Final answer:
The highest speed limit on designated highways for vehicles weighing 8,000 pounds or less and commercial buses varies by state and is usually between 55 to 75 mph.
Step-by-step explanation:
The highest speed limit on designated highways for vehicles weighing 8,000 pounds or less and commercial buses varies by state. In general, the speed limit for these vehicles is usually between 55 to 75 miles per hour (mph). However, it is important to note that each state in the United States has its own specific laws and regulations regarding speed limits, so it is always best to check the local laws in the specific state you are interested in.