When driving a placarded vehicle, what speed should you drive on the highway?

Hazmat drivers do not have a different posted speed limit than other commercial drivers, but they must drive especially defensively given the consequences of any incident. Drive at a speed safe for conditions, well below the limit when conditions are adverse (rain, snow, fog, traffic), take curves conservatively, maintain large following distances, and avoid sudden maneuvers. A passenger-vehicle crash is bad; a hazmat crash can be catastrophic. The defensive driving philosophy applies even more strictly: leave yourself enough margin that another driver's mistake or a road defect does not force you into an emergency maneuver with a placarded load.