Recent progress in the monitoring and prediction of the condition of infrastructure using sensing technologies has motivated researchers and infrastructure owners to explore the benefits of asset predictive maintenance, as an alternative to reactive maintenance. However, the application of predictive group maintenance for multi-system multi-component networks (MSMCN) has not received much attention in the literature or in practice. The paper presents an approach that prioritizes the maintenance of MSMCN of bridges, using a deterioration model of components with uncertainty, a lifecycle cost model, a predictive model for the optimal time for maintenance based on the latest inspection, a group maintenance model to reduce setup cost, and a scheduling model considering budget constraints. This model has been applied to a network of 15 bridges constituted by multiple heterogeneous components, and, compared with the Structures Investment Toolkit, it showed potential for a substantial decrease in maintenance costs, thus highlighting the practical significance of the presented approach.
As the concept of sustainable pavement gains prominence, a growing number of industrial wastes and recycled materials have been utilized in the pavement industry to preserve natural resources. This study investigates the potential use of waste glass powder-based geopolymer cement as a stabilizing agent in recycled waste glass aggregate (GA) bases. Two recycled materials, waste glass powder (GP) and class F fly ash (FF), were used as the raw materials in the preparation of geopolymer. Virgin aggregate (VA) was replaced by GA at varying replacement ratios as the pavement base materials, and the mechanical behaviors before and after geopolymer stabilization were evaluated. Without stabilization, the incorporation of over 10% GA caused significant detrimental effects on the California bearing ratios (CBR) of base materials, which should be carefully managed in pavement construction. However, all geopolymer stabilized samples showed decent strength properties, indicating the effectiveness of geopolymer stabilization. The use of GA reduced the drying shrinkage of base samples, although the mechanical properties were compromised. During the sample preparation, a higher curing temperature and relative humidity resulted in better mechanical behaviors, and the surface of GA could dissolve in alkaline solution and involve in the geopolymerization at 40 degrees C. The microstructure and minerology of geopolymer stabilizer of base materials were characterized by scanning electron microscopy (SEM) and X-ray defraction (XRD) analyses. This study confirmed the promise of using waste glass-based pavement base materials as the greener substitutes and the potential synergy between waste glass recycling and the pavement industry.
The structure design and mechanistic calculation of inverted asphalt pavements are mainly based on linear layer elastic theory with the assumption that the cement-treated subbase (CTB) is complete without cracks. This study investigates the optimal structure combination for inverted pavements according to calculated critical responses considering cracks in the CTB layer. A three-dimensional finite element (3D FE) model of inverted pavement with a transverse crack through the CTB layer was developed. Four full-scale inverted pavement sections were built, and a crack 0.01 m wide and 0.05 m deep was sawn on top of each CTB layer after construction. The 3D FE model was validated by strain and deformation measured in falling weight deflectometer tests and used for a parametric study of dominating structure combination factors. Variance analysis results show that interactions with thickness or stiffness of the asphalt concrete (AC) layer presented the most significant effect on critical responses, while CTB stiffness (12588 similar to 7668 MPa) had the least impact. Structure variation effect analysis results illustrated that 0.1 m aggregate base (AB) thickness is enough to prevent the CTB crack propagating to the surface. Thin AC structures are highly sensitive to variations in AC and AB stiffness. A thin AC and AB combination (0.05 and 0.10 m) can provide low critical strains similar to a thick AC and thin AB (0.15 and 0.10 m) combination if the stiffness of AC and AB can be maintained at 7175 and 358 Mpa, respectively, or higher. AC thickness of 0.1 m and the combination of thin AC and thick AB are two unfavorable conditions for inverted pavements.
This paper intends to analyze the Light Detection and Ranging (Lidar) sensor performance on detecting pedestrians under different weather conditions. Lidar sensor is the key sensor in autonomous vehicles, which can provide high-resolution object information. Thus, it is important to analyze the performance of Lidar. This paper involves an autonomous bus operating several pedestrian detection tests in a parking lot at the University at Buffalo. By comparing the pedestrian detection results on rainy days with the results on sunny days, the evidence shows that the rain can cause unstable performance and even failures of Lidar sensors to detect pedestrians in time. After analyzing the test data, three logit models are built to estimate the probability of Lidar detection failure. The rainy weather still plays an important role in affecting Lidar detection performance. Moreover, the distance between a vehicle and a pedestrian, as well as the autonomous vehicle velocity, are also important. This paper can provide a way to improve the Lidar detection performance in autonomous vehicles.
Water damage often occurs on porous asphalt pavement during service life because of the well-developed pore structure. Determining the adhesion and adhesion healing properties of high-viscosity modified asphalt (HVMA) under water condition is beneficial to understand the water damage process of porous asphalt. In this study, the modified binder bond strength test was first conducted to investigate the adhesion property and self-healing behavior of HVMA at different conditions. Then, the surface energy test was carried out to further characterize the differences in adhesion property of HVMA. Moreover, the gel permeation chromatography test and fluorescence microscopic test were used to investigate the influence of chemical composition and polymer morphology on the adhesion property of HVMA. Results show that the presence of water reduces the adhesion property of HVMA. The addition of polymers leads to an increasing adhesion strength and a decreasing self-healing ability of HVMA. The self-healing ability of HVMA improves with the increase of temperature, but also shows a decreased trend when the healing time is long at high-temperature water immersion. The effect of polymers on the adhesion property of asphalt has two aspects. First, the swelling of polymers leads to an increasing content of polar heavy components in HVMA, thus enhancing polarity adsorption between asphalt and aggregate. Moreover, a polymer-centered interfacial diffusion layer can be formed during the adsorption of light components, which increases the overlapping area of structural asphalt between adjacent aggregates. This can also improve the adhesion property at the asphalt-aggregate interface.
Hollow core concrete bridges have been widely constructed in China during the last two decades. The most simple span bridges, with standard lengths of 13 m, 16 m and 20 m, are hollow core concrete bridges. For this type of bridge, the hollow core slabs are precast and simply lifted into place. After the prefabricated hollow core slabs are put in place, the embedded rebars extending from the prefabricated slabs are bound together and the concrete is poured into the space between the slabs, forming a lateral hinge joints between the slabs. A lot of hollow core concrete bridges built early in the 1990s have small hinge joints and very few rebars embedded to form strong lateral connections between the slabs. With an increase of overweight vehicles and the continuous aging of the structures, structural deficiencies such as intensive cracks running through the mid-span and severe deflection progress rapidly resulting in loss of structural capacity and even collapse. The failure of hollow core concrete bridges usually initiates from the failure of the hinge joints, which are the weakest links of the system. When the hinge joints start to lose their ability to hold the adjacent slabs securely, more and more vehicle loads are shifted onto the slabs with deficient hinge joints, which worsens the condition of the slabs and eventually results in systematic failure. To save the hollow core concrete bridges from failure, the authors propose an effective strengthening method to stop the progress of the deficiencies and improve the capacity of the structure.
Traffic accidents in extra-long urban underwater tunnels are characterized by high numbers of causalities and severe traffic congestion. Analyzing drivers' saccade characteristics under different curvature conditions in urban underwater tunnels can provide solutions to reduce the rates of such accidents and increase traffic safety. This paper reports real vehicle tests conducted in extra-long urban underwater tunnels, on curved sections of radii of 400, 680, 1,000, 1,500, and 3,000 m, and also on straight sections. Indicators of drivers' saccade behavior, such as saccade angle, time, and frequency, and the saccade time ratio were evaluated. The coefficient of variation was used to analyze the discreteness of the saccade angle. The driver's saccade characteristics, such as saccade time and frequency, were explored by combining the visual distances for different curved sections. The results demonstrated that (a) small angles in the range of [0, 10 degrees] constituted the main distribution section of the driver's saccade angle in extra-long urban underwater tunnels, and the saccade angle discreteness increased with increase in the radius, (b) the driver's average saccade time increased while the average saccade frequency decreased with the increase of the radius, (c) the driver's visual load was higher for long straight sections and small-radius curves, (d) the driver's safety was generally higher on right-curving sections than on left-curving sections.
Traffic crashes occur usually because of a combination of human, roadway/environment, and vehicle factors. Pavement condition is closely related to these three factors as it is one of the most important roadway/environment factors and it affects driving behavior and vehicle performance at the same time. Previous studies have shown that pavement condition plays an important role in safety. This study develops four different safety performance functions to evaluate the effect of pavement roughness, measured by the International Roughness Index (IRI), on the number of crashes using the interstate highway data from five U.S. states representing different geographical and weather regions: Arizona, Colorado, Florida, Maryland, and Michigan. The modeling results identify many significant variables including traffic volume and proportion of trucks, through lane count, shoulder type, median width, high-occupancy vehicle (HOV) lane operation and HOV lane count, speed limit, area type along with IRI-related factors. The results indicate that increased IRI (deterioration of pavement quality) contributes to large numbers of total crashes. On interstate highways with speed limits of 70 mph and higher, the effects of IRI are relatively smaller. On the other hand, the effects of IRI increase with a larger traffic volume. Based on the modeling results, seven crash modification functions of IRI values by crash type and speed limit were estimated. The findings from this study are expected to be useful for both pavement and safety engineers to understand the relationship between IRI and safety on freeways.
In China, around 90% of traffic crashes at signalized intersections take place within the signal change intervals, especially during signal change from green to red. Hence, yellow time, which is a part of inter-green time, is of great significance to the safety of signalized intersections. The conventional calculation method for duration of yellow light (DYL) ignores the stochastic characteristics of drivers, which we believe is an important factor in this calculation. Therefore, the purpose of this research is to investigate a new approach to calculate DYL based on safety reliability theory in which the randomness of human factors is taken into consideration. Firstly, a comprehensive literature review concerning the conventional calculation methods of DYL is conducted. Secondly, a theoretical calculation method of DYL based on safety reliability theory is put forward which, different from the conventional methods, accounts for the stochastic characteristics of drivers. Additionally, a driving simulation experiment is designed to obtain two driving behavior parameters of Chinese drivers: perception-reaction time (PRT) and safe acceptable acceleration (SAA). Thirdly, a Monte Carlo simulation is employed to simulate the interactive process of PRT and SAA, and solve the proposed model. Finally, according to the Monte Carlo simulation results, a look-up table describing the relationship between DYL, safety reliability (50-90%) and approaching speed (15-40 km/h) is made. Results show that this method successfully incorporates the probabilistic nature of driving behavior. Taking the safety reliability into consideration can provide a more reasonable method to calculate the DYL of signalized intersections.
To avoid premature damage, a newly laid asphalt pavement repair must be allowed to cool sufficiently before opening to air traffic. This study examines the variations of temperature within different repaired asphalt layers during cooling, and makes recommendations with regard to the choice of temperature-based criteria for determining the earliest time to open a newly laid asphalt pavement section to air traffic in a busy airport. Using finite element simulation analysis, the cooling patterns of asphalt layers under the following conditions were studied: three different weather conditions (sunny daytime, cloudy daytime, and nighttime) with three different wind speeds. It is shown that the common practice of relying on surface temperature to determine the time for opening to traffic is unsatisfactory. This is because under most paving conditions, a large proportion of the newly laid asphalt layer would still have temperatures higher than the surface temperature. From finite element analysis for different paving and environmental conditions, it is recommended that the temperatures at an interior point be measured at either 1/2, 2/3, or 3/4 depth, and that nighttime paving be preferred. This study shows that for common asphalt pavement repairs of thicknesses up to 150 mm, taking the temperature at either 2/3 or 3/4 depth as the guide, a repaired asphalt layer, when opened to air traffic, would have its internal maximum temperature kept within 2 degrees C of the preset maximum allowable temperature. If the 1/2 depth temperature is selected as a guide, a margin of within 4 degrees C of the preset maximum allowable temperature can be achieved.
Vehicle-to-vehicle communications can be unreliable because of interference and information congestion, which leads to the dynamic information flow topology (IFT) in a platoon of connected and autonomous vehicles. Some existing studies adaptively switch the controller of cooperative adaptive cruise control (CACC) to optimize string stability when IFT varies. However, the difference of transient response between controllers can induce uncomfortable jerks at switching instances, significantly affecting riding comfort and jeopardizing vehicle powertrain. To improve riding comfort while maintaining string stability, the authors introduce a smooth-switching control-based CACC scheme with IFT optimization (CACC-SOIFT) by implementing a bi-layer optimization model and a Kalman predictor. The first optimization layer balances the probability of communication failure and control performance optimally, generating a robust IFT to reduce controller switching. The second optimization layer adjusts the controller parameters to minimize tracking error and the undesired jerk. Further, a Kalman predictor is applied to predict vehicle acceleration if communication failures occur. It is also used to estimate the states of preceding vehicles to suppress the measurement noise and the acceleration disturbance. The effectiveness of the proposed CACC-SOIFT is validated through numerical experiments based on NGSIM field data. Results indicate that the CACC-SOIFT framework can guarantee string stability and riding comfort in the environment of dynamic IFT.
Few previous studies have linked transit-oriented development (TOD) patterns and property values at the station level in the Chinese context. Using Shanghai as a case study, we obtained 21,094 transaction records within the 800 m radius catchment areas of 280 urban rail stations from a local property agency. A performance-based TOD indicator framework was established to capture built-environment features for density, diversity, and design dimensions. Using open-source geospatial data, we generated a series of TOD indicators for each station catchment area and further developed a composite TOD index with information entropy weighting. The results of multilevel regression models showed that within urban rail station catchment areas, residential properties with higher TOD levels were positively associated with higher value. In addition, increasing pedestrian and bike accessibility and integrating diversified urban functions around stations could create more value for nearby residential properties.
The introduction of mobile application-based ride hailing services represents a convergence between technologies, supply of vehicles, and demand in near real time. There is growing interest in quantifying the demand for such services from regulatory, operational, and system evaluation perspectives. Several studies model the decision to adopt ride hailing and the extent of the use of ride hailing, either separately or by bundling them into a single choice dimension, disregarding potential endogeneity between these decisions. Unlike developed countries, the literature is sparser for ride hailing in developing countries, where the demand may differ considerably because of differences in vehicle ownership, and availability and patronage of many transit and intermediate public transport (IPT) modes (the shared modes carrying 40% shares in some cases). This study aims to bridge these gaps in the literature by investigating three interrelated choice dimensions among workers in Chennai city: consideration of IPT modes, the adoption of ride hailing services and the subsequent usage intensity of ride hailing services. The main factors influencing these decisions are identified by estimating a trivariate probit model. The results indicate that sociodemographic and locational characteristics and the availability of IPT modes influence ride hailing adoption, whereas work-related constraints and perception of other modes affect its frequency. Work and non-work characteristics affect both the dimensions of ride hailing. Further, endogeneity is observed between ride hailing and IPT adoption after controlling for these variables, whereas evidence of endogeneity is absent among other dimensions. Mainly, the model separates the effect of the exogenous influences on the usage frequency level from their effect on the adoption of ride hailing services.
The standard traffic assignment problem (TAP) is often augmented with additional constraints to address non-standard applications. These models are called TAP with side constraints (TAPSC). Despite the rising significance of TAPSC models, the ability to efficiently solve them to satisfactory precision remains limited in real-world applications. The purpose of this paper is to fill this gap by integrating a recently developed high performance TAP solver, known as the path-based Greedy algorithm, with the augmented Lagrangian multiplier (ALM) method. This paper examines how precisely the subproblems in the ALM method should be solved to optimize the overall convergence performance. It is found that insufficiently converged subproblem solutions sometimes lead to catastrophic failures, although pursuing extremely high precision could also be counterproductive. Accordingly, it is proposed to adjust the precision required to solve the subproblems based on an approximate gap measured by the augmented Lagrangian. Results of numerical experiments show that adaptively adjusting the subproblem precision limit produces a 25% speed-up compared with the algorithm with a fixed limit.
Open-graded friction course (OGFC) is a low impact development practice that provides a better pavement drainage solution and safer driving conditions. However, there exists a gap in understanding how internal pores in OGFC mix affect hydraulic conductivity, particularly when OGFC suffers the most rutting damage under the effects of high temperature and heavy traffic loading. There is also a lack of research on determining the optimal maintenance timing for an OGFC pavement. This study aims at characterizing the relationship of volumetric and permeability properties for OGFC slab specimens and quantifying permeability deterioration over time using a developed precipitation simulator and permeability measuring device and rutting test. Seven test temperatures (40, 45, 50, 55, 60, 65, and 70 degrees C) were considered in the rutting test. The effect of clogging material size on permeability was also evaluated. The test results suggested that interconnected air void was lower than total air void, and higher rutting temperature resulted in reduced interconnected air void. The clogging experiment suggested that 0.3-0.6 mm material caused the most clogging while 0.075-0.15 mm material caused the least clogging. Based on this study, it is recommended to use a field measured rut depth as an alternative permeability indicator for determining optimal maintenance timing for an OGFC pavement using the correlation established between permeability and rut depth. A case study of OGFC pavement demonstrated that when the field measured rut depth reached 4.5 mm or higher, timely maintenance is needed.