In this study, tomograms of bituminous mixtures with a photon energy $\left(E\right)$ of 120 kV are taken with a multidetector X-ray scanner. These tomograms are cross-sectional images of the internal structure of specimens in a cutting plane surface. The purpose of taking these tomograms was to find out the main factor/factors causing different fatigue lives for replicated specimens using images of the internal structure of specimens. After taking the tomograms, the fatigue tests were carried out using repeated-loading indirect tensile test equipment. In addition to conventional fatigue model parameters, new parameters, which are acquired from the cross-sectional surface tomograms, are taken into consideration to be able to explain the variations in the fatigue lives of similar specimens. These new models help explain the variations in fatigue lives of similar specimens tested under identical conditions. Hence, tomograms will help us define the fatigue lives of specimens in a nondestructive way.

Due to their efficiency and economy, supersingle tires have gradually been replacing conventional dual tires in the trucking industry. According to recent studies, supersingle tires generate much higher vertical contact stresses than do conventional dual tires, resulting in larger deformations and more severe damage to the subgrade. In order to better assess the larger stresses generated by supersingle tires and their effect on the subgrade, analyses are done taking into account soil plasticity. In this paper, the effects of supersingle tires on subgrades for typical road cross sections are investigated using plane-strain two-dimensional and three-dimensional static and dynamic finite element analyses. The analyses focus on the sand and clay subgrades rather than on asphalt and base layers. The subgrades are modeled as saturated in order to investigate the effects of porewater pressures under the most severe conditions. The analyses suggest that current flexible pavement design methods are unconservative for the increased loads imposed by supersingle tires on the pavement system.

This study investigates the cost effectiveness of various levels of life-cycle preventive maintenance (PM) for three asphaltic concrete pavement functional class families. For each family, the effectiveness and cost associated with each of several alternative life-cycle PM strategies were estimated. For each strategy, effectiveness was estimated as the increase in service life relative to a base-case strategy, and the cost was estimated in terms of agency and user costs associated with the treatments comprising that strategy. Using the estimated costs and effectiveness, statistical models were developed to describe the relationship between life-cycle PM effort and its efficacy in extending the pavement life, per unit cost. It is shown that increasing PM is generally associated with increasing cost effectiveness (but only up to a certain turning point beyond which cost effectiveness decreases). It was determined that the maximum cost effectiveness and the corresponding level of annualized PM are influenced by the pavement functional class and cost components considered. A general methodology is hereby provided for pavement managers to estimate the expected changes in pavement service life arising from changes in PM expenditure.

This paper introduces an integrated approach to the development of construction and traffic management plans for the reconstruction of high-volume urban freeways. The Devore project, which rebuilds a 4.2 km stretch of the deteriorated concrete pavement (truck lanes) on Interstate-15 (I-15) in San Bernardino County in southern California, is used as a case study. Alternative closure timing, closure duration, and number of closed lanes were compared to identify the best rehabilitation strategy for the Devore reconstruction project. The perspectives of construction schedule, traffic inconvenience (road user cost and maximum delay), and agency costs were considered. The analysis concluded that full closure of one roadbed with counter-flow traffic during repeated three or four continuous weekdays, utilizing round-the-clock reconstruction operations, was the best strategy for both the public and the sponsoring agency. A delay in the start of construction from Spring to Fall 2004 is expected to cause a 5% seasonal traffic increase, which will result in a $4.5 million increase in road user cost and a 20% increase in maximum queue delay per closure.

The purpose of this study is to incorporate the correlation between different types of emissions into microscale vehicle emissions models. Simultaneous equations models were calibrated for two vehicle categories classified in a National Cooperative Highway Research Program project. One represents normal emitting vehicles, while the other represents high emitting vehicles. Among various vehicle operation conditions, only those represented by Bag 2 of the Federal Test Procedure cycle were considered in this study. The developed models were evaluated based on the criteria of root mean square errors and correlation coefficients between the estimated and measured emissions. The results indicate that the correlation between emissions of CO and HC can be significantly identified; thus, these two emission types should be included in the simultaneous equations models. In addition, the results indicate that simultaneous equations models can achieve better and reliable emissions estimation results compared with other vehicle emissions models, which implies that it is worthwhile to apply simultaneous equations models to other operation conditions.

Accurate and timely forecasting of traffic flow is of paramount importance for effective management of traffic congestion in intelligent transportation systems. In this paper, a novel nonparametric dynamic time-delay recurrent wavelet neural network model is presented for forecasting traffic flow. The model incorporates the self-similar, singular, and fractal properties discovered in the traffic flow. The concept of wavelet frame is introduced and exploited in the model to provide flexibility in the design of wavelets and to add extra features such as adaptable translation parameters desirable in traffic flow forecasting. The statistical autocorrelation function is used for selection of the optimum input dimension of traffic flow time series. The model incorporates both the time of the day and the day of the week of the prediction time. As such, it can be used for long-term traffic flow forecasting in addition to short-term forecasting. The model has been validated using actual freeway traffic flow data. The model can assist traffic engineers and highway agencies to create effective traffic management plans for alleviating freeway congestions.

Highway maintenance, like rehabilitation or resurfacing, on four-lane, two-way highways usually requires closing one or two lanes to set up a work zone. In this paper we evaluate several alternatives defined by the number of closed lanes, fractions of traffic diverted to alternate routes, and crossover of diverted traffic to opposite lanes. A methodology is developed to minimize the total cost, including agency cost, user cost, and accident cost, by optimizing work zone length for each alternative and finding optimal diversion fraction, while considering the characteristics of the detour route bypassing the work zone. Finally, guidelines for selecting the best alternative for different characteristics of traffic flows, roads, and maintenance processes are developed by deriving thresholds among alternatives.

This paper explores the impact of unscheduled navigational and surveillance equipment outages on airport performance during visual flight rules and instrument flight rules at San Francisco International Airport and Phoenix Sky Harbor International Airport. The following most common unscheduled short outages, which occurred during January 2000–December 2002, are analyzed in detail: very high frequency omnidirectional range (VOR), approach lighting system type 2 (ALSF-2), the secondary radar Mode $S$ , and air traffic control radio beacon system (ATCRBS). We explore the air traffic control procedures and responses to unscheduled outages, and develop a methodology to examine the effects of unscheduled outages on airport performance. Two Federal Aviation Administration databases, maintenance management system and aviation system performance metrics, are used to construct censored regression models (i.e., Tobit models) to assess the airport throughput performance during such unscheduled outages. It is found that airport arrival and departure throughputs do not deteriorate with VOR and ALSF-2 outages due to availability of air traffic procedures that allow alternative approaches into the airport. However, the unscheduled outages of secondary radar Mode $S$ and ATCRBS do cause airport throughput degradations.

The distribution of axle loads can vary geographically and seasonally; ignoring these variations may impact the accurate characterization of traffic and ultimately the design thickness of new and rehabilitated pavements. A study of axle load spectra at thirteen sites on rural arterials in Alabama examined the statistical and practical significance of these spatial and temporal differences. In most cases, daily and monthly axle load spectra exhibited statistically significant differences from the composite distributions. Differences between distributions observed at each direction at a site and the site average were statistically significant, as were differences between the distribution at each site and the statewide average. However, in most cases, the resultant impact on pavement thickness design was negligible. At 92% of the study sites, use of the statewide distribution in lieu of site-specific data resulted in no more than a difference of 0.3 for structural number for flexible pavement and a 0.7 inch (1.8 cm) difference in rigid pavement depth; these differences were considered insignificant from a practical perspective.