On traffic safety, agreed, long term, autonomous cars are the way to go. Some of the answer there is time and market forces, but I suspect a billion or two from the war on terrorism could move that along nicely. Faster technology evaluation and approval pipeline, more money for NSF funded core research, etc. But nearer term there are technologies that exist in high end cars that would lower traffic fatalities tomorrow if available in all cars. Blindspot object detection, lane departure alerts, etc. If the concern is about an objective attempt to lower the number of people who die each year, a dollar spent in this area is going to save more people than a dollar spent in airport security.
On diseases, if you're talking about a billion dollars to paradrop a few thousand doctors into africa to do contact tracing, then you have my support. If on the other hand you're discussing mobilizing the national guard to protect North America from Ebola, not so much, spend the money on the flu, which kills many more people world wide. If we do the right things in Africa, Ebola will never be more then a hideous way for a couple of people to die in the US. This is one of those situations where the "Protect the Homeland" mantra is worse then useless.
Min