Caltrans is fully closing a stretch of eastbound Interstate 80 in downtown San Francisco. The closure lasts 55 hours and affects drivers approaching the Bay Bridge. The shutdown covers about 1.6 miles, from 17th Street to Fourth Street. It runs from April 17 at 11 p.m. until April 20 at 6 a.m. Drivers from the Peninsula detour at Ninth Street to Bryant Street, then reenter at Fifth Street. The owner of Bay Area Flower Market, on Bryant Street, said he was unaware of the upcoming closure. He said churches pick up big flower orders on Saturdays, and he was concerned where his customers could park…