Justice Appiah

Examination of Houston's QuickRide Participants by Frequency of QuickRide Usage

QuickRide is an innovative project designed to more effectively use the capacity of the high-occupancy-vehicle (HOV) lanes on the Katy (I-10) and Northwest (US-290) freeways in Houston. Under this project, two-person carpools could pay

Safety effectiveness of actuated advance warning systems

2 to use the HOV lanes during the peak period, even though the lanes were normally restricted to vehicles with three or more occupants. This form of HOV lane is typically termed a high-occupancy toll (HOT) lane and can be an effective travel demand management and congestion mitigation tool. However, relatively little is known about drivers who choose to use the HOT lane option. The commute and socioeconomic characteristics of Houstons QuickRide participants are examined by their frequency of QuickRide usage. The study is based on a survey of QuickRide enrollees conducted in March 2003. It was found that QuickRide participation increases with increasing trip length, perceived time savings, and frequency of trips in the travel corridor. Participation decreases with increasing carpool formation times but is generally irresponsive to minor changes in the

Safety and Operational Impacts of Optional Flashing Yellow Arrow Delay

2 toll. QuickRide is also more likely to be used for commute trips than other trips. Socioeconomic characteristics such as age, household type, and education also have significant effects on QuickRide trip frequency. However, household size, occupation, and hourly wage rate were not good indicators of the frequency of QuickRide usage.

A Methodology for Comparing Non-Intrusive Traffic Detectors under Different Operating Conditions

Driver behavior within the dilemma zone can be a major safety concern at high-speed signalized intersections. The Nebraska Department of Roads (DOR) has developed and implemented an actuated advance warning dilemma zone protection system. This paper investigates the impact that system has had on safety at high-speed signalized intersections. The operating algorithm has been designed such that the system continually monitors an upstream detector, as well as traffic at the intersection, to predict the onset of the yellow signal indication. Flashing beacons are used to warn drivers of the impending end of the green indication. Although these systems have received positive reviews from the public—and commercial vehicle operators in particular—there has been no comprehensive analysis of their effect on safety. The focus of this research was to address this evaluative need and provide answers about the effectiveness of the Nebraska DOR system in improving safety. Crash records from before and after the implementation of the system at 26 intersections were compared. In addition, 29 control intersections were used to compare crash rates over time, and a fully Bayesian technique was employed to ensure that no exogenous variables affected the study. Results of the analysis were promising (an overall crash reduction rate of 8%) and suggested that the use of the system should be encouraged as an effective safety treatment for the dilemma zone problem at high-speed signalized intersections.

Microsimulation Analysis of Highway-Rail Grade Crossings: A Case Study in Lincoln, Nebraska

Considerable debate exists over whether to delay the start of the flashing yellow arrow (FYA) signal indication (e.g., with a red arrow signal indication) during the transition from a protected movement to a permissive movement in a leading left protected–permissive left turn. The 2009 Manual on Uniform Traffic Control Devices is silent on this topic. This paper reviews the state of the practice on the use of the optional FYA delay through a literature review, a survey of state departments of transportation, and consultations with practitioners and national experts. A simulation study was also used to assess the potential impacts of the optional FYA delay on traffic safety and operations. The state-of-the-practice review indicated some preference for the use of the red arrow signal indication because of the perceived safety benefit. For example, 71% of the responding state departments of transportation that use the FYA also delayed the start of the FYA. The simulation analysis showed significant safety benefits in a delay to the start of the FYA signal indication for all scenarios except the scenario with a low opposing through traffic volume, with no significant negative impacts on average delay, average queue length, or average stopped delay for either left-turning traffic or the intersection as a whole being found.

Safety Effects of Flashing Yellow Arrows Used in Protected Permitted Phasing: Comparison of Full Bayes and Empirical Bayes Results

The installation and maintenance of traditional traffic data collection technologies such as inductive loops can disrupt the smooth flow of traffic, undermine pavement quality, and be a significant safety concern to both motorists and construction personnel. Consequently, there has been a strong emphasis on the development and deployment of non-intrusive traffic detection systems. These devices serve as alternatives to conventional systems by allowing agencies to collect data at high traffic volume locations without compromising operations or safety. The main objective of this research is to investigate the accuracy, reliability, cost, and user-friendliness of various non-intrusive detectors. The study is based on data collected at a test bed in Nebraska where four types of non-intrusive detectors (Autoscope Solo Pro II video image detection system, ISS RTMS G4 microwave radar system, Wavetronix SmartSensor microwave radar system, and GTT Canoga Microloop magnetic induction system) have been deployed. A paired or yoked statistical analysis is used to compare the technologies “side-by-side” so that any environmental and traffic effects are accounted for. The study identifies the relative accuracy of each detection system for each traffic variable (volume, speed, and classification) as a function of environmental conditions, time of day conditions, and traffic conditions. In addition, the variances of the traffic parameter estimates are also provided so that transportation agencies will have reasonable operating bounds for the different technologies which are key input to their ATMS algorithm designs.

Resampling Methods for Estimating Travel Time Uncertainty: Application of the Gap Bootstrap

This paper examines the usefulness of supplementing railroad preemption operations at highway-rail grade crossings with variable message signs. Using the microscopic traffic simulation model, VISSIM, the effects on grade crossing operations of different train dwell times as well as different levels of driver response to a variable message sign in the vicinity of the crossing are assessed. The results affirm the potential usefulness of variable message signs for preventing lengthy queues and illustrate the importance of explicitly considering the delay experienced by vehicles on the blocked roadway in developing a traffic control strategy for highway-rail grade crossings.Copyright

Multivariate Analysis of High-Occupancy-Toll Lane Usage in Houston

Using the flashing yellow arrow (FYA) signal indication for the permissive portion of protected-permissive left-turn (PPLT) phasing has become an increasingly popular treatment for left-turn signals as drivers are believed to understand the FYA better than the traditional circular green indication. A before-and-after safety evaluation of deploying FYA at PPLT signals at 28 intersections in Virginia was conducted. Each of the study intersections had FYA for the permitted portion of the phase on at least one left-turn approach. The focus was on left-turns that operated in the protected-permissive mode (with circular green indication for the permissive portion) before being converted to PPLT operations with the FYA indication for the permissive portion (PPLT-FYA). Crash records from before and after the activation of FYA were compared using both the full Bayes and empirical Bayes approaches. The results indicate that using the FYA signal indication instead of the circular green indication had a statistically significant effect in reducing overall frequency and severity of crashes. For the intersections studied in this research, total crashes reduced by 12% following conversion from PPLT to PPLT–FYA. The results also indicated that the full Bayes approach to safety effectiveness evaluation can, at a minimum, provide similar results to the well-established empirical Bayes approach. The 95% credible intervals for the expected crash reduction rates estimated with the full Bayes method were generally narrow, suggesting a good degree of confidence in the estimates.

Dilemma Zone Protection on High-Speed Arterials

To a large extent, methods of forecasting travel time have placed emphasis on the quality of the forecasted value—how close is the forecast point estimate of the mean travel time to its respective field value? However, understanding the reliability or uncertainty margin that exists around the forecasted point estimate is also important. Uncertainty about travel time is a fundamental factor as it leads end-users to change their routes and schedules even when the average travel time is low. Statistical resampling methods have been used previously for uncertainty modeling within the travel time prediction environment. This paper applies a recently developed nonparametric resampling method, the gap bootstrap, to the travel time uncertainty estimation problem, especially as it pertains to large (probe) data sets for which common resampling methods may not be practical because of the possible computational burden and complex patterns of inhomogeneity. The gap bootstrap partitions the original data into smaller groups of approximately uniform data sets and recombines individual group uncertainty estimates into a single estimate of uncertainty. Results of the gap bootstrap uncertainty estimates are compared with those of two popular resampling methods—the traditional bootstrap and the block bootstrap. The results suggest that, for the datasets used in this research, the gap bootstrap adequately captures the dependent structure when compared with the traditional and block bootstrap methods and may thus yield more credible estimates of uncertainty than either the block bootstrap method or the traditional bootstrap method.