Transportation officials are looking to nearly double the width of Interstate 10 — boosting part of the highway to a staggering 24 lanes.
The wider I-10 would begin in Tempe, where U.S. 60 dumps drivers from the East Valley onto the interstate toward Phoenix. The extra lanes would continue to east Phoenix and could one day extend as far as Interstate 17.
The freeway’s size would be unlike anything in Arizona and would take time to get used to, transportation planners said. Even local officials struggled to grasp the freeway’s size when they first saw a diagram showing all the lanes.
“I’m thinking: 24 lanes, that’s not too bad — 12 on each side,” Tempe Vice Mayor Hut Hutson said. “All of a sudden it dawned on me — 12 on a side! I couldn’t believe it.”
The new design essentially adds another freeway on the outside of the existing highway. A barrier would separate the inner freeway from a new parallel road.
Other major metro areas have similar configurations, but the length of this segment could become the longest freeway section of this width, said Eric Anderson, the transportation planner for the Maricopa Association of Governments.
“No doubt it will be one of the widest freeways in the country,” Anderson said. “And maybe the widest.”
The first segment of the 24-lane freeway would run from U.S. 60 to about 40th Street, cost about $550 million and take three years to build. The association has the funds to start construction in 2011 or 2012. The work would include a new, more efficient interchange with state Route 143.
Planners are looking to widen I-10 from I-17 to the Loop 202 Santan Freeway, which could raise the project’s price to $1.3 billion. Officials don’t yet have the money for that much expansion, but Anderson said it’s being studied to prepare for traffic demands decades from now.
The widening that is funded would dramatically improve the freeway, easing one of the Valley’s most congested areas, Anderson said.
The wider I-10 would include a second HOV lane to run along the five or six lanes in place on most of I-10.
Other new lanes would be part of the parallel road, called a collector-distributor road. A concrete barrier would separate the outside road because freeways become bogged down once they get wider than about six lanes per direction, Anderson said.
Weaving is the major problem as drivers cross multiple lanes to reach an exit. The barrier between the two roads would only open up every several miles, which cuts weaving and makes the freeway more efficient than if it had the same number of lanes without a barrier, Anderson said.
Arizona Department of Transportation would likely expand the freeway to 24 lanes all at one time, Anderson said. Parts of the freeway in Tempe have 12 lanes, though at least one segment has 14 near the U.S. 60 interchange.
The Tempe segment of I-10 is a priority because of congestion and the amount of urban growth south and east of the interchange with U.S. 60. Also, traffic at the Broadway curve is projected to reach 450,000 vehicles a day in 20 years. That’s up from 294,000 a day now, a virtual tie with Arizona’s busiest freeway. The top spot is I-10 at state Route 51, where 303,000 vehicles pass a day.
Initial studies show it will take $200 million to $300 million to buy land for the wider freeway and relocate numerous businesses. It doesn’t appear the wider freeway would disturb cemeteries at the Broadway curve in Tempe or substantially carve into the buttes there, Tempe officials said.
Tempe is eager to see some of those lanes. But not all of them.
The city was supposed to get extra lanes on U.S. 60 and I-10 heading toward Phoenix starting this year, Tempe Mayor Hugh Hallman said. That was part of a deal Tempe struck with the ADOT seven years ago, when ADOT was widening U.S. 60, the mayor said.
ADOT wanted to widen U.S. 60 further, but Tempe objected because there wasn’t enough money to add lanes to I-10 at the same time. Without more lanes on I-10, the city argued, a bottleneck would just turn U.S. 60 into a parking lot during the morning rush hour.
But the original widening plan for I-10 was delayed as ADOT got requests from other communities to make the freeway even wider, Hallman said, breaking a deal to make I-10 a priority around U.S. 60.
“That promise has never been kept,” Hallman said.
ADOT has let too many other communities request improvements to I-10 and expanded the project to a nearly impossible scope, Hallman said. That resulted in the massive 24-lane proposal, Hallman said, instead of a more modest improvement that Tempe had expected sooner.
“Now we have a bigger parking lot, as was feared by Tempe residents, and lots of excuses.”
ADOT acknowledges the scope of the project expanded.
“When the U.S. 60 agreement was reached, it was thought the I-10 improvement study would be done or close to completion at this time and we’d be zeroing in on improvements at the U.S. 60 interchange,” ADOT spokesman Doug Nintzel said. “But the process has become much more complex.”
ADOT and MAG are looking to widen more of the freeway than originally thought and planning for needs 20 years from now, Nintzel said. Planners added a commuter rail study between Phoenix and Tucson. The route would run parallel to I-10 and could reduce the burden on the highway.
Hallman and Hutson support rail service and want to see how much it could change freeway use.
“That would relieve a lot of that traffic,” Hutson said. “I’d be interested in looking at that before I’d buy off on 24 lanes.”