ACTT Workshop: Idaho
The I-84 Corridor Improvements Project

2. Project Details

2.1. Project Overview

The I-84 Corridor Improvements Project consists of the sections of I-84 from the junction with SH-44 in Caldwell to Five Mile Road in Boise and from the Orchard Street Interchange to the Isaac's Canyon Interchange. The goal is to reconstruct these 22 miles, including the interchanges, as they are substandard and severely lacking capacity. Construction is slated to begin in the summer of 2007. ITD's goal is to reduce the construction timeframe from 12 to 6 years. Maintaining the existing number of lanes throughout construction will be the principal challenge.

Figure 1: Proposed improvements on I-84 from the junction with SH-44 to Five Mile Road.

Figure 2: Proposed improvements on I-84 from the Orchard Street Interchange to Eisenman (Isaac's Canyon).

2.2. Project History and Development

I-84 is the only major east-west link through southern Idaho. It connects Boise to Portland and Seattle to the west and to Salt Lake City and Denver to the east. In addition, I-84 serves as a major commuter route for residents of Treasure Valley.

I-84 from Orchard Interchange to Isaac's Canyon is situated in Ada County and runs through the Boise metropolitan area. Built in the 1960s, this once-rural corridor is now one of the fastest-growing urban centers in the Nation.

Traffic counts along this section of I-84 vary greatly, ranging from 21,000 vehicles per day (VPD) near the Gowen Interchange to 76,000 VPD near the Orchard Interchange. The threshold for I-84 between Orchard Street and Broadway Avenue is a level of service (LOS) D with an average daily traffic (ADT) of 70,000, which means that existing traffic volumes exceed the operational capacity of the roadway. And things will only get worse – 2035 traffic volumes are forecast at 156,000 VPD near the Orchard Interchange. The mainline and four of the interchanges (Orchard, Vista, Broadway and Gowen) will need to be rehabilitated in order to meet these travel demands.

The situation is similar on I-84 from SH-44 to Five Mile Road, where a corridor study completed in 2001 showed that residents could expect significant travel delays and LOS between E and F if major roadway improvements did not take place within a few years.

The ramp taper lengths at most of the entrance and exit ramps along this section of I-84 do not meet current AASHTO standards, and the I-84 vertical alignment needs to be adjusted to meet clearance requirements and improve the drainage of the pavement surface.

Furthermore, 2035 travel projections show 52,000 VPD near the junction with SH-44 and 180,000 VPD near Eagle Road. These traffic volumes far exceed the operational capacity of the existing roadway.

2.3. Project Challenges

The segment under study as part of the I-84 Corridor Improvements Project consists of a four-lane divided freeway. The concrete pavement is failing and is in urgent need of replacement. The ramp taper lengths at all of the entrance and exit ramps do not meet current design standards. Vertical clearance is an issue in several areas, as is pavement drainage.

Both segments of the I-84 corridor are part of the CIP Grant Anticipation Revenue Vehicle (GARVEE) Bond Program. Because the estimated cost is greater than the projected bond funding, construction will be staged based on corridor priorities. The Idaho Transportation Board has approved a five-year plan to design and construct approximately $250 million of improvements within the segment from SH-44 to Five Mile Road and approximately $187 million within the I-84 corridor from the Orchard Street Interchange to the Isaac's Canyon Interchange. The actual bond funding available will be subject to annual authorization by the Idaho legislature.

2.4. Project Status

Several projects are scheduled to be let in 2007 for I-84 from SH-44 to Five Mile Road.

An Environmental Assessment (EA) is underway for I-84 from Orchard Interchange to Isaac's Canyon. ITD anticipates that the NEPA process for this segment will be complete in mid-2007. Construction on portions of the project corridor is slated to begin in the fall of 2007.