A paved multipurpose pathway that stretches eight miles through part of Grand Teton National Park has received high marks from bicyclists since it opened in 2009, but some of those same bikers worry that a proposed federal law may force them off the adjacent highway and require them to use only the pathway. The situation is not unique to Grand Teton. A pending federal transportation spending bill, dubbed the “mandatory sidepath law” by opponents, would require cyclists to use paved bike paths on any federal lands where the path is within 100 yards of a federal road with a speed limit of 30 mph or higher.