The risk would surely increase with doubled speed, no? The Concorde was unsafe because of all the design constraints imposed by being able to go that fast.

Why do you think that the concode was unsafe? It had a single crash in over 25-years of operation, and that crash was due to runway FOD. That makes it probably the single safest passenger aircraft ever brought to service. In fact, it is probably one of the single safest forms of transportation ever.

The concord was involved in single accident resulting in death or injury, which was not due to a fault of its own.

> That makes it probably the single safest passenger aircraft ever brought to service. In fact, it is probably one of the single safest forms of transportation ever.

No, the Concorde was actually one of the least safest passenger aircraft in history, the least safest one on this list by a wide margin: http://www.airsafe.com/events/models/rate_mod.htm

It had so few flights, yet one of them was a catastrophic loss that killed all on board. Just compare it with, e.g., the Boeing 747-400: the Concorde had one full loss in 90,000 flights. The 747-400 has had 0.5 full loss equivalents in 8,420,000 flights. The stats for many other planes are similar.

The Concorde really was quite dangerous. And you can't blame it as "no fault of its own"; it suffered tire blowouts at a rate 30X of other planes, which had previously caused punctured fuel tanks. A tire blowout caused the fatal crash.