bluuebunny/crossref_metadata_2025 huggingface dataset:
Construction-Related Variability in Pavement Mat Density due to Temperature Differentials
Authors: Willoughby Kim A. , Uhlmeyer Jeff S. , Mahoney Joe P. , Anderson Keith W. , Pierce Linda M.
Published: April 2007

The work reported on is an extension of work done in Washington State to examine the systematic occurrence and variability in pavement mat density. The focus will be on the extent of the pavement that is affected by variable density due to temperature differentials and the fact that randomly based testing does not identify the occurrence of cyclic density differentials. Temperature differentials 14°C (25°F) or greater generally cannot be compacted to the same level of density as the surrounding mat and therefore lead to significant density differentials (increase in air voids of 2% or more). A cyclic pattern typically occurs, matching each delivered truckload of mix, although temperature differentials can occur randomly or not at all, depending on the remixing device. The largest extent of pavement is affected when no remixing occurs and temperature differentials develop for every truckload of hot mix. These temperature differentials can cover the entire width and affect up to 50% of the mat. If the delivered hot mix is thoroughly remixed before placement, temperature differentials are minimal. Although density will vary in any paving operation, it was found that a uniform temperature mat greatly increases the ability to achieve a uniform density. Because of this cyclic pattern of variable density, random sampling for in-place density does not properly identify or quantify this problem. It is recommended that temperature differential areas be determined during construction and excluded from the random sampling used for acceptance testing. The issue of variable densities due to temperature differences or aggregate segregation should be identified and eliminated at the start of the project.
Relationship Between Backcalculated and Laboratory-Measured Resilient Moduli of Unbound Materials
Authors: Flintsch Gerardo W. , Al-Qadi Imad L. , Park Youngjin , Brandon Thomas L. , Appea Alexander
Published: April 2007

The resilient moduli of an unbound granular subbase (used at the Virginia Smart Road) obtained from laboratory testing were compared with those backcalculated from in situ falling weight deflectometer deflection measurements. Testing was performed on the surface of the finished subgrade and granular subbase layer shortly after construction. The structural capacity of the constructed subgrade and the depth to a stiff layer were computed for 12 experimental sections. The in situ resilient modulus of the granular subbase layer (21-B) was then back-calculated from the deflections measured on top of that layer. The back-calculated layer moduli were clearly stress-dependent, showing an exponential behavior with the bulk stress in the center of the layer. Resilient modulus test results of laboratory-compacted specimens confirmed the stress dependence of the subbase material modulus. Three resilient modulus models were fitted to the data. Although all three models showed good coefficients of determination ( R2 > 90%), the K-θ model was selected because of its simplicity. The correlation between field-backcalculated and laboratory-measured resilient moduli was found to be strong. However, when the stress in the middle of the layer was used in the K-θ model, a shift in the resilient modulus, θ, was observed. This finding suggests that a simple shift factor could be used for the range of stress values considered.
Corps of Engineers Design of Geosynthetic-Reinforced Unpawed Roads
Authors: Tingle Jeb S. , Webster Steve L.
Published: April 2007

U.S. Army Corps of Engineers design procedure was reviewed to validate the existing criteria for geotextile-reinforced unpaved roads and to modify the criteria for the addition of stiff biaxial geogrids. Geogrid stiffness here refers to products demonstrating good torsional rigidity and aperture stability. The theoretical basis for the existing design procedure was reviewed to ensure that appropriate assumptions were used to derive the current design method. Historical test section results were used to validate the empirical bearing-capacity factors, Nc used for unreinforced and geotextile-reinforced base materials. In addition, an empirical bearing-capacity factor for geogrid reinforcement was derived to modify the existing design procedure for both geotextile and geogrid use. The relevant theory used in the development of the existing design method to establish the basis for the analyses is described. Previously unpublished test section results are presented and used to calculate experimental bearing-capacity factors, and the calculated factors are compared with the theoretical values used in the existing procedure. The results of the analyses support the use of the existing design procedure’s bearing-capacity factor for unreinforced sections; the existing bearing-capacity factor for geotextile-reinforced unpaved roads appears to be unconservative for the conditions of the full-scale test section presented. Finally, a bearing-capacity factor for the use of a geogrid and geotextile combination is recommended for modification of the existing Corps of Engineers design procedure.
Small Aircraft Transportation System as Implemented in Nebraska
Authors: Moussavi Massoum , Vargas Jaime A.
Published: April 2007

The Small Aircraft Transportation System (SATS) is an improved mode of air travel for personal transportation that makes use of the network of commercial and general aviation airports. It is a system of highly developed aircraft and ground facilities that can safely and affordably move people among several thousand of currently underused airports throughout urban, suburban, and rural America. The SATS is a combined program that consists of three main components: new vehicle technology, airspace infrastructure, and SATS service provider. The objective of this research was to study the SATS service provider component. It consisted of the definition and analysis of the demand forecast, airfield design, terminal area, and ground transportation access metrics and their interrelationships. A computer model that allowed the evaluation of different scenarios of planning and design of airfields for the SATS in Nebraska was also developed. The results of a base simulation for 2001 showed that 88 out of 91 Nebraska airports require some changes to be SATS compatible. The air traffic control and the terminal area components require the most changes. The runway length, runway surface, lighting, marking, aircraft parking, and fuel accessibility also require some minor changes and upgrades. The capacity and ground transportation access of all airports meet SATS requirements. An ongoing research effort continues to develop and calibrate the SATS metrics at regional and national levels. The results were merely preliminary work for SATS implementation in the state of Nebraska.
User Request Evaluation Tool and Controller–Pilot Data Link Communications: Integration Benefits Assessment
Authors: Rakas Jasenka , Hansen Mark , Jirajaruporn Wanjira , Bolic Tatjana
Published: April 2007

Explored are the benefits of integrating User Request Evaluation Tool (URET) and Controller-Pilot Data Link Communications (CPDLC). Controller-pilot voice-communication messages and aircraft traffic flows and conflicts are analyzed in great detail in one representative, URET-operating en route sector. On the basis of the mapped URET data and the real-world communication messages, a base case and two alternative scenarios were analyzed to estimate the number of clearances that are given to pilots to resolve aircraft conflicts a sufficient time before the start of the conflict, and to determine the reduction in frequency congestion possible if such messages were sent via data link. It was found that the highest frequency use, which corresponded to the first traffic peak, was reduced 27% after the second-scenario messages were removed from the base-case scenario. After removing the non-time-critical conflict-resolution messages, the total reduction was 59%. Frequency use during the highest number of aircraft conflicts was reduced 65% after all messages from the second and the third scenario were removed. Thus, the benefits of integrating CPDLC and URET are significant. If non-time-critical conflict messages were transmitted via data link in the integrated CPDLC and URET environment, they could considerably improve the frequency congestion. More important, the largest benefits would be experienced in situations involving a large number of aircraft conflicts, or during busy periods of traffic. These improvements could further help to reduce the number of communication errors (and the consequent air traffic control workload), as well as the number of operational errors.
Critical Assessment of Airport Demand Management Strategies in Europe and the United States: Comparative Perspective
Authors: Zografos Konstantinos G. , Madas Michael A.
Published: April 2007

The ever-tighter mismatch between the demand and supply of airport services has triggered policy discussions that bring to the forefront a challenging dilemma for decision makers and the various stakeholding groups in the airport domain: demand management or capacity enhancement? There are two solutions in the effort to reduce gridlock in the air transport system—to expand capacity, and to diminish or handle demand through time and space. One part of the answer lies with technology and operations aiming at building capacity and another with balancing and handling demand. Since the last decade of continuously increasing air traffic congestion, demand management strategies have gained increasing acceptance by airport authorities and policy makers as a potential vehicle of handling demand—by limiting in some way the demand for access to busy airfields or to congested airspace or by modifying the spatial and temporal distribution of demand, or by doing both. A critical review was done of the developments, practices, and research activities in Europe and the United States toward confronting the well-known aviation capacity gridlock. A triplet of analysis formed the base: the current state of affairs pertaining to the demand and growth patterns and prospects vis-à-vis supply-side developments; the discussion of the aviation capacity gridlock; and an in-depth analysis and critical assessment of the alternative demand-side solutions under the spectrum of all potential enhancement aspects (i.e., administrative, economic, hybrid measures).
Optimizing Intermodal Trip Planning Decisions in Interurban Networks
Authors: Zografos Konstantinos G. , Madas Michael A.
Published: April 2007

Travel and tourism activities and trip planning decisions involving the interoperability complexities and interdependencies introduced by inter-modal and interurban transportation networks constitute an ample opportunity area for deploying the state-of-the-art mobile Internet technologies. It is becoming increasingly necessary to provide travelers with real-time information to assist them in preplanning or replanning their transport and travel activities or particular trip elements during their trip, while being on the move. Trip planning decisions, either before or during the trip realization constitute a derived demand, pushed by demand for tourism activities. However, they represent the most critical chain of the decision-making process on the grounds that they eventually determine the feasibility and the realization of the whole travel activity. From a different perspective, terminal operators, regional authorities, and other transport and tourism organizations show a vast interest and actively pursue alternative ways of dealing with the requirements of the demand for travel and tourism services. An integrated system providing value added logistical services related to travel and tourism, the World in your H@nds on the Move–WH@M system, has been implemented to support and optimize the trip planning process. A study had three objectives: to discuss the way that intermodality can be supported by such a technological application; to present the architecture, operations, and the solution approach governing the trip planning modules; and to provide a brief demonstration of the relevant trip planning modules of the system.
Lessons from United Kingdom Airports on Ground Control Strategies
Authors: Humphreys Ian , Ison Stephen
Published: April 2007

Major airports are currently operating close to capacity, and in the medium long term, air traffic is likely to grow, despite the effects of September 11, 2001. One of the consequences will be increased airport ground access congestion and a deterioration of ground access time reliability. A major challenge for airports is to make efficient use of ground access capacity that is currently dominated by private car trips. In response to the problem in the United Kingdom, the government has instructed each of 27 airports to lead an Airport Transport Forum comprising key stakeholders, namely the airlines, airport owners, employers, local transport authorities, rail companies, bus companies, and local government. Each forum is responsible for producing an airport surface access strategy to encourage more efficient use of ground access capacity and to attract more trips to airports by public modes of transport. There was a review of the U.K. mechanisms for coordinating ground access, and a comparison and contrast of the strategies was proposed for reducing car dependency for surface access trips by employees to airports. Although there are differences in the operating contexts of U.S. and U.K. airports, it might be asked, What lessons can be drawn from U.K. airports? The strategies of variously sized U.K. airports were analyzed, and findings reveal evidence of good innovative practice for reducing car dependency and improving efficiency of ground access systems. There is potential for transferability to the U.S. airport environment.
Improved Design of Vertical Curves with Sight Distance Profiles
Authors: Hassan Yasser
Published: April 2007

Design of vertical alignment is one of the main tasks in highway geometric design. This task requires, among other things, that the designer ensure drivers always have a clear view of the road so they can stop before hitting an unexpected object in the road. Therefore, the ability to determine the required and available stopping sight distance (SSD) at any point of the vertical alignment is essential for the design process. Current design guides in the United States and Canada provide simple analytical models for determining the minimum length of a vertical curve that would satisfy the sight distance requirement. However, these models ignore the effect of grade on the required SSD. Alternative approaches and models have also been suggested but cover only special cases of vertical curves. Two specific models were expanded to determine the required SSD on crest and sag vertical curves. By comparing profiles of available SSD and required SSD on examples of vertical curves, it was shown that current North American design practices might yield segments of the vertical curve where the driver’s view is constrained to a distance shorter than the required SSD. An alternative design procedure based on the models was developed and used to determine the minimum lengths of crest and sag vertical curves. Depending on the approach grade, these new values of minimum curve length might be greater than or less than values obtained through conventional design procedures. Design aids were therefore provided in tabular form for designers’ easy and quick use.
Hydraulic Jumps in Broken-Back Culverts
Authors: Hotchkiss Rollin H. , Flanagan Patrick J. , Donahoo Kevin
Published: April 2007

A broken-back culvert has one or more changes in grade within the prismatic barrel profile. One section of a broken-back culvert is usually steep, with the steep slope contributing to high outlet velocities unless a hydraulic jump forms upstream from the culvert outlet. Predictive equations have been published for a wide range of experimental conditions but still do not describe the hydraulics of a jump as it traverses the steeply sloped section and the most downstream section of a broken-back culvert. A computer program, the Broken-Back Culvert Analysis Program (BCAP), analyzes the hydraulics of circular or box-shaped broken-back culverts and provides a comprehensive design tool for engineers. It predicts whether a hydraulic jump will occur and, if so, where it begins and ends. Analyses are performed for 10 discharges. Outputs include rating curves for headwater and outlet depths and outlet velocity and tabulations of hydraulic parameters for each discharge. The water surface profiles throughout the culvert, except through the hydraulic jump, are computed and are plotted on the screen. Experiments were performed with model culverts to assess the accuracy of the predictive equations in BCAP for headwater depth, the location of a hydraulic jump, and the hydraulic jump length. The predictions for the headwater depth at the culvert inlet matched the experimental observations well, but predictions for hydraulic jump location and length were less satisfactory. BCAP has been used for hundreds of design projects in Nebraska and has been downloaded almost 300 times from at least 22 different states. It is recommended that BCAP be improved as better experimental data become available.
New Energy-Absorbing High-Speed Safety Barrier
Authors: Reid John D. , Faller Ronald K. , Holloway Jim C. , Rohde John R. , Sicking Dean L.
Published: April 2007

For many years, containment for errant racing vehicles traveling on oval speedways has been provided through rigid, concrete containment walls placed around the exterior of the track. However, accident experience has shown that serious injuries and fatalities may occur through vehicular impacts into these nondeformable barriers. Because of these injuries, the Indy Racing League and the Indianapolis Motor Speedway, later joined by the National Association for Stock Car Auto Racing (NASCAR), sponsored the development of a new barrier system by the Midwest Roadside Safety Facility at the University of Nebraska–Lincoln to improve the safety of drivers participating in automobile racing events. Several barrier prototypes were investigated and evaluated using both static and dynamic component testing, computer simulation modeling with LS-DYNA (a nonlinear finite element analysis code), and 20 full-scale vehicle crash tests. The full-scale crash testing program included bogie vehicles, small cars, and a full-size sedan, as well as Indy Racing League open-wheeled cars and NASCAR Winston Cup cars. A combination steel tube skin and foam energy-absorbing barrier system, referred to as the SAFER (steel and foam energy reduction) barrier, was successfully developed. Subsequently, the SAFER barrier was installed at the Indianapolis Motor Speedway in advance of the running of the 2002 Indianapolis 500 race. From the results of the laboratory testing program as well as analysis of the accidents into the SAFER barrier occurring during practice, qualification, and the race, the SAFER barrier has been shown to provide improved safety for drivers impacting the outer walls.
Guardrail Connection for Low-Fill Culverts
Authors: Polivka Karla A. , Faller Ronald K. , Rohde John R.
Published: April 2007

A W-beam guardrail system was developed for attachment to the top slab of a low-fill concrete culvert. The guardrail design was constructed with a single, 2.66-mm-thick W-beam rail totaling 53.34 m in length. Over the culvert, W150×13.5 steel posts 946 mm long spaced 952.5 mm on center supported the W-beam rail. The research study included dynamic testing with a bogie vehicle and steel posts attached to a rigid foundation, computer simulation modeling with BARRIER VII, and two full-scale vehicle crash tests. The crash tests used three-quarter-ton pickup trucks and were conducted in accordance with the Test Level 3 (TL-3) requirements specified in NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features. The first test was successfully conducted on the guardrail system with the back sides of the posts positioned 457 mm away from the front of the culvert’s headwall. The second test was unsuccessfully performed on the guardrail system with the back sides of the posts positioned 25 mm away from the front of the headwall. The safety performance of the W-beam guardrail system attached to the top of a low-fill concrete culvert was determined to be acceptable according to the TL-3 criteria found in NCHRP Report 350. Recommendations for the final placement of the guardrail system with respect to the culvert headwall are also made.
Landscape Design in Clear Zone: Effect of Landscape Variables on Pedestrian Health and Driver Safety
Authors: Naderi Jody Rosenblatt
Published: April 2007

The relationship between landscape installations and safety or pedestrian activity was evaluated in pilot studies. The sites selected for study were those adjacent to or within the areas often referred to as the “clear zone” of the transportation corridor, an area shared by pedestrians and driver perception. Case study research on the impact of environmental mitigation on driver safety is summarized to identify the landscape installations in the clear zone that appear to have an effect on safety. This is followed by case study research on the identification of variables that encourage walking for health purposes. Preliminary findings indicate that the improved definition of spatial edge resulting from typical curbside and median landscape treatment in the clear zone appears to solicit positive behavioral responses by either attracting pedestrian activity or improving driver safety. It is not possible to draw definitive conclusions from the results because of the small sample sizes in the pilot studies (a pedestrian survey included 52 responses), but indications are that the landscape in the clear zone may be having a positive impact on safety or pedestrian activity under certain circumstances. Both pilot studies were conducted separately in Canada and the United States.
Draft State Utility Pole Safety Program for Alabama
Authors: Lindly Jay K.
Published: April 2007

The Code of Federal Regulations [23 CFR 645.209(k)] requires highway agencies to work with utility companies to initiate corrective measures to utility facilities that are found to be likely to cause injury to motorists. The contribution that a reduction in utility pole–related crashes could make to the overall highway safety effort in Alabama was studied, and methods of accomplishing such reductions were examined. A review of the programs of nearby states with utility pole safety programs shows that they address utility pole safety principally during state department of transportation (DOT) construction projects. Crash data investigations showed that a specific utility pole safety program would have a small effect on overall roadway safety in Alabama. Additionally, there is strong competition for safety funds. After examination of the situation for Alabama DOT-controlled roads, the limitation of pole remediation projects to active construction projects or to any sites that can be positively identified through the normal cost–benefit studies used for safety projects was endorsed.
Development of Energy-Absorbing Composite Utility Pole
Authors: Foedinger Richard , Boozer John F. , Bronstad Maurice E. , Davidson James W.
Published: April 2007

The serious hazard presented by unforgiving timber utility poles installed along the nation’s roadways has long been recognized by the roadside safety community. However, relatively little attention has been devoted to the development of safer utility poles beyond breakaway timber pole designs. A new generation of utility pole designs that use energy-absorbing composite materials offers a solution to the development and implementation of safer utility poles that have a cost advantage over breakaway timber poles and can be tailored to achieve the desired functional performance and energy absorption characteristics inherently without the need for additional strength members or add-on energy absorption devices. This research has resulted in the development of an energy-absorbing fiberglass-reinforced composite (FRC) utility pole design that meets structural performance requirements for environmental loading in accordance with the National Electrical Safety Code for Class 4 poles and safety performance criteria in compliance with NCHRP Report 350 Test Level 2 conditions for utility poles. Developmental testing and analyses were performed to support the development of a prototype design for demonstration testing. Full-scale crash testing has demonstrated the ability of the composite pole to absorb the vehicle’s impact energy by progressive crushing and fracture propagation as the vehicle is brought to a controlled stop. In addition to offering improved safety performance, the energy-absorbing FRC pole provides significant functional advantages, such as reduced weight, an improved strength-to-weight ratio, increased longevity, ease of installation, low maintenance, and resistance to environmental degradation.
Measured Distributions of Control Delay on Signalized Arterials
Authors: Colyar James D. , Rouphail Nagui M.
Published: April 2007

The Highway Capacity Manual and other traffic operations manuals give no guidance on the magnitude and factors affecting variability in control delay. However, knowing the variability in control delay has several useful applications, such as providing a more complete and statistically significant comparison of different signal timing or roadway geometric improvements. The objective of this research is to provide an exploratory analysis of the variability in signalized control delay using real-world measurements on an arterial corridor in Cary, North Carolina. Data were collected with a portable, onboard emissions and engine diagnostics measurement device, from which second-by-second speed data were recorded. A new method for estimating intersection control delay from second-by-second speed data is presented that attempts to take into account over-capacity conditions and closely spaced intersections. The data collection focused on recording a similar number of runs on a corridor before and after signal coordination was implemented. The results show that the distribution of control delay generally has a single, large peak at low delays, when the mean control delay was in the level-of-service A–B range, whereas the distribution becomes increasingly bimodal (two distinct peaks) as the mean control delay increases. Another finding is that there is a direct relationship between mean control delay and standard error of control delay, but there is still variability in the standard error that cannot be explained solely by the mean value. Finally, differences in the before and after runs showed that a real-world signal timing improvement can reduce both the mean and the standard error of control delay as well as alter the shape of the delay distribution.
Site Characteristics Affecting Operation of Triple Left-Turn Lanes
Authors: Sando Thobias , Mussa Renatus N.
Published: April 2007

The growth of traffic flow in urban areas has resulted in increased installation of triple left-turn lanes with the aim of reducing vehicle delays, queue lengths, and vehicle storage bay lengths by dividing the left-turn queue demand among three lanes. The study reported here analyzed the influence of a number of geometric factors found at 15 triple left-turn lane sites in Florida on saturation flow, lane usage, and lane utilization. A total of 2,395 lane cycles and 38,023 vehicles were observed. The observed saturation flows yielded a mean saturation flow of 1,859 passenger cars per hour of green per lane (pc/h/ln) with the 95% confidence interval of 1,810 pc/h/ln to 1,907 pc/h/ln. The Fisher least significant difference test and the Hsu multiple comparison with the best test were used to determine the statistical significance of the variables’ influence on saturation flows. The results showed that triple left-turn lanes on downgrades and with an angle of turn less than 90 degrees were the two characteristics that most contributed to high saturation flow, and triple left-turn lanes located on oneway streets and on curved approaches had the lowest saturation flow. Lane utilization was dependent on the geometrics of the intersections: shadowed left-turn lanes had lower utilization of the innermost lane compared with unshadowed lanes.
Integrated Simulation-Based Method for Estimating Arrival Type for Signalized Arterial Planning Applications
Authors: Washburn Scott S. , Courage Kenneth G. , Nguyen Thuha
Published: April 2007

One of the primary determinants of signalized intersection delay, and consequently signalized arterial level of service, is progression quality. Progression quality is represented by an arrival-type variable in the Highway Capacity Manual (HCM) procedure for calculating signal delay. Ideally, the arrival type is estimated from collected field data, in particular the percentage of vehicles that arrive at an intersection approach while that approach has the green signal indication. The Florida Department of Transportation prescribes the use of its ARTPLAN software program for planning-level analyses of signalized arterial level of service in the state of Florida. This software is a planning-level implementation of the arterial analysis methodology contained in Chapter 15 of the 2000 HCM. One of the inputs to this software program is arrival type. Given the significant impact this variable can have on delay, and subsequently level-of-service results, it is prudent to have as good an estimate of its value as possible. However, collecting accurate data on progression quality is very difficult, and the intent behind a planning-level analysis is that detailed field data should not be required. Consequently, the blanket HCM recommendations for arrival type are often applied in these analyses without much consideration of how appropriate these values really are for the specified roadway, traffic, and control conditions. A method developed to estimate arrival-type values with a simulation-based approach from the planning-level inputs of ARTPLAN is described. Also provided is a summary of simulation-derived arrival-type values from a large number of sample data sets.
Limitations of Passenger-Car Equivalent Derivation for Traffic Streams with More Than One Truck Type
Authors: Demarchi Sergio Henrique , Setti José Reynaldo
Published: April 2007

Heavy vehicles can have a major impact on traffic streams, particularly on grades. Traditionally, these impacts have been expressed in terms of a passenger-car equivalent (PCE), which is used to convert a mixed traffic stream into a hypothetical passenger-car stream. When the stream contains more than one truck type and truck characteristics differ significantly, it would be desirable to derive PCEs for each truck type. Limitations of current methods of PCE derivation are discussed, and it is demonstrated that PCEs derived individually for each truck type account for only part of the impact caused by trucks on traffic. As a result, distortions are created in the estimation of equivalent flow rates when the traffic composition is different from the one used in the derivation of PCEs. A work-around solution based on the estimation of an aggregate PCE is discussed, and a quantitative analysis of the errors associated with the use of each type of PCE is presented. The results indicate that the errors in the estimation of equivalent flow rates are negligible for densities less than 10 veh/(km-lane) but increase significantly with the increase in density. Equivalent flow rates calculated with aggregate PCEs are not exempt from errors, especially if the traffic mix is different from the one used for the base stream, but these errors were found to be smaller than those caused by the use of PCEs derived individually for each truck type.
Comparison of Capacity Models for Two-Lane Roundabouts
Authors: Hagring Ola , Rouphail Nagui M. , Sørensen Henning A.
Published: April 2007

Multilane roundabout capacity models are presented and contrasted in the context of a case study. A two-lane roundabout in Copenhagen, Denmark, was investigated, and data were collected that enable the estimation of critical gaps, follow-on times, entry capacity, and delay. The primary objective of this research was to evaluate the need for more complex capacity models than currently exist in order to properly represent driver gap-acceptance behavior at multilane roundabouts. The complexity arises when drivers are assumed to simultaneously accept pairs of critical gaps in the outer and inner circulating lanes before they enter the roundabout. This approach requires that circulating-lane headways and critical gaps be evaluated independently and not be superposed in a single traffic stream as most current capacity guides assume. The approach also implies that circulating-lane volume allocation can have a considerable impact on entry capacity. The field results indicated that indeed there were differences in the gap-acceptance behavior for drivers entering in the right approach lane, with critical gaps estimated at 3.68 s and 4.49 s for the inner and outer circulating lane, respectively, at the test site. In contrast, drivers entering in the left approach lane exhibited no difference in critical gaps among lanes (4.64 s for the inner lane and 4.68 s for the outer lane). Finally, the lane allocation of circulating flow did have a significant impact on capacity, particularly at large circulating-flow rates. This finding implies that the origin and destination of the flow constituting the circulating traffic must be accounted for in estimating capacity. Even small errors in capacity estimation were found to have a significant impact on delay and level of service.
Stability Analysis Based on Instantaneous Driving Behavior Using Car-Following Data
Authors: Ranjitkar Prakash , Nakatsuji Takashi , Azuta Yoichi , Gurusinghe Gemunu Senadeera
Published: April 2007

An attempt is made to analyze the stability of a platoon using experimental data measured by real-time kinematic (RTK) Global Positioning System (GPS) receivers. Car-following experiments were conducted on a test track using 10 passenger cars. Various speed patterns were tested for the lead car, including random, constant, and sinusoidal, giving different driving conditions. The responses of the following drivers were measured by RTK GPS receivers in each car. The stimulus–response car-following concept was examined, assuming that the reaction time might vary over time. A graphical method was modified to estimate the time-variant reaction time more efficiently. A new algorithm was proposed to estimate the sensitivity factor using Lissajou’s diagram between relative speed and acceleration. The statistical analysis showed that intrapersonal variability was higher than interpersonal variability for both reaction time and sensitivity factor. However, the influence of the driver’s position in the platoon and speed patterns was low. It was found that the reaction time was distributed in a lognormal function for most of the drivers. The variations in the estimated values for the sensitivity factor were relatively high. The stability analysis showed that the average responses of drivers were unstable both locally and asymptotically. The influence of speed fluctuation frequency was found insignificant for the stability of the platoon.
Probabilistic Traffic Flow Breakdown in Stochastic Car-Following Models
Authors: Jost Dominic , Nagel Kai
Published: April 2007

Whether traffic displays multiple phases (e.g., laminar, jammed, synchronized) has been much discussed. Computational evidence is presented that a stochastic car-following model can be moved from two phases (laminar and jammed) to one phase by changing one of its parameters. Models with two phases show three states. Two of them are homogeneous and correspond to the two phases. The third state consists of a mix of the two phases (phase coexistence). Although the gas–liquid analogy to traffic models has been widely discussed, no traffic-related model ever displayed a completely understood stochastic version of that transition. A stochastic model is important to the understanding of the potentially probabilistic nature of the transition. If indeed two-phase models describe certain aspects correctly, predictions for breakdown probabilities can be made. Alternatively, if one-phase models describe these aspects better, there is no breakdown. Interestingly, such one-phase models can still allow for jam formation on a small scale, which may give the impression of two-phase dynamics.
Modeling Platoon Dispersal Pattern of Heterogeneous Road Traffic
Authors: Arasan V. Thamizh , Kashani Shiraj Hussain
Published: April 2007

The quality of progression of a road traffic stream is one of the critical characteristics that must be quantified for operational analysis of traffic signals, particularly on urban roads. The parameter that has been found to best describe this characteristic of traffic streams is the arrival type. Though precise quantification of arrival type has been found to be difficult, the platoon ratio is a useful measure for this purpose. Thus, the quality of arrival of a traffic stream can be assessed by knowing the corresponding value of the platoon ratio. Study of arrival type over a wide range of traffic characteristics warrants theoretical modeling of traffic flow. In the study reported, an attempt was made to model heterogeneous traffic flow using an innovative technique. The developed model was used to study the arrival type of traffic streams, queue accumulation, and queue dissipation on approaches to traffic signals. The dispersal pattern of traffic platoons after vehicles pass a traffic signal was studied in detail. The effect of variation in traffic composition on traffic platoons was also analyzed.
Nonequilibrium Continuum Traffic Flow Model with Frozen Sound Wave Speed
Authors: Jin W. L. , Zhang H. M.
Published: April 2007

Results are presented from a recent study on a variation of a new non-equilibrium continuum traffic flow model in which traffic sound speed is constant. Hence this model is called the frozen-wave model. This model resembles the Payne–Whitham model but avoids the “back-traveling” of the latter. For this frozen-wave model, the Riemann problem is analyzed for its homogeneous system, two numerical solution methods are developed to solve it, and numerical simulations are carried out under both stable and unstable traffic conditions. These results show that under stable conditions, the model behaves similarly to the Payne–Whitham model. However, under unstable traffic conditions, it has nonphysical solutions or no solutions when a vacuum problem occurs. This study, on the one hand, provides a more complete picture of the properties of this frozen-wave model and reduces the risk of improper applications of it. On the other hand, it also highlights the need to adopt a density-dependent sound speed.
Two-Phase Bounded-Acceleration Traffic Flow Model: Analytical Solutions and Applications
Authors: Lebacque J. P.
Published: April 2007

A two-phase traffic flow model is described. One phase is traffic equilibrium: flow and speed are functions of density, and traffic acceleration is low. The second phase is characterized by constant acceleration. This model extends first-order traffic flow models and recaptures the fact that traffic acceleration is bounded. Calculation of analytical solutions of the two-phase model for dynamic traffic situations is shown, a set of calculation rules is provided, and some examples are analyzed.
Evaluation and Design of Maximum Green Time Settings for Traffic-Actuated Control
Authors: Kim Jin-Tae , Courage Kenneth G.
Published: April 2007

A study is described that was conducted to develop an improved average green time estimation model for traffic-actuated control and to suggest a maximum green time design method that analytically minimizes intersection control delay. Improvements in the green time estimation model include revisions in the concept of additional queue service time, explicit treatment of right turns in lane groups containing both through and right-turning vehicles, and other improvements that include updates based on recent studies and modifications in the approaches taken for the modeling procedure. The proposed maximum green time design procedure consists of four components: ( a) estimation of the average green time of a traffic-actuated phase, ( b) performance evaluation of the system through the 2000 Highway Capacity Manual (HCM) procedure, ( c) formulation of an overall average control delay minimization problem, and ( d) a search process to find the most efficient set of maximum green time parameters that minimize the average control delay at an intersection. Using simulation as a surrogate for field data collection, it was demonstrated that the proposed average green time estimation models offer better results than the one in the 2000 HCM. In addition, it was suggested that on the basis of the improvements demonstrated in terms of design, the proposed maximum green parameter design procedure represents an advancement of the methodology for analysis of signalized intersections.
Performance Management System Data for Monitoring Performance: Example with Superpave®
Authors: Hudson W. R. , Monismith C. L. , Dougan C. E. , Visser W.
Published: April 2007

A project was undertaken to examine how pavement management and related data in various state departments of transportation (DOTs) can be used to evaluate the performance of new materials and to validate new design concepts. Evaluation of the performance of Superpave® was used as an ideal example for demonstrating the potential. No performance analyses have been presented to date. The project started with fact-finding visits to the DOTs of Maryland, Florida, Indiana, Arizona, and Washington. From the findings, a Pathfinder study was coordinated for Maryland, where all required data from seven Superpave projects were collected, transferred to an electronic file, and subsequently entered into a web-based system, developed by the University of Washington, where the data could be analyzed. The project results show that it is possible for state DOTs to assemble a database that can be used to evaluate the performance of Superpave and other design and new materials concepts. The project was not large or long enough to make a complete evaluation, but it did determine the feasibility of the concept and its applicability among five states.
Three-Dimensional Finite Element Analysis of Jointed Plain Concrete Pavement with EverFE2.2
Authors: Davids William G. , Wang Zongmu , Turkiyyah George , Mahoney Joe P. , Bush David
Published: April 2007

The features and concepts underlying EverFE2.2, a freely available three-dimensional finite element program for the analysis of jointed plain concrete pavements, are detailed. The functionality of EverFE has been greatly extended since its original release: multiple tied slab or shoulder units can be modeled, dowel misalignment or mislocation can be specified per dowel, nonlinear thermal or shrinkage gradients can be treated, and nonlinear horizontal shear stress transfer between the slabs and base can be simulated. Improvements have been made to the user interface, including easier load creation, user-specified mesh refinement, and expanded visualization capabilities. These new features are detailed, and the concepts behind the implementation of EverFE2.2 are explained. In addition, the results of two parametric studies are reported. The first study considers the effects of dowel locking and slab-base shear transfer and demonstrates that these factors can significantly affect the stresses in slabs subjected to both uniform shrinkage and thermal gradients. The second study examines transverse joint mislocation and dowel looseness on joint load transfer. As expected, joint load transfer is greatly reduced by dowel looseness. However, while transverse joint mislocation can significantly reduce peak dowel shears, it has relatively little effect on total load transferred across the joint for the models considered.
Three-Dimensional Finite Element Analysis of Doweled Joints for Airport Pavements
Authors: Kim Jiwon , Hjelmstad Keith D.
Published: April 2007

Various aspects of the structural behavior of doweled joints, including load transfer, in rigid airport pavement systems are investigated by using nonlinear three-dimensional finite element methods. The finite element models include two concrete slab segments connected by dowels. The concrete slab and supporting layers are simulated by continuum solid elements. Solid elements can capture the severe local deformation in the concrete slab in the vicinity of wheel loads. They allow the modeling of nonlinear material response of the supporting layers and of frictional contact between the concrete slabs and supporting layers. These features generally are not considered in classical analytical approaches. The structural behavior of the doweled joint is investigated for various design and loading conditions, including tire pressure, slab thickness, dowel looseness, and different landing gear configurations. An attempt is made to quantify the amount and efficiency of load transfer through the dowels. According to the finite element results, 15% to 30% of the applied wheel load is transferred to the adjacent slab segment by the dowels in an intact joint, depending on design and loading conditions. In addition, 95% of the transferred shear force is carried only by the 9 or 11 dowels that are closest to the applied load.
Commitments and Modal Usage: Analysis of German and Dutch Panels
Authors: Simma A. , Axhausen K. W.
Published: April 2007

Travelers commit themselves to particular behaviors through the ownership of cars and season tickets. They trade a large one-time payment for a low or zero marginal cost at the point of use. It can be assumed that these commitments influence travel behavior and future commitment situations. Apparently, none of the literature addresses the choice between the commitment to one or the other mode and its impacts on travel behavior as well as the temporal dimension. Models that use structural equation modeling to test a priori hypotheses on the paths linking car availability, ownership of a season ticket for public transportation, and modal usage during three different time periods are presented. Modal usage is operationalized as the number of trips by car and public transport. The models are based on two different panel surveys (in Germany and the Netherlands). The results show that there is a high degree of stability in car ownership and a relatively high degree of stability in season ticket ownership (for Germany only). The commitments influence modal usage, whereby the influence on one mode is higher than the influence on the other mode. The relationship between the two modes is a substitutive one.
Independent Mobility Among Teenagers: Exploration of Travel to After-School Activities
Authors: Clifton Kelly J.
Published: April 2007

The degree of independent pursuit of travel and activities by teenage populations is examined. Specifically, the kinds of after-school trips that teenagers make, the degree of independence in their travel, and the characteristics of those teenagers who are granted greater license to travel independently are explored. The research design uses data from the 1995 Nationwide Personal Transportation Survey to investigate these questions. In particular, the first trip made directly after school is examined to evaluate the degree of independence in travel. The results demonstrate that as teenagers age they gain independence in their daily travels. However, this independence comes with increased reliance on the automobile. Younger teenagers are using alternative modes at a much higher rate than older teenagers, if only for the trip home from school, but they appear to abandon walking and transit use as soon as the automobile becomes an option.