Impact probabilities and impact velocity distributions are computed for
collisons among populations of orbiting bodies using a formalism that takes
into account the geometry of intersecting Keplerian orbits. We consider impacts
of near-Earth asteroids (NEAs) by various populations, including other NEAs,
main-belt asteroids, and terrestrial planets. Contrary to current meteorite
models, a typical NEA is twice as likely as a main-belt asteroid to be disrupted
by impact with a main-belt body. Lifetimes of NEAs against collision with
terrestrial planets are similar to results of Monte-Carlo studies. Rates of impact
on terrestrial planets, as a function of NEA size, and the corresponding impact
velocity distributions are important for consideration of impact hazards.