Scaff's goal is to put 100,000 runners and walkers on the H-3 freeway on May 11, 1997 for a one-time-only 10-mile race on the unopened roadway that winds around the Koolau Mountains and into Halawa Valley.
The race would finish inside Aloha Stadium.
"We have the potential of doing everything we thought we could," said the 62-year-old Scaff, who helped to found the Honolulu Marathon and organizes the Great Aloha Run.
"This is the Sistine Chapel of running to me."
Only a few races have ever had 100,000 finishers, and proving the numbers is difficult. The 1988 Bay to Breakers race had an estimated 110,000 finishers and is in the Guiness Book of Records as history's largest footrace.
Scaff said if he doesn't get more than 100,000, he'd be happy to have the largest completely timed footrace in history. Guiness has no such category now but Scaff said he has asked the publishers to establish one for the H-3 Run. The record keepers have made no promises, but Scaff is confident that they'll consider it if the race draws what he expects.
Ryan Lamppa of the United State Road Racing Information Center in Santa Barbara, Calif., said Scaff's biggest competition would come from the Bay to Breakers run, and a race in Barcelona, Spain, which have both timed between 60,000 and 70,000 finishers.
The Great H-3 Run will be the only pedestrian sports event ever conducted on the highway. Scaff said that fact, coupled with the breathtaking scenery along the route, will make it an attractive draw.
The H-3 course will have a six-percent uphill grade for the first three miles. The course crowns about two-thirds of the way through the mile-long tunnel and is a downhill course from that point.
The 30-page entry booklets will be available in selected locations by mid-July for $3 apiece. Scaff said the entry fee will be $39 for local residents and $44 for nonresidents. He said the fee will go up at the end of the year.
Department of Transportation spokesperson Marilyn Kali said the state has given its tentative OK for the run. Final approval is pending state review of a comprehensive race plan which Scaff said will be 30 pages long.
The event is also at the mercy of the state's ability to complete the inbound lane in time. Kali said that she's confident the inbound lane will be ready but the outbound lane won't be ready until July 1997.
Scaff said he expects one Japanese travel firm (Nippon) to bring in about 20,000 participants. He said he has also gotten the word out to a number of major running clubs on the mainland, such as the New York Road Runners Club.
But the Koolau race plan is complicated by some factors.
One is that it will be held just after Japan's Golden Week, when Japanese citizens have gone back to work.
Another is that it is scheduled between two of the world's largest footraces - the Lilac Bloomsday Run (Spokane, Wa.) and the San Francisco Bay to Breakers.
Both could affect Scaff's effort to attract tens of thousands of mainland entries.