This road sign means:

This is a speed limit sign. It indicates the maximum legal speed that you may drive on the road where it is posted. At times of rain, snow, ice, or other less-than-ideal conditions, you may have to drive more slowly than the posted limit.

• You must travel at the speed indicated.
• The maximum legal speed on the roadway is 55 mph.
• You must travel through the intersection at the posted speed.
• None of the above.