The business of marathons is in full stride, with organizers of the ING Miami Marathon and Half Marathon saying registrations are trending 18 percent higher than last year and could hit 20,000 runners for the first time. The 2010 ING Miami Marathon brought in an estimated $18.74 million in spending by non-local participants and $33.36 million in economic impact overall, according to Temple's Sport Industry Research Center. The study indicates that 67 percent of non-local participants came by air and 35 percent rented a car. Slightly more than one-third of non-local participants were combining their race with a vacation.