Am I allowed to drive a scooter on every highway in the US?

A couple states- Ohio is one I think say minimum 250cc, Texas may be other. Federal light class is 150 cc break not allowed on interstate. so a 250 +cc to be sure as minimum would be OK.

As long as it is powerful enough to keep up with traffic.

Although there are many highways that I wouldn't take a scooter anywhere near.

it depends on the state, but generally you need atleast 250cc, for either a scooter or motorcycle. If whatever you ride cannot do 70mph consistantly, you are a hazard to the road and are going to be constantly in danger of being hit from the rear.

On the Interstate highways (freeways), it would need at least a 125-cc engine to be able to keep up with traffic. On non-freeways, you may be able to ride it on the shoulder. That will vary by state.

California 350 or better to ride freeways or highways.

Geez, scooters are dangerous enough on city streets, with those tiny wheels and bizarre steering head angles.

If you want to be on freeways more than in an emergency to get somewhere, get a REAL motorcycle would be my advice.

Depends on displacement.

250cc and up will go fast enough not to get you killed.

Less than that and people will be pissed at how slow

you're going.