You are driving a tall commercial vehicle and the posted clearance on a bridge ahead reads 13'6". Your vehicle is 13'4" tall. What should you do?

1. Proceed at normal speed since you have 2 inches of clearance
2. Proceed slowly and carefully because the actual clearance may be less than posted due to repaving, settling, or load shift
3. Speed up to minimize the time under the bridge
4. There is no concern; posted clearances always have a 1-foot safety margin