33 CFR §117.41

1. (a)Drawbridges permanently maintained in the fully open to navigation position may discontinue drawtender service as long as the drawbridge remains fully open to navigation. The drawbridge must remain in the fully open position until drawtender service is restored.
2. (b)If a drawbridge is normally maintained in the fully open to navigation position, but closes to navigation for the passage of pedestrian, vehicular, rail, or other traffic, the drawbridge must be tended unless:
   1. (1)Special operating requirements are established in subpart B of this part for that drawbridge; or
   2. (2)The drawbridge is remotely operated or automated.