Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

This research aims to determine the reasonable scale of toll highways in China by considering factors including effects of non-debt investments; agency costs of construction, maintenance, and system operations; user travel time costs; debt repayment; and toll revenue generation. A bilevel optimization model is proposed, in which the lower-level optimization uses origin-destination (O-D) travel demand for network traffic assignments and the upper-level optimization uses data on link-based traffic volumes generated from the lower-level model and other influencing factors as inputs to determine a reasonable scale of toll highway network. The model is applied to determine the reasonable scales of expressways in provinces of Hebei, Jiangsu, Jilin, and Shaanxi located in the central, eastern, northeastern, and western economic regions that form a predominant portion of toll highways in China. It is revealed that the current expressway network scales in all four provinces are higher than the reasonable scales by 22–38%. The provinces are faced with extremely high asset–debt risks that are likely to get worse in the future if the toll highways continue to be constructed using the same financing and investment scheme. It is recommended to seek alternative financial resources such as private capitals for expressway construction and management to reduce the risks of highway financial affordability.

Wireless communication among vehicles and roadside infrastructure, known as connected vehicles, is expected to provide higher-resolution real-time vehicle data, which will allow more effective traffic monitoring and control. Availability of connected vehicle technology among the vehicle fleet will likely grow gradually, but it will possibly remain limited, with many drivers potentially being unwilling to transmit their locations. This is problematic given that research has indicated that the effectiveness of many connected vehicle mobility applications will depend on the availability of location data from a minimum of 20–30% of roadway vehicles. In an effort to improve the performance of connected vehicle applications at low connected vehicle technology penetration rates, the authors propose a novel technique to estimate the positions of noncommunicating (unequipped) vehicles based on the behaviors of communicating (equipped) vehicles along a signalized arterial. Unequipped vehicle positions are estimated based on observed gaps in a stopped queue, and the forward movements of these estimated vehicles are simulated microscopically using a commercial traffic simulation software package. In simulations, the algorithm made more correct than incorrect estimates of unequipped vehicle positions in the same lane and within 7 m longitudinally. When applied to a previously developed connected vehicle traffic signal control strategy in simulation, the location estimation algorithm produced small improvements in delays, speeds, and stopped delay when compared to an equipped-vehicle-only scenario at penetration rates of 25% or less. The location estimation algorithm is generic, and it could be applied to other connected vehicle applications to improve performance at low penetration rates.

Broken rails are the most frequent cause of freight-train derailments in the United States. Consequently, reducing their occurrence is a high priority for the rail industry and the U.S. Federal Railroad Administration. Current practice is to periodically inspect rails to detect defects using nondestructive technology such as ultrasonic inspection. Determining the optimal rail inspection frequency is critical to efficient use of infrastructure management resources and maximizing the beneficial impact on safety. Minimization of derailment risk, costs of inspection vehicle operation, rail defect repair, and corresponding train delay are all affected by rail inspection frequency. However, no prior research has incorporated all of these factors into a single integrated framework. The objective of this paper is to develop an analytical model to address the trade-offs among various factors related to rail defect inspection frequency, so as to maximize railroad safety and efficiency. The analysis shows that the optimal inspection frequency will vary with traffic density, rail age, inspection technology reliability, and other factors. The optimization model provides a tool that can be used to aid development of better-informed, more effective infrastructure management and accident prevention policies and practices.

Various approaches have been deployed for evaluating the performance of bus rapid transit (BRT) systems based on qualitative, economic and quantitative parameters. In the present study, the performance evaluation of the bus rapid transit system (BRTS) in Indian cities using a microsimulation technique has been attempted. Base networks of Delhi and Ahmedabad BRT corridors were developed, calibrated, and validated using specialized software. After the validation process, speed versus volume to capacity (V-C) ratio equations were developed for mixed vehicle (MV) and bus lanes, respectively, of both the corridors considered in the study. These equations were optimized to find out the optimum value of V-C ratio on the MV and bus lanes, which were found to range between 0.64 and 0.75. An average value of 0.688 V-C ratio was derived in this study for BRTS based on the calculated optimal values. Then, the concept of user equilibrium (UE) was deployed to understand when the travel speeds in both an MV lane and a bus lane of a BRT corridor reach the point of congestion. Based on this study, it can be concluded that 0.688 V-C ratio is the optimal flow value for BRT corridors. This implies that up to 0.688, both the MV lane users and bus lane users will enjoy reasonable travel speeds and smaller delays. If the V-C ratio is exceeded on either bus lane or MV lane(s), then the BRT system becomes untenable for the MV lane and bus lane users, instead creating traffic congestion.

Pavement conditions significantly influence the generation of nuisances that influence the environment and increase the costs borne by society. This paper presents a new tool designed to monetize and incorporate environmental impacts in decision-making processes. The Pavement Environmental Impact Model (PEIM) is the first attempt to adapt the Impact Pathway Approach (IPA) to assess the emission, dispersion, and impact of noise, air pollution, and greenhouse gases so that environmental impacts can be included in the economic models of pavement management units. The results of a simulation performed with PEIM for an urban collector road with annual average traffic of 10,000 vehicles per day and a linear density of 240 people per kilometer showed that, within the assumptions/limitations of PEIM, environmental costs were expected to range from 876,000 to 1,983,000 Canadian dollars per kilometer per year for pavement roughness ranging from 1 to $4\mathrm{m}/\mathrm{km}$. Moreover, although noise costs are consistently disregarded in pavement management, it was expected to represent 54% of the total environmental costs when pavement roughness was above $1.75\mathrm{m}/\mathrm{km}$. Results demonstrate that PEIM is a suitable tool for roughly estimating environmental costs and helping pavement management units to choose the optimal management alternative.

The design of mini-roundabouts has been around and practiced in Europe for decades. It has been a successful and low-cost intersection configuration using existing external boundaries of intersections. Nevertheless, accessible traffic capacity models for mini-roundabouts do not exist. This study provides design recommendations and a simulation approach for capacity models of mini-roundabouts from U.S. data. Two geometries are selected that have a 7 or 10 m (24- or 36-ft) approach width typical of conventional intersections. The mini-roundabouts are best defined by the inscribed circle diameter of 15 and 23 m (50 and 75 ft). Field data are collected on drivers’ behavior and decisions for a mini-roundabout design in order to calibrate simulation models. A microscopic traffic simulation software is used to model the selected prototype designs for capacity estimations. The defining feature for mini-roundabouts is the traversable central and splitter islands for large vehicles that make through or left-turn movements. The linear regression models presented estimate the capacity of the mini-roundabouts to be lower than that of the single-lane roundabout. However the mini-roundabout has a higher capacity per square foot of land, which would be an innovative solution for urban areas for increasing capacity at existing all-way stop-controlled intersections at lower cost than single-lane roundabouts.

The AASHTO mechanistic-empirical pavement design guide (MEPDG) pavement performance models and the associated AASHTOWare pavement ME design software are nationally calibrated using design inputs and distress data largely from the national long-term pavement performance (LTPP). Further calibration and validation studies are necessary for local highway agencies’ implementation by taking into account local materials, traffic information, and environmental conditions. This study aims to improve the accuracy of MEPDG/pavement ME design pavement performance predictions for Iowa pavement systems through local calibration of MEPDG prediction models. A total of 70 sites from Iowa representing both jointed plain concrete pavements (JPCPs) and hot mix asphalt (HMA) pavements were selected. The accuracy of the nationally calibrated MEPDG prediction models for Iowa conditions was evaluated. The local calibration factors of MEPDG performance prediction models were identified using both linear and nonlinear optimization approaches. Local calibration of the MEPDG performance prediction models seems to have improved the accuracy of JPCP performance predictions and HMA rutting predictions. A comparison of MEPDG predictions was also performed between two software programs to assess if the local calibration coefficients determined from one software program is acceptable with the use of another software program, which has not been addressed before. Few differences are observed between one software program and MEPDG predictions with nationally and locally calibrated models for: (1) faulting and transverse cracking predictions for JPCP; and (2) rutting, alligator cracking, and smoothness predictions for HMA. With the use of locally calibrated JPCP smoothness (IRI) prediction model for Iowa conditions, the prediction differences between the two software programs are reduced. Finally, recommendations are presented on the use of identified local calibration coefficients with the two software programs for Iowa pavement systems.

This research assesses the current practices used to determine the correct speed limits when widening two-lane highways with $88.51\hspace{0.17em}\mathrm{k}\mathrm{m}/\mathrm{h}\hspace{0.17em}(55\hspace{0.17em}\mathrm{mi}/\mathrm{h})$ speed limits to multilane highways with curb and gutter cross sections. A number of related tasks have been encompassed in this study. The speed studies were conducted at 32 sites that had recently been upgraded from two-lane roadways to four or five-lane roadways with curb and gutter profiles. The speed variances and speeding rates at these sites were examined and compared with corresponding data from similar sites on two-lane roadways. Apart from the field test study, a series of human factor studies that used the DS-600c driving simulator system at the University of Tennessee was conducted to assess the effects of curb and gutter profiles and posted speed limits on driver speed–selection behaviors. In addition, a study of the effects of speed limits, in combination with curb and gutter, on crash rates was performed using crash data from the Highway Safety Information System (HSIS). Based on the research findings, the study authors recommend that the alternative standard that allows the use of designed speeds and posted speed limits in excess of $72.42\hspace{0.17em}\mathrm{k}\mathrm{m}/\mathrm{h}\hspace{0.17em}(45\hspace{0.17em}\mathrm{mi}/\mathrm{h})$, along with the use of correctly sloping curbs, should be developed by the traffic agencies.