Ivana Tasic

Evaluation of Transit Signal Priority Options for Future Bus Rapid Transit Line in West Valley City, Utah

This paper presents an analysis of different transit signal priorities (TSPs) for a future bus rapid transit (BRT) corridor in West Valley City, Utah. The goal was to find the optimal TSP strategy for estimated and planned traffic and transit operations. The study used VISSIM microsimulation software in combination with ASC/3 software-in-the-loop simulation. Four models were used in the analysis: no TSP, TSP, TSP with phase rotation, and custom TSP. The results showed that TSP with phase rotation and custom TSP could both be considered for implementation. TSP with phase rotation would provide significant benefits for BRT, with minimum impacts on vehicular traffic. Custom TSP would provide major benefits for BRT in travel times, delays, and stops. However, this strategy has more impact on vehicular traffic. Custom TSP is an advanced strategy that still needs examination and improvement. The study provides a set of instructions on how the described strategies can be implemented in field traffic controllers.

Use of Spatiotemporal Constraints to Quantify Transit Accessibility: Case Study of Potential Transit-Oriented Development in West Valley City, Utah

Accessibility emerges as the transportation performance measure that emphasizes the benefits to transportation system users and captures more than the speed of travel. Transit accessibility shows how easy it is for an individual to travel to a desired destination by using public transit. However, for transit to be considered as an option in mode choice at all, there has to be a feasible transit route leading from a given origin to a desirable destination within the available time frame. This study used spatial and temporal constraints and a set of transit features that affected access to transit to develop a conceptual framework for transit accessibility measurements in a potential transit-oriented development (TOD) location in West Valley City, Utah. As this network develops more transit-friendly features, temporal and spatial accessibility indicators will provide useful information on the opportunities that users can reach by using transit. The proposed methodology was based on traffic and transit data from the case study network and used an open source tool to perform transit accessibility measurements by calculating the number of accessible transit stops from each origin. The methodology considered network features, acceptable walking time, available time budget, transit schedule variability, and spatial constraints as impact factors in accessibility measurements. The goal of the study was to establish a feasible set of transit accessibility indicators that would be used for both the case study street network and transit service modifications to transform the network into a transit-friendly and eventually a TOD environment.

Implementation of transit signal priority and predictive priority strategies in ASC/3 software-in-the-loop simulation

This paper presents an application of the ASC/3 Software-in-the-Loop (SIL) simulation in Transit Signal Priority (TSP) implementation and analysis. Two options of the ASC/3 controller software were examined: built-in TSP features, and the controller logic processor as a means to develop custom-defined Predictive Priority Strategies (PPS). The study is using a VISSIM simulation model of a planned transportation network with a Bus Rapid Transit (BRT) line in West Valley City, UT. The results show big possibilities for SIL simulation for transit priority analysis. Since the logic processor is not available in simulation softwares traffic control emulators, SIL simulation can offer many options for custom-defined traffic control strategies beyond the standard operations. All of the described strategies can be implemented in the field controllers, without the need for new hardware or software.

Applications of Generalized Additive and Bayesian Hierarchical Models for Areal Safety Analysis: Case Study of an Urban Multimodal Transportation System in Chicago, Illinois

Areal crash modeling has gained increased attention in the past decade because of initiatives to incorporate safety performance–based decision making in transportation planning. Particularly in urban multimodal transportation systems, safety outcomes may be influenced by long-term planning decisions at the area and network levels. How multimodal facilities are layered and prioritized eventually affects conflicts that may result between modes, influencing expected crash frequencies and severities for various road user types. The emphasis on areal crash modeling has opened the door for various innovative statistical methods, applied to explain factors that contribute to crashes, as well as to address issues that arise in spatially aggregated count data. These issues include spatial autocorrelation, ecological fallacy, and the modifiable areal unit problem. Previous studies used generalized linear models with fixed and random effects to address these issues, while the Bayesian framework has become a dominant approach in areal crash analysis—particularly at the county level—in the past decade. This paper explores an alternative frequentist approach to areal crash modeling with generalized additive models with smooth functions across the location and compares these models to negative binomial and Bayesian hierarchical models. The results, based on data from Chicago, Illinois, show that generalized additive models can account for spatial autocorrelation in the data, particularly when autocorrelation is lower and more data are available to reduce the number of potentially omitted variables.

Street Connectivity Versus Street Widening: Impact of Enhanced Street Connectivity on Traffic Operations in Transit-Supportive Environments

Highly connected street networks increase accessibility for multimodal transport, but their effects on the efficiency of still-dominant vehicular traffic is rarely addressed. As interest increases in transforming typical suburban developments from car-oriented to multimodal environments, the effects of redesigned street networks in the period before the expected mode shift need to be clarified. This paper addresses the effects of enhanced connectivity on traffic operations and uses part of the West Valley City, Utah, network as the potential transit-oriented development (TOD). Because the predicted traffic demand for 2040 requires modifications to this network, the question is whether enhanced connectivity as a TOD-supportive approach can accommodate that demand and replace the traditional street widening solution. Twelve scenarios were modeled and evaluated: the existing state, five scenarios with different levels of street connectivity, five street-widening scenarios, and a scenario with reduced speed areas based on traffic-calming practices. Macro- and microsimulation models were used iteratively to build, calibrate, and evaluate the modeled scenarios. The results at the intersection, corridor, and network levels showed that enhanced street connectivity represented a competitive alternative to the traditional capacity expansion approaches that usually involve street widening. As connectivity increased, the network designs with enhanced connectivity accommodated more traffic than the designs with street widening and therefore opened new routes and provided a better dispersion of intrazonal traffic. New scenarios that encompass changes in mode split are proposed for future research efforts.

Chapter 11 – Implementation of Transit Signal Priority and Predictive Priority Strategies in ASC/3 Software-in-the-Loop Simulation

This chapter presents an application of the Advanced System Controller series 3 (ASC/3) Software-in-the-Loop (SIL) simulation in Transit Signal Priority (TSP) implementation and analysis. Two options of the ASC/3-controller software are examined: built-in TSP features, and the controller logic processor as a means to develop custom-defined Predictive Priority Strategies (PPS). The study is using a VISSIM simulation model of a planned transportation network with a Bus Rapid Transit (BRT) line in West Valley City, Utah. The results show big possibilities for SIL simulation for transit priority analysis. Since the logic processor is not available in simulation software’s traffic control emulators, SIL simulation can offer many options for custom-defined traffic control strategies beyond the standard operations. All of the described strategies can be implemented in the field controllers, without the need for new hardware or software.