Traffic Study-Pampa

ALMA SCHOOL ROAD AND PAMPA AVENUE/SRP DRIVEWAY

TRAFFIC ENGINEERING STUDIES

CITY OF MESA TRANSPORTATION

MESA, ARIZONA

JANUARY 30, 2001



INTRODUCTION

At the request of Ms. Roberta Laidman of 1160 W. Obispo Avenue and Mr. Ron Mellinger of 1152 W. Obispo Avenue, a traffic signal warrant study was conducted for the intersection of Alma School Road and Pampa Avenue/Salt River Project (SRP) driveway. Ms. Laidman and Mr. Mellinger are concerned about safety and delay at the intersection. A location map is attached. See Figure 1.

PHYSICAL AND TRAFFIC CHARACTERISTICS

Alma School Road is a fully improved major arterial street consisting of two northbound lanes, two southbound lanes, and a continuous left turn lane. Alma School Road carries approximately 45,000 vehicles per day and has a posted speed limit of 45 mph. Street lighting is provided, and parking is prohibited.

Pampa Avenue is a fully developed 34 foot wide residential street which serves as an access street for the neighborhoods east of Alma School Road. Parking is prohibited on the south side of Pampa from Alma School Road to a point fifty feet east of Alma School Road, and street lighting is provided. Pampa Avenue carries approximately 1,000 vehicles per day on its westbound approach to Alma School Road and has a posted speed limit of 25 mph.

A driveway for the SRP service center is located on the west side of Alma School Road directly across from Pampa Avenue. Approximately 150 vehicles per day exit from this eastbound approach to Alma School Road.

Land use in the area includes the SRP facility on the west side of the intersection, single family residential homes on the northeast corner, and a park/retention basin on the southeast corner. No homes face onto Alma School Road. Existing traffic control consists of stop signs for eastbound and westbound traffic on Pampa Avenue/SRP driveway.

ANALYSIS

Traffic counts were taken on October 3, 10, and November 30, 2001. The counts were taken at different times due to equipment and count location difficulties. Of the eleven signal warrants that are evaluated for a traffic signal study, the four hour volumes, peak hour delay, and peak hour volume warrants were satisfied for traffic volumes. Copies of counts and summaries of traffic signal warrants are attached. See Appendix A.


Delay observations were conducted on January 24, 2001 from 7:00 am to 8:00 am and from 5:00 pm to 6:00 pm. These time frames were chosen because traffic count data indicated them to be the peak traffic times. Observations were also conducted between 2:50 pm and 3:30 pm. The 7:00 am to 8:00 am time frame and 2:50 pm to 3:30 pm time frame coincide with Dobson High School arrival and release times, respectively. There is a rear entrance to the high school located on Saguaro Circle west of Alma School Road.

During the 7:00 am to 8:00 am observations there were 17 eastbound vehicles and 95 westbound vehicles that approached the intersection. Of the 17 eastbound vehicles, 10 (or 59%) turned right and 7 (or 41%) turned left. Of the 95 westbound vehicles that approached the intersection, 47 (or 49%) turned right and 48 (or 51%) turned left. There were no through vehicles observed for either direction. There was one pedestrian and one bicyclist observed crossing Alma School Road in the area of the intersection. These crossings were done one lane at a time as gaps in traffic became available.

Average delay for all drivers on Pampa Avenue/SRP driveway approaching Alma School Road during this observation was approximately 22 seconds per vehicle. Delays up to two and a half minutes were observed for three left turning drivers on Pampa Avenue between 7:40 am and 7:50 am. The average delay for left turning drivers on Pampa Avenue/SRP driveway was approximately 30 seconds. This delay is to be expected for drivers on a minor residential street/driveway approaching a major arterial street during the peak traffic times. Drivers on Pampa Avenue/SRP driveway making right turns, the movement made by 51% of the approaching traffic, experienced little delay.

The 2:50 pm to 3:30 pm observation for pedestrians coincides with the release of Dobson High School. During this time frame, there were 11 pedestrians and bicyclists observed crossing Alma School Road at or near intersection. Adequate gaps in traffic were present for the majority of these crossings. Typically, these crossings were made in a conscientious manner. Pedestrians crossed half of the street at a time as lanes cleared and gaps in traffic became present.

During the 4:00 pm to 5:00 pm observations there were six eastbound vehicles and 68 westbound vehicles that approached the intersection. Of the six eastbound vehicles, four (or 67%) turned right and two (or 33%) turned left. Of the 68 westbound vehicles, 36 (or 53%) turned right and 32 (or 47%) turned left. There were no through vehicles observed for either direction. There was one pedestrian observed crossing Alma School Road in the area of the intersection. This crossing was made in a conscientious manner with the pedestrian crossing half of the street at a time when gaps were available.

Average delay for all drivers on Pampa Avenue/SRP driveway approaching Alma School Road during this observation was approximately 15 seconds per vehicle. The average delay for left turning drivers on Pampa Avenue/SRP driveway was approximately 18 seconds. Although left turning drivers on Pecos Avenue experienced more delay than the right turning drivers, the overall average delay is less than what would be experienced if a traffic signal were to be installed. Adequate gaps in traffic were available for all movements.

The four hour volumes, peak hour volume, and peak hour delay warrants were satisfied for traffic volume. However, the peak hour volume and the peak hour delay warrants are intended for application when traffic conditions are such that the minor street suffers undue delay in entering or crossing the major street.

Field observations indicate that the overall delay experienced by drivers on Pampa Avenue/SRP driveway approaching Alma School Road is less than what would be experienced if a traffic signal were to be installed on the basis of these warrants. Installation of a traffic signal based on the four hour volumes warrant alone would not improve the overall operation of this intersection.

A review of accident frequency history revealed two reported intersection related accidents between January 1, 1998 and December 31, 1998. Of these two accidents, neither were of the right-angle type. A right-angle accident is the type of accident that is considered potentially preventable by the installation of a traffic signal.

Between January 1, 1999 and December 31, 1999 there were three reported intersection related accidents. Of these, two were of the right-angle type.

Between January 1, 2000 and December 1, 2000 there have been three reported intersection related accidents. None of these accidents was of the right-angle type. Collision diagrams are attached. See Figures 2, 3, and 4.

RECOMMENDATION

Because of the low amount of observed delay, lack of potentially preventable accidents, and that the installation of a traffic signal based only on the four hour volumes warrant will not improve the operation of this intersection, it is recommended that a traffic signal not be installed at the intersection of Alma School Road and Pampa Avenue/SRP driveway.

Although some delay exists for left turning drivers during the morning peak hour, the delay that exists for all drivers approaching the intersection is less than what would be created if a traffic signal were to be installed at this intersection. Installation of a traffic signal would likely increase the overall delay for drivers on Alma School Road.


Report by: Dale Brunk, Jr., Senior Traffic Studies Analyst