Shannon Warchol

Quality Assurance and Quality Control Processes for a Large-Scale Bicycle and Pedestrian Volume Data Program

Phase 1 of North Carolina’s Non-Motorized Volume Data Program (NMVDP) was conducted in the North Carolina Department of Transportation Divisions 7 and 9 in the Triad–Piedmont region of North Carolina. Continuous count stations (CCSs) were installed to monitor bicyclist and pedestrian traffic at 12 locations and began collecting data in late 2014. These stations covered a mix of sites across different land uses, travel patterns, and volume groups. Sites performed automated detection of pedestrians on sidewalks, bicycles and pedestrians on shared-use paths, bicycles in bicycle lanes, bicycles on sidewalks, and bicycles in mixed traffic. This paper summarizes the programmatic elements developed and implemented to select, install, and ensure high data quality for the 12 CCSs. These elements include agency coordination, site selection, equipment procurement and setup, equipment validation, equipment maintenance, data handling, quality assurance and quality control checks, and data reporting and analysis. After piloting this program in one region, the research team identified several changes to test when the NMVDP was expanded to a new region of the state to improve the quality of data collected: conduct weekly inspections of the data and perform validation to promptly identify maintenance issues, investigate the development of hourly data checks to implement, use a simpler interquartile range check, and consider developing automation to check data.

Safety Evaluation of Seven of the Earliest Diverging Diamond Interchanges Installed in the United States

Diverging diamond interchanges (DDIs) are increasingly popular because they provide improved traffic operations and cost savings. On the basis of theory, DDIs should be safer than conventional diamonds, but previous empirical safety studies have been limited. The objectives of this work were, therefore, to conduct a broader safety evaluation of DDIs and to recommend a crash modification factor (CMF) for the conversion of a conventional diamond to a DDI. The team analyzed seven of the earliest DDIs in the United States. Four were in Missouri and other sites were in Kentucky, New York, and Tennessee. The team collected more than 28 site years of crash and other data before intersection conversion and more than 19 site years of data after their conversion. The primary analysis was before and after with comparison sites to account for trends and potential simultaneous event biases. The results showed that crashes were reduced at most of the sites, and the team recommended a CMF of 0.67, meaning that installation of a DDI to replace a diamond should reduce all crashes by 33%. The reduction in injury crashes was even larger, with the team recommending a CMF of 0.59. Other analyses indicated that DDI installation should mean a substantial reduction of angle and turning crashes, with some reduction in rear-end crashes as well, although rear-end crashes will still be the dominant crash types after DDI installation. Clearly, DDIs offer potential safety benefits, and agencies should consider them strongly as replacements for conventional diamonds.

Use of Microsimulation to Evaluate Signal-Phasing Schemes at Diverging Diamond Interchanges

Even though diverging diamond interchanges (DDIs) have been the subject of research for more than a decade, the effort to standardize interchange signal timing has developed only recently. A three-factor fully crossed experiment was conducted to investigate the influence of crossover spacing and increased volumes on the performance of DDI phasing schemes. PTV Vistro software and the dynamic bandwidth assessment tool were used to optimize the split, cycle length, and offset of each of the 72 treatments. PTV Vissim software was used to collect microsimulation data. Mean interchange delay and mean stops per vehicle were selected as measures of effectiveness. Pairwise comparisons were used to determine whether an existing preferred phasing scheme could minimize delays or stops under three cases: (a) given spacing and increased volume, (b) given volume independent of spacing, and (c) given spacing independent of increased volume. The data revealed that a two- or three-critical-movement phasing scheme usually resulted in the lowest mean interchange delay and the fewest stops. Overall, the results provide an initial signal timing scheme for practitioners given a crossover spacing, an increased volume, or both. Future work will include exploring low volumes, balanced interchange volumes, and their effects on the four-critical-movement phasing scheme, as well as the effect of closely spaced adjacent intersections.

Innovative Method for Remotely Fine-Tuning Offsets Along a Diverging Diamond Interchange Corridor

Diverging diamond interchanges (DDIs) are relatively new in the United States, and signal coordination between the crossovers and adjacent intersections is challenging. This paper provides a method for remotely fine-tuning offsets for a DDI and its adjacent intersections. The proposed method uses the dynamic bandwidth analysis tool (DBAT). The tool uses actuated phase times from the signal controller to optimize the dynamic bandwidth on the basis of that entry data set. Four performance measures evaluated the proposed method: delay, stop severity index, maximum queue, and vehicle trajectory plots. The test results confirmed that DBAT provided a better offset solution than other bandwidth optimization tools that generally optimized programmed bandwidth only and did not account for early return to green caused by skipped or gapped-out movements. Under the DBAT offsets, delay for the through movements on the corridor decreased by 52.8% for northbound vehicles and 46.83% for southbound vehicles. The average delay reduction over all measured paths for uncongested and congested scenarios was 13.88% and 3.50%, respectively. The proposed method and workflow can significantly reduce the offset retiming work process. Normally, this manual process takes more than a day, but the proposed method can be completed in less than an hour without visiting the study site. Furthermore, the proposed method can coordinate any set of movements, as well as multiple travel paths. The authors believe that the proposed method and workflow will significantly help both retiming and new timing of arterial signal coordination along DDI corridors and other signal systems.

Signal Timing for Diverging Diamond Interchanges: Fundamentals, Concepts, and Recommended Applications

A diverging diamond interchange (DDI) is an innovative interchange design that is being used with increasing frequency in the United States because of the ability to use existing right-of-way and infrastructure frequently. This paper documents the state of the practice in DDI signal phasing with principles established in the Signal Timing Manual, namely, that it uses consistent phase numbering in a logical format to describe each of the phasing concepts being considered and discussed in this paper. Although some literature exists on several methods of signal phasing for DDIs, inconsistency in the reporting leaves practitioners scratching their heads when attempting to decipher what phasing scheme to use. In response, three fundamental phasing schemes are presented, one each for volume patterns with two, three, and four critical movements. Each scheme is described with a consistent naming convention, and, when possible, each is manipulated to provide varying coordination strategies. In addition, concepts such as use of actuation and barriers to improve coordination are described, and methods for reducing lost time are introduced. Other supplemental information related to preemption and pedestrians is discussed briefly. In conclusion, practitioners are given some basic guidance on when one phasing scheme may be more appropriate than another.