Construction underway on State Highway 21 widening project in Boise

The Idaho Transportation Department (ITD) has started construction to widen State Highway 21 between Technology Way and Surprise Way in Boise.

The project began Monday, May 16 and is expected to finish in late July. Planned improvements include a new center turn lane, wider shoulders, and dedicated right turn lanes at the intersections of Grand Forest Drive, Lake Forest Drive, Old Oregon Trail Road, and Surprise Way. An acceleration lane will also be installed for traffic turning onto southbound SH-21 from Surprise Way. When complete, this stretch of highway will feature two 12-foot wide travel lanes, a 14-foot center turn lane, and 6-foot shoulders.

Construction will begin on the south side of the highway. When paving is done, traffic will shift to the new pavement as crews complete paving on the north side of the road.

The anticipated work schedule is Monday through Friday, 7 a.m. to 7 p.m., with work pausing on Memorial Day, Independence Day, and July 5.

Motorists should plan for reduced speeds through the construction zone, traffic shifts, and periodic delays with flaggers directing traffic. Access will be maintained to all neighborhoods throughout the project. ITD and the Idaho State Police urge motorists to slow down and pay attention when driving in work zones, where increased speeding fines and other penalties apply. Please plan ahead and visit for information on the state highway or interstate system.

For more information and project updates, visit