The crash closed two westbound lanes for nearly an hour during rush hour Thursday evening, Idaho State Police report.
The crash happened about 6 p.m. just west of the Garrity Boulevard exit on Interstate 84.
Drivers Chrystal Hunt, 31, of Nampa and Jordan Graham-Ax, 28, of Eagle slowed for traffic, but the Toyota pickup behind them, driven by Gregory Harreld, 38, of Nampa, did not, ISP reports. Harreld's pickup hit the rear of Graham-Ax's car, pushing into Hunt's sport utility vehicle. A fourth vehicle, driven by Earnest Treadwell, 73, of Sunset, Utah, failed to stop and hit the pickup, repeating the impact for the first three cars, ISP reports.
Harreld, Hunt, and Graham-Ax were transported by ambulance to Saint Luke's Medical Center in Nampa. Harreld was not wearing a seat belt at the time of the crash, ISP reports.
Two lanes were blocked for approximately 50 minutes while crews worked to clear the scene. The crash is under investigation.