ABSTRACT

The City of Tucson and the Pima Association of Governments (PAG), in an effort to improve safety and operations near Highway-Rail Interchanges (HRI’s), are experimenting by installing a pre-signal at the intersection of the Union Pacific Railroad and the interchange of Prince Road and I-10 in Tucson, Arizona. The new signal will require approaching vehicles traveling westbound on Prince Road to stop before the Union Pacific Railroad track, and will operate in conjunction with the nearby signal at the Prince Road/I-10 Interchange to increase safety in the area. This pre-signal will be used as a pilot experiment to determine if similar signals should be implemented at other HRI’s throughout Tucson and Pima County.

The University of Arizona ITE Student Chapter (UAITE) is conducting a before/after study of the Prince Road/Union Pacific HRI. The before/after study involves collecting data on the westbound approach and eastbound traffic on Prince Road, including traffic volumes and turning movements for the two directions, delay and traffic violations for the westbound approach where the new signal will be installed, and the railroad crossing gate status. The before data were collected using video obtained from the Autoscope cameras installed at this intersection. The following picture, taken by the Autoscope cameras facing east from the Prince Road/I-10 interchange, shows the Prince Road/Union Pacific HRI. To collect the data, the UAITE team split the work as follows: two people collected traffic volumes and turning movements for passenger cars; two people collected gate violation information and traffic volumes for trucks and buses; four people collected queue data; and one person collected gate status. The amount and times to collect the data were determined by our mentor and are as follows: traffic volumes, turning movements, delay and traffic violations were recorded for one weekday (4 hours) and one weekend- day (1 hour); gate status was recorded for the same weekday and weekend-day for a 24- hr period.

The before data were collected from video taken on April 3 (weekend-day) and on April 7 (weekday) 2004. The after data were collected on September 29 (weekday) and on October 9 (weekend-day) 2004. The reasons for not collecting the data right after the installation of the pre-signal (beginning of July) and for not waiting until the end of September are two-fold. First, we would like to study the interchange in normal conditions when high traffic volumes operate (note that Tucson experiences much lower traffic volumes in summer) and when school buses and other school trips are occurring. Second, we wish to avoid concerns expressed in the ITE Manual of Transportation Engineering Studies regarding to the warm-up period that is needed for users to adapt correctly to the new treatment.

One of the limitations of collecting the data from video is that visibility was restricted. In order to estimate the number of vehicles in queue no visible, arrival rates were calculated.

The preliminary findings of this study estimate larger queue lengths for the westbound approach with the installation of the new signal. The average weekday delay per vehicle on the approach, based on the study hours, was increased by 10 seconds. In addition, traffic volumes seem to be consistency in both the before and after studies. Safety effects related to school buses could not be determined with the collected data.

The UAITE project team:

Mentor: John H. Warner, P.E., DMJM + Harris UAITE faculty advisor: Dr. Mark Hickman

Students: Andrew Desautels Nikifor Banchoff Laura McPhee Kerry Ruiz Jonathan Fell Sudeshna Mitra William Hanson Alan Flaxman Francis Pierson Robert Smith Quinn Quihui Felipe Ladrón de Guevara* Oliver Martinez

*Student Coordinator