A vehicle-to-infrastructure (V2I) connected vehicle system was installed along Redwood Road in Salt Lake City, Utah, United States, in November 2017 using dedicated short-range communication (DSRC) radios to connect transit buses to traffic signals. One of the goals of this system was to improve the schedule reliability of the bus by providing signal priority at traffic signals when the bus is behind its published schedule by a certain threshold. Data for the analysis were obtained from the DSRC communications, the Automated Traffic Signal Performance Measures (ATSPM) system, and the transit operations system. The robust data available from these three systems allow for detailed analysis of priority requests made, requests served, and bus on-time performance in a way that is not possible without these data sets. By comparing actual schedules of the four DSRC-equipped buses over a 4-month period from April to July 2018 with buses which do not have the ability to request signal priority, it has been determined that the equipped buses meet their published schedule about 2% to 6% more frequently, depending on direction and time of day, with the most significant improvement of 6% in the southbound PM peak.

Diverging diamond interchanges (DDIs) are an emerging interchange configuration that eliminates the need for left-turn phases in conventional diamonds and may be less expensive to construct than some alternative geometries. This paper examines signal timing for DDIs. DDI signal timing typically has used a two-phase configuration that reflects the two competing movements at the crossover points at each inter section of the DDI. This configuration inherently contains some inefficiency: (a) there is potential for internal queuing under two-phase configuration and (b) it is possible for the inflow demand to exceed outflow capacity of the interchange. This paper uses high-resolution event data to develop performance measures for evaluating operations at a DDI in Salt Lake City, Utah. Alternatives to the existing signal timing within the two-phase configuration are modeled and tested with a field deployment. The field deployment demonstrated the ability to prioritize ramp or through vehicles within the two-phase configuration. Additionally, a new three-phase configuration was developed and deployed to address the internal queuing that occurs with two-phase timing. With this new configuration, the flows from one DDI intersection to the other are balanced, and progression within the DDI is improved. With the implementation of the three-phase configuration, the percentage of vehicles arriving on green at the heaviest internal movement within the DDI increased from 53% to 92%. To illustrate these performance measures and improved DDI operation qualitatively, a video from a tethered unmanned aerial vehicle demonstrated the vehicle arrival characteristics by overlaying vehicle detection and signal state graphics on the video.

In 2017, a connected vehicle (CV) corridor utilizing dedicated short-range communication (DSRC) technology was built along Redwood Road, Salt Lake City, Utah. One main goal of this CV corridor is to implement transit signal priority (TSP) when the bus is behind its published schedule by a certain threshold. With the data generated by the transit vehicles, transmitted through the DSRC system, logged by traffic signal controller, and coupled with the Utah Transit Authority (UTA) data from transit operation system, some performance data of the TSP can be analyzed including TSP requested, TSP served, bus reliability, bus travel time, and bus running time. For providing better signal coordination to buses, the signal plan for this CV corridor underwent retiming in October 2018. This research aims to compare the TSP performance before and after the signal retiming. The field data of August, September, November, and December in 2018 were selected to perform this evaluation. Results show that the TSP served rate after signal retiming is 35.29%, which is higher than that of 33.12% before signal retiming. In addition, compared with the signal plan before October, bus reliability northbound and southbound on the CV corridor was improved by 2.4% and 1.47%, respectively; bus travel time and bus running time were reduced as well.

Second-by-second GPS trajectories, called trip traces, of vehicles moving along an arterial provide the highest fidelity measure of corridor operations. However, large samples of such contiguous trajectories are not always possible because of varying techniques to reset probe vehicle IDs for data privacy, varying probe data penetration rates, and varying vehicle routing. This paper analyzes changes in segment travel time using the Mann–Whitney U test and proposes a method for creating a composite travel time metric using trip trace data. These techniques were applied to a four-corridor signal improvement and upgrade project in southeastern Salt Lake County. The study found that on average three out of the four corridors decreased in composite median travel time, by 32 s, 16 s, and 14 s. Interquartile range (IQR) was used to assess travel time reliability and the IQR travel time reduced (improved) on average by 33 s, 23 s, 18 s, and 1 s. In addition, a rank-sums method for statistically comparing the two composite travel time distributions is applied to the results. The four corridors had a total of 48 links and were evaluated during five time-of-day periods. Out of the 240 link-periods, the rank-sums analysis method found that overall, 68 link-periods improved and 13 link-periods slowed, at a 95% significance level. The annualized user benefit from the improvements was estimated at $2.2 million for the four corridors.

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