bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Steric Hardening Effect of Thin Asphalt Films in Presence of Aggregate Surface
Authors: Huang Shin-Che , Robertson Raymond E. , Branthaver Jan F. , McKay John F.
Published: April 2007

The interaction between asphalt and aggregate surfaces before and after low-temperature storage (reversible, irreversible, or both) at various film thicknesses was investigated by means of the sliding plate geometry with standard Pyrex glass plates and machined aggregate plates. The study of storage and setting in thin films of asphalts on aggregate surfaces indicates that asphalts interact differently and unpredictably with aggregate surfaces. The phenomenon of steric hardening in thin films appears to be retarded (compared with the same phenomenon in bulk asphalts) during short storage times but is enhanced in contact with aggregate surfaces after several weeks’ storage.
Laboratory Generation and Evaluation of Paving Asphalt Fumes
Authors: Kurek Joseph T. , Kriech Anthony J. , Wissel Herbert L. , Osborn Linda V. , Blackburn Gary R.
Published: April 2007

A novel laboratory asphalt fume generator was developed and validated against fumes collected on personnel monitors from field paving sites and above paving asphalt storage tanks. Once the apparatus was validated, fumes were generated from eight core Strategic Highway Research Program (SHRP) single crude asphalts, as well as from synthetically produced positive and negative control asphalts. The fumes were characterized using a number of analytical techniques, including gas chromatography/mass spectrometry, gas chromatography with flame ionization detection, UV/fluorescence, and a short-term bioassay called the modified Ames test. For comparison purposes, the same methods were applied to fume condensate preparations from the National Institute of Occupational Safety and Health (NIOSH) animal skin-painting studies. On the basis of the chemical and biological tests, these SHRP asphalt fumes were found to have a lower carcinogenic potential than a NIOSH fume fraction found to be noncarcinogenic in the NIOSH studies.
Detection of Coal Tar Materials in Asphalt Pavements by Using Chemical and Biological Methods
Authors: Blackburn Gary R. , Kriech Anthony J. , Kurek Joseph T. , Osborn Linda V.
Published: April 2007

Recent reports have linked exposure to asphalt fumes to higher rates of cancer in workers employed in mastic asphalt pavement operations in Denmark. The conclusion that asphalt fume exposure was responsible for cancer rests heavily on the proper connection for or the absence of confounding exposures, especially to coal tar fumes. Coal tar was used in paving in Denmark before and during World War II. However, significant debate has occurred about when its use was discontinued. Potential methods for detecting coal tar in historically dated pavements placed in the city of Copenhagen were examined. It was found that there are clear chemical marker compounds and tests that can determine the presence of coal tar materials in an asphalt aggregate mixture. The results of a short-term biological test called the modified Ames assay also correlated well with the presence or absence of coal tar–derived materials. Results show that coal tar usage in Denmark extended until at least 1970.
Comparison of Field- and Laboratory-Generated Asphalt Fumes
Authors: McCarthy Bernard M. , Blackburn Gary R. , Kriech Anthony J. , Kurek Joseph T. , Wissel Herbert L. , Osborn Linda V.
Published: April 2007

Studies conducted by the National Institute of Occupational Safety and Health (NIOSH) evaluated the carcinogenicity of fumes collected from a catalytically prepared roofing asphalt at 232°C and 316°C using a laboratory generator. The fume condensate from these studies was found to cause a carcinogenic response. However, the uniqueness of the roofing asphalt and the laboratory-generation method makes it difficult to assess the meaning of this study in the context of paving asphalt. Fumes from paving asphalt operations were compared compositionally with the fumes generated and used in the NIOSH animal studies. In addition, the impact of temperature on asphalt fume composition was examined. The results showed that fume composition is greatly affected by the conditions under which the fume is generated, the design of the laboratory fume generator having the most significant effect on the type of fume produced. Fumes collected at field paving sites bear little resemblance chemically to the roofing fume used in the animal study. Most important, the compounds most likely responsible for the carcinogenicity in the animal studies were not present in fumes found in the field paving sites studied.
Field Performance of Modified Asphalt Binders Evaluated with Superpave Test Methods: I-80 Test Project
Authors: Anderson David A. , Maurer Dean , Ramirez Timothy , Christensen Donald W. , Marasteanu Mihai O. , Mehta Yusuf
Published: April 2007

In the early 1980s heavy-duty pavements in Pennsylvania showed evidence of excessive rutting. As a consequence, the Pennsylvania Department of Transportation adopted several changes in its materials specifications and mixture design procedures. In addition, a number of modified binders were evaluated in an experimental test road that was constructed in 1989 in Clearfield County on Interstate 80. The construction was a 175-mm thick asphalt concrete overlay over an existing portland cement concrete pavement. Although the construction predated Superpave, original samples of the asphalt binder and loose asphalt mix were retained and were characterized using Superpave test methods. Field performance evaluations were performed immediately after construction and in subsequent years, giving a record of rutting, cracking, raveling, and overall visual performance. Overall, the mixtures have performed well during their 9 years of service. However, differences in the performance of the mixtures with the different binders are evident. These differences are related to the properties of the binder and the properties of the mixture as measured with the Superpave mixture and binder tests.
Collaborative Evaluations of Low-Temperature Superpave Performance-Graded Asphalt Binders
Authors: Wegman Dan , Weigel Jack , Forsberg Alan
Published: April 2007

Superpave developed the specifications and selection of performance-graded asphalt binders to address performance in the field. To facilitate the implementation of Superpave, highway agencies are sharing information and working with industry. Wisconsin, Iowa, and Minnesota have collaborated to develop a joint certification program to streamline the process and promote partnerships with suppliers. The low-temperature grading of the Superpave asphalt binders is of special interest in severe climates. Several projects are examined that have incorporated Superpave asphalt binders, including new construction, reconstruction, overlays on rehabilitated highways, and overlays on existing highways. The projects vary from low-volume highways to high-volume Interstates to an airport in an extremely severe climate. The projects, which have been in place for several years, have been evaluated for their field performance, especially for behavior at low temperatures. The new asphalt binders have been found to increase the resistance to thermal cracking on newly constructed roads and to inhibit reflective cracking on overlays.
Chemical and Rheological Characteristics of Styrene-Butadiene-Styrene Polymer-Modified Bitumens
Authors: Lu Xiaohu , Isacsson Ulf
Published: April 2007

Styrene-butadiene-styrene (SBS) polymer-modified bitumens were prepared in the laboratory and characterized using rheological and chemical methods. The results showed that morphology of the modified binders was influenced by bitumen composition and polymer content. Polymer modification was found to improve the rheological properties of bitumens. The degree of modification was dependent on the base bitumen and SBS content and structure. It was also observed that aging resulted in degradation of the SBS polymer. Changes in the rheological properties of aged modified binders were dependent on a combined effect of bitumen oxidation and polymer degradation, which varied with the source and grade of bitumen and type and content of polymer. Generally, the aged modified binders showed better rheological properties than aged base bitumens. The study also indicated that aging index is not suitable for evaluating the aging susceptibility of polymer-modified binders.
Mechanism of Interaction of Asphalt Cement with Crumb Rubber Modifier
Authors: Abdelrahman Magdy A. , Carpenter Samuel H.
Published: April 2007

The nature of the interaction process between asphalt cement and crumb rubber modifier (CRM) has not been fully understood. Two main types of mechanisms that affect the produced binder properties are reported: particle swelling and degradation (devulcanization and depolymerization). These mechanisms occur as the binder is subjected to different combinations of interaction time and temperature. Insight into the mechanisms by which the interaction between the two materials takes place through monitoring the changes in the rheological parameters of the binder is provided. The effects of the interaction process variables, time and temperature, are explained. The effect of CRM properties, including particle size and material source, is also discussed.
Airport Privatization: Issues for the United States
Authors: De Neufville Richard
Published: April 2007

The worldwide trend to privatize airports has led Congress to direct the Federal Aviation Administration to experiment with privatization. Because there always is a public interest in the operation of major commercial airports, which are both vital assets to the community and potential monopolies, it is generally impractical to transform airports into wholly private businesses. Most privatization projects involve substantial regulation of the private investors, detailing the design of airport services, the prices charged, and their openness to users. Worldwide experience provides three lessons: ( a) U.S. airports are among the most privatized in the world, and there is little scope for privatization in the United States compared to elsewhere; ( b) Major aspects of airport direction must remain under government control because of the public interest in these facilities; and ( c) Privatization takes a long time because the process requires considerable negotiation between the stakeholders in the airport business, and there are no simple solutions. The fundamental choice in the privatization is how the government should sustain the public interest in open access to and fair rates for airport services. The major alternatives are ( a) government regulation, an inherently adversarial process; or ( b) government ownership and partnership in the development of airports, a more collaborative approach. The partnership approach, applied by airport authorities throughout the United States and Canada, is arguably the better alternative in practice. It assures the public interest in fair operations and permits local communities to express their needs for sufficient airport capacity.
Development of a New Orientation Index for Airport Terminals
Authors: Dada E. S. , Wirasinghe S. C.
Published: April 2007

Some people have difficulty locating their destinations in airport terminals in spite of the availability of signs. The reasons for this wayfinding problem are numerous, and they include the complexity of the terminals as well as the wayfinding aids within them. An improved quantitative measure of human orientation called the visibility index (VI) is investigated. The effects of the number of signs or decision points and the number of level changes on visual access were investigated in an experiment in a complex building at The University of Calgary. A relationship between the slowness in reaching a destination, the number of decision points, and the number of level changes was developed. A survey of 32 common terminal activity centers was conducted. The ranks and weights of these activity centers were determined based on responses of airport users at three airports. The weight and the slowness factor were incorporated into the VI model, which was tested at Vancouver International Airport.
Options for Airport Approach Noise Control: Flight Procedures, Aircraft Certification, and Airport Restrictions
Authors: Caves R. E. , Kershaw A. D. , Rhodes D. P.
Published: April 2007

The use of larger aircraft and high-bypass engines has made the approach noise at airports more critical, but the methods used to control it rely on rather tenuous relationships between aircraft noise certification and the noise experienced by the communities around airports. Also, the options for alleviating approach noise are perceived to be fewer than for the takeoff case. The effect of a variety of possible approach flight procedures is explored. All of these procedures terminate in a conventional 3-degree final glide path, on the maximum noise levels under the flight path. In comparison, the effect of varying the glideslope angle on noise at the approach certification point is reported. It is concluded that the most promising procedures for alleviating noise in the areas some distance from an airport are the Continuous Descent and the Decelerating approaches. The current use of these techniques is limited by the incompatibility with air traffic control procedures. The more severe noise levels closer to the runway threshold could be significantly alleviated by the use of steeper approaches without serious consequences for the aircraft operators. It is argued that, if the airports are to be discouraged from their current practice of unilaterally imposing environmentally induced constraints on operations, a modified noise certification procedure is needed that better relates to the actual behavior of aircraft and the location of the disturbance. Options for this are considered, and it is concluded that only a full systems analysis—including airlines, air traffic control, airports, and the regulators—can synthesize an effective noise control methodology.
Systems Engineering Framework To Assess the Impacts of Very Large Capacity Aircraft in Airport Operations and Planning
Authors: Trani Antonio A. , Venturini Alceste P.
Published: April 2007

A methodology is presented to investigate the effect of Very Large Capacity Aircraft (VLCA) operations at existing and future airports. The procedure that is described investigates airport and airline impacts of VLCA operations using a systems engineering approach to understand the trade-offs between economic and technological operational factors. Specific topics discussed in this analysis are ( a) the effect of VLCA on airport capacity, ( b) development of new geometric design guidelines, ( c) landside impacts and gate compatibility issues, ( d) airside capacity impacts, and ( e) possible noise and pavement design impacts. These aspects are modeled using the Systems Dynamics methodology, which permits a blend of technological and socioeconomic variables into the same model. Realistic parametric templates of feasible aircraft designs are defined using computer methods, and the impacts of proposed designs in airport operations, capacity, and economics are explored. The analysis focuses on the airside and landside capacity, geometric design constraints, and pavement and acoustic impacts of VLCA operations. A systems engineering perspective is used when aircraft design inputs have quantifiable outcomes on airport capacity, on infrastructure changes, and ultimately, on the cost of operations. Cost-effective ways to facilitate the operations of VLCA at existing and future airports are identified, including new design guidelines.
Runway Overrun Risk Assessment
Authors: Caves R. E. , Kirkland I.
Published: April 2007

It is likely that, in the near future, airports in the United Kingdom will be asked to show that they have recognized the risks of their individual operations and have minimized them as far as is practicable. Normal protection for the aircraft is provided in the International Civil Aviation Organisation’s Annex 14 by the 60-m strip at the end of a runway and a recommendation for the installation of a Runway End Safety Area of at least 90 m. In fact, airports vary considerably both in the likelihood of incurring an overrun and in the consequences. Annex 14 provides protection almost regardless of individual airport circumstances. Individual risk studies would be an expensive operation if they were carried out for each airport. An alternative proposition would be to carry out one risk study using data that have taken account of the differences in operations, the results of which would be applicable to every airport. This would result in a simple risk assessment tool that could be used by aerodrome staff with no risk-assessment experience. The methodology that is to be used and preliminary results are reported.
Rail’s Share of Airport Access: Examining the Data
Authors: Newmark Gregory
Published: April 2007

Currently, many U.S. cities are exploring the possibility of constructing rail connections to their airports. The perceptions of rail’s role in serving ground-access needs may not be in accordance with what is actually experienced at existing airport rail systems. Data from these existing systems could help planners forecast ridership at proposed new systems. The data from existing systems is not always reported in a consistent manner that facilitates the useful comparison of airport rail systems. This lack of information is addressed. Comparable data on current ridership at eight airport rail stations are provided, and a standard method for collecting these data is presented, along with common sources of error that can lead to misrepresentations of airport station rail ridership. In addition to this discussion of the data collection process and its pitfalls, cross-checking techniques and suggestions for improved future data generation are detailed. Current ridership trends are also included. The findings show that most airport rail connections serve less than 6 percent of air passenger needs and between 8 and 14 percent of airport employee ground-access needs. Furthermore, the examination of the published data demonstrates the many ways in which error can affect the calculations and subsequent presentation of these statistics.
Measured Pile Setup During Load Testing and Production Piling: I-15 Corridor Reconstruction Project in Salt Lake City, Utah
Authors: Attwooll William J. , Holloway D. , Rollins Kyle M. , Esrig Melvin I. , Sakhai Si , Hemenway Dan
Published: April 2007

As part of the I-15 Corridor Reconstruction Project through downtown Salt Lake City, nine sets of full-scale load tests were performed at locations selected as representative of the subsurface conditions along the corridor alignment. Static compression, uplift, and lateral load tests were conducted at each test site location. The test program included dynamic monitoring of pile installation and restrike events using high-strain testing and analysis methods. Dynamic test results from restrike events on companion piles compared well with the measured static axial compression load test capacities. Subsurface conditions along the alignment range from deep clays to dense alluvial sands above the groundwater table. The piles derive their support from shaft friction or a combination of shaft friction and endbearing, depending on the strata present. The test and subsequent production piles are consistently indicating large capacity gains with time (setup), regardless of the subsurface conditions. The setup in the soft to stiff lakebed clays is attributed to remolding of the clays during pile driving and subsequent reconsolidation. The setup in the dense sands is comparable with setup described by others in dense marine sands. Relationships were developed to predict long-term pile capacity based on dynamic test results from the end of installation and on data from the beginning of restrike. These relationships are being used during production pile installation and restrike events as an integral part of pile evaluation, troubleshooting, and quality control/quality assurance acceptance procedures.
Measured Time Effects for Axial Capacity of Driven Piling
Authors: Long James H. , Kerrigan John A. , Wysockey Michael H.
Published: April 2007

The results of a study to quantify effects of time on pile capacity are presented herein. The main focus of this paper is to present results from a database developed from various pile tests reported in the literature and to present some observations based on the pile test data. Both sands and clays are shown to experience setup. A database containing 80 pile load tests (both static and dynamic) was collected and sorted into three groups according to the primary subsurface profile: sands, clays, and mixed soil. Capacity-versus-time relationships are plotted for each soil type, but particular attention is given to the increase in capacity of pile in sand with time. It is shown that the load test results can provide an upper-bound estimate and a lower-bound estimate. Estimating the effect of time on pile capacity in sand can be important for reuse of existing piling and also can be helpful for quantifying just how much to expect capacity to increase with time if pile load tests show that capacities are coming up short.
Characterization of Pile Capacity with Time in the Cooper Marl: Study of Applicability of a Past Approach To Predict Long-Term Pile Capacity
Authors: Camp William M. , Parmar Harpal S.
Published: April 2007

The Cooper Marl is a massive geological group, consisting of stiff, cohesive calcareous soils, which serves as the bearing stratum for the large majority of deep foundations in the Charleston, South Carolina, area. It has long been recognized that piles driven into the material experience tremendous setup, or capacity gain with time. Numerous driven piles that bear within the Cooper Marl have been statically or dynamically tested at various times after installation. This pile-testing database has been used to backcalculate the coefficients of a logarithmic expression ( Q/Q0 - 1 = Alog t/t0) that predicts pile capacity gain with time. For the largest data set, composed of 305-mm (12-in.) prestressed concrete (PSC) piles, the calculated coefficients are fairly similar, which seems to support the viability of the method and use of the equation. By using the calculated coefficients, long-term pile capacity of 305-mm (12-in.) PSC piles driven into the Cooper Marl should be able to be predicted based on the results of short-term restrike or load test data. The data also indicate that the coefficients of the expression are dependent on the pile size and that the rate of the capacity gain with time generally decreases as the pile size increases.
Numerical Procedure for Predicting Pile Capacity—Setup/Freeze
Authors: Titi Hani H. , Wije Wathugala G.
Published: April 2007

In geotechnical engineering practice, the increase over time of pile capacity after installation is sometimes referred to as pile setup or freeze. Pile setup, which is often associated with piles driven into saturated clays and silts, is mainly attributed to soil consolidation around the pile. Field observations have shown that pile setup is significant and continues to develop for a long time after pile installation. Pile foundations are usually expensive. Therefore, taking a small percentage of pile setup into consideration will result in cost reduction and savings in piling projects. This paper presents a general numerical procedure to predict pile setup by simulating the behavior of the pile during its different life stages: installation, subsequent consolidation, and loading. The Hierarchical Single Surface modeling approach, the strain path method, and the nonlinear finite element analysis of porous media were used in the analyses. The procedure was verified by successfully predicting the field behavior of pile segment models installed into soft marine clay. Numerical experiments were also conducted to demonstrate the applicability of the numerical procedure to full-scale driven piles. Piles with diameters of 0.3 m and 0.5 m and a length of 10 m were considered in the analyses.
North Carolina Department of Transportation Experience with Predesign Load Testing
Authors: Fargher John , Abar Nariman , Batts Jamey , Keaney Brian , Byrne Sean
Published: April 2007

Load test programs performed in the predesign stage provide the greatest potential for savings in more economical foundation designs. The North Carolina Department of Transportation’s (NCDOT) first experience with predesign load testing was on the Neuse River Bridge project in 1994. The practice was used on all major bridges thereafter. This paper presents a case history of those projects detailing the load testing, outcome, and estimated cost savings. Through the case history, the paper discusses both the successful application of load test programs and the results that were achieved. A description of the NCDOT’s experience and practice of predesign load testing of deep foundations is presented. The philosophy and considerations used by the NCDOT to evaluate and develop load test programs are discussed. The effects on design and construction practices that have resulted from load testing and experiences in mitigating constructibility problems and construction claims through the use of load test programs are described. The progression of the NCDOT’s load test experiences and integration of new load test technologies are also presented.
Value of Methods for Predicting Axial Pile Capacity
Authors: Long James H. , Bozkurt Diyar , Kerrigan John A. , Wysockey Michael H.
Published: April 2007

The purpose of this paper is to compare the value of predicting capacity using dynamic formulas, wave equation analysis, and dynamic monitoring without load tests. A database of pile load test results is used to quantify the precision associated with predictive methods. These methods are quantified and ranked using a “wasted capacity index” (WCI) to quantify the effect of precision. The WCI is a measure of how inefficiently a method predicts capacity. A precise method will be very efficient and accordingly have a low WCI. On the other hand, a less precise method requires a more conservative design and thus a greater WCI. The value of the wasted capacity index is calculated from the precision of the method and the reliability required for the pile foundation. The WCI is presented for the following methods: Engineering News (EN) formula, Gates formula, wave equation analysis program (WEAP), measured energy (ME) approach, pile driving analyzer (PDA), and CASE Pile Wave Analysis Program (CAPWAP).
Finite Element-Based Seepage Design Charts for Sheet Piles Penetrating Heterogeneous Media
Authors: Najjar Yacoub M. , Naouss Wissam A.
Published: April 2007

Seepage and exit-gradient quantities due to flow around sheet piles embedded in geological strata are of great significance to geotechnical bridge foundation engineers because these quantities play an essential part in producing an overall economical and efficient design. In this research study, an effective and accurate method for obtaining seepage and exit-gradient estimates under similar hydraulic structures was developed. To achieve this objective, the finite element method was successfully implemented for providing seepage and exit-gradient estimates under single sheet piles penetrating heterogeneous media. The data obtained from the numerical model were compiled and plotted to form different sets of design charts. These charts could be used efficiently for obtaining seepage and exit-gradient estimates under the aforementioned hydraulic structure. The results obtained from the finite element model were compared and verified against existing relevant mathematical approximation and other techniques. Designers and practitioners in the geotechnical bridge engineering fields would greatly benefit from these charts because of their simple yet accurate estimates. Moreover, the applicability of the developed design charts was demonstrated through solution of various design problems.
Using Video Data To Measure Vehicle Operating Modes for Prediction of Emissions
Authors: Botha Jan L. , Elia Jeffrey A. , Washington Simon P. , Young Troy M.
Published: April 2007

An alternative method for measuring vehicle modes of activity is examined. Emerging emissions models will require as input information on vehicle modes of operation, such as cruise, accelerations, decelerations, and idle. Measurement of vehicle modes of activity was carried out as part of a research project for which the overall objective was to determine a procedure or protocol for estimation of modal activity distributions for different road facilities. Video data collection was one of the methods used to measure modal activity. The video data collection and analysis process is described, preliminary findings and lessons learned are presented, and future needed research is identified. A major finding was that the video method enabled collection of large amounts of data that may not be possible to collect with instrumented vehicles. Although a standard for the required accuracy of modal activity data does not exist, it appears that questions regarding the accuracy of the video data may have to be resolved. Another major conclusion is that, on the basis of the video data, comparisons of modal activity distributions for different freeway sections and flow rates indicate that there are no statistically significant differences between modal activity distributions when acceleration is considered, but speed distributions in some cases varied significantly. Since the freeway sections considered do not reflect all possible freeway types and driver populations, the conclusions cannot be generalized. However, they do provide some important insights into the variability of modal activity for emissions predictions on the basis of data for commuters in California.
Forecasting Dynamic Vehicular Activity on Freeways: Bridging the Gap Between Travel Demand and Emerging Emissions Models
Authors: Roberts Craig A. , Washington Simon , Leonard John D.
Published: April 2007

New emissions models for predicting carbon monoxide, hydrocarbons, and oxides of nitrogen require as input not only average speed but various measures of dynamic vehicular activity such as accelerations, decelerations, and idle events as well. Current travel demand modeling of transportation networks does not provide estimates of dynamic vehicular activity but, instead, forecasts traffic volumes and travel speeds. Simulation models could provide estimates of dynamic vehicular activity, but simulation models are not used or validated for the development of regional emissions inventories. Until simulation models are used for regional planning purposes, improvements to travel demand models (TDMs) must be forthcoming if the benefits of new emissions models are to be realized. There are at least two solutions for bridging the gap between TDM outputs and new, data-intensive emissions models. The first solution is the development of statistical models that forecast dynamic vehicular activity as a function of TDM outputs: average traffic speeds and volumes. The second solution is the identification of mutually exclusive and collectively exhaustive regions of the speed-flow regime whereby representative dynamic driving sequences or cycles are characteristically different, particularly with respect to vehicular emissions. The present focus is on dynamic activity on freeways. A brief background of the research problem is first provided, along with stated research goals. The field study conducted to collect the necessary data on freeways is then described. The statistical task of identifying homogeneous regions of the speed-flow regime with respect to emissions activity is then discussed. Finally, the process by which typical dynamic driving activity is generated is given, followed by research conclusions and issues that require further study.
Estimating Emissions and Fuel Consumption for Different Levels of Freeway Congestion
Authors: Barth Matthew , Scora George , Younglove Theodore
Published: April 2007

To improve upon the speed correction factor methodology used by conventional emission models (i.e., MOBILE and EMFAC), the Environmental Protection Agency is introducing in its latest version of MOBILE (version 6) a new set of facility-specific driving cycles. These cycles represent driving patterns for different facility types (e.g., highway and arterial) and congestion conditions. Using a state-of-the-art comprehensive modal emissions model developed under NCHRP Project 25-11, one is able to predict the integrated emissions and fuel use values for these cycles for a wide variety of vehicle-technology categories. These facility-congestion results are then compared with steady-state emissions-fuel use measurements that were made in deriving the modal model. Furthermore, cruise modes that have mild speed perturbations are also investigated. All of these results are then compared with the speed correction equations used in the conventional emissions factor models. It is found that the mild acceleration perturbations at high speeds can lead to significantly higher emissions compared with the steady-state values. Because of this, the new high-speed freeway driving cycles (representing higher levels of service) in many cases have (modeled) emissions higher than those for the cycles that represent lower levels of service. Fuel consumption by speed does not change drastically in the comparisons.
Integrated Approach to Environmental Rating for Light Vehicles
Authors: Thomas Martin , DeCicco John
Published: April 2007

Consumer education and other market-oriented approaches to environmental protection require coherent information on the environmental performance of the products in question. Although light-duty vehicles are a focus of numerous federal and state policies, information on the environmental performance of vehicles is fragmented. Heightened interest in market-oriented approaches motivates the development of a more integrated approach to motor vehicle environmental information. An environmental rating methodology for light-duty vehicles was developed on the basis of principles of life-cycle assessment and environmental economics. The method was designed given the limitations of the available data by make and model in the U.S. market. It combines the impacts of traditionally regulated (criteria) pollutants with those of greenhouse gas emissions, covering both the vehicle life cycle and the fuel cycle, by using a mass-based characterization of vehicle manufacturing impacts. This methodology was applied in a consumer-oriented publication that was first released in early 1998 that will be updated annually. The data issues, assumptions, and analysis methods used to develop these vehicle ratings are addressed. The application of the methodology to model year 1998 is summarized. Finally, research needs for updating and refining the methodology are identified.
Total Energy Cycle Energy Use and Emissions of Electric Vehicles
Authors: Singh Margaret K.
Published: April 2007

A total energy cycle analysis (TECA) of electric vehicles (EVs) was recently completed. The EV energy cycle includes production and transport of fuels used in power plants to generate electricity, electricity generation required to charge EV batteries, EV operation, and vehicle and battery manufacture. The key assumptions and results of the EVTECA are summarized. The total energy requirements of EVs are estimated to be 24 to 35 percent lower than those of the conventional, gasoline-fueled vehicles that they replace, whereas the reductions in total oil use are even greater: 55 to 85 percent. Greenhouse gas (GHG) emissions are 24 to 37 percent lower with EVs. EVs reduce total emissions of several criteria air pollutants [volatile organic compounds (VOCs), carbon monoxide (CO), and nitrogen oxides] but increase total emissions of others [sulfur oxide (SOx), total suspended particulates, and lead] over the total energy cycle. Regional emissions except possibly those of SOx are generally reduced with EVs. The limitations of the EVTECA are discussed, and its results are compared with those of other evaluations of EVs. In general, many of the results (particularly the results for oil use, GHGs, VOCs, CO, SOx, and lead) of the analysis are consistent with those of other evaluations.
Conducting Statistical Tests of Hypotheses: Five Common Misconceptions Found in Transportation Research
Authors: Washington Simon
Published: April 2007

Most statistical methods use hypothesis testing. Analysis of variance, regression, discrete choice models, contingency tables, and other analysis methods commonly used in transportation research share hypothesis testing as the means of making inferences about the population of interest. Despite the fact that hypothesis testing has been a cornerstone of empirical research for many years, various aspects of hypothesis tests commonly are incorrectly applied, misinterpreted, and ignored—by novices and expert researchers alike. On initial glance, hypothesis testing appears straightforward: develop the null and alternative hypotheses, compute the test statistic to compare to a standard distribution, estimate the probability of rejecting the null hypothesis, and then make claims about the importance of the finding. This is an oversimplification of the process of hypothesis testing. Hypothesis testing as applied in empirical research is examined here. The reader is assumed to have a basic knowledge of the role of hypothesis testing in various statistical methods. Through the use of an example, the mechanics of hypothesis testing is first reviewed. Then, five precautions surrounding the use and interpretation of hypothesis tests are developed; examples of each are provided to demonstrate how errors are made, and solutions are identified so similar errors can be avoided. Remedies are provided for common errors, and conclusions are drawn on how to use the results of this paper to improve the conduct of empirical research in transportation.
Incorporating Geographic Correlation When Sampling a Transportation Network
Authors: Pierce B. K. , Kinateder J. G.
Published: April 2007

Estimating characteristics of motor vehicles and their occupants based on sampling road segments and vehicles on those road segments is inherently a statistical sampling problem. An important aspect to sampling transportation networks that has not been previously examined in detail is addressed here; it incorporates the correlation between road segments in a traffic network into the sampling design. An approach for estimating the correlation between links in a transportation network is described, and a recommended approach for incorporating this correlation into the sampling design is presented. Also, the implementation and evaluation of these approaches relative to simple random sampling without replacement is illustrated by using four sampling scenarios typically encountered when sampling a transportation network.
Safety and the Choice of Degree of Curve
Authors: Hauer Ezra
Published: April 2007

Consider a horizontal curve set between two tangents forming a given deflection angle. Choosing a larger degree of curve (shorter radius) will make the tangents longer and the curve shorter and sharper. The question examined here is how this simultaneous change of several geometric elements affects the overall accident frequency. After a review of the relevant literature it is shown that increasing the degree of curve always increases the expected accident frequency. Also a simple way to compute the approximate amount of accident increase is described. It can be shown that the choice of degree of curve has large safety consequences when the deflection angle is large. This is not currently reflected in geometric design standards. It can also be shown that, contrary to commonly held opinion, adding x meters to the radius has the same effect on accident frequency regardless of whether the radius is 100 m or 1000 m. Finally, the effect of tangent length on curve accidents is added to the mix and a computational scheme to aid the selection of the degree of curve in specified circumstances of tangent lengths and deflection angle is provided.
Simplified Approach To Forecast Highway Crash Rates of Selected Special Population Subsets
Authors: Dissanayake Sunanda , John Lu J. , Chu Xuehao
Published: April 2007

Time series models developed by regression to forecast highway crash rates in association with some selected special population subsets are described here. Such models are useful for assessing the safety performance of the subsets because the problems inherent in subsets are different from those of the average highway population. They also enable high-risk groups to be identified, not only under present conditions but also in the future. Two sets of models were developed: one for the state of Florida and the other for United States. The population subsets considered included older drivers, young drivers, international tourists, and school-age children as nonmotorists. Among the different model formats tried, the negative exponential was the best fitting and gave reasonably good fitness, as indicated by considerably high R2 values varying from 0.784 to 0.974. The main purpose of the model building was to forecast the crash rates by each population subset at various time points within the study horizon. Previous studies by other researchers where forecast values were compared with actual values have indicated that most of the complex models were incapable of explaining the future situation. As such, the opinion of the authors is that simple models with year as the independent variable could be advantageous for forecasting the safety performance of the highway system for special population groups.
Development of Access Spacing Guidelines for Nonfreeway Weaving Environments
Authors: Jacobson Marc , Nowlin Lewis , Henk Russell H.
Published: April 2007

Access on the frontage road in close proximity to exit ramp terminals can amplify the amount and severity of weaving that occurs and can lead to operational and safety problems on the frontage road. Research activities directed at evaluating the operation of frontage roads with unsignalized marginal access located at different distances from exit ramp terminal points and developing guidelines for appropriate spacing under these conditions are summarized here. The basic research approach consisted of ( a) analyzing accident data; ( b) observing operations in the field to identify distances required to safely make weaving maneuvers; and ( c) developing an analytical model to predict the density of the weaving section on the frontage road as a function of frontage road volume, exit ramp volume, total driveway volume, frontage road configuration, and exit ramp to access spacing. The model was developed from the results of a computer simulation (using CORSIM) that was calibrated with field data from several frontage road sites in Texas. Results of the accident and weaving (field observation) analyses were used to develop a recommended minimum distance of 140 m between exit ramp terminal points and the nearest frontage road access; the analytical model was used to develop desirable spacing distances ranging from 140 to 300 m. The model was also used to identify possible level-of-service boundaries that can be used to assess the quality of service provided on a particular section of frontage road.
Effects of Access Control on Safety on Urban Arterial Streets
Authors: Brown Henry C. , Tarko Andrzej P.
Published: April 2007

Access control techniques are used to improve traffic performance and safety on highways. One important benefit of access control is improved safety. For a quantitative assessment of the benefits of access control on safety, impact models are needed to predict crash frequencies based on the geometric and access control characteristics of the segments. The objective of this research was to develop regression models to predict crash frequencies on urban multilane arterial segments. To develop these models, data were collected on geometric and access control characteristics of the segments and the number of crashes on the segments by severity type. Negative binomial regression models were developed to predict the total number of crashes, number of property-damage-only crashes, and number of fatal and injury crashes. The three models have a similar structure. The exposure-to-risk variables include segment length, number of years, and annual average daily traffic. The significant factors include density of access points, proportion of signalized access points, presence of an outside shoulder, presence of a two-way left-turn lane, and presence of a median with no openings between signals. The results indicate that access control has a beneficial effect on safety.
Effect of Speed Limit Increases on Crash Injury Severity: Analysis of Single-Vehicle Crashes on North Carolina Interstate Highways
Authors: Renski Henry , Khattak Asad J. , Council Forrest M.
Published: April 2007

The recent congressional action revoking the national maximum speed limits has rekindled the debate over safety and travel time tradeoff. The effect of speed limit increases on the most severe occupant injury in a crash is analyzed here. Single-vehicle crashes on Interstate highways in North Carolina ( N = 2729) are examined. Two analysis methods are used: a paired-comparison analysis and an ordered probit model. Increasing speed limits from 88.5 to 96.6 km/h (55 to 60 mph) and from 88.5 to 104.6 km/h (55 to 65 mph) increased the probability of sustaining minor and nonincapacitating injuries, but increasing speed limits from 104.6 to 112.7 km/h (65 to 70 mph) did not have a significant effect on crash severity. There were too few fatal crashes to draw conclusive results for this category of injury severity. Crashes involving the face of a guardrail were more severe on segments where the speed limit was raised than on comparison segments or study segments before the limits were increased. These findings may be conservative because study segments with good safety records were chosen for the speed limit increases.
Fatal Crash Rates in the Southeastern United States: Why Are They Higher?
Authors: Stamatiadis Nikiforos , Puccini Giovanni
Published: April 2007

The southeastern region of the United States has been experiencing consistently higher fatality crash rates compared with other regions of the country. This region also has a number of socioeconomic characteristics that differ from the national average, including lower median household income, higher percentages of the population below the poverty level, higher percentage of the area classified as rural, and lower percentage of high school completion and university attainment. It is then possible to assume that these socioeconomic characteristics could influence highway safety by affecting the age and type of vehicles owned, the condition of these vehicles, and the attitudes of the drivers toward safety and risk-taking behaviors. The objectives of this study were to identify potential socioeconomic factors that could contribute to the higher fatality crash rates in the Southeast and to develop preliminary relationships between socioeconomic characteristics and crash trends that could explain these higher numbers and rates. Driver and vehicle characteristics from the fatal accident reporting system database were related to socioeconomic and demographic census variables based on the zip code of the drivers’ residences. Crash rates were obtained by the quasi-induced exposure methodology for single- and multivehicle crashes. The results indicate that these socioeconomic characteristics have an effect on single-vehicle crashes but they have no significant effect on multivehicle crash rates.