Showing papers in "Transportation Research Record in 1993"

Predicting earthquake-induced landslide displacements using Newmark's sliding block analysis

Abstract: A principal cause of earthquake damage is landsliding, and the ability to predict earthquake-triggered landslide displacements is important for many types of seismic-hazard analysis and for the design of engineered slopes. Newmark's method for modeling a landslide as a rigid-plastic block sliding on an inclined plane provides a workable means of predicting approximate landslide displacements; this method yields much more useful information than pseudostatic analysis and is far more practical than finite-element modeling. Applying Newmark's method requires knowing the yield or critical acceleration of the landslide (above which permanent displacement occurs), which can be determined from the static factor of safety and from the landslide geometry. Earthquake acceleration-time histories can be selected to represent the shaking conditions of interest, and those parts of the record that lie above the critical acceleration are double integrated to determine the permanent landslide displacement. For approximate results, a simplified Newmark method can be used, which estimates Newmark displacement as a function of landslide critical acceleration and earthquake shaking intensity.

Regional Versus Local Accessibility: Implications for Nonwork Travel

Abstract: The question of how alternative forms of development affect travel patterns has recently been the focus of a heated debate, much of which centers on the effects of suburbanization in particular. The concept of accessibility provides an important tool for resolving this question. By measuring both the accessibility to activity within the community, or "local" accessibility, and the accessibility to regional centers of activity from that community, or "regional" accessibility, the structure of a community is more fully characterized. The research summarized uses the concepts of local and regional accessibility to test the implications for shopping travel of alternative forms of development in a case study of the San Francisco Bay Area. The results show that higher levels of both local and regional accessibility are associated with lower average shopping distances but are not associated with differences in shopping frequency. As a result, higher levels of both local and regional accessibility are associated with less total shopping travel. However, the effect of high levels of local accessibility is greatest when regional accessibility is low and vice versa. These findings suggest that policies should be directed toward enhancing both types of accessibility, but that the effects may work against each other to some degree.

Time dependent, shortest-path algorithm for real-time intelligent vehicle highway system applications

Abstract: An algorithm is introduced that calculates the time-dependent shortest paths from all nodes in a network to a given destination node for every time step over a given time horizon in a network with time-dependent arc costs. Unlike other time-dependent algorithms, this approach can handle networks where the travel cost is not necessarily the travel time itself. The algorithm is based on the general Bellman's principle of optimality. It descretizes the horizon of interest into small time intervals. Starting from the destination node, it calculates the paths operating backwards. A proof of the correctness of the proposed algorithm is presented. The algorithm is efficiently implemented and coded on a CRAY Y/MP-8 supercomputer and tested on a large actual street network as well as several random networks. The motivation for this study was the need to compute time-dependent shortest paths in a real-time environment in connection with intelligent vehicle highway systems. The suitability of the proposed algorithm for such applications is demonstrated.

Predicting maximum pavement surface temperature using maximum air temperature and hourly solar radiation

Abstract: A simple method is proposed to calculate the maximum pavement temperature profile on the basis of maximum air temperature and hourly solar radiation. The method was developed to be used mainly for Strategic Highway Research Program binder and mixture specifications and as a quick method of determining maximum pavement temperature for various regions in the United States and Canada. The method is based on the energy balance at the pavement surface and the resulting temperature equilibrium. Reasonable assumptions are made regarding thermal properties of the asphalt concrete. The accuracy of the method was tested by applying it to some field cases for which measured pavement temperatures were available. In 83% of the cases, the proposed equation predicted the pavement temperature within 3 deg C, which is well within reasonable limits, considering the numerous uncertainties that exist in material properties, accuracy of measurements, variability of environmental factors (wind, sunshine, etc.), and inclination of the pavement surface in receiving radiation.

Use of a three-dimensional, dynamic finite element program for analysis of flexible pavement

Abstract: Predominantly flexible pavement structural response to loads is predicted by using an elastic multilayer analysis. This type of analysis is based on the assumption that pavements are subjected to static loads and that paving and subgrade materials are linear elastic materials. In this paper, ABAQUS, a three-dimensional, dynamic finite element program (3D-DFEM), was used to analyze flexible pavements subjected to moving loads at various speeds. A number of material models were used to represent actual material characteristics such as viscoelasticity and elastoplasticity. The validity and then the application of 3D-DFEM to flexible pavement analysis were examined. Validation was accomplished by analysis of both static and dynamic cases. The static and dynamic verification studies indicated that 3D-DFEM can be used with confidence to predict actual pavement response from moving loads.

Estimation of travel choice models with randomly distributed values of time

Abstract: The value of time is a key concept in transport planning in terms of the economic valuation of travel time savings and the relative importance of time versus cost in travel forecasting models. A standard method for deriving values of time is to use the tradeoff ratio implied by the time and cost coefficients estimated in travel choice models. In actual choice situations, it is impossible to observe all the factors that affect the relative importance of time and cost. Thus, a method for estimating discrete travel choice models was derived and demonstrated with a randomly distributed value of time. In the case studies considered, significant improvements in model fit were obtained when distributed values of time were allowed. In prediction, more realistic responses were found by using the distributed value of time model than by using models with a fixed value of time.

Accident prediction models for freeways

Abstract: The modeling of freeway accidents continues to be of interest because of the frequency and severity of these accidents and the congestion associated with them. Some difficulties with conventional modeling techniques are identified. A distinctive approach is presented, whereby generalized linear modeling is used with both macroscopic and microscopic data to develop regression model estimates of a freeway section's accident potential and an empirical Bayesian procedure is used for refining these estimates.

Light-rail transit stations and property values: a hedonic price approach

Abstract: What are the effects of proximity to light-rail transit (LRT) stations on the value of single-family homes? Two forces are at work. Proximity to LRT stations may improve the accessibility of residents to the central business district and the rest of the urban area. Further, proximity to rail stations may result in transportation cost savings for nearby residents. These effects should be positively capitalized in property values. Alternatively, without attention to design, LRT stations may impose negative externalities on nearby properties, with a resulting decline in house values. Which of these effects predominates in the housing market with respect to station proximity? A study was undertaken to analyze sale prices of homes in metropolitan Portland, Oregon. Two distance models to LRT stations were compared. The first showed a positive capitalization of proximity to LRT stations for homes within 500 m (1600 ft or 1/4 mi) of actual walking distance. This effect was equally felt for all homes within that distance zone. The second model found a statistically weak negative price gradient for homes within the 500-m zone. This implies a positive influence of proximity the closer the home is to an LRT station.

Simulation model of activity scheduling behavior

Abstract: The simulation model of activity scheduling behavior presented is influenced by recent theories of activity scheduling and production system modeling. The basic assumption underlying the model is that activity scheduling is a sequential process in which consecutive steps lead to the final schedule. Every step in this respect is modeled as a choice of an action to perform on a preliminary schedule. The behavior of the model was tested using simulations in different hypothetical spatio-temporal settings. The simulations were conducted repeatedly, varying the values of the parameters of the model systematically. In general, the simulations resulted in realistic schedules. The proposed approach therefore offers possibilities to model activity scheduling realistically. The next step, however, should be to develop calibration methods so that parameter values can be derived from observed behavior. Interactive simulations may be a promising technique in this respect.

Shear strength and compressibility of tire chips for use as retaining wall backfill

Abstract: Scrap tires that have been cut into chips are coarse grained, free draining, and have a low compacted density, thus offering significant advantages for use as lightweight fill and retaining wall backfill. The engineering properties needed to put tire chips into use are presented. The properties determined for tire chips, from three suppliers, are gradation, specific gravity, compacted density, shear strength, compressibility, and coefficient of lateral earth pressure at rest. The 76-mm (3-in.) maximum size and high compressibility of the tire chips necessitated design and fabrication of custom-made testing equipment. The tests showed that the tire chips are composed of uniformly graded, gravel-sized particles that absorb only a small amount of water. Their compacted density is 0.618 to 0.642 Mg/cu m (38.6 to 40.1 pcf), which is about one-third that of compacted soils. The shear strength was measured in a large-scale direct shear apparatus. The friction angle and cohesion intercept ranged from 19 to 25 degrees and 8 to 11 kPa (160 to 240 psf), respectively. The compressibility tests showed that tire chips are highly compressible on initial loading, but that the compressibility on subsequent unloading and reloading cycles is less. The horizontal stress was measured during these tests and showed that the coefficient of lateral earth pressure at rest varied from 0.26 for tire chips with a large amount of steel belt exposed at the cut edges to 0.47 for tire chips composed entirely of glass-belted tires.

Determination of service levels for pedestrians, with european examples

Abstract: Qualitative evaluation of pedestrian precincts is important for providing adequate facilities for the elderly, the physically challenged, and children, who are most inclined to use this mode of travel Evaluation has been attempted by using the qualitative criteria of safety, security, comfort and convenience, continuity, system coherence, and attractiveness After the levels of activity and use in the pedestrian environments in Munich and Rome were studied, pedestrian environments have been classified into six service levels

Network performance under system optimal and user equilibrium dynamic assignments: implications for advanced traveler information systems

Abstract: A comparative assessment was undertaken of network cost and performance under time-dependent system optimal (SO) and user equilibrium (UE) assignment patterns, with particular reference to the effectiveness of advanced traveler information systems (ATIS). Both SO and UE solutions were found using a new simulation-based algorithm for the time-dependent assignment problem. Experiments were conducted using a test network with signal-controlled junctions under progressively increasing network loading intensities. A diagnosis of system performance for various intensities of loading was effected using network-level traffic descriptors for both SO and UE assignments. The results affirm the validity of a meaningful demarcation between SO and UE assignments in urban traffic networks and provide useful insights for macroscopic network-level relations among traffic descriptors. These results suggest that ATIS information supply strategies based on SO route guidance could considerably outperform descriptive noncooperative information strategies, especially at moderate to high congestion levels in the network. The results also illustrate the time-dependent nature of the gains achieved by an SO assignment vis-a-vis a UE assignment in a congested traffic network.

Integrated approach to vehicle routing and congestion prediction for real-time driver guidance

Abstract: The generation and dissemination of driver guidance that can be used for real-time diversion of traffic are expected to be implemented through the use of real-time traveler information systems. To implement these functions, a system structure consisting of a surveillance module, a congestion prediction module, and a control and routing (CAR) module is proposed, with the focus on the approaches that may be used for congestion prediction and the strategies that may form the basis for routing. It is argued that a congestion prediction capability is critical for the effectiveness of an on-line traveler information system. Such a capability is required to accurately forecast traffic conditions that may exist in the near future. The use of a dynamic traffic assignment model for congestion prediction is suggested. Such a model consists of dynamic driver behavior and network performance modules as well as origin-destination updating capability. Alternatively, statistical time-series methods may be necessary to generate predictions of future traffic conditions. The advantages and difficulties of adopting either approach are discussed. The predicted congestion information is passed to the CAR module to develop diversion strategies to alleviate both recurring and nonrecurring congestion. The role of routing strategies and update frequency in determining guidance effectiveness is discussed.

Traffic volume reductions due to winter storm conditions

Abstract: When hazardous driving conditions exist on roads, road users have less desire to travel. As a result of snow and icy conditions, a reduction in traffic movement occurs. The decrease in traffic movement is almost unexamined so far. During a research project conducted in 1991-1992 to study the impact of snow and ice control operations on traffic accident rates, the need for estimating the decrease in traffic movement urged such calculations. The reductions in traffic volumes generated as a result of adverse snow and icy conditions were measured, grouped, and correlated during various weather conditions in four states (Illinois, Minnesota, New York, and Wisconsin). Traffic volumes reductions factors during different winter storms conditions were calculated and reported.

Application and interpretation of nested logit models of intercity mode choice

Abstract: A clear understanding of the sources and amount of ridership on a new or improved travel mode is critical to evaluating the financial, travel flow, and external impacts of proposed improvements. The multinomial logit model traditionally used to model intercity mode choice may not adequately reflect traveler behavior because it restricts the relative probability of choosing between any pair of existing modes to be unchanged when other modes are introduced or changed. The nested logit model provides a computationally feasible generalization to the multinomial logit model, which allows for specified mode pairs to exhibit increased sensitivity to changes in service. Full information estimation of nested logit models allows efficient use of information and yields results directly comparable to multinomial logit models. Business travel in the Ontario-Quebec corridor of Canada is examined. A set of nested logit structures that allow for various combinations of differential sensitivity to changes in service quality of rail is estimated. Nested logit structures with bus-train or car-train nests prove superior to the multinomial logit model. Both of the nested logit models predict larger increases in rail shares than the multinomial logit model in response to rail service improvements, but the source of that increased ridership differs between the nested logit structures. This points to the need for models of individual choice that retain the advantages of nested logit while allowing pairwise similarity between alternatives.

Effects of physicochemical factors on asphalt oxidation kinetics

Abstract: Oxidative aging of asphalt is a primary cause of asphalt hardening in pavements, thus contributing to various forms of pavement cracking. Although the changes in asphalt physical properties on oxidative aging are primarily the result of the formation of oxygen-containing functional groups in the asphalt, the sensitivity of an asphalt to these oxidation products varies widely with asphalt source (composition). An understanding of the kinetics of oxidation in the pavement temperature range is confounded by both the complex composition of asphalt and its thermally reversible microstructure. To better understand the mechanisms of age hardening, the kinetics of asphalt oxidation were investigated from the pavement temperature range [60 deg C (140 deg F)] through the higher temperature range of commonly used accelerated laboratory tests [130 deg C (266 deg F)]. It was found that asphalts with different component compatibilities may exhibit similar age hardening kinetics at the low end of the pavement temperature range, but quite different kinetics at the high end of the range. This is because the aging kinetics become highly dependent on how temperature affects the molecular microstructure. A new microstructural model of the age hardening of asphalt cement is presented that proposes that the kinetics of aging in the pavement temperature range is largely governed by physicochemical factors related to the state of dispersion of the molecular microstructure rather than the inherent reactivity of the molecular components with oxygen. The model is supported by results of past and present research.

Estimation of safety at two-way stop-controlled intersections on rural highways

Abstract: The application of the generalized linear modeling approach to the development of a model relating unsignalized intersection traffic demands to accident frequency is described. Several techniques for assessing model fit have been described and any inherent limitations noted. The model was based on the product of the intersection traffic demands raised to a power. This model form was found to explain a large portion of the variability in accidents among intersections of similar geometry and traffic control. The analysis of accident data for 125 two-way stop-controlled intersections supports the theory that the distribution of accident counts can be described by the negative binomial distribution. Also supported is the assertion that the mean accident frequency for the group of similar intersections is gamma distributed. Knowledge of these distributions and their parametric values can be used to identify hazardous locations and the true effect of safety treatments on accident frequency.

Gender differences in commuter travel in tucson: implications for travel demand management programs

Abstract: This paper reports on part of a study funded by the U.S. Department of Labor to evaluate whether individual transportation demand management (TDM) measures differentially affect salaried men and women in various household situations. Working women with children are the least able to make drastic changes in their daily activities but may be the most affected by employer sanctions and financial penalties. The study found that in Tucson, Arizona, women are (a) substantially more dependent on he private car driven alone than are comparable men, (b) far less likely to have switched to alternative modes, and (c) more likely to have chosen different alternative modes when they did switch. Moreover, there were differences between the sexes in travel time and distance to work, none of which could be explained by income or occupation. When workers were asked how effective various TDM strategies would be in increasing their use of alternative modes, women were more likely to see all potential strategies in a favorable light. Moreover, women were more responsive to strategies that addressed their domestic responsibilities (for example, their need to transport children or respond to family emergencies). Ultimately, while being more favorably disposed to TDM measures, women were less likely to give up driving alone because travel modes that are slower and less flexible than the private car may severely affect their working and family lives. These findings show the need to identify the equity consequences of specific TDM requirements, to target appropriate individual measures to working women, and to develop ways to offset the negative impacts on working mothers.

Models Of Commuters' Information Use And Route Choice: Initial Results Based On A Southern California Commuter Route Choice Survey

Abstract: This paper presents a statistical analysis of commuters' route choice behavior and the influence of traffic information. The analysis is based on a 1992 computer-aided telephone interview survey of Los Angeles area morning commuters. The results underscore the important relationship between the use of traffic information and the propensity to change routes. In addition, important relationships are uncovered relating the influence that commuters' socioeconomic characteristics and the level of traffic congestion they face have on traffic information use and route- change frequency. The results' important implications for advanced traveler information systems (ATIS) development are discussed.

Environmental and travel preferences of cyclists.

Abstract: Current recommendations for designing bicycle facilities are most often based on experience rather than on findings from scientific inquiry This study pools cyclists' opinions on environmental design issues, substantiating experts' knowledge about designs for cycling environments The study examines the influence of personal characteristics, travel resources, and travel constraints on cyclists' environmental preferences, evaluations of cycling conditions, and decisions to bicycle for transportation Questionnaires were distributed to 552 cyclists at four recreational bicycle tours in Michigan during the summer of 1992 Analysis of variance and correlations were used to investigate relationships of interest Cyclists indicated their preferences for different types of cycling facilities and the importance that they placed on environmental factors such as traffic volume and surface quality when choosing cycling routes Age was positively correlated with preference for on-road facilities (striped bike lanes, wide curb lanes), with importance placed on surface quality, scenery, and bike safety education Age was negatively correlated with preference for bike paths separated from the roadway Safety, scenery, terrain, and bike safety education were more important to women on average than to men As expected, cycling experience was negatively correlated with preference for off-road facilities and concerns about safety, traffic, and terrain Bike safety education was rated almost as high as the need for bike lanes, to improve community cycling conditions Thirty-two percent of the cyclists surveyed commute by bicycle; 68 percent run errands by bicycle Commute distance was strongly associated with the likelihood and frequency of commuting by bicycle

Rubber soils as lightweight geomaterials

Abstract: The literature review and laboratory testing results from an on-going research study, which investigates the feasibility of using rubber soils as lightweight geomaterial in highway construction, are presented. An overview of conventional lightweight materials; generation and disposal options for scrap tires; a summary of the various field and laboratory studies on the use of shredded tires as lightweight fill; results from compaction, compressibility, and permeability testing of compacted rubber soils samples; and the salient conclusions of this study are also presented. The use of shredded tires in highway construction offers technical, economic, and environmental benefits under certain conditions. The benefits are reduced weight of fill and backfill pressures. Shredded tires serve as a good drainage medium and have longer life. Tire chips are practically indestructible and available in abundance at practically no cost. Recycling large quantities of discarded tires has a positive impact on the environment. Potential problems are leachate of metals and hydrocarbons, fire risk, and large compressibility of tire chips. Information about stress-strain-strength behavior of tire chips for design and performance prediction of tire embankments and long-term environmental impacts of shredded tires is lacking.

Load reduction on rigid culverts beneath high fills: long-term behavior

Abstract: Three full-scale tests with the imperfect ditch method are described. The imperfect ditch method involves installing a compressible inclusion above rigid culverts to reduce the vertical earth pressure. Superlight expanded polystyrene blocks are used as the compressible material. In the first test, the instrumented culvert was a 1.95-m diameter concrete pipe beneath a 14-m-high rockfill embankment. In the second test, a 1.71-m diameter concrete pipe was used beneath a 15-m-high rock fill, and in the third, the culvert is a cast-in-place concrete box culvert with a 2.0-m width beneath 11 m of silty clay. The culverts were built between 1988 and 1989, and the instrumentation measured earth pressure, deformation, and temperature. The full-scale measurements show considerable reduction in the vertical earth pressure: that on top of the pipes in the granular fill was reduced to less than 30 percent of the overburden and that on the box culvert beneath the clay fill was reduced to less than 50 percent of the overburden. The deformation of the expanded polystyrene was 27 percent in the rock fill and 42 percent in the clay. The long-term observations show that there is no increase in earth pressure on and deformation of the pipes beneath the rock fill. There is a slight increase in deformation of the expanded polystyrene in the clay. Use of this method in Norway has realized cost reductions of the order of 30 percent and has made it possible to use concrete pipes beneath higher fills.

Statistical evaluation of the effects of highway geometric design on truck accident involvements

Abstract: This paper illustrates how the Poisson regression model can be used (1) to evaluate the effects of highway geometric design on truck accident involvement rates, and (2) to estimate and quantify the uncertainties of the expected reductions in truck accident involvements from various improvements in highway geometric design. The data source used in this study was the Highway Safety Information System (HSIS), a highway safety data base administered by the Federal Highway Administration (FHWA). Five years of highway geometric, traffic, and truck accident data for rural Interstate highways in one of the HSIS State from 1985 to 1989 were used for illustrations.

Dynamic interactive simulator for studying commuter behavior under real-time traffic information supply strategies

Abstract: A new simulator for laboratory studies of the dynamics of commuter behavior under real-time traffic information (advanced traveler information systems) strategies is described, and a set of laboratory experiments that used this simulator is discussed. The purpose of the experiments was to examine the bahavioral processes underlying commuter decisions on route diversions en route and day-to-day departure time and route choices as influenced by the provision of real-time traffic information. Both the real-time and day-to-day dynamic properties of traffic networks under alternative information strategies--particularly issues of convergence to an equilibrium, stability, and benefits following shifts in commuter trip timing decisions--will also be investigated in the experiments.

Hybrid genetic algorithm to optimize signal phasing and timing

Abstract: Signal timing optimization involves the selection of four basic design elements: phase sequence, cycle length, green split, and offset. None of the available signal timing models is considered adequate to optimize all four design elements, particularly in two-dimensional networks. Among the current models, TRANSYT-7F is most effective for timing, but it does not optimize phasing. Researchers have considered several methods for enhancing TRANSYT-7F to include phasing optimization but thus far no method has proven practical. An exhaustive search of possible phasing combinations is computationally prohibitive; thus a new approach is needed. Genetic algorithms (GAs) are heuristic probabilistic search procedures that have been applied to a wide range of engineering problems. The use is investigated of a GA in combination with the TRANSYT-7F optimization routine to select all signal timing design elements. The main purpose of the GA in the proposed scheme is to optimize phase sequences. Two implementations of the GA model are presented. In the first, the GA and TRANSYT-7F optimization routines are executed concurrently to achieve an optimal solution. In the second, the GA is allowed to optimize cycle length, phase sequences, and offsets. Then TRANSTY-7F is used to adjust the resultant signal timing. The results suggest that both implementations have potential for optimizing signal phasing and timing. However, the first method produces more consistent results. It also requires longer execution time.

Stated preference approach to modeling the adoption of telecommuting

Abstract: Many researchers have suggested the potential use of telecommuting as a substitute for travel to reduce traffic congestion, energy consumption, and air pollution. The effectiveness of this working arrangement as a strategy to address these policy issues, however, will depend on the level of adoption and on the impacts of usage on individuals' travel behavior. This paper discusses the process of individuals' adoption of telecommuting, given that the alternative is made available by the employer. A review of the relevant research concerning individuals and the process of adoption of telecommuting is presented. On the basis of the state of the art, a framework to model this process is proposed. An empirical study conducted to demonstrate the proposed framework is described. The implications of the main findings of this study policy design are analyzed and directions for further research are suggested.

Smoothing algorithms for incident detection

Abstract: The majority of automatic incident detection algorithms aim to identify traffic incident patterns but do not adequately investigate possible similarities in patterns observed under incident-free conditions. A classification of major traffic disturbances on freeways is presented. On the basis of this classification, an incident detection logic is developed with the traffic features that result in the best distinction between an incident and other disturbances. The new logic, DELOS (Detection Logic with Smoothing), employs smoothed detector occupancy measurements to signal an incident when significant temporal changes of the smoothed occupancy occur. Three types of smoothers--average, statistical median, and exponential--are considered, leading to corresponding algorithms. The structure of the proposed algorithms is presented and compared with previous algorithms. Comparative evaluation of test results with rush-hour traffic and incident data from I-35W in Minneapolis reveals the improved performance of the proposed method.

Nonlinear elastic viscous with damage model to predict permanent deformation of asphalt concrete mixes

Abstract: The development and use of a nonlinear elastic, viscous with damage model are discussed. The model is proposed as a constitutive relation for asphalt concrete mixes to permit prediction of permanent deformation. The model is intended to capture the macrobehavior of mixes, including (a) the dilatancy observed when the mix is subjected to shear strains, (b) the increase of effective shear modulus under increased hydrostatic pressure, (c) the significant variation of behavior with changes in temperature and rates of loading, and (d) the residual accumulation of permanent deformation under repetitive loading. This model has been developed as part of the Strategic Highway Research Program A-003A efforts to characterize the permanent deformation characteristics of asphalt-aggregate mixes. A new series of tests proposed for the determination of the material properties is presented; modeled and observed responses from a simple validation test are compared; and the use of the model to predict permanent deformation response in an asphalt concrete pavement section is illustrated.

Comparative assessment of travel characteristics for neotraditional designs

Abstract: The claim that transportation benefits can be derived from neotraditional neighborhood design is explored. Conventional transportation planning models are used as tools to evaluate the performance differences of two hypothetical street networks designed to replicate a neotraditional and a conventional suburban community. Relative transportation benefits are measured in terms of vehicle kilometers traveled, average trip lengths, and congestion on links and at intersections. This comparison provides an assessment of how well the two networks in question deal with trips generated by the activities that they serve. All aspects of the modeled communities are held constant except for the actual configuration of the networks. The results of this evaluation indicate that equivalent levels of activity (defined by the land uses within the community) can produce greater congestion with conventional network structures and that corresponding average trip lengths are generally longer. The ultimate goal is to determine if one network type, because of the nature of its design, can result in a more efficient transportation system. The results indicate that neotraditional designs can improve system performance.

Demand for aircraft gates

Abstract: Demand for aircraft gates, which is defined as the number of aircraft expected to require the service provided at a terminal building at any given time during one day's operation, depends on flights scheduled and their actual behavior relative to those schedules. The schedules provide a deterministic element to the process of generating the actual number of aircraft at gates, and deviation from these schedules provides a stochastic element in the process. A model that incorporates these two elements has been developed to estimate gate requirements at airports. The results of applying the model to an actual operation of aircraft gates have demonstrated the ability of the model to describe gate occupancy as a function of time of day with reasonable accuracy. The results have also shown that a common gate use strategy (i.e., first-come, first-served discipline) requires fewer gates than strategies under which the use of gates is restricted to flights of a particular air carrier or sector. Furthermore, it has been demonstrated, given a scheduling practice involving bank operations, how the time internal between banks influences the requirement for gates.