The trip from Philadelphia to Pullman, Wash., requires two plane changes and more than 12 hours of travel time.

John Wooten, former vice president of player personnel for the Philadelphia Eagles, made the cross-country trip to see Ryan Leaf in a scheduled workout at Washington State University in 1997, when scouts were debating whether Leaf or another top-rated college quarterback, Peyton Manning, should be the No. 1 overall pick in the draft.

When some three dozen travel-fatigued scouts arrived at the campus, Leaf let them know he had changed his mind; he didn’t feel like practicing that day after all, Wooten recalled. Physically, Leaf had everything. But his indifference on the doorstep of the draft influenced Wooten more than Leaf’s perfect grades for arm strength and accuracy.

Projecting success among quarterbacks in the NFL “is as difficult as it seems,” Wooten said. But such incidents “are the kinds of things that you draw on.”

Intangible, hard-to-quantify attributes provide, perhaps, the biggest distinction between quarterbacks destined for busts in Canton, Ohio, and those who end up as busts. This season’s rise of the accuracy-challenged Tim Tebow for the Denver Broncos perfectly illustrates the imperfect science of projecting quarterback success in the NFL.

Team executives say there remains no more difficult task, even with sophisticated player evaluation tools. The NFL’s draft history proves it.

John Elway, Terry Bradshaw, Michael Vick and Manning share a trait with JaMarcus Russell, David Carr, Tim Couch, Vinny Testaverde and Steve Bartkowski: All were No. 1 overall draft picks. Not all lived up to expectations. Some were disasters.

“You study it, you ask questions,” former Washington Redskins and Houston Texans executive Charley Casserly said. “You try to do physical and psychological analyses. At the end of the day, you don’t know. I would challenge anyone who tells you they know. They don’t.”

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Successful NFL quarterbacks require excellence in realms a stop watch can’t evaluate, against complex defenses that in many cases look nothing like what they saw in college. They need to learn, lead, direct, react quickly and stay cool regardless of circumstance. Poise and restraint are considered more valuable than aggression, unlike the formula for virtually every other position.

Experts say teams err in their quarterback evaluations when they fail to give proper weight to such factors, overemphasize a particular physical limitation or simply overreach in their desperation to find someone for the most important position on the field.

“Probably half the teams in the league don’t have a good starting quarterback,” said Tom Donahoe, director of football operations for the Pittsburgh Steelers. “When you’re in a situation where you don’t have one, you’re desperate. . . . Some of the guys picked in the top 10, they shouldn’t be picked in the top ten. You see it every year.”

Casserly and the Washington Redskins took Heath Shuler third overall in 1994; Shuler’s career ended after five disappointing seasons. Leaf, the second overall pick behind Manning in ’98, is remembered as one of the biggest busts of all time. Russell got a $61 million contract in 2007; he was out of the game in three years.

“There was a huge checkpoint on Russell, on passion for the game and character,” said Jimmy Johnson, the former Dallas Cowboys and Miami Dolphins head coach who is now a Fox NFL Sunday analyst. “Oakland decided he was big enough and could throw the ball well enough that they were going to ignore those things.”

Scouts say a bad attitude should sink a top quarterback prospect regardless of his skills, but certain physical deficits, even significant ones, can be addressed or overcome. Drew Brees, taken in the second round of the 2001 draft, was considered too small coming out of Purdue; Joe Montana, a third-rounder in 1979, lacked arm strength; Dan Marino, taken 27th in the 1983 draft, showed no mobility.

The latter two players are in the Hall of Fame. Brees won a Super Bowl and is among the top quarterbacks in the league.

There are plenty of other examples. Brett Favre went in the second round in 1991. Aaron Rodgers was taken with the 24th pick in the 2005 draft. Tom Brady sat around until the sixth round of the 2000 draft; he was selected after quarterbacks Chad Pennington, Giovanni Carmazzi, Chris Redman, Tee Martin, Marc Bulger and Spergon Wynn.

“The biggest thing scouts did during my time and my history with them is they overanalyzed,” Johnson said. “Let’s look at Tim Tebow; he’s kind of the topic of the year. . . . ‘What kind of decision-maker is he? Pretty good. Accuracy? Not very good. Size and speed are excellent; intelligence is very good; character off the charts. (But) when you go through all of that, you go back and say: ‘Is he a good player?’ “

Before Sunday’s loss to the New England Patriots, Tebow, selected 25th overall in the 2010 draft, had led the Broncos to four straight come-from-behind victories and a 7-1 record.

In Johnson’s first year as head coach of the Dallas Cowboys, team officials and scouts wrangled over the choice for first overall pick: Troy Aikman or Tony Mandarich, a 6-6, 315-pound offensive lineman then called by Sports Illustrated the “best offensive line prospect ever.”

Mandarich had higher grades for his position than Aikman did for his, said Wooten, who was then the Cowboys’ director of pro personnel. “Our room was greatly divided,” Wooten said. “The position (some scouts) took was based on the measurements; Tony Mandarich was better at his position than Troy was at his position, and you generally take the one that has better numbers.

“I’d seen Troy and I’d seen Mandarich, and my thought was: This is the quarterback you need to have a championship team. This guy can take you to the next level.”

Johnson made the ultimate call, and the Cowboys selected Aikman first overall. The Green Bay Packers took Mandarich at No. 2. Aikman led Dallas to three Super Bowl titles and was selected to six Pro Bowls. Mandarich succumbed to drug and alcohol addiction and never met expectations.

Assessing intangible traits can require detective-like methods, team officials say. Personal interviews with the players and those around him can offer more critical information than anything gained on a strength chart or even the Wonderlic intelligence exam given to all NFL prospects. Wooten said he relied on two main tricks: talking to student trainers, especially female ones, and collegiate coaches.

“If she gives him a rave report, you got the right guy. If she says, ‘Oh, he’s OK . . .’ She doesn’t want to say anything bad,” he said, but “the way she answers gives you great insight.”

Wooten also shies away from players considered unmotivated because they aren’t yet on an NFL team’s payroll.

“You inevitably hear a coach say to you, ‘When he starts getting paid, it’s going to be different,’ ” Wooten said. “That should send a red flag. I have been around long enough to know that money doesn’t make players better. If anything, it makes them worse.”

Despite the history, the red flags and the warning signs, mistakes are likely to continue. In 19 of the 41 drafts held since 1970, quarterbacks were selected with the first overall pick. Four quarterbacks, Cam Newton, Jake Locker, Blaine Gabbert and Christian Ponder, were picked in the first round this past spring.

Three have started. Overall No. 1 Newton has an 82.3 quarterback rating, 15th best in the NFL and just behind Tebow, who has an 83.6 rating. Ponder is 28th at 72.3 and Gabbert is 32nd at 65.6.

Then there’s Andy Dalton, selected in the second round by the Cincinnati Bengals. Some say he’s been the best of the group. He’s ranked 18th, at 81.0.

“Because the position is so critical, teams do reach at the quarterback position,” Casserly said. “If you don’t have one, you can’t play.”