Edge Line Pavement Markings : Technical Report (TTI 5862-1)



Item 11.

Bioretention for Stormwater Quality Improvement in Texas : Pilot Experiments (TTI 5949-2)



Item 12.

Characterization of In-Use Emissions from TxDOT's Non-Road Equipment Fleet : Final Report (TTI 5955-2) 7

Item 13.

Quantifying the Purchasing Power of Public Transportation in Texas : Technical Report (TTI

Item 14.

Estimated Impacts of the 2010 Census on the Texas Transit Funding Formula : Summary Report on Findings (TTI 6199-P1)

Item 15.

Analysis and Recommendations on Protecting Waterways from Encroachment (TTI 6225-1)................ 

Item 16.

Development of the Texas Revenue Estimator and Needs Determination System (T.R.E.N.D.S.) Model (TTI 6395-TI-1)................................................................................................................

Item 17.

Assessment and Validation of Managed Lanes Weaving and Access Guidelines (UTA 5578-1)................ 





6194-1)7

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Research and Technology Implementation Office

February 2011


Research Digest Item 1 Impact of Overhang Construction on Girder Design UNIVERSITY OF TEXAS AT AUSTIN. CENTER FOR TRANSPORTATION RESEARCH (CTR)

CTR 5706-1 • 2010 Economical constraints on the design of bridges usually necessitate the use of as few girders as possible across the bridge width. The girders are typically uniformly spaced transversely with the deck extending past the fascia girders, thereby resulting in an overhang. While designers commonly employ rules of thumb with regard to the geometry of the overhang, these rules of thumb generally address only the deck in-service strength and deflection requirements, and the effect due to construction load is not considered. In particular, the impact of the overhang on fascia girder behavior during construction is not well understood. Overhang construction often leads to a torsional load on the girder system that can lead to problems in steel and concrete girder bridges during construction. The main issue with concrete girder bridges is excessive lateral rotation in the fascia girder, which can cause potential problems of construction safety and maintenance. Field problems on concrete bridges have been reported in the state of Texas where the fascia girders experienced excessive rotation during construction. For steel girder bridges, the unbalanced overhang loading can lead to both local and global instability. Locally, the overhang brackets often exert a large force on the web plate that can distort the web and increase the magnitude of the plate imperfection. Global stability problems have occurred primarily on bridge widening projects where a few girders are added to an existing bridge system. The girders in the widening are usually isolated from the existing bridge and the unbalanced load from the overhang can cause excessive twist that intensifies the global stability of the girder system. The objective of this study was to improve the understanding of the bridge behavior due to the unbalanced loading from the overhangs and to identify critical factors affecting the girder behavior. The study was also aimed at developing simple design methodologies and design recommendations for overhang construction. The research included field monitoring, laboratory tests, and parametric finite element analyses. The data from the field monitoring and laboratory tests were used to validate finite element models for both concrete and steel girder bridges. Based on the validated models, detailed parametric studies were conducted to investigate the effects of the unbalanced loading. Results from the parametric studies were used to identify the geometries of girder systems that are prone to problems with the overhangs as well as to provide design suggestions. In addition, a closed-form solution for lateral rotation in the fascia girder in a concrete girder bridge was derived using a rigid-body model, and was used to develop design methodology and design recommendations for overhang construction. (206 pages) Full-text PDF of this report is available for free download from: http://www.utexas.edu/research/ctr/pdf_reports/0_5706_1.pdf

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Research and Technology Implementation Office

February 2011

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Research Digest Item 2 Emerging Trade Corridors and Texas Transportation Planning : Technical Report UNIVERSITY OF TEXAS AT AUSTIN. CENTER FOR TRANSPORTATION RESEARCH (CTR)

CTR 5973-2 • 2010 This report describes the major trends in intermodal shipping that are impacting Texas intermodal trade corridors. Key supply and demand forces that underpin intermodal service and routing options are provided. Intermodal development from a technological and shipping industry perspective is described, including the impacts of the global economic recession beginning in late 2007. This is followed by an overview of Texas trade patterns with various trading partners with particular attention paid to those relationships that are in a current state of flux. A review of current and future corridors used for handling international intermodal trade shows the comparative strengths and weaknesses of different routing options for intermodal cargo shipping. Texas ports officials regard the new Panama Canal lock system due to open in 2014 as critical to future demand so a chapter is devoted to examining the system and current status. The inherent economics of different corridor options is enhanced by the development of marine and rail cost models that explore the basic tradeoffs for transportation providers in choosing different corridors. Finally, suggested infrastructure and economic milestones driving changes in trading patterns are given particularly as they relate to the Texas economy and its transportation system. (142 pages) Full-text PDF of this report is available for free download from: http://www.utexas.edu/research/ctr/pdf_reports/0_5973_2.pdf

Item 3 Potential Use of Longer Combination Vehicles in Texas : First Year Report UNIVERSITY OF TEXAS AT AUSTIN. CENTER FOR TRANSPORTATION RESEARCH (CTR)

CTR 6095-1 • 2010 Trucking remains the only major freight mode not to benefit from increases in size and weight regulations since 1982. The need for more productive trucks both longer (LTL) and heavier (TL) is growing with economic activity, rising fuel costs and concerns over environmental impacts from emissions. This study covers the first year activities of a two-year TxDOT-sponsored study into potential LCV use in Texas. It describes current U.S. LCV operations and regulations, operational characteristics of various LCV types, safety issues, and environmental and energy impacts, together with pavement and bridge consumption associated with LCVs. Methods to measure both pavement and bridge impacts on a route basis are described. A survey of current U.S. LCV operators provides an insight into business characteristics, vehicles, drivers, performance, and safety. The overall study benefited from three sources of direction: an advisory panel from TxDOT, an industry panel comprising heavy truck and LCV operators, and finally an academic team from the University of Michigan Transportation Research Institute. In the second year of the study, a series of routes and LCV types will be evaluated in Texas using methods developed in the first year and approved at a study workshop. (142 pages) Full-text PDF of this report is available for free download from: http://www.utexas.edu/research/ctr/pdf_reports/0_6095_1.pdf

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Research and Technology Implementation Office

February 2011

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Research Digest Item 4 Synthesis of Innovative Contracting Strategies for Routine and Preventive Maintenance Contracts UNIVERSITY OF TEXAS AT AUSTIN. CENTER FOR TRANSPORTATION RESEARCH (CTR)

CTR 6388-1 • 2010 TxDOT is faced with a need to expand their maintenance contracted services due to shortage of in-house personnel and expertise. As a result, TxDOT had a need to investigate maintenance contracting strategies to identify those efficient strategies that might be implemented to help them achieve their maintenance goals. This study investigated current maintenance contracting practices in TxDOT and other state DOTs, and produced a selection framework, guide and case studies to assist maintenance personnel in selecting and implementing appropriate contracting strategies for maintenance outsourcing. A prototype selection algorithm was created to help decision makers identify contracting strategy for achieving outsourcing goals and accommodating maintenance circumstances. (218 pages) Full-text PDF of this report is available for free download from: http://www.utexas.edu/research/ctr/pdf_reports/0_6388_1.pdf

Item 5 Synthesis of Innovative Contracting Strategies Used for Routine and Preventive Maintenance Contracts UNIVERSITY OF TEXAS AT AUSTIN. CENTER FOR TRANSPORTATION RESEARCH (CTR)

CTR 6388-P1 • 2010 This document can be used by Maintenance Division and district personnel at all levels to encourage implementation of innovative methods for outsourcing more extensive maintenance activities within TxDOT. These research objectives were accomplished through the following research tasks: 1.) Assemble a comprehensive list of innovative road maintenance contract strategies and criteria for evaluating their effectiveness; 2.) Investigate the effectiveness of TxDOT contract strategies and practices for accomplishing road maintenance; 3.) Investigate the effectiveness of other DOTs’ contract strategies and practices for accomplishing road maintenance; 4.) Compare TxDOT’s maintenance contract strategies to other states and develop a decision aid for selecting and implementing appropriate strategies; 5.) Summarize the findings and present the results. The scope and limitations of this research are presented here to properly use and apply the results of this project. Through a literature review, the researchers identified 14 delivery methods for maintenance contracting that are being used in North America, South America, Australia, Northern Europe and England. An on-line questionnaire was developed and distributed to state highway agencies in all 50 states and the 25 TxDOT districts. The questionnaire identified the 14 delivery methods and asked respondents to identify all of the methods they use to outsource maintenance activities in their agency. The research Project Monitoring Committee (PMC), in conjunction with the researchers, selected six TxDOT districts and five state DOTs (other than TxDOT) to conduct in-person interviews about specific contracting methods. (x, 120 pages) Full-text PDF of this report is available for free download from: http://www.utexas.edu/research/ctr/pdf_reports/0_6388_P1.pdf

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Research and Technology Implementation Office

February 2011

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Research Digest Item 6 The Texas Perpetual Pavements : Experience Overview and the Way Forward TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI)

TTI 4822-3 • 2010 Since 2001, the State of Texas has been designing and constructing perpetual pavements on some of its heavily trafficked highways where the expected 20-year truck-traffic estimate of 18 kip ESALs is in excess of 30 million. To date, there are 10 in-service perpetual pavement (PP) sections, typically consisting of about 22 inches total thickness of HMA layers and supported on an 8-inch thick treated (lime or cement) base, resting on a well compacted subgrade soil. This report provides an overview of the Texas construction and evaluation experience of PPs including structural design, materials and mix-designs, construction and quality issues, and performance history. The research methodology and scope of work included data collection, extensive laboratory and field testing, computational modeling, and performance evaluations. Based on the research findings, recommendations for the future Texas PP design, construction, and performance monitoring are provided in this report. Overall, performance to date is satisfactory with no major structural distresses. However, construction related joint and cracking problems were observed on a few projects. Laboratory and field experience has also indicated workability, compactibility, and constructability related problems with the Stone Filled (SF) HMA mixes, which serve as the main structural load-carrying layers. Recommendations have accordingly been made to improve or replace the SF mix-designs. Recommendations are also provided for the structural design of future Texas PPs; the current PP designs were found to be conservative with potential for further optimization. The results generated support the transition to higher design moduli values, yielding a 6 or more inch structural thickness reduction in the total HMA thickness. (164 pages) Full-text PDF of this report is available for free download from: http://tti.tamu.edu/documents/0-4822-3.pdf

Item 7 Texas Perpetual Pavements : New Design Guidelines TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI)

TTI 4822-P6 • 2010 As part of a research study that was initiated to validate, among other objectives, the Texas perpetual pavement (PP) concept, this product documents the revised guidelines and recommendations for the design, construction, and performance evaluation of Texas PP structures. Design recommendations include guidelines for structural thickness design, design and analysis software (FPS 21W and the MEPDG), the mechanistic-empirical (M-E) strain response criteria, materials and HMA mix-designs, and layer moduli values. Recommendations for future PP construction improvements and performance evaluation strategies are also documented in this publication. (54 pages) Full-text PDF of this report is available for free download from: http://tti.tamu.edu/documents/0-4822-P6.pdf

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Research and Technology Implementation Office

February 2011

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Research Digest Item 8 Field and Laboratory Investigation of Warm Mix Asphalt in Texas TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI)

TTI 5597-2 • 2010 During the first half of this research study, TxDOT had only placed 1000 tons of warm mix asphalt (WMA) as part of a demonstration project. By the end of this three year study, TxDOT had placed more than 1,000,000 tons of WMA and allowed its use in all dense-graded mixtures through the implementation of a special provision 341---020. This research project was focused on evaluating all aspects of WMA and identifying the effects of WMA technologies on mixture design, lab performance characteristics, and field performance. An ongoing implementation study is underway to continue to monitor performance of WMA field sections. Researchers found that WMA technologies improve the compactibility of mixtures which can lead to a reduction in design asphalt content if incorporated in the mixture design process. Laboratory tests indicate that warm mix asphalt is initially less stiff than hot mix but stiffens considerably during the first year of service and with increases in laboratory oven curing time/temperature. Field performance of warm mix projects has, thus far, been comparable to hot mix projects. X-ray CT and ground penetrating radar testing indicate the uniformity of WMA construction may be better than that for hot mix construction. (144 pages) Full-text PDF of this report is available for free download from: http://tti.tamu.edu/documents/0-5597-2.pdf

Item 9 Development, Calibration, and Validation of Performance Prediction Models for the Texas M-E Flexible Pavement Design System TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI)

TTI 5798-2 • 2010 This study was intended to recommend future directions for the development of TxDOT's Mechanistic-Empirical (TexME) design system. For stress predictions, a multi-layer linear elastic system was evaluated and its validity was verified by comparing the measured tensile strains under accelerated pavement (ALF) loading with the computed values. After reviewing all existing pavement performance models, the VESYS model was recommended for predicting flexible pavement layer rutting and an Overlay Tester-based fatigue cracking model was proposed, which includes both crack initiation and propagation models. For hot-mix asphalt (HMA) rutting predictions, the dynamic modulus test and repeated load test are proposed to provide material properties. The proposed HMA rutting model was calibrated using the rutting data from the NCAT test track and the Texas LTPP-SPS 5 test sections. The proposed fatigue cracking models were calibrated with performance data from NCAT. Resilient modulus and permanent deformation testing is recommended for base and subgrade materials and future research efforts are required to improve the repeatability of the permanent deformation test. For stabilized bases the traditional fatigue models are recommended and calibration factors were proposed based on existing accelerated pavement test data. A field experiment was conducted to evaluate the adequacy of the LoadGage program to compute allowable axle load limits for thin pavements. On sections trafficked to failure, very good results were obtained when moisture correction factors were applied to the laboratory measured engineering properties. Implementation should proceed by incorporating the proposed models and default material properties into a design software package, upgrading the available repeated load equipment, performing additional calibration, and developing additional default values for a wide range of Texas materials. (216 pages) Full-text PDF of this report is available for free download from: http://tti.tamu.edu/documents/0-5798-2.pdf

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Research and Technology Implementation Office

February 2011

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Research Digest Item 10 Evaluation of Potential Benefits of Wider and Brighter Edge Line Pavement Markings : Technical Report TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI)

TTI 5862-1 • 2010 This report documents the findings of a two-year study that investigated the potential benefits of wider edge line pavement markings. There were four general tasks discussed in the report: 1) review of literature, 2) survey of the state of the practice, 3) summary of recent safety analyses, and 4) a human factors nighttime study of the impact of wider and brighter edge line pavement markings. The results show that states are increasing their use of wider edge lines, and safety studies are beginning to show evidence supporting the use of wider edge lines for two-lane highways. The human factors study included surrogate safety measures, such as lateral placement, edge line encroachments, and driver eye glance patterns. The results from these metrics all support positive safety findings. Pavement marking brightness had less of an impact than pavement marking width on these operational metrics. In this study, there was no attempt to relate pavement marking retroreflectivity to safety. The researchers recommend the use of wider pavement markings on two- lane highways with additional experimentation to verify the benefits described in this report. (136 pages) Full-text PDF of this report is available for free download from: http://tti.tamu.edu/documents/0-5862-1.pdf

Item 11 Bioretention for Stormwater Quality Improvement in Texas : Pilot Experiments TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI)

TTI 5949-2 • 2010 This report summarizes the results of pilot-scale bioretention experiments. Five steel boxes of 6 ft (L) x 6 ft (W) x 4 ft (D) were constructed, each of which has different type of vegetation: (1) shrubs, (2) grass species in Texas department of Transportation (TxDOT) Bryan District seed mix, (3) native grasses, (4) Bermuda grass, and (5) no vegetation as the control. Vegetation was given 14 months to establish before testing. Synthetic runoff containing predetermined pollutants with target concentrations was used. The results indicate that the pilot bioretentions effectively removed zinc (Zn), lead (Pb), total suspended solids (TSS), and ammonia-nitrogen (NH3-N) from stormwater runoff, but exported copper (Cu), nitrate nitrogen (NO3-N), total nitrogen (TN), and total phosphorus (TP). Vegetation plays an important role in NO3-N and TN removals due to root uptake and the denitrification processes in root zone. However, vegetation could negatively affect water quality if the soil infiltration rate is significantly increased by its root system. This effect was specifically obvious on the TSS removal, in which the control box with the longest detention time had better performance than the vegetated boxes. The results suggest that bioretention is useful to treat stormwater runoff from TxDOT highways, but the design specifications developed in other states should be revised to reflect Texas' unique climate and environmental conditions. Challenged and learned lessons are described in the report. (56 pages) Full-text PDF of this report is available for free download from: http://tti.tamu.edu/documents/0-5949-2.pdf

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Research and Technology Implementation Office

February 2011

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Research Digest Item 12 Characterization of In-Use Emissions from TxDOT's Non-Road Equipment Fleet : Final Report TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI)

TTI 5955-2 • 2010 The objective of this document is to present the findings of the study characterizing in-use emissions of TxDOT's nonroad diesel equipment. This document presents literature reviews of emission reduction technologies and emission control measures practiced by the state of Texas and other states, discusses selection of TxDOT's non-road equipment and emission reduction technologies for emissions testing, and shows the in-use emissions of TxDOT's diesel equipment before and after installing and utilizing the selected emission reduction technologies (hydrogen enrichment and fuel additive technologies) using portable emission measurement systems (PEMS). Emissions measurements and data comparison and analysis have been performed with the technologies. The selected technologies did not show statistically significant NOx emissions reductions. From additional analysis with other pollutants, both technologies did not show any benefits in terms of emissions reductions. An optimization model has also been developed as part of this research and can be used to maximize the benefit of deploying other emission reduction technologies (that are proven effective) among TxDOT's non-road diesel fleet. (140 pages) Full-text PDF of this report is available for free download from: http://tti.tamu.edu/documents/0-5955-2.pdf

Item 13 Quantifying the Purchasing Power of Public Transportation in Texas : Technical Report TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI)

TTI 6194-1 • 2010 Investments on public transportation in Texas contribute to the state and local economy by improving transportation options, which in turn creates benefits for individuals, businesses, and governments. Many different agencies provide public transportation services in Texas. Each of these agencies buys goods and services on an individual basis. The purpose of this research is to quantify the purchasing power of public transportation in Texas and to estimate the economic impact on state and local economies. The research also documents how cooperative purchasing can leverage buying power to reduce the cost of equipment, goods, and services and reduce the time and expense for administration of procurement activities for public transportation providers. Case study examples illustrate opportunities for public transportation providers to leverage buying power through cooperative purchasing. (252 pages) Full-text PDF of this report is available for free download from: http://tti.tamu.edu/documents/0-6194-1.pdf

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Research and Technology Implementation Office

February 2011

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Research Digest Item 14 Estimated Impacts of the 2010 Census on the Texas Transit Funding Formula : Summary Report on Findings TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI)

TTI 6199-P1 • 2010 The purpose of this report is to document the impact of the projections for the 2010 Census on federal and state funding for rural transit districts and the impact on state funding for eligible urban transit districts. Appendices A and B document the IDSER projections of 2010 population and land area for each county and urbanized area (from Project 0-6199 Technical Memorandum #2, "Impact of Census 2010 on Population Factors Affecting Apportionment of FTA Funds and on the Designation and Population of Urbanized Areas in Texas"). The research approach for this task relies on the population and land area projections by county and urbanized area by IDSER (see Technical Memorandum #2). Researchers identified the changes in population and land area by transit district for existing rural and urban transit districts. Based upon the allocation of population and land area by transit district, researchers identified how new urbanized areas will affect current transit districts. Researchers developed three population growth scenarios to reflect the possible impacts of new urbanized areas. Researchers applied each of the population growth scenarios to the current Texas transit funding formula to identify the impacts on funding by transit provider. Based up on the outcomes of the funding analysis, researchers documented findings and key policy implications for application of the Texas transit funding formula based on projected changes in population and land area. (x, 108 pages) Full-text PDF of this report is available for free download from: http://tti.tamu.edu/documents/0-6199-P1.pdf

Item 15 Analysis and Recommendations on Protecting Waterways from Encroachment TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI)

TTI 6225-1 • 2010 The purpose of this project was to investigate and determine hazards to navigation (encroachments) in the Texas Portion of the Gulf Intracoastal Waterway (GIWW) that originate from shore, and to make recommendations for mitigating these hazards in the future. The research team collected various types of data to identify encroachment hazards and understand how and where obstacles are built including incident data from the U. S. Coast Guard; survey information from vessel operators; data from physical inspection of the waterway; survey information from developers, economic development corporations, and shippers; survey information from county and local officials in all coastal counties; and information on permitting procedures data from the various federal, state, and local jurisdictions involved with shoreline development. This study concludes that the major problems caused by development of structures that encroach into the waterway are the narrowing of the channel, lack of strategic mooring or push-in (hold-up) places needed in inclement weather, and congestion caused by additional inexperienced recreational boaters. This study results in a guidebook for permitters and a guidebook for developers on the types and quantity of structures that should be permitted along the GIWW. The guidebooks should help develop and permit “smart” development with regard to navigation through better cooperation between governmental agencies on permitting development and a focus on the agglomeration, clustering, and density of development on the waterway, and increased cooperation between developers, governmental agencies, and the barge industry in maintaining the GIWW for its primary use of moving goods effectively and efficiently to promote and support Texas and U.S. commerce. (182 pages) Full-text PDF of this report is available for free download from: http://tti.tamu.edu/documents/0-6225-1.pdf

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Research and Technology Implementation Office

February 2011

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Research Digest Item 16 Development of the Texas Revenue Estimator and Needs Determination System (T.R.E.N.D.S.) Model TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI)

TTI 6395-TI-1 • 2010 The original purpose of Project 0-6395-TI was to assess the usefulness and viability of the Joint Analysis Using Combined Knowledge (J.A.C.K.) model as a planning and forecasting tool. What originally was named the J.A.C.K. model was substantially revised, expanded and renamed the Texas Revenue Estimator and Needs Determination System (T.R.E.N.D.S.) model. The T.R.E.N.D.S. model is designed to provide transportation planners, policy makers and the public with a tool to forecast revenues and expenses for the Texas Department of Transportation (TxDOT) for the period 2010 through 2035 based on a user-defined level of transportation investment. The user, through interactive windows, can control a number of variables related to assumptions regarding statewide transportation needs, population growth rates, fuel efficiency, federal reimbursement rates, inflation rates, taxes, fees and other elements. The output is a set of tables and graphs showing a forecast of revenues, expenditures and fund balances for each year of the analysis period based on the user-defined assumptions. The version of the model developed under this project is a beta-test version to solicit comments from metropolitan planning organizations (MPOs) across the state. (76 pages) Full-text PDF of this report is available for free download from: http://tti.tamu.edu/documents/0-6395-TI-1.pdf

Item 17 Assessment and Validation of Managed Lanes Weaving and Access Guidelines UNIVERSITY OF TEXAS AT ARLINGTON (UTA)

UTA 5578-1 • 2010 The goal of this project was to establish spacing requirements for access points to managed lanes with respect to the location of entrance and exit ramps on the general purpose lanes of the freeway. Traffic entering the freeway destined for the managed lane must weave across the general purpose lanes. Traffic exiting the freeway from the managed lane must also perform this maneuver. The results are based on microscopic simulation using the VISSIM model. The simulation model was carefully calibrated using data collected on IH 635 (LBJ Freeway) in Dallas, Texas. A genetic algorithm was used in the calibration. The model was subsequently validated using data collected at a nearby site along IH 635. The weaving was analyzed as a Type C two-sided weave. Capacity was estimated by gradually increasing flow in the general purpose lanes for each set of conditions until the simulation model throughput was less than the input flows, indicating the formation of queues. The specific conditions included ramp flows (500 to 1250 veh/hour), ramp to managed lanes flows (100 to 400 veh/hour), general purpose lanes to managed lane flows (200 to 800 veh/hour), and length of weave (1000 to 4000 feet). The principal determinant for spacing was the weaving flow (ramp to managed lane flow), with a minimum weaving distance of 2000 to 3500 feet for flows from 200 to 400 veh/hour. A desirable minimum distance of 4000 feet was found. All results were for four general purpose lanes. (128 pages) Full-text PDF of this report is available for free download from: http://www.uta.edu/ce/faculty/williams/report0-5578-1.pdf

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Research and Technology Implementation Office

February 2011

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CTR Research Digest, Feb. 2011 issue