bluuebunny/crossref_metadata_2025 huggingface dataset:
Rural Two-Lane Passing Headways and Platooning
Authors: Gattis J. L. , Alguire Mary S. , Townsend Kristy , Rao Shreenath
Published: April 2007

Field observations and video records were made at three northwest Arkansas locations where vehicles on a two-lane rural highway encountered passing/climbing lane sections. At all three sites, vehicles had traversed roadway sections with limited passing opportunities before they encountered passing sections on slight to moderate upgrades. By studying traffic at such sites, one can observe the behaviors of motorists who may have been restrained by slower traffic ahead, but who then encounter a relatively unconstrained environment that allows them to pass if they have been displeased or frustrated with any constraint. It was concluded from the data that at higher traffic volumes (450 vehicles per hour or higher in one direction), the arrival rate of vehicles in the samples taken probably did not follow a Poisson distribution. A simple linear regression equation was developed to express the proportion of vehicles in platoons as a function of the total one-direction traffic volume. Two of the sites had shorter passing lanes, whereas the passing lane at the third site was almost twice as long as those at the other two sites. Passing success declined when headways were greater than 2.0 sec. At both the short-passing-lane and the long-passing-lane sites, when headways were 3.0 sec or more and platoon speeds were 80 kph (50 mph) or more, 85 percent of drivers did not exhibit a desire to pass. This suggests that many drivers find a low level of congestion or platooning on two-lane rural roads to be tolerable.
Effects of Inadequate Driveway Corner Clearances on Traffic Operations, Safety, and Capacity
Authors: Gan Cheng-Tin , Long Gary
Published: April 2007

Inadequate driveway corner clearances can result in traffic operational, safety, and capacity problems. These problems can be caused by blocked driveway ingress and egress movements, incomplete turning maneuvers, conflicting intersection turning movements, confusing right-turn signal indications, insufficient weaving and merging section lengths, and various other conflicts. The effects of driveway corner clearances on safety cannot be examined easily through safety records given the current condition of the available crash and system inventory data. This provides incentives for applying theoretical traffic conflict analysis. A simple conflict analysis showed an increase in merging and crossing conflict points for driveways situated near intersections. Inadequate corner clearance can have a capacity-reducing effect. Driveway capacity may be reduced by ( a) vehicles on the arterial blocking driveway egress movements and ( b) a decreased opportunity for left-turn egress movement on arterial streets designed for platoon progression. Intersection capacity can also be reduced by a decrease in saturation flow rates due to driveway ingress and egress movements.
Model for Minimum Driveway Corner Clearances at Signalized Intersections
Authors: Long Gary , Gan Cheng-Tin
Published: April 2007

A signalized intersection typically operates under both saturated and undersaturated traffic flow conditions at different times of the day. When an intersection operates under saturated flow conditions, its ability to dissipate traffic becomes a primary matter of concern. On the other hand, safety is often the major concern due to higher vehicular travel speeds associated with undersaturated flow conditions. The minimum corner clearance distances required under the two different flow conditions are not the same. To be effective, minimum corner clearances must be set such that the needs under both types of flow conditions are satisfied. Existing guidelines for minimum corner clearances were reviewed, and none were found to address the capacity issue. A new model designed to meet both capacity and safety needs is proposed. The model produces a refined minimum corner clearance distance by applying a set of adjustment factors to an initial minimum corner clearance, a procedure similar to that of the familiar Highway Capacity Manual for adjusting the ideal saturation flow rate. Unlike existing guidelines, the proposed model is flexible, is much less discrete for continuous variables, and can easily incorporate as many factors affecting corner clearance as needed.
Operational Impact of Split Intersections
Authors: Polus Abishai , Cohen Ronen
Published: April 2007

High volumes at urban and suburban intersections may cause considerable delay to vehicles during the peak periods, particularly when the left-turning volume is combined with high through volumes in both directions. The operational impact resulting from converting a major conventional cross intersection into two smaller signalized intersections is analyzed and evaluated. The two intersections are constructed along the minor road, allowing the left-turn movement from the major road to operate simultaneously with the through movement and to be stored in more lanes on the minor road. The general advantages and disadvantages of a split intersection are discussed. It is shown that the split increases capacity because of better efficiency resulting from ( a) the smaller geometry of each intersection, which reduces “lost time,” compared to the geometry of a single larger intersection, ( b) a reduction in the number of signal phases from four to three and an increase in the effective green time for all movements, and ( c) an increase in the number of lanes available for storage of the left-turn movement. It is also shown that delay is reduced, particularly when the flow is close to saturation. The impact of the cycle length and the left-turn volume is evaluated. Further analysis ascertains the minimum distance between the two smaller intersections under two scenarios: ( a) a minimum distance for storage of the left-turn movement and ( b) a longer distance to reduce delays and to allow for the simultaneous start of the green time for the through movements in the two intersections. It is concluded that the longer distance is feasible mainly for new intersections in suburban areas where the right of way is available.
Operating Speed on Suburban Arterial Curves
Authors: Fitzpatrick Kay , Shamburger C. Brian , Krammes Raymond A. , Fambro Daniel B.
Published: April 2007

Free-flow speeds were collected at both a control section and a curve section at 14 surburban sites with horizontal curves and 10 suburban sites with vertical curves. The scatter plots of the 85th percentile speed versus approach density indicate that when the approach density is between 3 and 15 approaches per km, approach density does not influence speed. Regression analysis indicated that the curve radius for horizontal curves and the inferred design speed for vertical curves can be used to predict the 85th percentile speed on curves for vehicles on the outside lane of a four-lane divided suburban arterial. For horizontal-curve sites, a curvilinear relationship exists between curve radius and the 85th percentile speed. A linear relationship provided the best fit between the inferred design speed and the 85th percentile speed for the vertical curve sites. For the horizontal and vertical curve sites, the speed at which 85th percentile speed becomes less than the inferred design speed is lower for suburban arterials than for rural highways. Drivers on suburban horizontal curves operate at speeds greater than the inferred design speed for curves designed for speeds of 70 kph or less, whereas on rural, two-lane roadways, drivers operate at speeds greater than the inferred design speed for curves designed for speeds of 90 kph or less. For vertical curves, the speeds at which drivers operate greater than the inferred design speed are 90 kph for suburban arterials and 105 kph for rural highways. These results are within 12 kph of the observed 85th percentile speeds on nearby control sections (approximately 80 kph for suburban arterials and 100 kph on rural highways).
Formulation and Validation of Operating Speed-Based Design Consistency Models by Bootstrapping
Authors: McFadden John , Elefteriadou Lily
Published: April 2007

Current U.S. policy for designing rural two-lane highways is based on design speed to ensure consistency among consecutive highway segments. The design speed concept, however, does not ensure that a consistent alignment will be achieved. A recent FHWA-sponsored project (Horizontal Alignment Design Consistency for Rural Two-Lane Highways) led to three operating speed-based geometric design consistency models, which have not yet been validated. Traditionally, the validation of such models involves the collection of additional data. The statistical technique known as “bootstrapping” was used to formulate and validate the operating speed-based geometric design consistency models by using the existing FHWA database. Bootstrapping involves random sampling with replacement from the existing database, which becomes the population. One-half of the original data collected are used in formulating the models. The remaining half of the data are subsequently used for validation. The models resulting from bootstrapping were statistically equivalent to the models developed in the FHWA study. In addition, the model validation indicated that the bootstrapping technique used to validate the operating speed models is a viable alternative means of validation. It was concluded that bootstrapping is a very useful tool that can be exploited in many related areas in the transportation field, especially because of the large amounts of data typically required in developing and validating empirical models.
Enhanced Technology Transfer Through Strategic Planning, Partnering, and Model Integration
Authors: Anderson John A. , Kilareski Walter P. , Goodspeed Charles H.
Published: April 2007

A new approach to technology transfer (T2) under way at the Pennsylvania Local Technical Assistance Program (LTAP) is presented. The approach arose from a need to increase T2 efficiency and effectiveness. The model and processes draw from functional theories and methods within the areas of business, education, evaluation, and organization. T2 is a dynamic and complex process often treated and associated with the more concrete disciplines of training and education. Until recently, little existed to conceptualize and apply a systematized deployment and assessment of T2 intended for infrastructure improvement in transportation. The processes and models presented offer creative responses to pertinent issues in this area. Strategic planning principles based on Bryson’s model for public and nonprofit organizations, coupled with network-based decision-making software used by the Pennsylvania LTAP center, are described. Strategic objectives common to other key organizations were identified to arrive at a partnering scheme that penetrates three organizational functions: strategic operations, product/service development, and implementation/marketing. Central to this partnering scheme is a new T2 integration model. This customer-driven model provides a framework for integrating strategic objectives among partners, a basis for guiding shared research and development activities, a systematic and economic approach to T2, and a methodology for evaluating T2 effects. Critical issues in transportation T2 are addressed, and proactive responses and practical steps now under way in Pennsylvania are offered.
New Partnership Between Universities and State Departments of Transportation in the Rocky Mountain Area: The TEL8 System
Authors: Wilson Eugene M. , Ksaibati Khaled
Published: April 2007

In 1995, the Mountain-Plains Consortium in the Rocky Mountain area initiated TEL8. TEL8 is a satellite-based telecommunications system serving 10 sites in FHWA’s Region 8. Each site consists of in-room audio and video equipment that receives and transmits live sound and picture, coding/decoding compression equipment, and a satellite transmission system. Each site is capable of sending and receiving signals from other sites in several modes of conferencing ranging from broadcast to multipoint two-way conferencing. The goals of TEL8, its development, and lessons learned are presented along with cost data for this cutting-edge technology. The many applications, including formal graduate course work, informally scheduled learning opportunities, and open communication forums, are also discussed. The system provides a network for interaction among the six departments of transportation and four regional universities. A user assessment of this form of distance learning is compared with more traditional forms using results of several client-based surveys.
Using Technology To Help Overcome Institutional Obstacles to Improved Crash Records Processing
Authors: Miller John S.
Published: April 2007

Although advanced technologies have the potential to improve crash records processing, a number of recurrent institutional properties must be examined to comprehend the limits and rewards of these technologies. These properties include the diversity of crash-data users and providers, the dynamic nature of crash records processing, and the lack of a single entity that reaps all the benefits and bears all the costs of crash records processing. Although not inherently bad, these properties contribute to a number of problems with crash records processing, such as lack of access to crash data, inconsistencies among crash data bases, and disincentives to implementing new technologies or organizational changes that would make crash data more accessible, timely, or practical. With data obtained from a comprehensive inventory of Virginia’s computerized crash records systems, the feasibility of using technology to address these properties and the resultant problems was examined. A framework for assessing whether a proposed change will help solve short-term problems or overcome long-term obstacles was proposed.
Geographic Information System Platform for Road Accident Risk Modeling
Authors: Saccomanno F. F. , Chong K. C. , Nassar S. A.
Published: April 2007

Road accident risk assessment requires a thorough understanding of both the vehicle accident involvement process and the severity of resultant injuries. A geographic information system (GIS) platform is especially suited to this type of problem because it provides an efficient system of linking a large number of disparate data bases, it provides a spatial referencing system for reporting output at different levels of aggregation, it allows input of both historical and statistical accident experience in estimating accident risk at different locations and times, and it allows controls on a myriad of risk factors explaining variations in accident involvement and injury severity. A GIS-based accident risk model developed for the Ontario highway network is described. The model provides estimates of accident risk at four levels of spatial aggregation as specified by the user: networkwide, route-specific, route-section-specific and site-specific.
Effect of Median Treatment on Urban Arterial Safety: An Accident Prediction Model
Authors: Bonneson James A. , Mccoy Patrick T.
Published: April 2007

The development of a model for predicting the safety of an urban arterial street with a specified median treatment is described. The median treatments considered are raised-curb median, two-way left-turn lane (TWLTL), and undivided cross section. The model calibration was based on maximum-likelihood techniques, an assumed negative binomial distribution of the residuals, and a nonlinear relationship between accident frequency and daily traffic demand and segment length. Several conclusions were formulated on the basis of the model developed. One conclusion is that average daily traffic demand, driveway density, unsignalized public street approach density, median type, and adjacent land use are significantly correlated with accident frequency. In general, accidents are more frequent on street segments with higher traffic demands, driveway densities, or public street densities. Accidents are also more frequent when the land use is business or office as opposed to residential or industrial. The undivided cross section was shown to have a significantly higher accident frequency than the TWLTL or raisedcurb median treatment when parallel parking is allowed on the undivided street. When there is no parking allowed on either type of street, the difference between the undivided, TWLTL, and raised-curb median treatments is less distinct; however, the raised-curb median treatment tends to yield the lowest accident frequency in most situations.
Age and Gender as Predictors of Injury Severity in Head-on Highway Vehicular Collisions
Authors: Mercier Cletus R. , Shelley Mack C. , Rimkus Julie B. , Mercier Joyce M.
Published: April 2007

Whether age or gender or both influenced severity of injuries suffered in head-on automobile collisions on rural highways was assessed. The initial hypothesis was that, because of physiological changes, and possibly other changes related to aging (including loss of bone density), older drivers and passengers would suffer more severe injuries when involved in head-on collisions. Results of logistic regression analysis indicate that four separate factors, incorporating 14 individual and interactive variables, were strongly related to injury severity. Individual variables included age of driver or passenger (either linear or quadratic), position in the vehicle, and form of protection used, along with a set of interactive variables (such as age and position). The importance of age-related effects in injury severity is verified by hierarchical and principal components logistic regression models, amplifying findings of exploratory stepwise logistic analysis. Variations in findings resulted when the population was divided by gender. Although age remained a very important factor in predicting injury severity for both men and women, use of lap and shoulder restraints appeared to be more beneficial for men than for women, while deployed air bags seemed more beneficial for women than for men.
Relationship Between Volume-to-Capacity Ratios and Accident Rates
Authors: Zhou Min , Sisiopiku Virginia P.
Published: April 2007

The general relationships between hourly accident rates and hourly traffic volume/capacity ( v/c) ratios were examined. A 26 km (16 mi) segment of Interstate I-94 in the Detroit area was selected as the study segment. The v/c ratios were calculated from average hourly traffic volume counts collected in 1993 and 1994 from three permanent count stations. Accident rates were derived from hourly distributed number of accidents in the same 2 years. The correlation between v/c values and accident rates follows a general U-shaped pattern. The study of all observed accidents combined indicates that accident rates are highest in the very low hourly v/c range, decrease rapidly with increasing v/c ratio, and then gradually increase as the v/c ratio continues to increase. U-shaped models also explain the relationship between v/c and accident rates for weekdays and weekend days, multivehicle, rear-end, and property-damage-only accidents. On the other hand, single-vehicle, fixed-object, and turnover accidents, and accidents involving injury and fatality follow a generally decreasing trend with increasing v/c ratio. Traffic conflict is viewed as a major contributing factor to high accident rates observed in the high v/c range, whereas night conditions and driver inattention were identified as explanatory factors for the occurrence of high accident rates in the low v/c ranges.
Occurrence of Secondary Crashes on Urban Arterial Roadways
Authors: Raub Richard A.
Published: April 2007

Analysis of incidents and crashes occurring along urban arterial roadways suggests that as many as 15 percent of the crashes occurring along these roadways may have been, in part, caused by an earlier incident. To conduct the analysis, data covering reported vehicular crashes, fires, disablements, traffic enforcement, and other incidents affecting roadways were collected from seven contiguous urban municipalities in the Northern Chicago, Illinois, metropolitan region. Crashes represented 35 percent of the incidents; traffic enforcement, 30 percent; and disabled vehicles, 27 percent. Other events represented the remaining 8 percent. To associate an initial event with a subsequent crash, any crash that occurred on roadways affected by the primary event, within the duration of the primary event plus 15 min, and within 1600 m of that event (based on use of geographic information systems software) was assumed to have been related. Analysis of 1,796 incidents in the data base identified 97 secondary crashes related to 81 initial incidents. A random sample of all events in the data base showed that only 3.6 percent of the crashes instead of 15 percent might be expected to fall within the required temporal and spatial limits in relation to an earlier event. This finding suggested that the selected events may not have been random occurrences. Finally, analysis of the secondary crashes showed that 1 of every 10 may have been related to an earlier crash; 1 of every 11 to a disabled vehicle, and up to 1 of every 40 to a police stop for a major traffic violation. What must be studied in greater detail is the degree of relationship between the initial event and the subsequent crash. This can only be done through better crash reporting, in which officers clearly indicate any associated events that may have been contributing factors.
Seasonal Variation in Frequencies and Rates of Highway Accidents as Function of Severity
Authors: Brown Bruce , Baass Karsten
Published: April 2007

After a study of the identification of dangerous highway locations in Quebec, the appropriateness of comparisons with U.S. statistics was questioned. It was noted that between 30 and 50 percent of highway accidents in Quebec are associated with harsh meteorological conditions, including rain, snow, hail, and icy conditions, and it was implied that these conditions would contribute to a poorer safety record. To better understand the seasonal variation of highway accidents, monthly numbers and rates of highway accidents of differing severities were examined. The analysis uses all police-reported accidents associated with numbered roads in the Montérégie region of Quebec between 1989 and 1992. Monthly rates of victims per 100 million vehicle km traveled are calculated, as well as the frequency (number) of victims deceased, severely injured, and with minor injuries. Material-damage-only accidents are similarly tabulated. The lowest numbers and rates of death and serious injury occur in winter months. However, accidents with material damage only are most frequent, and have their highest rates, in winter months. Winter is associated with low mortality and serious injury and high numbers and rates of minor accidents. There is a negative correlation between the monthly rankings of injury rates when severe injuries and deaths are compared with material-damage-only accidents. These results underline a point that deserves more attention: conditions associated with mortality and serious injury are in many ways distinct and different from conditions associated with minor injuries and material-damage-only accidents and are poorly, and even negatively in the present example, correlated with these conditions.
Effects of Air Bags on Severity Indexes for Roadside Objects
Authors: Council Forrest M. , Mohamedshah Yusuf M. , Stewart J. Richard
Published: April 2007

The effects of vehicle air bags on the severity of off-road, fixed-object crashes as indicated by the effect that the air bag has on severity indexes (SIs) for fixed objects were studied. In an earlier study, preliminary indications based on data from one state were that the presence of an air bag might reduce SIs for various fixed objects by 35 to 75 percent. This study extends that work by adding data from two other states and from additional crash years. Severe-injury SIs were developed for different roadside objects for two samples of late-model vehicles, one with air bags and one without. The states chosen for use in this effort were those in which injury could be linked to a specific object struck. The data also were chosen to reflect a newer vehicle fleet (i.e., vehicle year 1989 or later) and more recent crashes (i.e., those occurring between 1990 and 1994). Although there were some inconsistencies within classes of objects and between states, analyses indicated that the air bag appears to be related to decreases in the proportion of serious or fatal driver injuries of 10 to 30 percent for point objects such as trees and utility poles, 40 to 50 percent for guardrails, and 10 to 20 percent for other barriers. For many of the objects tested, the results were not statistically significant, probably because of the sample sizes available.
Use of Centrifuge and Numerical Modeling in Design of Pier 400 at the Port of Los Angeles
Authors: Muraleetharan Kanthasamy K. , Arulmoli Kandiah , Wittkop Richard C. , Foxworthy John E.
Published: April 2007

Port of Los Angeles (POLA) is involved in the creation of 235 ha (580 acres) of new land called Pier 400 by dredging and landfilling behind rock dikes. Because of the complicated nature of the project, POLA chose a fully coupled, elastoplastic, dynamic finite-element code called DYSAC2 as part of the seismic design of Pier 400. The predictions made by DYSAC2 were first validated using dynamic centrifuge model tests. Centrifuge model tests consisting of gravel dikes retaining sand backfills overlying stratified foundation soils also provided insight into the expected deformation mechanisms of Pier 400 cross sections. Centrifuge models indicated that the dikes will move more or less as a rigid block with most of the lateral deformations being concentrated in the foundation soils. These observations were confirmed by analyses of centrifuge models and Pier 400 cross sections using DYSAC2. Because of the rigid body movement of the dikes, a hybrid analysis procedure, between simplified Newmark’s method and the DYSAC2 analysis procedure in sophistication, was developed for the lateral deformation calculations of the Pier 400 cross sections. The hybrid method is similar to Newmark’s method, but yield acceleration values are calculated using average excess pore pressures predicted by DYSAC2 in the foundation soils and the landfill. In essence, the Pier 400 design team and POLA used results from sophisticated fully coupled procedures and centrifuge model tests together with traditional embankment analysis techniques and engineering judgment to produce a viable and safe seismic design of Pier 400 dikes and landfill.
Predicting Collapse Potential of Soils with Neural Networks
Authors: Juang C. H. , Elton David J.
Published: April 2007

Collapsible soils are known to experience a dramatic decrease in volume upon wetting. This can be very detrimental to structures founded on collapsible soils. Whereas field testing might be the most reliable way to determine collapse potential, the engineer often sees it as the last resort. Neural network models for predicting the collapse potential of soils on the basis of basic index properties are presented. Field data, consisting of index properties and collapse potential, are used to train and test neural networks. Various network architectures and training algorithms are examined and compared. The trained networks are shown to be able to identify the collapsible soils and predict the collapse potential.
Neuronet-Based Approach To Modeling the Durability of Aggregate in Concrete Pavement Construction
Authors: Najjar Yacoub M. , Basheer Imad A. , McReynolds Richard L.
Published: April 2007

The durability of aggregate used in concrete pavements construction is commonly assessed by subjecting small concrete beams containing the aggregate to cyclic freezing and thawing. The durability of aggregate and concrete specimens is quantified by measuring the durability factor (DF) and percent expansion (EXP). A typical durability test may last 3 to 5 months and involve high costs. It was assumed that the durability of aggregate used as a constituent in concrete elements may be related to some easily measured physical properties of the aggregate. A data base obtained from records of the Kansas Department of Transportation contained a total of 750 durability tests. The observed wide scatter in the experimental data when DF or EXP is related to one physical parameter suggested the use of artificial neural networks to model durability. Neural network models were developed to predict durability of aggregate from five basic physical properties of the aggregate. The models were found to classify the aggregates with regard to their durability with a relatively high accuracy. In addition, the models were used to assess the reliability of prediction. To illustrate the use of the models, numerical examples are presented.
Reliability-Based Performance Model for Large Bridge Component Systems
Authors: Destefano P. D. , Grivas D. A.
Published: April 2007

A method for modeling the performance of large bridge components subjected to normal loading and deterioration effects using reliability engineering techniques is presented. Development of the method was motivated by the need to advance a practical performance model for large bridge rehabilitation decision analysis. The modeling scope includes three basic elements: performance assessment, system modeling, and failure rate analysis. Two fundamental assumptions of the developed performance model are that (a) bridge components are systems of independent critical elements and (b) each element’s failure rate is constant throughout its functional service life. The model is used to qualitatively assess the performance of bridge components with respect to reliability and enables the estimation of two important rehabilitation planning indices, functional service life and expected damage. An application of the model is illustrated in an example involving a comparative evaluation of the performance of two large bridge deck systems. The bridges selected have similar traffic, maintenance, and environmental conditions; however, they have significantly different design characteristics. It is concluded that the performance model provides a viable approach to qualitative and quantitative evaluation of bridge performance over time. The research efforts described are part of a larger, comprehensive project to develop and enhance the bridge management system of the New York State Thruway Authority.
Reliability Evaluation of AASHTO Design Equations for Drilled Shafts
Authors: Isenhower William M. , Long James H.
Published: April 2007

A reliability evaluation of the AASHTO design equations for drilled shafts is described. The evaluation computed the variance of a data base containing load tests to failure on 30 straight-sided drilled shafts using first-order, second-moment methods applied to the AASHTO design equations. The computed variance was compared with the measured variance of the data base. The measured variance was found to exceed the computed variance for approximately 75 percent of the load tests. This is believed to result from important factors affecting the axial capacity of the drilled shaft not being included in the AASHTO design equations. It is speculated that the missing factors are related to common variations in construction practices for drilled shafts.
Evaluation of Steel Slag Fine Aggregate in Hot-Mix Asphalt Mixtures
Authors: Kandhal Prithvi S. , Hoffman Gary L.
Published: April 2007

Since a considerable amount of steel slag is produced in the southwestern part of Pennsylvania around Pittsburgh, where natural fine aggregate sources are limited, an evaluation was undertaken to determine the feasibility of using “cured” steel slag fine aggregate in hot-mix asphalt (HMA) mixtures. The objectives of this work were to (1) correlate fine aggregate expansions to the “parent” coarse aggregate expansions, (2) determine properties of dense-graded Pennsylvania ID-2 wearing coarse mixtures made with various sources of steel slag and crushed limestone fine aggregate, and (3) recommend appropriate specifications and test criteria for implementing the use of steel slag fine aggregate, if justifiable. Expansive characteristics of the steel slag aggregates were determined by Pennsylvania Test Method 130. HMA mixtures made with steel slag aggregates and limestone aggregate (control) were subjected to hot-water conditioning and Lottman freeze-and-thaw conditioning to determine potential problems, such as swell and moisture-induced damage. An excellent correlation existed between the average total expansion of the fine aggregate fraction and that of the “parent” coarse aggregate. No significant problems with swell and moisture-induced damage were noted in HMA mixtures containing steel slag fine aggregate and limestone coarse aggregate. Specifications and test criteria were recommended for the use of steel slag fine aggregate in HMA mixtures.
Characterization of Asphalt Cements Modified with Crumb Rubber from Discarded Tires
Authors: Daly William H. , Negulescu Ioan I.
Published: April 2007

Blends with up to 20 percent ground vulcanized rubber (both crumb and 200-mesh powder particles) from recycled tires were prepared with asphalt cements of various grades (AC-5 to AC-30) and evaluated using dynamic mechanical analysis (DMA). Blends produced from powdered rubber particles exhibited Newtonian behavior at high temperatures. Similar behavior was not observed with crumb rubber blends. The mechanical properties of asphalt-rubber blends depend on the concentration of rubber additives, the particle sizes, and the chemical composition of the asphalt. The dynamic mechanical characteristics of all blends are discussed in terms of G*sin δ and G″ comparative data are presented according to the Strategic Highway Research Program binder specifications. Pressure aging vessel (PAV) tests of the asphalt-rubber blends revealed a significant difference between crumb rubber and powdered rubber additives. Simple blends of crumb rubber with asphalts ranging in grade from AC-5 to AC-30 exhibited phase separation during a thin-film oven aging test. In contrast, blends with powdered rubber appeared to remain compatible or at least partially compatible through the PAV process, and the blends retained the physical properties associated with the additive. The DMA data suggest that the low-temperature cracking resistance of asphalt–powdered rubber blends is enhanced.
Use of Superpave Technology for Design and Construction of Rubberized Asphalt Mixtures
Authors: Takallou H. Barry , Bahia Hussain U. , Perdomo Dario , Schwartz Robert
Published: April 2007

The effect of different mixing times and mixing temperatures on the performance of asphalt-rubber binder was evaluated. Four different types of asphalt-rubber binders and neat asphalt were characterized using the Strategic Highway Research Program (SHRP) binder method tests. Subsequently, mix designs were carried out using both the SHRP Levels I and II mix design procedures, as well as the traditional Marshall mix design scheme. Additionally, performance testing was carried out on the mixtures using the Superpave repetitive simple shear test at constant height (RSST-CH) to evaluate the resistance to permanent deformation (rutting) of the rubberized asphalt mixtures. Also, six rectangular beams were subjected to repeated bending in the fatigue tester at different microstrain levels to establish rubberized asphalt mixtures’ resistance to fatigue cracking under repeated loadings. The results indicate that the Superpave mix design produced asphalt-rubber contents that are significantly higher than values used successfully in the field. Marshall-used gyratory compaction could not produce the same densification trends. Superpave mixture analysis testing (Level II) was used successfully for rubberized asphalt mixtures. Results clearly indicated that the mixture selected exhibited acceptable rutting and fatigue behavior for typical new construction and for overlay design. Few problems were encountered in running the Superpave models. The results of the RSST-CH indicate that rubber-modified asphalt concrete meets the criteria for a maximum rut depth of 0.5 in.; and more consistent results were measured for fatigue performance analysis using the repeated four-point bending beam testing (Superpave optional torture testing). The cycles to failure were approximately 26,000 at 600 microstrain.
Evaluation and Selection of Aggregate Gradations for Asphalt Mixtures Using Superpave
Authors: Anderson R. Michael , Bahia Hussain U.
Published: April 2007

The design of asphalt mixtures is a complex process that requires the proper proportioning of materials to satisfy mixture volumetric and mechanical properties. The majority of time spent in the mix design process is used in evaluating and selecting aggregate gradations to meet project requirements. The latest set of requirements for asphalt mixtures is the Superpave system, developed during the Strategic Highway Research Program. This system incorporates materials selection, evaluation of trial aggregate structures, selection of design asphalt binder content, moisture sensitivity, and, in some cases, determination of performance properties of the selected asphalt-aggregate blend. The selection of a design aggregate structure reduces to selecting an aggregate gradation that will meet minimum volumetric and densification criteria, and selecting an aggregate structure that will provide adequate resistance to permanent deformation, fatigue, and thermal cracking. In the Superpave volumetric mix design process, achieving voids in mineral aggregate (VMA) is the most difficult task facing the mix designer. One phase of this evaluation focuses on providing Guidelines to achieve VMA requirements with Superpave mix designs. This phase was accomplished by evaluating the existing database of information on Superpave mix designs at the Asphalt Institute. The second phase examines the relationship between properties determined during the Superpave volumetric mix design process, and material properties determined by mix analysis tests.
Evaluation of Materials From Northeast Texas Using Superpave Mix Design Technology
Authors: McGennis Robert B.
Published: April 2007

During 1994 and 1995, asphalt overlay performance problems in the form of disintegration, rutting, and raveling were experienced in the Atlanta District of the Texas Department of Transportation (TxDOT). An investigation of the damage by TxDOT engineers in Atlanta identified the cause as extreme moisture susceptibility of asphalt mixtures containing locally available crushed gravel. A task force was assembled to identify tests and specifications to allow use of local gravel aggregates while, at the same time, precluding future moisture damage problems. The resources of the South Central Superpave Center were mobilized to assess whether Superpave mix design tests and criteria would have identified the mixtures as troublesome in ways other than moisture sensitivity. Because TxDOT already uses a moisture damage test very similar to the Superpave moisture sensitivity evaluation, no Superpave moisture damage tests were conducted. The Superpave mix design evaluation indicated that one or more Superpave aggregate tests, gradation requirements, and volumetric and compaction properties would have precluded use of the materials.
The Superpave Gradation Restricted Zone and Performance Testing With the Georgia Loaded Wheel Tester
Authors: Watson Donald E. , Johnson Andrew , Jared David
Published: April 2007

Guidelines for the new hot-mix asphalt design system, Superpave, were developed under the Strategic Highway Research Program. One of the most controversial components of this system is the aggregate gradation restricted zone. This restricted zone was adopted as a gradation specification primarily to deter the use of high levels of natural sand in high-performance mixes. By designing mixes with gradations that avoid the restricted zone (i.e., limit natural sand), the internal strength provided by internal friction could be improved. Some agencies question the validity of the restricted zone. The specified gradations of many current mixes contain bands that enter the restricted zone, but the mixes have performed well for years in actual field conditions. The Georgia Department of Transportation (GDOT) currently specifies several standard mixes with gradations that enter the restricted zone and still perform well. These high-performance mixes contain good quality, 100 percent manufactured aggregates and no natural sand. GDOT recommends that the Georgia loaded wheel tester or some other proof tester be incorporated into the mix design process to screen mixes before rejecting them solely because their combined gradation enters the restricted zone. If mixes having combined gradations that enter the restricted zone are categorically rejected, mixes that are economical for the purpose intended may be rejected in the process.
Methodology Development for Estimating External Benefits and Costs of High-Speed Ground Transportation in the United States
Authors: Shearin Gui
Published: April 2007

The social, economic, and environmental benefits and costs of implementing high-speed ground transportation (HSGT) service could offset some of the investment required for implementation. These potential impacts are called “externalities” or “external benefits and costs” because they are external to the economic market for HSGT service. The methodology framework used to project external benefits and costs of HSGT for the commercial feasibility study under the auspices of the FRA is described. The externalities are defined and classified, and the general approach to estimating externalities and applying the resulting methodologies is discussed. The principles of two key methodologies for estimating reduced delay to airport and highway users from diversions to HSGT are summarized. A quantitative overview of the results is presented for the California, Chicago hub, and Northeast corridors. Social benefits and costs were found to be an important part of the potential benefits of high-speed rail. Except for some low-speed technologies, only the combined public and user benefits exceed costs. The “traditional” time-saving benefits dominate the public benefits, comprising 92 to 98 percent of total public benefit. Environment (emission) benefits went down with rail speed because of proportionately lower diversions from highway and higher diversions from air with higher rail speed. Significant work remains in developing and applying benefit/cost techniques to rail evaluation: procedures for calculation of environmental benefits are the most undeveloped; in general, procedures for rail impact evaluation are not yet standardized and are developed on a case-by-case basis.
Cross-Corridor Comparison of Operating Costs for High-Speed Ground Transportation
Authors: Allen Duncan W.
Published: April 2007

The U.S. Department of Transportation’s commercial feasibility study (CFS) of high-speed ground transportation (HSGT) included a detailed estimate of operating and maintenance (O&M) costs for eight HSGT technologies across nine intercity corridors in the United States. The number of cases examined in detail provides a wealth of information that can support general conclusions about HSGT O&M costs under the normative assumptions of the CFS. These conclusions are expressed primarily in terms of six parameters: the nominal maximum authorized speed of the technology; revenue seat-miles; revenue seat-hours; corridor passenger traffic density; specific trip length; and corridor length. The total O&M unit costs per passenger-mile estimated for the CFS are related to these parameters: It is concluded that most of the variation among operating and maintenance cost estimates can be explained by a set of four descriptive parameters in conjunction with a choice of technology option; for a given corridor length and amount of transportation provided, the total O&M costs for other than maintenance of way increase only modestly with higher speeds and more advanced technologies; maintenance of way costs exhibit economies of scale but can vary widely among corridors, depending on the ownership and operating arrangement for the corridor, the lowest unit-cost option for a corridor is strongly determined by traffic density and by the potential for market growth with increased operating speeds; the importance of specific trip length relative to passenger traffic density increases with density; and generalizations drawn from CFS results in terms of corridor length or density alone do not necessarily apply to other corridors, particularly when one or more of the other four parameters differ.
Cost of Speed: Analysis of Capital Cost Estimates for High-Speed Ground Transportation Systems
Authors: Harrison John A.
Published: April 2007

The Intermodal Surface Transportation Efficiency Act of 1991 required the U.S. Department of Transportation to evaluate the commercial feasibility of high-speed ground transportation—a family of technologies ranging from incremental rail improvements to high-speed rail and magnetic levitation (Maglev) systems—in selected urban corridors. The evaluation involved estimating travel times, capital costs, operation and maintenance costs, and ridership for proposed service frequencies and then computing the potential return on investment from fares and other potential revenues. The results are documented in a U.S. Department of Transportation report generally referred to as the commercial feasibility study (CFS). Two elements of the CFS are addressed here: travel times and capital costs in four illustrative corridors—Chicago to St. Louis; Los Angeles to San Francisco; Eugene, Oreg., to Vancouver, B.C.; and Miami to Tampa via Orlando. Analysis of the results reveals common cost trends: for average speeds up to about 200 km/hr (125 mph), the initial investment required is generally in the range $1.6 to $3 million per route-kilometer ($2.6 to 4.8 million per route-mile). Above this speed regime (which varies by corridor), the initial investment increases steadily with speed, generally reaching $10 to $12 million per route-km ($16 to $19 million per route-mi) for very-high-speed rail systems and from $14 to $19 million per route-km ($23 to $31 million per route-mi) for Maglev systems. Analysis of the capital cost estimates reveals that despite the wide range of initial costs for the high-speed options, the cost per minute of trip time saved is remarkably consistent in corridors of similar length and with similar terrains. Cost-effectiveness plots are provided, allowing the reader to compare the performance of each of the four corridors in terms of trip time savings and cost per route-kilometer.