That's like asking how safe are minivans. A well built, well maintained and sensibly used tandem bike don't come with any special risks. Ride it like a fool, ignore the upkeep, and a tandem - just like any vehicle - can bea death trap.
Kinda-sorta. Not many bikes are rated for two adults, so handling and braking will be poor. There's also a good chance of damaging your wheels and tires due to the overload. But if you're riding...
A tandem is faster. Basically it has pretty much the same air drag as a single rider but it has two people powering it along. It's not twice the speed, as much riding is done in a speed range where...
Most states prohibit riding on the intestates, due to safety concerns. Those which do, however, only allow such riding in wide-open "lesser-populated" areas such as Wyoming. Many cross-country...
No, unfortunatly it is absolutly illegal, you will be fined if you are seen putting bicycles on other peoples cars, you may however ride the bike on top of the car