Interstate 10 / Houghton Traffic Interchange Study

The Arizona Department of Transportation (ADOT), in partnership with the Federal Highway Administration (FHWA), initiated a design concept study and related environmental studies to evaluate an interchange reconstruction at Houghton Road and Interstate 10 in Tucson, Arizona.

Considerable growth is anticipated along the Interstate 10 (I-10) corridor in the coming years, with projections indicating volumes will increase by 50% by 2045. Similarly, Houghton Road expects substantial increases in traffic, with projections showing a 500% increase north of I-10 and 200% increase south of I-10. The reconstructed interchange would provide relief for motorists accessing existing and planned residential and business developments in the surrounding areas.

The purpose of this study is to develop and evaluate options to reconstruct the traffic interchange (TI) at Houghton Road and recommend an alternative that will meet long-term transportation needs, satisfy the requirements of the National Environmental Policy Act (NEPA), and obtain public support.

This study will address the following improvements:

  • A reconstructed TI at Houghton Road to accommodate projected traffic volumes and provide full highway access (including parallel-type entrance and exit ramps in both directions), and
  • Reconstructed Houghton Road from north of Rocket Road to south of I-10.

Houghton Road is a principal arterial road that serves north-south traffic in the southeastern part of Tucson and Pima County. It provides access to the Pima County Fairgrounds (one mile south of I-10) and several businesses and residential areas (several miles north and south of I-10). The land adjacent to Houghton Road north and south of I-10 is owned by the State of Arizona and is undeveloped. The nearest access points to and from I-10 in this area are provided via the Rita Road TI approximately two miles to the west (MP 273.14) and the Wentworth Road – Colossal Cave Road TI approximately four miles to the east (MP 279.37). The Houghton Road TI is at MP 275.49.

If you’re curious to see how a DDI works, watch this video from the Illinois Department of Transportation (IDOT). Recently IDOT constructed a DDI at I-88 and Route 59 near Chicago. This DDI’s design is similar to what is being planned for I-10/Houghton Rd TI.

Meetings and Events


The Arizona Department of Transportation and the Federal Highway Administration hosted an open house about the proposed replacement of the traffic interchange at Interstate 10 and Houghton Road. The meeting was held Thursday, Feb. 8, 2018.

About the Project

ADOT is beginning the design process for a project to replace the traffic interchange at I-10 and Houghton Road, a primary roadway that serves north-south traffic in the southeastern part of Tucson and Pima County. The interchange was included in a prior Design Concept Report for a larger section of Interstate 10 in the Tucson area and has been scheduled for replacement in 2020. The project team is proposing a Diverging Diamond Interchange (DDI) to provide relief for motorists accessing existing and planned residential and business developments in the surrounding areas.


Questions and Comments

Your input is important and will be considered during the design process. If you are unable to attend the open house, you can provide comments or ask questions in these ways:

  • Call the ADOT Project Information Line at: 855.712.8530
  • Email: [email protected]
  • Mail written comments to ADOT Communications: 1655 W. Jackson Street, MD 126F, Phoenix, AZ 85007

Frequently Asked Questions


Did ADOT consider any other options for the traffic interchange at Houghton Road?

Yes. During the predesign phase, ADOT studied whether a Diverging Diamond Interchange (DDI), a conventional Diamond Interchange, a Single-Point Urban Interchange or Twin Roundabouts would perform best at I-10 and Houghton Road. The DDI was carried forward for further evaluation because it rated the best at handling peak volume turning movements, provides lower intersection delay than the Diamond and Single Point Interchange alternatives, features one of the lowest construction costs of the alternatives considered, and is supported by the agency stakeholders. Several DDIs are planned for construction in Arizona, but none currently exist in the state. More than 80 DDIs are in use and functioning successfully across the country.

Are DDIs safe?

Safety is among the many benefits of a DDI, as they have been shown to reduce the number and severity of collisions while also reducing wrong-way movements. DDIs reduce the number of traffic “conflict points” compared to other interchange designs and, because of reduced speed limits and the angles at which vehicles cross the intersection, the severity of collisions decreases. In a study by the Federal Highway Administration, researchers compared the DDI to other interchange designs. The study found that at locations where a DDI is constructed, the interchange experienced a 50-percent reduction in overall collisions and a 60-percent reduction in fatal collisions. DDIs also have safety benefits to the cyclists and pedestrians who travel through them. Pedestrians travel through the center of the DDI in a wide median that is barrier separated from the travel lanes. The crossings are shorter and protected with signals. Read the FHWA study.

How does traffic flow on a DDI?

The Diverging Diamond Interchange is new to Tucson and Arizona and operates differently than the interchanges familiar to many motorists in the area. The major difference is that, as motorists approach the overpass from each direction, they are directed to the opposite side of the road at signalized intersections. While it may appear confusing when viewing maps and illustrations, road markings make it feel quite intuitive. The completed interchange will have pavement striping, curbed islands and medians, traffic signals and signing to provide a simple and efficient driving experience for the driver. When driving through a DDI, the striping and signage are very similar to driving on a one-way road that happens to cross another one-way road and permits left-turn movements without crossing opposing traffic or waiting for a traffic signal.

What are the primary benefits of the DDI at I-10 and Houghton Road?

The DDI has been shown nationally to reduce the number and severity of crashes and, because of its geometry, can reduce the possibility of wrong-way movements by motorists. The new interchange also will reduce traffic congestion and shorten delays experienced at the interchange, which serves a part of Tucson and Pima County where consistent growth and development are expected to continue.

Where else in the United States are DDIs being used?

As of July 2017, 88 DDIs were in use in Colorado, Delaware, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Maryland, Michigan, Minnesota, Missouri, Nebraska, Nevada, New Mexico, New York, North Carolina, Ohio, Oregon, Pennsylvania, Tennessee, Texas, Utah, Virginia, Wisconsin and Wyoming.

I-10 / Houghton Traffic Interchange layout graphic