Milan Zlatkovic

Microscopic Modeling of Traffic Signal Operations: Comparative Evaluation of Hardware-in-the-Loop and Software-in-the-Loop Simulations

Currently, there are three different methods to model traffic signal operations in microscopic simulation models: the simulation models controller emulator, hardware-in-the-loop simulation, and software-in-the-loop simulation. Although all three methods can be based on the same industry standard code, their different implementations suggest potential operational differences. This study investigates operational differences of the three methods by examining how each method operates in five experimental scenarios. Each of the scenarios differs from the others in network size (one intersection to five intersections) and operational strategies (pretimed, actuated, actuated–coordinated, and two different signal transition logics). Ten 75-min simulation runs with 100-ms simulation resolution were executed for each experiment with the three signal control modeling alternatives. The results showed that for basic signal control operations, such as pretimed and isolated actuated operations, the three alternatives provided similar results as indicated by the average green time allocation and different operational measures of effectiveness. When advanced controller operations were used, such as signal transition logic, the simulation model emulator showed significantly different behavior than that observed in hardware-in-the-loop and software-in-the-loop simulations.

Development and Evaluation of Algorithm for Resolution of Conflicting Transit Signal Priority Requests

The goal of this study was the development and evaluation of an algorithm for resolving conflicting requests for transit signal priority (TSP). This algorithm was designed to work with actual traffic controllers without the need for new hardware or software installations. The algorithm was tested in VISSIM microsimulation and ASC/3 software-in-the-loop controllers on an intersection that will be upgraded to serve two conflicting bus rapid transit (BRT) lines. The ASC/3 logic processor was used to control built-in TSPs in the case of conflicting requests and to develop custom-TSP strategies that would not rely on built-in TSP. Custom TSP provides a much higher level of TSP for transit vehicles than built-in TSP, and it creates opportunities for more adaptable TSP control. The results showed that the widely used first-come, first-served policy for resolution of conflicting TSP requests was not the best solution. Such a policy could perform worse than a policy that provided no priority. For the analyzed intersection, the first-come, first-served option even increased BRT delays by 13% more than did the no-TSP option. The presented algorithm can help resolve the problem of the conflicting TSP requests. The algorithm worked best when combined with several TSP strategies. For the custom-TSP strategies, the application of the algorithm reduced BRT delays by more than 30%, with minimal impact on vehicular traffic. The algorithm shows promising results, and with small upgrades, it can be applied to any type of TSP.

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.

Predictive Priority for Light Rail Transit: University Light Rail Line in Salt Lake County, Utah

The goal of this paper is to assess the operational implementation of strategies for predictive light rail priority through microsimulation. A 2-mi corridor in Salt Lake County, Utah, where the University Line of light rail line operates, was studied. The study used VISSIM microsimulation models to analyze light rail operations and the effects that light rail priority has on transit and vehicular traffic. Results showed that although the existing priority strategies had no effects on vehicular traffic along the corridor, they reduced train travel times by 20% to 30%. Left turns along the main corridor were slightly affected by the priority. Although the priority strategies could have minor to major effects on vehicular traffic along side streets through increased delays, they reduced train delays by 2.5 min along the corridor. Enabling priority at the 700 E intersection (where the priority was currently not active) would help reduce delays for trains by an additional 10%, with a small increase in vehicle delays. However, the coordinated north–south through movements would experience minimum impacts. Three recommendations emerged from the study: enable priority at 700 E to improve transit without major effects on vehicular traffic; reset priority parameters at intersections adjacent to light rail stations so that the priority call encompasses station dwell times; and consider removing the queue jump strategies, so as to reduce delays for the corridor through movements and help preserve coordination patterns.

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.

35M MAX: the first bus rapid transit system in Salt Lake County

Bus rapid transit (BRT) is becoming one of the most popular transit services in the USA. A total of 106 miles of BRT service is scheduled for deployment in the State of Utah in future years. This research looked at the first BRT deployment in West Valley City, Salt Lake County, Utah. The 10.8 miles long BRT line was launched on July 14, 2008, and shortly after the launching the first operational data became available. In addition, a series of surveys were conducted to gain feedback from the users of the BRT system. Preliminary results show significant improvements in transit operations, with a 33% increase in ridership, reductions of close to 15% in travel times and improved reliability. Survey results show a high degree of acceptance among the system users. In general, the BRT system has proven itself to be very successful, bringing significant improvements to transit riders.

Performance-Based Warranty Contracts for Pavement Markings: Experience and Lessons Learned in the State of Utah

In 2012, the Utah Department of Transportation (DOT) implemented a performance-based warranty on a portion of an I-15 pavement marking project. The awarded contract requested a contractor warranty on the implemented markings for a total of 6 years. This contract represented the first time that the Utah DOT had requested a warranty on pavement markings and the first time that Interstate maintenance funds had been used for them. This paper documents lessons learned from preconstruction, construction, and postconstruction phases of this project, collected through surveys of key Utah DOT personnel. The paper also includes a literature review on pavement marking warranty contracts in general, a review of the I-15 performance-based warranty contract, and reviews of previous pavement marking contracts of similar size that were based on material and workmanship warranties. Overall, the performance-based pavement marking warranty project was seen as a success. Considering that this approach to pavement marking projects is still innovative, significant potential has been shown, and state agencies should consider this direction for large-scale pavement marking projects, as well as for other construction projects in which performance can be clearly defined and measured. Because these types of Interstate freeway projects satisfy both capital improvement and preventive maintenance requirements, the projects are good candidates for FHWA support, as well as for additional funds obtained through state transportation commissions.

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.

A Corridor-Level Evaluation of GPS-Based Transit Signal Priority

Global positioning system (GPS)-based transit signal priority (TSP) has advantages in providing flexible and conditional signal priority to transit vehicles. This study compared the effectiveness of different combinations of operational patterns and TSP strategies and assessed their impacts on side-street traffic operations. Micro-simulation analytical tools were applied to two testbeds of Utah Transit Authority’s Bus Route 33 and bus rapid transit (BRT) Line 35 MAX. Eight scenarios were created for Route 33 that included the existing conditions and combinations of regular/BRT operational patterns with traditional TSP, GPS-based TSP, conditional TSP implementations. Three scenarios were created for 35 MAX, also considering the existing traditional TSP condition, GPS-based TSP, and conditional TSP implementations. Results confirmed similar operational effectiveness of GPS-based TSP when compared to traditional TSP. Conditional TSP had smaller impacts on side-street traffic while providing transit vehicles considerable amounts of delay reduction and travel time saving.