"He kept saying, 'This isn't how it's supposed to be happening,' " state trooper Ron Ferraro said of the nervous father.
Nine minutes later, the second boy was delivered in an ambulance on the Wantagh State Parkway.
The babies, each weighing about 6 pounds, were doing fine Saturday night. So were the relieved parents.
"Nobody teaches you this," Bryan said. "You look at the movies and read the books, but nothing prepares you."
The boys' names -- Gavin John and Declan Michael -- were chosen. A bag was packed.
This was the couple's second pregnancy. They had their first son, Dylan, two years ago.
Saturday's drama started when Siobhan's water broke, jarring her awake. They left their home around 7 a.m., headed to the hospital in their Ford Edge.
Suddenly, her contractions intensified and Siobhan asked Bryan to pull over on the Southern State Parkway.
"I'm going to deliver," she told him.
As Bryan called 911, Siobhan, 32, a financial manager with Revlon, tried to remain calm, doing her best to "hold in the babies."
Ferraro, the trooper, arrived shortly before Nassau County police and medical technicians.
"This was the first call I've seen like this where it wasn't a false alarm," he said.
As the ambulance arrived, so did Gavin.
Mom "literally delivered the baby on the stretcher on the road, with cars going by," said Nassau Officer Ron Gerlin.
"I was crying because it was so painful and I had no painkillers," Siobhan said. "They really wanted to come out."
For Thomas Dehaan, the medical technician who delivered Gavin, it was his ninth birth but the first on a highway.
But when Siobhan couldn't hold back the second twin, the ambulance pulled off the Wantagh State Parkway. This time, medical technician Larry Shapiro made the delivery.
Minutes later, the babies, bundled in thermal blankets, were carried into the hospital's delivery unit by officers.
"They were so cute, like candy in wrappers," said Leila Ayers, a nurse in the unit. "They were moving around, looking at the world. I thought it was beautiful."