This is a loaded question if ever I saw it, who's saying its getting 300k overture?
If it is stop right there, I have a constant 75k (supposed) ovt results on a .com name which gets absolutely 0 type ins because there not real searches for the terms, I have 2, 20k ovt terms and various others I used to buy based on ovt results, one which peaks near 100k. Since I stopped and came to my senses, I have posted many times about how overture can often misrepresent searches in various ways and how it can be mislead by various parties.
If it really is (and adwords tools confirms a high score), then your looking at length and trends. People like to compare things, people like obvious terms, people like to see different things depending on what there searching for. Are they expecting to see pictures and movies? Can you hide the obvious typo with a banner? Are they expecting to see comparisons, is it in a profitable industry to convert to?, which parking provider are you with, do their results appear in google? do the clicks turn into sales? do they want information rather than a product?
Honestly I could go on with this list for an entire page but i'll sum it up for you. Its impossible to predict unless your very good at finding PPC/traffic names, you'll see themes eventually that are being typed in and make money and hopefully those names will be being typed in based on your research.
Just be very sure your not basing all your research from ovt, as its likely you'll be disappointed in the actual traffic.
Previous experience - Adwords tools - Google results (with quotes) - Choice of Industry - ovt results (for a rough guide) - knowledge of the industry