bluuebunny/crossref_metadata_2025 huggingface dataset:
Method for Identifying Vehicle Movements for Analysis of Field Operational Test Data
Authors: Ayres Greg , Wilson Bruce , LeBlanc Jon
Published: April 2007

The independent evaluation of a roadway-departure crash-warning system will involve identifying and classifying conflicts and near-collisions from a vast quantity of field data. The classification of these events includes identifying vehicle movements such as negotiating a curve, making a turn, changing lanes, and merging. A unified algorithm that relies solely on vehicle kinematic data is developed for identifying such movements. The method works reliably for various types of road surfaces, road types, speeds, and conditions. The algorithm relies on metrics such as heading angle, lateral position, radius of curvature, and peak yaw rate—calculated from yaw rate and vehicle speed data—to classify vehicle-movement events from a large file of vehicle data. Tuning parameters for the algorithm, set both analytically and empirically, are provided. The results of the tests show that the algorithm makes correct identifications of vehicle movement about 80% of the time. The highest success is for turns, followed by curves and lane changes. Although these numbers improve on previous methods, there is additional room for improvement that gives impetus for future work.
User Perceptions and Preferences of Advanced Driver Assistance Systems
Authors: Molin Eric J. E. , Marchau V. A. W. J.
Published: April 2007

The introduction of electronic advanced driver assistance systems (ADASs) in road vehicles is expected to improve traffic efficiency and safety significantly. Successful implementation of these systems in the near future will largely depend on the willingness of people to buy and use these systems. This willingness is explored by estimating a model that specifies how ADASs are perceived in terms of contributing to personal driving goals and how these goals, in turn, influence overall preferences for ADAS. Therefore, drivers of cars and trucks throughout Europe had been requested to complete a stated-preference experiment in which they had to indicate to what extent they perceived that various ADAS alternatives would change their personal driving goals. In addition, drivers were requested to rate the selected ADAS descriptions in terms of overall attractiveness to have the described system in their vehicle. Structural equation modeling (SEM) has been applied to estimate simultaneously how the ADA subsystems are perceived in terms of personal driving goals and how the personal goals and price, in turn, affect overall preference. The results indicate that the different ADASs have different effects on the various personal goals. Furthermore, the results indicate that especially changes in safety and comfort levels affect overall preferences and to a lesser extent changes in travel time while fuel consumption has the least effect.
Regional Transit Program for Welfare to Work in Chicago, Illinois: Three Years Later
Authors: Hunt Kim L. , Czerwinski Jon
Published: April 2007

The impact of the welfare-to-work (WtW) regional public transportation program on participants in Chicago, Illinois, is reviewed 3 years after an initial study. The regional transportation program provided free transit passes and vanpool services to participants during their first 6 months of employment and training on regional transit options for job developers. WtW participants' travel patterns were noted, social service contractors were interviewed, and Temporary Aid to Needy Families (TANF) clients were examined. In 2000, pass use for WtW participants and regular 30-day pass users was determined to be almost identical because of the strong economy of the late 1990s. Three years later, travel patterns suggested that participants were beginning to find employment farther from home, many in the job-rich O'Hare Airport corridor, and that the costs and benefits of sending low-income workers to distant work locations needed to be assessed. Although providing fare subsidies that allow low-income workers to take advantage of existing infrastructure may be helpful, transportation solutions probably will not be enough to make a meaningful and sustained impact. The regional transportation program illustrates the need for holistic approaches to social policy. The disproportionate level of transit dependency, longer travel times, and significantly higher use of public transit in many of the Chicago communities that have the highest numbers of TANF clients than in the city as a whole point to a serious need for affordable housing near job centers in the Chicago region.
Development of Bay Area Rapid Transit System Expansion Criteria and Process
Authors: Deakin Elizabeth , Payne Marianne , Menotti Val
Published: April 2007

In 1999, the San Francisco Bay Area Rapid Transit (BART) District Board, in California, adopted a policy creating a framework for BART system expansion that placed new emphasis on cost-effectiveness, ridership generation, multimodal access, transit-oriented development, local partnerships, and the use of appropriate transit technologies. The board directed staff to develop criteria and a detailed process for implementing these goals. The resulting expansion planning process and criteria for the BART system, adopted by the BART board in December 2002, are described along with the method used to develop the criteria and process. Some of the implementation issues that have arisen are assessed. The process uses a strategic opportunities assessment as an initial sketch-planning evaluation tool and then applies criteria and a rating system to evaluate preliminary proposals as well as project alternatives that proceed to environmental review and beyond. The rating system also indicates to local jurisdictions the kinds of access and land development that would support a BART investment. As part of the process, localities are encouraged to prepare a ridership development plan that puts in place transit-supportive plans, zoning, infrastructure, and services. Extensive consultation with the board and other stakeholders helped build understanding of the issues and solid board support for the new planning process and criteria. Application of the new process has led to transit-supportive plans and zoning changes in several local jurisdictions. Some jurisdictions are not prepared to make the land use changes needed for a "high" project rating and are considering lower-cost transit alternatives.
Comparing Transit-Oriented Development Sites by Walkability Indicators
Authors: Schlossberg Marc , Brown Nathaniel
Published: April 2007

Transit-oriented development (TOD) represents an integrated approach to transportation and land use planning. An often unspoken but key component to TOD theory is pedestrian access between the transit stop and the immediately surrounding area. Understanding the opportunities for pedestrian movement should be a key component in understanding and evaluating TOD projects. The TOD-pedestrian link is addressed by using 12 geographic information system (GIS) based walk-ability measures, within two geographic scales, and across 11 TOD sites in Portland, Oregon, to visualize and quantify the pedestrian environments at each site. The main addition to the larger research on TOD and pedestrian access is the classification of the street network into pedestrian-friendly and pedestrian-hostile categories. Subsequent analysis based on this refined street data is conducted to identify the quantity of different street types, densities of "good" intersections and dead ends, and the catchment areas pedestrians are likely able to reach. The presence and location of pedestrian-hostile streets have a significant, negative influence on the pedestrian environment surrounding transit stops, often cutting off more-pedestrian-friendly environments from the transit stops. The three primary sections include a comparative TOD ranking, a detailed explanation (visual, quantitative, and textual) of the relationships between individual walkability measures and overall TOD rankings, and a presentation of possible refinements for future GIS-based walkability analysis.
Asset Management Strategy to Meet Long-Term Transit Fleet Needs of State Departments of Transportation
Authors: Khasnabis Snehamay , Bartus Joseph , Ellis Richard Darin
Published: April 2007

State departments of transportation (DOTs) that provide the bulk of matching funds to local transit agencies for the purchase of new buses are duly concerned about the escalating costs of new buses and the lack of sufficient funds to keep up with bus replacement. An asset management strategy is presented for state DOTs to meet their long-term fleet needs. It is a two-stage process: ( a) allocating capital dollars for the dual purpose of purchasing new buses and rebuilding existing buses (taking into consideration the needs of all the constituent transit agencies) and ( b) distributing funds among the agencies in an equitable manner. The proposed management strategy includes two optimization models. Model 1 attempts to maximize the weighted fleet life of all the buses that are being purchased and rebuilt for a given peer group, within the constraints of a fixed budget. Model 2 is designed to maximize the remaining life of the entire peer group composed of the existing buses as well as those being replaced or rebuilt. The need for every single bus that is eligible for replacement is addressed in the model through either replacement or rebuilding. A comprehensive case study depicting a 7-year planning cycle for the entire fleet of medium-sized buses in the state of Michigan is used to demonstrate the strategy. A plan for evaluating the strategy is also presented and demonstrated. Results show that the strategy is viable and that it can be used for the designated purpose with fleet data that are currently available to the transit agencies. Even though the strategy is demonstrated with medium-sized buses, it will function efficiently with buses of different sizes and with a different number of agencies.
Economic Benefits of Coordinating Human Service Transportation and Transit Services
Authors: Burkhardt Jon E.
Published: April 2007

In many communities, multiple public and private agencies and organizations provide transportation services to people who have special transportation needs. These providers often receive funding from many sources, including federal, state, and local government programs as well as charitable and nonprofit programs. Program-specific funds are often accompanied by service objectives for specific clienteles and by unique rules and requirements. If such transportation services operate separately, independently, and in an uncoordinated fashion, they frequently demonstrate serious economic and service problems. Coordination can address such problems. Coordination strives to maximize the efficient use of resources such as vehicles, personnel, and funding. It attempts to reduce service duplication, increase vehicle sharing, and improve service quality. It can lower the cost of providing transportation, and communities can apply the cost savings to increase service or simply reduce costs. New research has found that significant economic benefits—including increased funding, decreased costs, and increased productivity—can be obtained by coordinating human service agency transportation and transit services. Implementing successful coordination programs could generate combined economic impacts (after considering all costs) of about $700 million per year to transportation providers (human service agencies and transit agencies) in the United States. Total benefits (beyond those benefits accruing just to transportation providers) are even greater. Particularly successful coordination strategies include transit agencies providing trips for Medicaid clients, nontransit agencies providing Americans with Disabilities Act and other paratransit services, transportation providers shifting para-transit riders to fixed-route service, local human service agencies coordinating their trips, and communities expanding transit services into unserved areas.
Simulation-Based Evaluation of Electronic Energy Storage Devices in Buses for Reducing Emissions
Authors: Yu Lei , Munghor Leonard A. , Yi Ping , Teng Hualiang
Published: April 2007

Emerging concerns about emissions and increasing energy costs have led to interest in developing and applying electronic devices for energy storage (popularly known as flywheel batteries or simply flywheels) in transportation applications to recover the energy used in braking rather than dissipating it as heat. Each time a vehicle stops, its kinetic energy is dissipated as heat. Fuel is then used to accelerate the vehicle again. A flywheel energy storage device that stores the braking energy and then reuses it for acceleration has the potential to improve fuel economy and reduce pollution. It is important to evaluate the application of this technology in transit buses to assess better any need for increased development. A three-step computer simulation is used to evaluate the reduced emissions of carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxides (NOx) in a flywheel-equipped bus. First, drive cycles over which buses operate are specified. Second, because flywheel energy storage reduces the effects of acceleration and deceleration to the engine, the emissions models (which are sensitive to acceleration and deceleration modes) are identified and selected. Finally, emissions are computed and compared with emissions for a bus without a flywheel. Results indicate conceptually that the flywheel application reduces acceleration effects, which in turn significantly reduce emissions. It is therefore strongly recommended that the flywheel energy storage device be further researched for transportation applications.
City CarShare in San Francisco, California: Second-Year Travel Demand and Car Ownership Impacts
Authors: Cervero Robert , Tsai Yuhsin
Published: April 2007

Two years into the introduction of City CarShare in San Francisco, California, nearly 30% of members have gotten rid of one or more cars, and two-thirds stated that they opted not to purchase another car. By City CarShare's second anniversary, 6.5% of members' trips and 10% of their vehicle miles traveled were in carshare vehicles. Matched-pair comparisons with a statistical control group suggest that, over time, members have reduced their total vehicular travel. Because carshare vehicles tended to be small and fuel-efficient, per capita gasoline consumption and greenhouse gas emissions among members also appeared to go down. Suppressed travel likely reflected a combination of influences: reduced car ownership, more judicious and selective use of cars for particular trip purposes, and multiple-occupant carshare trips. Carsharing, however, has also enhanced mobility and allowed members to reach more destinations in and around San Francisco conveniently and to do so more quickly. Because it widens mobility choices and offers a resourceful form of automobility, carsharing is a welcome addition to the urban transportation sector in cities such as San Francisco.
Policy Considerations for Carsharing and Station Cars: Monitoring Growth, Trends, and Overall Impacts
Authors: Shaheen Susan A. , Schwartz Andrew , Wipyewski Kamill
Published: April 2007

Since the late 1990s, more than 25 U.S. shared-use vehicle programs—including carsharing and station cars—have been launched. Given the presumed social and environmental benefits, the majority of these programs received some governmental support, primarily in the form of start-up grants and subsidized parking. As of July 2003, 15 shared-use vehicle programs were in existence, including 11 carsharing organizations, 2 carsharing research pilots, and 2 station car programs. Over the past 5 years, membership in U.S. carsharing programs has experienced exponential growth. Despite this expansion, the social and environmental impacts and long-term sustainability of these services remain unclear. As part of a U.S. shared-use vehicle survey (August 2002 to July 2003), market growth and trends as well as limited, systematic evaluation of program impacts were documented. Although 80% of shared-use programs implement internal customer surveys (initially or as follow-up), few independent studies have been conducted to date. Across organizations, participant use and program benefits are measured with various study tools and metrics. Given current shared-use vehicle growth and the ongoing interest of policymakers and governmental agencies in this concept, a longitudinal monitoring approach to better understand market developments, social and environmental impacts, and targeted policy strategies is recommended. Furthermore, it is concluded that coordinated, programwide data collection (consistent survey instruments and performance measures) could enhance overall market awareness and the credibility of shared-use vehicle organizations in leveraging additional public support.
Interoperability Options for Shared-Use Vehicle Systems
Authors: Barth Matthew , Li Weixiang , Todd Michael
Published: April 2007

Different models of shared-use vehicle systems (SUVSs) continue to grow worldwide, in particular in North America. SUVS models include carsharing, station cars, and other system forms. In general, these models coinstitute fleets of vehicles used by several different individuals throughout the day. As these systems continue to expand in number and size, the need for interoperability will increase. Furthermore, interoperability will play an important role with other transportation modalities as well (e.g., transit). There have already been several discussions on interoperability in carsharing; the general idea is to allow a user from one system to use a different system easily when traveling in a different area or on a different mode (in the case of transit). Interoperability will likely result in higher customer convenience and satisfaction and lead to greater market penetration of this and other forms of transit. A number of interoperability issues for SUVSs are examined in detail, taking into account the point of view of the customer, the operator, and the vehicle manufacturer. Issues such as reservation systems, vehicle access, billing, and insurance are addressed. Several technical solutions for interoperability are proposed, drawing on similarities in the arenas of electronic toll collection and automated banking.
Free Transit for Low-Income Youth: Experience in San Francisco Bay Area, California
Authors: McDonald Noreen , Librera Sally , Deakin Elizabeth
Published: April 2007

In August 2002, AC Transit—the principal bus operator serving the eastern shore of the San Francisco Bay—began distributing free bus passes to low-income middle school and high school students in the transit service district. The program developed in response to grassroots community activism and growing political pressure to remove the burden of school transportation costs from low-income households. Advocates argued that school transportation costs were a barrier that prevented poor children from participating in after-school activities and, in severe cases, led to missed days of school. Funding for a pilot bus pass program was provided by the transit agency, the Metropolitan Transportation Commission, local agencies, and several nonprofit organizations. The University of California, Berkeley, was funded to carry out an evaluation of the program during the first year of the program. Before-and-after travel and activity surveys, interviews, focus group meetings, and analysis of attendance data were used in the evaluation. Findings after 1 year of implementation indicate that the free bus pass program increased student bus ridership and after-school participation but did not increase overall school attendance. Increases in bus use were greater among pass holders, in areas with high levels of bus service, and among high school students.
Transit Customer Response to Intelligent Transportation System Technologies: Survey of Northern Virginia Transit Riders
Authors: Conklin Joana , Englisher Larry , Shammout Khaled
Published: April 2007

The Northern Virginia Transportation Commission conducted a study to inventory and review transit-related intelligent transportation system (ITS) projects in the region, evaluate approaches to performance measurement, research the benefits associated with these projects, and establish an ongoing performance monitoring process. The project included interviews with transit managers and vendors and an intercept-mail-back survey of Northern Virginia transit riders. Results of the survey conducted in April 2003 are summarized. Surveys were distributed to more than 14,000 Northern Virginia transit riders at several large transit stations over the course of several weekdays. Approximately 16% of the transit riders who received the questionnaire responded. Specifically, the survey instrument addressed demographic and socioeconomic characteristics, use of computers and the Internet, attitudes toward the current use of technology on transit, the importance of various technology uses, behavior changes as a result of transit ITS, familiarity with and frequency of use of various ITS applications in Northern Virginia, and usefulness and ease of use of ITS applications. Overall, survey respondents were widely supportive of the current use of technology on transit services in the region and, to a large extent, supportive of expanded technology use. The currently offered transit ITS applications have generally been viewed as useful, and the feeling that they are easy to use is widespread— an important accomplishment for the region.
Transit District Customers in San Mateo County, California: Who, Why, Where, and How
Authors: Zhou Yushuang , Viswanathan Krishnan , Popuri Yasasvi , Proussaloglou Kimon E.
Published: April 2007

Faced with declining transit market share and increasing population and jobs, transit agencies must go beyond the traditional approach of trying to find the balance between maximizing ridership and meeting the needs of those who depend most on transit. Innovative approaches that account for customer perceptions and attitudes toward transit must make transit a more attractive option for customers. The efforts of the San Mateo County (California) Transit District (Sam Trans) to understand customer attitudes and perceptions and create market segments that reflect and account for traveler attitudes are reported. The study uses a structural equation modeling approach along with cluster analysis to identify market segments in the population that can be targeted for new services to be offered by Sam Trans. In addition, the results of the market segmentation are applied spatially so that Sam Trans can customize its response to address individual market areas. The results of the market segmentation were applied based on a mode choice model that determines the market share for competing automobile, bus, and enhanced transit modes. Sam Trans is provided with the means of identifying the spatial and modal distribution of their service market on the basis of customer needs. This approach allows Sam Trans to design transit services that compete more effectively in the target geographic markets addressing the needs of individual market segments.
Expansion of Airport Capacity at London Heathrow Airport
Authors: Janic Milan
Published: April 2007

Civil aviation has been confronted with the problem of matching its capacity to growing demand long term. This has been a particularly important issue at some large European and U.S. airports where increasing operational, economic, and, particularly, environmental constraints have affected expansion and development. The long-term matching of capacity to demand at London Heathrow Airport in England is discussed. This analysis includes predicting airport demand relative to annual number of aircraft movements and number of passengers, designing solutions for providing capacity, and generating scenarios for long-term matching of capacity to demand. The results indicate that until the year 2020 the airport will permanently struggle with congestion both airside and landside.
Trend Analysis of Controller-Caused Airspace Incidents in New Zealand, 1994-2002
Authors: Majumdar Arnab , Ochieng Washington Yotto , Nalder Peter
Published: April 2007

The New Zealand government takes airspace safety very seriously. The level of safety in New Zealand airspace is measured by the number of recorded airspace incidents. An airspace incident can be thought of as a failure in the chain of operations in the air traffic system when it is provided with air traffic service (ATS). Some of these incidents result in a loss of separation between aircraft, varying from slight to very serious with a significant risk of collision, known as a near collision. New Zealand's Civil Aviation Authority (CAA) identifies the causal factors for all airspace incidents with the Reason model of human error divided into three areas: active failures committed by individuals involved in the incident, local factors relating to the task and the ATS environment, and organizational factors originating in the managerial and organizational spheres of the ATS provider. On the basis of CAA's database, trends in controller-caused incidents in New Zealand airspace from 1994 through 2002 are analyzed in six categories: loss of separation, ATS coordination deficiency, near collisions, ATS clearance or instruction deficiency, ATS flight planning system deficiency, and ATS flight information deficiency. The results indicate that execution errors predominate for active failures, whereas poor concentration or lack of attention, inadequate checking, and controller workload are the dominant local factors. For the organizational factors, inadequate control and monitoring, inadequate specifications and procedures, and poor resource management dominate. These results can be used for a better understanding of controller working practices and ATS organization for enhanced airspace safety.
Throughput Effect of Time-Based Metering at Los Angeles International Airport
Authors: Hansen Mark , Peterman Dale
Published: April 2007

The throughput effect of Traffic Management Advisor (TMA) metering for Los Angeles International Airport was estimated with censored regression. Under TMA metering, traffic management coordinators receive advisories about when individual flights should be scheduled to enter the terminal area, accounting for the unimpeded time and constraints related to separation requirements and capacity constraints. Tests of TMA metering at Los Angeles began in spring 2002; mandatory use during the morning peak period started in November 2002. This analysis focuses on observed counts during periods when metering is and is not in effect and takes into account other relevant factors such as weather, visibility, and demand. Demand is used as a censoring variable that places an upper limit on the observed count. A significant increase in achievable arrival throughput under instrument conditions was found in the morning peak period, but a significant decrease was observed under visual conditions. These results are consistent with field reports, which suggest that under visual meteorological conditions, TMA was assigning unnecessary metering delays. The success of the censored regression methodology in capturing these effects suggests that it would be useful for various other applications in which the effect of some event on airport capacity must be ascertained.
Airfield Pavement Condition Assessment
Authors: Greene J. , Shahin M. Y. , Alexander D. R.
Published: April 2007

The current methodology used by the U.S. Air Force for assessing and rating airfield pavement condition is presented. Factors addressed in the ratings include the pavement-condition index (PCI), structural index, friction characteristics, and foreign-object damage (FOD) potential. The PCI is a score from 0 to 100 that is determined by a visual survey of pavement distress based on procedures in ASTM D 5340. The structural index is a ratio of the aircraft classification number (ACN) to pavement classification number (PCN). ACN represents the structural impact an aircraft will have on a pavement, and PCN represents the structural capability of the pavement to support aircraft. Friction characteristics are primarily determined for runways through the use of a variety of measuring equipment. The FOD index is used to indicate the potential for FOD problems generated by the pavement; it is determined on the basis of pavement distresses collected during the PCI survey. Also presented are procedures used in determining each of the above factors and the ways in which these factors are used collectively to determine the overall rating of airfield pavements.
National Park Service Road Inventory Program: Quality Assurance Sampling Considerations for Automated Collection and Processing of Distress Data
Authors: Selezneva Olga , Mladenovic Goran , Speir Richard , Amenta James , Kennedy James
Published: April 2007

The National Park Service Road Inventory Program (RIP) uses automated collection and processing of pavement-condition data. The study examines various approaches to quality assurance (QA) sampling used to evaluate those data. The RIP includes automated collection and processing of pavement-condition and roadside-inventory-feature data at 258 national parks, covering over 5,000 mi of paved roads. Evaluating the quality of some data elements requires manual data assessment conducted by trained data analysts. Because of the high volume of the collected and processed data, it is economically impractical to check quality of all data manually. To overcome this difficulty, a search for an appropriate QA data sampling methodology was conducted. The goal of the investigation was to determine appropriate statistical procedures and required sample sizes so that conclusions based on QA sample testing could be extrapolated to the whole data set with a certain level of confidence. Evaluation of QA sampling approaches, including the selection of statistical procedures for QA testing, determination of QA sample sizes, and development of the procedures for evaluating the QA testing results applicable to the RIP, is presented. The results will be of interest to practitioners involved in automated collection of pavement data and to researchers involved in the design of statistical testing procedures for engineering QA applications.
Infrared Thermography for Asphalt Crack Imaging and Automated Detection
Authors: Oloufa Amr A. , Mahgoub Hesham S. , Ali Hesham
Published: April 2007

A research project evaluated the application of infrared thermography for the detection of asphalt cracking. Such detection has generally relied on image processing of pictures and videos of asphalt produced by analog and digital cameras that operate in the visual range of light. The presence of shadows, poor light conditions, white cracks, and a variety of other problems have presented serious challenges to automated crack identification and detection in this frequency region. The research reported here is primarily aimed at testing the hypothesis that asphalt cracks cause changes to surface conditions and emissivity, leading to perceived temperature differentials that can be exploited by infrared detectors in cameras. The research involved the production of tens of images from both conventional and infrared cameras. Several parameters were evaluated for both flexible and rigid pavements, including choice of infrared detection range, various lenses, and exposure during day and night hours. Under the right conditions, infrared thermography can yield superior results and allow the identification of tiny cracks about 1 mm in width, which are virtually impossible to detect with conventional cameras.
Context-Sensitive Design: Will the Vision Overcome Liability Concerns?
Authors: Jones Richard O.
Published: April 2007

During the 1960s the American public began to demand transportation projects with less impact on the community and its environment, even at the cost of reduced safety and mobility. Congress enacted laws and established public policy objectives to protect and enhance the nation's environment and cultural resources. More recently, Congress has encouraged flexibility in highway design to accomplish these objectives. AASHTO, TRB, state departments of transportation, and FHWA have developed a process, which has come to be called context-sensitive design/context-sensitive solutions (CSD/CSS), to meld design with these objectives. The process is envisioned to result in a transportation project reflecting community consensus on purpose and need, with project features addressing equally safety, mobility, and protection and enhancement of the natural environment. This vision requires the exercise of flexibility in design—the balancing of competing interests. Some are concerned that increased exposure to tort liability will result should design standards or guidelines become too flexible, because they would fail to treat safety as a paramount concern. This assumes that safety is considered a paramount concern both in transportation design and in tort law. This assumption is shown to be erroneous; Congress has established statutory requirements and public policy clearly demonstrating that safety, while it is a primary consideration in design, is not to be a paramount consideration. Safety should be balanced with mobility, protection and enhancement of the natural environment, and preservation of community values. Some court decisions, particularly in the federal sector, recognize and grant design immunity to policy judgments that balance competing interests in the design process. Ultimately, tort law must coincide with public opinion and public policy to be in the public interest. Therefore, tort law will adjust to accommodate CSD/CSS processes, reducing liability exposure. CSD/CSS decisions must be documented with a view of telling the whole story to juries in future tort litigation. Such documentation will greatly assist agency counsel in explaining and proving the reasonableness of design decisions in the context within which they were made. The CSD/CSS vision, it is believed, will overcome liability concerns, both in the short term and in the long term.
Midwest Guardrail System for Standard and Special Applications
Authors: Faller Ronald K. , Polivka Karla A. , Kuipers Beau D. , Bielenberg Robert W. , Reid John D. , Rohde John R. , Sicking Dean L.
Published: April 2007

Development, testing, and evaluation of the Midwest Guardrail System were continued from the original research started in 2000. This new strong-post W-beam guardrail system provides increased safety for impacts with higher-center-of-mass vehicles. Additional design variations of the new system included stiffened versions using reduced (half and quarter) post spacings as well as a standard guardrail design configured with a concrete curb 152 mm (6 in.) high. All full-scale vehicle crash tests were successfully performed in accordance with the Test Level 3 requirements specified in NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features. The research study also included dynamic bogie testing on steel posts placed at various embedment depths and computer simulation modeling with BARRIER VII to analyze and predict dynamic guardrail performance. Recommendations for the placement of the original Midwest Guardrail System as well as its stiffened variations were also made.
LS-DYNA Simulation Influence on Roadside Hardware
Authors: Reid John D.
Published: April 2007

Several new roadside safety appurtenances that can be directly linked to the use of nonlinear finite element analysis with LS-DYNA are being installed along the nation's roadways. These advances can be attributed to FHWA's sponsored research program known as Centers of Excellence in DYNA3D Analysis. Some of the simulation efforts at the Midwest Roadside Safety Facility over the past 10 years are documented to help educate the roadside safety engineer and to promote the use of simulation. Noteworthy progress has been made in the use of LS-DYNA for the design and analysis of roadside safety hardware, and it is believed that a great deal more progress is possible.
Aesthetic Initiative Measurement System: A Means to Achieve Context-Sensitive Design
Authors: Nassauer Joan Iverson , Larson David
Published: April 2007

The aesthetic character and visual quality of transportation corridors as seen by local and visiting travelers in Minnesota were investigated. Highway corridor landscapes were broadly defined to include the entire "view from the road." This definition is intended to contribute to the substance of context-sensitive design by selecting characteristics of landscapes seen from the road that will be relevant for highway design and planning. It assumes that highway travel experiences can have a significant effect on the perceived attractiveness of the places where people live, work, and travel. The aesthetic initiative measurement system (AIMS) was developed and tested to provide a method for the Minnesota Department of Transportation (MnDOT) to use to understand and monitor how travelers perceive the attractiveness of Minnesota's highway corridors and to inform planning, design, construction, and maintenance decision making with specificity. Development of the AIMS methodology involved MnDOT staff from several disciplines and local citizens in understanding perceptions of the value of Minnesota's highway planning, design, engineering, and maintenance choices. AIMS researched the problem of identifying what landscape characteristics seen from the highway are noticed for their aesthetic quality by travelers. AIMS measured the relative aesthetic value of those characteristics and then used those measurements to document the benefits for design and planning to monitor and compare landscape aesthetic values across space and time.
Overlooked Local Sediment Scour Mechanism
Authors: Sheppard D. Max
Published: April 2007

A heretofore overlooked mechanism is described for the removal of sediment in the vicinity of a structure, such as a bridge pier, located in erodible sediment and subjected to water flow. The strength of this mechanism depends on, among other things, the ratio of structure width to sediment grain size, b/D50. The mechanism results from the pressure gradient field imposed on the bed by the mean flow around the structure. The large pressure gradients created by the structure are confined to a relatively narrow region near the structure. The forces due to the pressure gradients acting on the sediment grains near the structure decrease with increasing values of b/D50. This mechanism helps explain the functional dependence of equilibrium local scour depth on b/D50 observed in both laboratory and field tests. It also explains why, in general, physical model local scour tests tend to overpredict prototype scour depths.
Evaluation of Use of Synthetic Lightweight Aggregate in Hot-Mix Asphalt
Authors: Mallick Rajib B. , Hooper Frederick P. , O'Brien Sean , Kashi Mohsen
Published: April 2007

Successful use of synthetic lightweight aggregates made from waste fly ash and plastics can help in conserving mineral aggregates and reusing waste materials. The objective of this study was to evaluate the use of synthetic lightweight aggregate made from waste fly ash and plastics in hot-mix asphalt. The scope of this laboratory study included preparation of aggregate blends and mixes with different percentages of synthetic lightweight aggregates, compaction of samples, testing of samples, and analysis of results. Mixes were made with 0%, 5%, 10%, 15%, and 20% synthetic lightweight aggregates by weight of aggregates. Tests included bulk specific gravity, theoretical maximum density, resilient modulus, and indirect tensile strength at 25°C on unconditioned and conditioned samples as well as rut testing with wheel tracking equipment at 60°C. Test results were analyzed statistically to determine the effect of synthetic lightweight aggregates on hot-mix asphalt properties. The results indicate that the inclusion of synthetic lightweight aggregates enhances stiffness and resistance against rutting and moisture-induced damage of hot-mix asphalt. A relatively high absorption was noted for mixes containing 20% synthetic lightweight aggregates. The main conclusions are that synthetic lightweight aggregate has excellent potential for being used as part of hot-mix asphalt, and 15% by weight of aggregate appears to be an optimum amount for use. Further work should be pursued to determine the effect of synthetic lightweight aggregate on low-temperature properties of hot-mix asphalt.
Aggregate Orientation and Segregation in Laboratory-Compacted Asphalt Samples
Authors: Hunter Alistair E. , Airey Gordon D. , Collop Andrew C.
Published: April 2007

Different laboratory compaction methods can produce volumetrically identical asphalt mixture specimens but with widely varying mechanical properties. Provided that the mixture design is constant, variations in mechanical properties are probably due to differences in the structure of the aggregate-bitumen matrix. The objective of this study is to investigate the structure of the internal aggregate-bitumen matrix created by different laboratory compaction methods and compare it with mechanical performance. Three types of laboratory compaction are considered: gyratory, vibratory, and slab. Image analysis techniques have been used to provide quantitative information on the orientation and distribution of aggregates on horizontal planes within asphalt mixture specimens, and the results indicate that circumferential alignment of aggregate particles occurs in gyratory and vibratory compacted specimens. This behavior is more pronounced for larger aggregate particles and in those with an aspect ratio (maximum length/maximum width) greater than two. Slab-compacted specimens display a more random particle orientation. The distribution and segregation of aggregates has been considered relative to the center of each horizontal asphalt-specimen cross section. While overall levels of aggregate particle density are similar across all compaction methods considered, greater segregation occurs in vibratory-and gyratory-compacted specimens. Repeated load axial testing was done on specimens compacted by each method. The results indicate higher resistance to deformation in the vibratory- and gyratory-compacted samples than in volumetrically identical slab-compacted samples.
Comparison of Falling-Head and Constant-Head Techniques: Estimating Field Permeability of Hot-Mix Asphalt Pavements
Authors: Hall Kevin D.
Published: April 2007

Permeability of hot-mix asphalt continues to generate considerable interest in the asphalt materials, design, and construction community. Ongoing studies of permeability report advances in permeability testing techniques for both laboratory-based and field-based testing methods. The University of Arkansas (UAF) has developed a constant-head field permeability test device for use on in-place asphalt pavements. One constructed test section and 16 in-service pavements, including both new construction and overlays of existing pavements, were tested with the UAF device and a falling-head field permeameter originally developed by the National Center for Asphalt Technology. At each field test site, cores were taken from the pavement and tested in the laboratory by the falling-head, constant-tail method described in ASTM PS-129. At a minimum, two field permeability measurements were taken at each site with each permeability device; at least three cores were taken from each test site for testing in the laboratory. The total data set for this study includes more than 40 direct comparisons of each field method and the laboratory results. The data indicate that falling-head and constant-head field methods yield significantly different permeability results but display similar test variability (based on replicate tests). Further, field permeability measured by the falling-head method was significantly different from corresponding laboratory results, while constant-head field results were not significantly different from laboratory results. Relative differences between field devices in the initial applied hydraulic head and the test area footprint may contribute to observed differences.
Effect of Moisture Damage on Material Properties and Fatigue Resistance of Asphalt Mixtures
Authors: Kim Yong-Rak , Little Dallas N. , Lytton Robert L.
Published: April 2007

Dynamic mechanical analysis (DMA) has been used successfully to evaluate complex characteristics of fatigue damage and fracture of asphalt binders and mastics by measuring fundamental viscoelastic properties and damage characteristics. DMA was used to define the effect of moisture on fatigue damage and to concentrate on the fatigue damage susceptibility of the sand and asphalt mixture mastic fraction. Dynamic frequency sweep and time sweep tests were performed on cylindrical sand-asphalt samples in a dry state and after being subjected to moisture saturation. Test results clearly indicate that moisture reduces viscoelastic stiffness, fatigue resistance, and eventually fatigue life of sand-asphalt. The mechanistic role of moisture in fatigue was analyzed and quantified by using nonlinear viscoelastic theory based on pseudovariable concepts and a continuum damage fatigue model. The effect of material surface energies, which is strongly related to fracture and damage, is further discussed by using DMA fatigue test results and varying surface energy characteristics of individual mixture constituents. The DMA experimental procedure and analysis is an efficient way to identify the influence of moisture and to compare sand-asphalt mixtures in terms of moisture susceptibility.
Application of Genetic Algorithm in Asphalt Pavement Design
Authors: Tsai Bor-Wen , Kannekanti Venkata Narasimham , Harvey John T.
Published: April 2007

The main purpose of this study is to demonstrate the applicability of the genetic algorithm (GA) to solve nonlinear optimization problems encountered in asphalt pavement design. The fundamentals of the GA are briefly discussed, and three case studies are presented. The first case study is an example showing the backcalculation of layer moduli with deflection data from a falling weight deflectometer and a layered-elastic program. The second case study demonstrates how to construct the master curve, either from a mix flexural frequency sweep test or from a binder rheometer test, and how to apply the master curve in pavement design. The last case shows how to apply the GA to characterize the binder discrete relaxation spectrum with a generalized Maxwell solid model. The results indicate that the GA is successful in resolving the nonlinear optimization problem. The GA presents some difficulty in terms of computing efficiency; however, several techniques have been developed to alleviate this problem.
Effect of Different Axle Configurations on Fatigue Life of Asphalt Concrete Mixture
Authors: Chatti Karim , El Mohtar Chadi S.
Published: April 2007

The fatigue life of an asphalt mixture under different truck axle configurations was determined directly from the indirect tensile cyclic load test by using load pulses that were equivalent to the passage of an entire axle group or truck. The dissipated energy approach was adopted in analyzing the results and determining the number of repetitions to failure for each case; a unique fatigue curve that can be used for multiaxle configurations was developed. Trucks consisting of up to 11 axles and axle groups of up to 8 axles were studied. The results indicated that the normalized damage per load carried decreased with an increasing number of axles within an axle group. Additionally, the fatigue lives predicted by using single load pulses were compared with the measured ones from the different axle groups and trucks.