Journal of Transportation Engineering, Part A: Systems

This paper presents a methodology for quantifying the effectiveness of different methods used to improve the railway track performance on soft subgrades. This methodology consists of quantifying the changes in track stiffness from vertical track deflection (VTD) measurements taken before and after the track was upgraded, and the evaluation of the roughness of the track that has developed since the track was upgraded. A case study is presented to explain the steps of this methodology. These upgrades consist of changing the rail from $49.6\text{-}\mathrm{kg}/\mathrm{m}$ ($100\text{-}\mathrm{lb}/\mathrm{yd}$) bolted rail to $57\text{-}\mathrm{kg}/\mathrm{m}$ ($115\text{-}\mathrm{lb}/\mathrm{yd}$) continuously welded rail (CWR), embankment reconstruction, and using a layer of geogrid at the subballast–subgrade interface. The results of the study show that the VTD measurements are capable of measuring changes in track deflection, and thus modulus, due to the upgrading of the track structures with a high enough resolution to distinguish between the differing test sections. The track geometry measurements suggest that not enough time or train traffic had passed to degrade the track geometry to a level that would start indicating issues in performance. The paper also evaluates the relative effectiveness of the different remediation methods at this study site. Replacement of jointed rail with heavier CWR significantly increased the track stiffness, more so than excavation of the subgrade and reconstruction of the embankment. The combined effect of CWR and the substructure upgrades further improved the track modulus. The geogrid can be used with CWR to reduce the amount of subballast required without an increase in track deflection.

An existing vehicle dynamics model was used to define design parameters up to which steady-state cornering conditions apply and consequently lift the restrictions of the point mass model. Besides a passenger car, the motion of a two-axle truck was examined as well for both loaded and unloaded conditions. In order to assess critical safety concerns in terms of vehicle skidding, a range of design speed values paired with control design elements from standard design guidelines as well as certain values of peak friction coefficients were used. The unloaded truck was found to be the most critical vehicle in terms of reaching a maximum constant speed, termed as safe speed. Furthermore, the authors provide modeling examples toward the development of a tool for practitioners to concurrently assess the impact of road geometry and friction in terms of defining the vehicle’s safe speed and, consequently, take certain actions. These actions include the adoption of acceptable arrangements for the above values, as well as scheduling accurate friction improvement programs.

Unavailability of sufficient parking spaces during various periods at rest areas results in illegal and unsafe parking at on/off-ramps and other unauthorized areas, which may lead to traffic safety hazards. In this research, the authors attempt to understand truck parking utilization by developing econometric models by using truck global positioning system (GPS) data to predict truck parking utilization at rest areas to improve truck parking management and ensure proper use of parking spaces. Count models, including Poisson and negative binomial models, were developed in addition to generalized ordered-response probit (GORP) models to understand the factors that affect truck parking utilization. The GORP model that subsumes the Poisson model as a special case was found to provide the best data fit. The model results suggest that several factors positively contribute to truck parking utilization (e.g., truck volume on the adjacent roadway, number of lanes) at rest areas, whereas factors such as on/off-ramp violations decrease truck parking utilization. In addition, parking utilization was found to vary considerably throughout the day.

The pressure distribution under the crossties plays a key role in railroad performance. This study conducts laboratory testing to investigate the pressure distributions under two different types of crossties, steel and timber. For each type, this study employs only a single tie. Five pressure cells are placed equidistantly under the rail crosstie between the two rails to measure the pressure distribution. Both static and cyclic loadings are applied during the test. The pressure distributions are compared between the steel and timber crossties. The effect of the cyclic loading on the pressure distribution also is explored. It is found that pressure distribution is different for steel and timber crossties. Cyclic loading could change the pressure distribution under both steel and timber crossties, but the effect of cyclic loading is more obvious on the steel crosstie than on the timber crosstie. Differences exist in pressure distribution between loading and unloading processes.

The effects of pavement type on fuel consumption have received considerable attention in recent years, yet the influence of asphalt mixes characteristics and vehicle speed on fuel consumption excess has not been evaluated. This paper evaluates the effects of asphalt concrete (AC) characteristics and vehicle speed on fuel consumption excess using a three-dimensional (3D) finite-element (FE) approach. Finite-element modeling is used to simulate three flexible pavements typically used for low, medium, and high traffic volume. The effects of AC mixes with different binders and varying percentages (0, 15, and 40%) of reclaimed asphalt pavement (RAP) on fuel consumption excess are evaluated. The FE models are validated based on field stress and strain measurements obtained from the Louisiana Accelerated Loading Facility (ALF). Energy dissipation is calculated for the whole FE model due to materials’ viscous properties and is used as an input in fuel consumption estimation. Results indicate that fuel consumption due to energy dissipation constitutes only a very small fraction of the total vehicle fuel consumption. Nevertheless, pavements with the stiffer mix, i.e., the mixes with high percentage of RAP, consume less energy. Therefore fuel savings can be expected when increasing the stiffness of AC layers using RAP materials. Fuel consumption excess is lowest at the highest speed and increases with decreasing speed. The fuel consumption excess is higher for pavements with greater thickness of the AC layer, indicating a noticeable impact of AC thickness on fuel consumption excess.

In recent years, extreme weather has occurred frequently, which has exerted a harmful influence on ballastless track. This paper analyzes the heat transfer mechanism between ballastless track and the environment and presents bottom boundary conditions of the track temperature field based on theoretical derivation. A three-dimensional model is established for calculating the track temperature distribution while considering the geographical location and environmental conditions. A field test verifies this calculation model, and the temperature characteristics of the ballastless track under continuous hot weather are analyzed. The results indicate that the proposed method of determining the bottom boundary condition of ballastless track based on the climatic data is efficient and accurate. Under continuous hot weather, the long-term daily mean air temperature and stronger solar radiation cause continuous increase of the whole track temperature. As a consequence, the track temperature is 5–10°C above the air temperature, and there is a larger temperature gradient, which may induce curling deformation of the unitary ballastless track and buckling defects of the longitudinally-coupled slab. For maintenance of track structure, the proposed method is expected to predict the track defects caused by extreme weather based on the weather report.

An automatic traffic recorder (ATR) makes it easy to detect a vehicle’s speed and the number of axles because it produces highly precise data; thus, it can be used to obtain major traffic characteristics for several purposes such as vehicle classification. However, the failure of a piezo sensor or inductive-loop sensor often results in missing data. Moreover, there is no method available for evaluating the life of a sensor installed in a pavement. Therefore, such sensors require maintenance after a failure occurs, resulting in a large amount of missing traffic volume data. If the quantified life expectancy of a sensor could be obtained, a maintenance and rehabilitation strategy could be established and the economic feasibility could be determined. In this study, the 5-year maintenance history of a sensor newly installed in a national highway was reviewed. Normal, gamma, lognormal, and Weibull distributions were fitted to the data, and the results were compared. The Weibull distribution was used to predict the life. When the maintenance histories of piezo and inductive-loop sensors were fitted to the Weibull distribution, the scale parameters were 79.23 and 89.72 and the shape parameters were 3.28 and 2.83 for the piezo sensor and loop sensor, respectively. The mean life and median life of the piezo sensor were calculated to be 71.05 and 70.85 months, respectively. Those of the loop sensor were 79.92 and 78.82 months, respectively.

As urban traffic congestion grows, traffic engineers must find ways to maximize the efficiency of traffic signal control. Different control strategies, including actuated, coordinated, and adaptive, have their own strengths and weaknesses; therefore, it is necessary to comprehensively evaluate these control modes to understand which strategy is most appropriate for users. This research carries out a case study to evaluate the adaptive performance of Adaptive Control Software Lite (ACS-Lite) versus conventional coordinated-actuated and fully actuated, noncoordinated control. The test was done along two congested arterials around Disneyland in Anaheim, California. The results indicated that adaptive control did not perform as well as the well-calibrated and finely-tuned time-of-day coordination. These results also indicated that for this type of congested network, the adaptive signal control is best suited to improving the efficiency when traffic demand is unpredictable, variable, and in low volume. During peak hours, when traffic demand was high and predictable, conventional coordinated time-of-day plans performed better. Future research could aim to improve adaptive control by adopting more coordinated features and utilizing high-resolution data to improve the overall efficiency.

Highway capacity manuals (HCM) have incorporated the effect of heavy vehicles (HVs) in the form of passenger car equivalents (PCEs) for estimating highway traffic conditions, which include the road’s slopes, the length of the road, the geographical characteristics, and the ratio of HVs to other types of vehicles on the road. The PCEs of HVs are critical for designing, operating, and evaluating highways. In order to analyze the effects of HVs on highway traffic flow, the real-time automatic vehicle classification (AVC) data were collected for three different major highways (four-lane, six-lane, and eight-lane highways, respectively) in the Seoul metropolitan area for the 2 months from August to September 2011. The purpose of this study was to examine the effect of HVs on traffic flows using real-time AVC data and to analyze the relationship among the average speed, the HV ratio, the flow rate, and the number of lanes. The findings revealed that the average speed decreased when the flow rate and HV ratio increased for the six-lane and the eight-lane highways. The average speed also decreased as the flow rate increased for the four-lane highway. However, the average speed stabilized when the HV ratio was in the range of 25–45% and recovered when the HV ratio exceeded 45%; this result implied a need to reexamine the existing methods of deriving the HV factors for the HCM.