The drawspan for the Port Isabel Drawbridge, mile 666.0, must open on signal; except that, from 5 a.m. to 8 p.m. on weekdays only, excluding federal, state, and local holidays, the drawspan need open only on the hour for pleasure craft. The drawspan must open on signal at anytime for commercial vessels. When the drawspan is open for a commercial vessel, waiting pleasure craft must be passed.