Repairs begin next week on the aging bridges that carry Interstate 84 across Hood River, leading to around-the-clock single lane closures in both directions and ramp closures.  The concrete decks are deteriorating on the I-84 structures over Hood River between exits 63 and 64.  The first phase of the project takes place from March through May, with a second phase this fall and a third next winter.  One lane in both directions of Interstate 84 will be closed during each phase of construction, there will be traffic shifts with reduced lane and shoulder widths, and speed limits in the work zone will drop to 50 miles per hour.  Nighttime ramp closures at exits 63 and 64 will take place periodically from 10 p.m. to 5 a.m. Monday through Thursday nights, primarily at the beginning and end of each phase.  Cyclists using the shoulder of I-84 will need to use an alternate route during construction, while pedestrians can continue using the overcrossings and trails under I-84 with minor delays.