A 23-mile stretch of Interstate 10 is being considered for expansion from Phoenix to Casa Grande. The Arizona Department of Transportation and the Maricopa Association of Governments are determining whether an extra lane should be added in both directions.

“Under NEPA, the National Environmental Policy Act, the study also looks at potential impacts to the natural and social environments and then looks for ways that those can be avoided, minimized or mitigated," said Steve Elliott, a spokesman for ADOT.

The agencies will study the possible expansion for 18 months and determine the timing and cost of a project, which would need final approval.