The roads in America are two to three times wider. The racing is generally safer in America because of this. Even though they often don't close down the roads except for a temporary period of time while the bike racers pass. Also, TDF is the world's largest bike race. A lot more people, traffic and cars in the motorcade.

Usually there are at least 20-30 riders who have to abandon the race every TDF because of injury. Ten or so because of broken bones or other serious injury. So I would say that the TDF is statistically much more dangerous.