I want to create a walk under double track bridge for an O scale layout. My plan shows an 8 foot span supported at each end by 1.5" x 4.5" boards. The underside bracing would be two 1 x 2's (3/4" x 1.5") the full length of the span. Is this design sufficient that the deck surface will not sag? The aisle width would be no more than six feet, so if necessary the end supports could be moved a foot in on each end leaving the unsupported width about 6 feet instead of eight feet.
