The couple, both seniors at Anderson University in Indiana, had been enjoying the day at the Holiday World theme park. Boyle said she had no idea what was coming when they boarded a ride called The Voyage.
"The whole time I was just sweating uncontrollably, heart was pounding," Crecelius told RTV 6, the ABC affiliate in Indianapolis.
To capture the moment, Crecelius had a friend record the pair from the seats in front of them. He later apologized because using a cell phone is against the park's rules.
The video begins with Crecelius reciting a speech with a cheesy but adorable metaphor.
"At one point in time you had mentioned to me that life is like a roller coaster. And it's got its up and downs, it's got twists and turns, and it even throws you for a loop sometimes. And though you can go by yourself, it's a lot more fun to go with another person."
As he says this, his girlfriend listens politely. When Crecelius gets to the next line and pulls out a ring, however, Boyle puts her hands over her face in shock.
"So I wanted to ask you if you wanted to be my roller coaster buddy. Allie, will you marry me?"
By the time they hit the first drop, Boyle has nodded yes and started crying tears of joy.
"I cried the rest of the evening just 'cause I was so overwhelmed with everything," Boyle said. "It was a very Austin proposal."