I drive a relatively small car for the US, and it's about the minimum I would consider safe at 70MPH. But, if you are spending 98% of your time in the city then simply renting a larger car becomes very viable. You can rent a mid size SUV at ~600$ per week and for a longer vacation you can upsize for minimal cost. Further, if your flying somewhere your car becomes meaningless anyway.
PS: Remember a tiny electric could end up saving you 250+$ / month.
https://en.wikipedia.org/wiki/Insurance_Institute_for_Highwa...
In Rural areas the opposite is true. High speed car vs car and car vs tree accidents are most common.
Though bigger doesn't equal safer. I remember someone else pointing out that large vehicles don't increase safety overall, they decrease it. If you consider two large trucks hitting each other is typically worse than two smaller passenger vehicles doing the same. It's only large truck vs small car that is slightly safer. Less than one might think because large vehicles tend to roll over more often.
In its class (which only had 3 cars), the Mini was safer than the Smart but the Hyundai Accent was much much worse.
But there were lots of bigger cars that were at the same rating or worse:
* Buick Lacrosse 2WD
* Cadillac DTS
* Cadillac Escalade 4WD
* Chevrolet Camaro
* Chevrolet Silverado 1500 Ext 4WD
* Chevrolet Silverado 1500 Crew 4WD
* Chevrolet Suburban 1500 2WD
* Ford Expedition 2WD
* Ford F-150 Super 4WD 39
* Mercury Grand Marquis
* Toyota Avalon
* Toyota Tundra Crew Max 2WD
[0] http://www.cbsnews.com/htdocs/pdf/Driver_DeathRates_sr5001_e...
They put in a tridion protection cell[0] and moved the engine to the back to offer SOME crumple at the front. The Euro NCAP rated it 4/5, IIHS rated it "good" but it later failed the partial frontal collision test ("poor").
A Smart Car likely would do alright in most collisions. Although it somewhat benefits from the large crumple zones of every other vehicle has on the road. If two Smart Cars collided head on, the results might be worse than if a Smart Car collided with any other vehicle type.
That all being said, just because Smart managed it, doesn't mean every small car is equally safe. Without the tridion cell and SOME crumple zone, it would be a much less safe vehicle.
[0] http://auto.howstuffworks.com/smart-car1.htm