Photo by Tudor Van Hampton Chicagos $1-billion Red Line rehab falls on the heels of a $530-million modernization of its Brown Line, which wrapped up in 2009. The Red Line is one of the busiest transit routes in the U.S. A $1-billion program to modernize Chicago Transit Authority's Red Line—the backbone of the city's century-old urban rail and one of the busiest routes in the U.S.—is about to get under way.The long-overdue project will rehab Chicago's most traveled passenger rail, which serves 240,000 daily riders. The train stations are outmoded, and track deterioration has prompted slow zones that bog down