Most of the miles on my Vino were on 2 lane rural roads with speed limits up to 65 mph. You can safely ride on such roads, but you cannot ride with traffic. Think bicycle. I ride just to the inside of the solid white line to the right, and if a vehicle comes up behind me (yes you have to watch your mirrors), and there is oncoming traffic (which happens about 20% of the time on these roads) I just move across the line onto the paved shoulder. I do wear a white helmet and an orange reflective vest. Before I got into scooters, I rode pedal mopeds on the same roads, and also used to ride bicycles on them. I have never came close to getting hit.
Some think that you have to be able to maintain freeway speed and have some in reserve just to ride on the freeway. That's not the case either. I put 20,000 freeway miles on a Honda Rebel 250 that topped out at about the speed limit, with nothing in reserve, and slowed down considerably when going up even slight grades, or in headwinds. Again I dressed for visibility, stayed in the right lane, and watched my mirrors. Never had any problems. Many times I came up behind some old vehicle pulling a trailer at 50-55 mph when the speed limit was 75. I just fell in behind them, turned my headlight off, and took the opportunity to ride at a more reasonable speed for the bike.
I made 3 trips from Phoenix to San Diego and back on I-8 on my Vino 125. That's over 800 miles, with speed limits of mostly 75 mph. But it is also a mostly deserted road with mostly truck traffic, and you can see for miles ahead of you. While climbing mountains, the Vino got down to 30 mph, but I never felt like I was in any danger except from the cops.
I am planning to buy a new scooter in the next few days that will not do 75 mph. My main reason for buying it is the engine is big enough to be freeway legal. I don't plan on a lot of freeway riding, but some is unavoidable if you are actually going to get anywhere. I know it won't keep up with left lane traffic, and I will ride accordingly. Many places out west it is legal to ride bicycles on the shoulders of freeways, simply because there is no other way to get somewhere.
Now, on the urban freeways, like the 101, 202, 60, and 51 around metro Phoenix you would have to be crazy to get on one of those with anything that won't do at least 100 mph, and reach it quickly. Unlike wide open cross country interstates, traffic on these is like a stampede, 6 lanes wide bumper to bumper (think LA) there is no slow lane, and speeds vary from 0 to over 80 mph, often changing back and forth every few minutes. LOTS of rear end collisions and even pileups due to cell phone impaired drivers. I try to stay off these roads even in a car.