Praprut Songchitruksa

Getis-Ord Spatial Statistics to Identify Hot Spots by Using Incident Management Data

Traditionally, data have been collected to measure and improve the performance of incident management (IM). While these data are less detailed than crash records, they are timelier and contain useful attributes typically not reported in the crash database. This paper proposes the use of Getis–Ord (Gi*) spatial statistics to identify hot spots on freeways from an IM database while selected impact attributes are incorporated into the analysis. The Gi* spatial statistics jointly evaluate the spatial dependency effect of the frequency and attribute values within the framework of the conceptualized spatial relationship. The application of the method was demonstrated through a case study by using the incident database from the Houston, Texas, Transportation Management Center (TranStar). The method successfully identified the clusters of high-impact accidents from more than 30,000 accident records from 2006 to 2008. The accident duration was used as a proxy measure of its impact. The proposed method could be modified, however, to identify the locations with high-valued impacts by using any other attributes, provided that they were either continuous or categorical in nature and could provide meaningful implications. With improved intelligent transportation system infrastructure and communication technology, hot spot analyses performed with IM data of freeway network and arterials in the vicinity have become a much more promising alternative. Freeway management agencies can use the results of hot spot analysis to provide visualized information to aid the decision-making process in the design, evaluation, and management of IM strategies and resources. The limitations of the method and possible future research are discussed in the closing section of the paper.

Dynamic Traffic Assignment Evaluation of Hurricane Evacuation Strategies for the Houston-Galveston, Texas, Region

The Houston–Galveston, Texas, region has experienced several major hurricanes in recent years. During the evacuation for Hurricane Rita in 2005, the Texas Department of Transportation (DOT) decided to implement contraflow operations on I-45 to relieve massive evacuee congestion departing Houston to the north. The decision to implement contraflow was a difficult one because it involved multiple jurisdictions and required extensive coordination of manpower and resources from various entities. After the Hurricane Rita experience, the Texas DOT implemented a new strategy, referred to as “evaculane,” in which evacuation traffic could use the outside paved shoulder as a traveling lane when an evacuation was under way and evaculane signing beacons were activated. The objective is to increase capacity along key evacuation routes while avoiding the need for full-scale contraflow operation whenever possible. The evaculane on I-10 was successfully put into use during the Hurricane Ike evacuation in 2008. With the widening and completion of evaculanes on I-10 and US-290 as well as a partial contraflow plan for the I-45 corridor, the Texas DOT sponsored a study to develop a decision support tool to help determine whether these strategies would adequately handle the evacuation demand for various Houston–Galveston region evacuation scenarios. This paper describes the quantitative assessment of the performance of alternative evacuation strategies using a dynamic traffic assignment model, DynusT. The evaluation results indicated the evaculanes on I-10 and US-290 can sufficiently handle high evacuation demand on both routes without contraflow operation. In addition, a partial contraflow plan for I-45 was shown to provide sufficient capacity to handle high evacuation demand in lieu of full-scale contraflow operation.

Portable Toolbox for Monitoring and Evaluating Signal Operations

Traffic signal operators are often faced with the challenge of assessing the performance of signal operation and troubleshooting day-to-day operational issues. In many cases, the problems can be specific to a certain time of day or exclusive traffic patterns; this specificity makes it more difficult to pinpoint the problems without spending hours or even days at the sites. With limited resources and budget constraints, public agencies need to find a more efficient and cost-effective approach to operating and maintaining an ever-increasing number of signals within their jurisdictions. To address this challenge, the authors developed a portable tool that consists of a field-hardened computer that interfaces with the traffic signal cabinet through special enhanced bus interface units. The toolbox consists of a monitoring tool and an analysis tool. The monitoring tool monitors and logs relevant events within the cabinet that provide input for analyzing intersection operations. These inputs include signal status, detector call status (including pedestrian calls), preempt status, and coordination status. The analysis tool then analyzes the log files for each day and produces user-friendly reports in hourly average and cycle-based formats. The measures of effectiveness produced by the tool include signal data (e.g., phase time, phase failures, queue clearance time), pedestrian data (e.g., pedestrian calls per hour and average time to service pedestrian), and preempt data (e.g., type of preempt, time of preempt, and duration of preempt). The analyst can install the tool in the signal cabinet and log the data for subsequent evaluation and troubleshooting in the office. The tool was deployed and field-evaluated at two signalized intersections in Texas. The results generated from the tool were found to be in good agreement with observations at the test sites.

Impacts to Transit from Seattle, Washington, Urban Partnership Agreement Program

This paper describes the impacts on transit that were observed in the evaluation of the Urban Partnership Agreement in Seattle, Washington. In December 2011, variable tolls were instituted on the SR-520 bridge in Seattle. Transit service frequency was enhanced approximately 11 months before tolling. The Seattle findings compared favorably with other congestion pricing projects across the United States and the world. Ridership across the SR-520 bridge increased 10% after the new service was added. It increased another 14% after tolling. The larger increase that came after tolls was similar to that observed in Stockholm, Sweden, and Minneapolis, Minnesota. Speeds across the bridge increased by 14 to 18 mph. That increase was higher than the increase observed in London but lower than the increase observed in Miami, Florida, and in Minneapolis. In the pretoll survey of SR-520 bus riders, 19% said they were influenced to take transit by the enhanced transit service. An even greater percentage, 55%, said the tolls influenced them to take transit. In Atlanta, Georgia, Miami, and Minneapolis, the percentage of riders influenced by the tolls was 45%, 53%, and 23%, respectively. In the posttoll survey, 57% of riders said the tolls on SR-520 had improved their personal travel. Altogether, these findings reconfirm that congestion pricing can create a tangible incentive to take transit.

Advancing Safety Performance Monitoring at Signalized Intersections Through Use of Connected Vehicle Technology

Crash-based safety evaluation is often hampered by randomness, lack of timeliness, and rarity of crash occurrences. This situation is particularly true for technology-driven safety improvement projects that are frequently updated or replaced by newer ones before adequate crash data for a reliable and defensible before-and-after evaluation can be gathered. Surrogate safety data are commonly used as alternatives to crash data; however, the current practice is resource intensive and prone to human errors. The advent of connected vehicle technology allows vehicles to communicate with each other and with the infrastructure wirelessly. Through this platform, vehicle movements and signal status at facilities can be automatically and continually monitored in real time. This study explored the viability of long-term monitoring of connected vehicle data for evaluation of safety performance. A safety monitoring application that used connected vehicle data to detect potential safety indicators at signalized intersections was proposed. As limited saturation of onboard equipment (OBE) was expected in near-term evolution, development focused on a roadside equipment application to process data elements from OBE by way of vehicle-to-infrastructure communications through standard message sets. A microscopic simulation was designed to evaluate effectiveness of the proposed safety indicators in detection of degrading safety performance. A signalized intersection test bed was created in VISSIM, while the wireless communications capability and the application were implemented in a car-to-devices application programming interface. Evaluation results indicated that the application could effectively detect changes in safety performance at full market penetration. Future research needs to quantify the combination of penetration rates and monitoring periods that can yield effective detection of changes in safety performance at intersections with varying operating characteristics.

Guidance for Cost-Effective Selection of Pavement Marking Materials for Work Zones

Pavement markings provide important information to motorists, especially in a work zone environment where alignments are often changed from what is typical. Unlike normal roadway applications, work zone pavement markings are often placed on the roadway for a limited period of time, such as during an interim phase of construction. The performance and total cost for each material may vary greatly depending on a number of factors, such as traffic volume, surface type, and project duration. The objective of this study is to develop a systematic approach to provide practitioners with objective guidance for selecting cost-effective pavement marking materials for work zones that meet specific performance requirements. A Monte Carlo simulation and sensitivity analyses were conducted to establish a cost-based decision support guidance given a set of factors influencing the performance of marking materials. Four types of materials considered in this study were paint, thermoplastics, temporary tapes, and traffic buttons. The analysis results indicated that traffic buttons perform slightly better at shorter phase durations and moderate traffic levels on the concrete surface. The use of thermoplastics was recommended as the lowest-cost alternative only on the asphalt surface with moderate project durations and traffic levels. Paint markings are recommended for short-duration projects regardless of traffic conditions or pavement surfaces. DOI: 10.1061/(ASCE)IS.1943-555X.0000043.

Quantifying the Effectiveness of Performance-Based Pavement Marking Maintenance Contracts

Pavement markings play a vital role in the safe and efficient movement of traffic. In 2010, FHWA began the process of amending existing regulations and issued a notice of proposed amendments to adopt minimum pavement marking retroreflectivity levels. Performance-based pavement marking maintenance contracts (PBPMMCs) are one of the latest mechanisms used to maintain adequate pavement marking performance levels. The Texas Department of Transportation has issued two PBPMMCs, but the effectiveness of these contracts compared with other contracting mechanisms from a performance or safety perspective has not been investigated. This study quantified the effectiveness of PBPMMCs by evaluating the delivered pavement marking performance and safety performance. When compared with other contracting mechanisms, the evaluations found inconclusive evidence as to the benefit of the PBPMMC from a safety and marking performance standpoint. The results are inconclusive perhaps because the markings were maintained adequately before the PBPMMC or because the PBPMMC did not provide a significant improvement in the marking systems.

Predicting Pavement Marking Service Life with Transverse Test Deck Data

Pavement marking test decks are an effective way to evaluate the quality of marking in the field. Transverse test decks provide accelerated wear on markings in the wheelpath area and can provide a side-by-side comparison of different pavement marking materials. The drawback is that the relationship between transverse and long-line pavement marking test decks is relatively unknown. This study was developed to provide better understanding of the relationship between the accelerated wear area on a transverse marking and how it relates to typical wear on a longitudinal marking. The objective of the study was to develop a model for predicting long-line pavement marking retroreflectivity values from transverse pavement marking test deck data. These models and associated parameters can be used to estimate the retroreflectivity of an edge line marking or the amount of time it will take for the edge line marking to reach a given retroreflectivity level. The user needs only the transverse retroreflectivity readings and an initial or assumed initial edge line retroreflectivity value.

Effect of left-turn operational mode on pedestrian safety: development of models and guidelines

Pedestrian safety is a growing concern at signalized intersections. Pedestrians crossing a street at an intersection are exposed to interactions with turning vehicles, and these interactions sometimes result in crashes. Conflicts and crashes can be reduced by implementing protected turn phases. However, the inclusion of protected turn phases in a traffic signal cycle typically causes an increase in vehicular delay, which tends to offset the benefit of reduced crashes. The left-turn operational mode (permissive, protected–permissive, or protected) is typically chosen on the basis of vehicular traffic concerns such as volumes of left-turning and conflicting through vehicles, lane geometry, and sight distance. Historically, pedestrian safety has not been considered a factor in the selection of the left-turn operational mode. Pedestrian safety models have been calibrated with field data. The models allow pedestrian–vehicle conflict frequency and pedestrian compliance with signal indications to be estimated on the basis of volumes and site conditions. These models, along with vehicular delay analysis, form the basis for pedestrian-safety-based guidelines that were developed for choosing the left-turn operational mode. The guidelines are based on identifying threshold conditions for which a change in left-turn mode results in a reduction in road user costs.

Probability Model for Understanding the Effects of Detector Delays on Right-Turn-on-Red Traffic

Detector delay as a useful detector timing feature is often recommended for minimizing disruptions on major movements caused by one or more minor movements. However, this benefit of detector delay is not always certain because the applicability of detector delay is subject to a combination of gap demand, gap availability, critical gap acceptance, follow-up headways, and other factors. The improper use of detector delay could be costly to traffic on minor streets. With little literature on the subject, the complex relationship between detector delays and different critical factors has not been fully understood. An analytical model that estimates the probability of clearing right-turn-on-red queues within the period of detector delay is presented. This probability is the first step toward an understanding of how this detector feature affects an intersections operational efficiency. The gap-finding process of multiple right-turn-on-red vehicles is divided into several realistic cases and analyzed in detail. Insights about the process described in each case are applied to derivation of a probability model. Validation of the model is conducted with more than 4,000 simulation runs. A close fit is found between the computed probability and the simulated data with errors no larger than 5.7% of the targeted values. The method for deriving the probability model provides a stepping-stone toward deriving the delay distributions for right-turn-on-red traffic.