Every day, 96,000 vehicles move through Ina and Oracle, the Northwest's busiest intersection.
It has capacity for about 80,000 movements.
Ina and Oracle is a bottleneck. Because of longer traffic signal cycles, everyone stops. Traffic can back up in all directions. Particularly, lines of vehicles trying to turn northbound onto Oracle from westbound Ina can be dozens of vehicles deep at rush hour.
In 2006, the Regional Transportation Authority identified Ina and Oracle as "a critical intersection," and allocated $5 million for its improvement. The Arizona Department of Transportation and the Pima County Department of Transportation spent more than a year identifying and evaluating potential improvement alternatives, "keeping in mind we only had $5 million," said Jim Schoen, senior principal engineer for Kittelson & Associates.
Due to limited funds, "we're not going to be able to take care of all of it," Schoen told a meeting of the Northwest Transportation Coalition last week.
But there is a plan, a two-part solution that is progressing toward finalization.
Most definitive is the construction of dual right-hand turn lanes for westbound traffic turning north from Ina onto Oracle. For $1.377 million, Pima County has purchased a former Shell gas station at 7210 N. Oracle, on the intersection's northwest corner. While that acquisition "does take a good chunk" of the $5 million, Schoen said use of the property would allow construction of two turn lanes for the heavy northbound traffic.
Dual turn lanes should "more than double capacity" for northbound traffic, cutting delays and backups "in half, if not more," Schoen said. Back-ups to the Westward Look Resort, and sometimes beyond, should be largely eliminated. A fourth lane would be added to northbound Oracle, "to give right-turn traffic plenty of room to move over," Schoen said. All that can be fit into the existing right-of-way.
That improvement "doesn't benefit anyone else who goes through the intersection," Schoen acknowledges, so other possibilities have been investigated. And dismissed, at least one by ADOT, which is responsible for Oracle Road because it is a state highway.
Of all those 96,000 daily vehicle movements, about 4,000 are making left turns off Ina northbound or southbound. Engineers recognized those motorists add 25 seconds to every traffic signal cycle, on average, so they've tried to figure out a way to move those people through with the least effect upon others.
They've found one alternative palatable to all — what has been called the "Michigan left," moving people through the intersection along Ina to make U-turns that take them north or south.
"We're calling it the 'indirect left,'" Schoen said. "We're changing the vernacular from Michigan left."
Left-hand turners would move to points up to 700 feet away from the center of Oracle and Ina, where they would enter turning lanes regulated by new traffic signals on Ina Road, then make U-turns. "Distance from the intersection is influenced by the need for storage" of vehicles during busy times, Schoen said.
One indirect left U-turn would be created at the north entrance to Safeway in La Toscana Village along Ina; the other would begin at a point south of Tohono Chul Park. People leaving the Safeway plaza on its north side won't be able to turn left onto Ina. "Bulb-outs" would be constructed at those signal lights so that larger vehicles and trucks making the U-turn would be accommodated.
"Everyone would move through the intersection except left-turners," Schoen said. "That should decrease everyone's delay by 25 percent, which is a significant savings."
Most of the pedestrian traffic at the intersection is north-south. Wider medians within the intersection would give pedestrians more space. Sidewalks would be built next to Ina "as far as we can." Bus pullouts would be added and/or improved.
Good signage is imperative, Schoen acknowledges.
The strategy is to have final improvements identified in early 2011, with construction to start late next summer, finishing before the holidays. Construction shouldn't take that long, Schoen said, in the range of four months. Ben Goff, deputy director of the Pima County Department of Transportation, said "we're not tearing up the road, no pipes, no utilities. It's not a major intersection construction project."
Public outreach has taken place, and is continuing.
"A small percentage have said 'we don't like this,'" Schoen said. Transient motorists through the intersection "are pleased with the idea we were going to cut down wait times."
"You'll hear a lot more about this," Schoen said. "Final decisions haven't been made."
Ina-Oracle the seventh-busiest
Ina and Oracle is the seventh-busiest intersection in all of Pima County, with more than 96,000 vehicles passing through it every day.
That volume is projected to reach 126,000 vehicles each day in the years to come.
The intersection is "woefully inadequate," creating a bottleneck in the regional transportation system, according to Pima County Department of Transportation analysis.
Long signal light cycles, up to three minutes, create "long queues and delays," increase "cut throughs" in nearby residential neighborhoods, and impact access to businesses such as Casas Adobes Plaza on the southwest corner, and La Toscana Plaza on the southeast corner. Pedestrians, bicyclists and transit stops add to the complication.
Ina and Oracle are "two regionally significant roadways," and there are few if any alternatives for parallel routes, said Jim Schoen, senior principal engineer with Kittelson & Associates. "Traffic demand is going to increase."
That said, Ina and Oracle does not have "a poor safety history," Schoen said. On average, there are 75 crashes per year, most of them rear-end collisions. "There is a lot of volume, but it's a relatively safe intersection," he said.