Journal of Transportation Engineering, Part A: Systems

Predicting and providing information about bus arrival time to passengers accurately is a very important aspect of advanced public transportation systems (APTS), a major functional area of intelligent transportation systems. However, the information provided to passengers should be reliable. The reliability of such information provided to passengers depends on the prediction method used, which in turns depends on the input data used in the method. This means that identifying the most significant/appropriate input data and using them in the method are important. So, in the present study, travel time pattern analysis was carried out to find the most significant inputs by performing statistical tests for each day of the week separately. Also, a model-based Kalman filtering algorithm was developed to predict bus travel time by using the identified patterns effectively based on temporal discretization under heterogeneous traffic conditions. The performance of the proposed algorithm showed a clear improvement in prediction accuracy when compared with a prediction method using space discretization.

In general, the use of superelevation and changes in a road’s transverse slope are typically based on the road’s design speed to provide safety and comfort for a vehicle driving on a horizontal curve. However, due to the difference between operating and design speeds, there has always been uncertainty in determining the margin of safety using superelevation. This paper discusses the assessment of the safety margins obtained from the application of superelevation in horizontal-curve design. The assessment uses geometric design guides and a reliability index to determine any uncertainties in the design parameters. In addition, adjusted design charts of superelevation values related to the radius of horizontal curves at various levels of probability of noncompliance are provided. The results show that the adjusted superelevation values are generally greater than those derived from current standards. The adjusted design charts can help designers select an appropriate superelevation value for a particular horizontal curve for highways that have geometric constraints. These adjusted charts may also aid designers in predicting the consequences and safety margins associated with the selection of superelevation alternatives required to approve geometric designs that involve violations of the standard requirements due to environmental constraints.

An advance-warning flasher alerts drivers of the imminent onset of a yellow light at a signalized intersection, and it is widely used to reduce crash frequency and severity. Recently, a more-aggressive countermeasure, a speed-limit reduction, is being used at high-speed signalized intersections in addition to advance-warning flashers. In this paper, six high-speed intersection approaches in Nebraska were evaluated to assess the operational effects of no speed-limit reduction, an $8.0\mathrm{km}/\mathrm{h}$ ($5\mathrm{mi}/\mathrm{h}$) speed-limit reduction, and a $16.1\mathrm{km}/\mathrm{h}$ ($10\mathrm{mi}/\mathrm{h}$) speed-limit reduction in the vicinity of high-speed signalized intersections equipped with advance-warning flashers. The placement of speed-limit-reduction signs resulted in significant reductions in observed speeds only when upstream drivers were traveling at speeds higher than a comfortable range—1.8 to $4.0\mathrm{km}/\mathrm{h}$ (1.1 to $2.5\mathrm{mi}/\mathrm{h}$) higher than the regulatory speed limit. The likelihood of this condition being satisfied was higher in case of $16.1\mathrm{km}/\mathrm{h}$ ($10\mathrm{mi}/\mathrm{h}$) drop; however, it was not found to be true when the speed limit was dropped by $8.0\mathrm{km}/\mathrm{h}$ ($5\mathrm{mi}/\mathrm{h}$). Also, the compliance rates to the regulatory speed limit varied from 15 to 85%, highlighting the fact that ambient conditions have a much greater influence on drivers’ speed choices as compared to the regulatory speed limit. This research provides further evidence that speed-limit reductions, in conjunction with advance-warning flashers, appears to be an effective safety countermeasure; however, their effects will be dependent on the amount of speed-limit reduction and observed speeds.

This study develops various crash modification factors (CMFs) for combinations of traffic and roadway cross-sectional elements at noncurved (i.e., straight) and curved roadway sections using the cross-sectional method. Generally, a CMF estimates the expected changes in crash frequency after a single specific treatment is implemented on a roadway. The results indicate that increasing lane width, increasing shoulder width, and their combination are safety effective in reducing crash frequency in general. In particular, it was found that crash frequency decreases as the lane width increases until 3.51 m (11.5 ft) width and it increases as the lane width exceeds 3.51 m. The crash rates start to decrease again after 3.81 m (12.5 ft). The results also indicate that the developed nonlinearizing link function derived nonlinear relationship between crash rates and lane width, and this relationship was clearly reflected in the generalized nonlinear models (GNMs). Moreover, there is a significant interaction impact between lane and shoulder widths at segments with a horizontal curve whereas the interaction term is not significant at noncurved segments. It was also found that the CMFs for increasing lane and shoulder widths are decreasing as annual average daily traffic (AADT) level increases. Based on the findings from this study, it is recommended to apply the proposed methodology of utilizing the GNMs with interaction terms in the cross-sectional method to (1) estimate more accurate CMFs for single treatments and combinations of treatments and (2) reflect the nonlinearity of crash predictors and interaction impacts among variables.

Different capacity-utilization levels may incur different service risks to the railway system. Previous capacity research has mainly focused on capacity measurement without evaluating the potential risks from an increase in the capacity-utilization level. This research proposes a new concept, namely, risk in capacity utilization, by using expected recovery time to quantify the service risk in capacity utilization. A corresponding computational process was also developed to assess the expected time for the railway operation to recover after potential disruptions. Results from the case study demonstrate that the service risk in capacity utilization can be obtained and compared by using the proposed concept and process. A minor increase in the capacity-utilization level in peak hours may incur a substantial risk to service reliability. In order to adjust the service plan to a desired reliability level, the locations and time intervals causing a high level of capacity risk can also be pinpointed in the risk-evaluation process. It is therefore important and beneficial to incorporate this evaluation procedure in the service-design process to ensure service reliability to customers.

Providing drivers with open sight distance on entrance ramps can help prevent wrong-way entries at interchange terminals. For partial-cloverleaf (parclo) interchange terminals with close-spaced two-way ramps, appropriate intersection balance and median barrier lengths can provide motorists with a better view of entrance ramps and a better turning radius. A current best intersection balance practice by Washington State Department of Transportation (WSDOT) is to locate the stop line at no more than 60% of the way through the intersection. However, this has not been proven for safety benefits. To fill this void, this paper provides a comprehensive evaluation of the impact of stop line positioning based on wrong-way crash data analysis. Effects of different lengths of the median barriers used to separate two-way ramps on left-turn driver sight distances were also investigated by analyzing driver perspectives of roadway information with a three-dimensional (3D) simulation and analytical methodology. Conclusively, the current best practice was proven effective in deterring wrong-way driving, and general guidelines for appropriate median barrier lengths on two-way ramps were developed.

One obstacle to the optimal time for pavement maintenance treatments based on the expected performance or cost-effectiveness is the lack of posttreatment performance models at different timings. This study first summarized the current effectiveness/cost-effectiveness evaluation methods. Then, the posttreatment performance model was established based on the pretreatment performance model and other factors such as traffic and environment. By incorporating the incremental posttreatment performance models into the effectiveness evaluation, an optimization method was developed to calculate the dynamic effectiveness/cost-effectiveness and to select the optimal performance threshold. Investigation of 243 sections from the long-term pavement performance (LTPP) database showed that when the pavement deteriorated very fast, an early age treatment was recommended, whereas when the pavement condition was good and the deterioration rate was not fast, a higher optimized international roughness index (IRI) threshold was recommended. In addition, the optimal IRI thresholds for fog seal and crack seal are lower than those of thin overlay, chip seal, and slurry seal, indicating that it is more effective or cost-effective to apply fog seal and crack seal treatments at a relatively early age.

Two full-scale pavement sections built in 2012 at the National Center for Asphalt Technology (NCAT) Test Track were used to assess the structural contribution of cold central-plant recycling (CCPR) with 100% reclaimed asphalt pavement (RAP) and foamed asphalt as a recycling agent (CCPR-foam). The two test sections performed effectively, presenting no evidence of pavement damage during a two-year period of accelerated traffic loading in which 10 million equivalent single-axle loads (ESALs) were applied. Furthermore, ride quality was not significantly affected with the application of traffic. Frequent deflection testing over the duration of the study revealed that CCPR-foam exhibited a similar response to temperature as that observed for conventional asphalt concrete (AC). A procedure based on backcalculated modulus data was followed to determine the structural layer coefficients for the CCPR-foam layers. The layer coefficients were found to vary from 0.14 to $0.15{\mathrm{cm}}^{-1}$ ($0.36–0.39{\mathrm{in.}}^{-1}$). Quantifying the structural coefficient allows this material to be effectively used in the AASHTO empirical method of pavement thickness design currently employed by many U.S. states.

Recent years have seen increasing deployment of radar-based technologies for vehicle detection at signalized intersections in the United States, mainly because they are nonintrusive, accurate, and robust to varying lighting, weather, and environmental conditions. In this paper, a radar-based detection technology is evaluated in the context of various weather and environmental conditions. High-resolution (100-ms sampling interval) data were collected in the field from two representative test sites. The detection errors were correlated with varying weather and environmental conditions using data-mining techniques, such as conditional inference trees and regression models. It shown that false and stuck-on call errors tend to increase under more-adverse weather conditions (e.g., rain and thunderstorms). Visibility, glare, and uneven shadows appear to be irrelevant. The near-side mounting location is associated with reduced missed-call, false-call, and dropped-call errors.