"He was 300 to 500 yards south of the Cottman Avenue exit, and appeared to be hit head-on," First Deputy Commissioner Richard Ross Jr. said.
State police identified the driver of the other vehicle as 47-year-old John Leck, Jr., of Levittown. They said he was charged with drunken driving and homicide by vehicle.
Ross said Leck entered the highway at Cottman Avenue.
"At 55 m.p.h., or whatever speed they were going, they could close 300 yards in a matter of a second," Ross said. "I don't believe Officer Lorenzo had a moment to react."
The 23-year veteran of the force was pronounced dead at the scene, and the highway was closed between the Bridge Street and Allegheny Avenue interchanges for hours.
Leck, who was driving a gray Audi A6, was treated for injuries at Aria Health Torresdale before being taken into custody by state police.
Lorenzo was the second policeman from the region to die in a traffic accident Sunday. In Millville, Cumberland County, Officer Christopher Reeves, an eight-year veteran, was killed in a two-car crash at 2:15 a.m., according to police reports. Details of the crash were not available.
In Philadelphia, Lorenzo served eight years in the 25th Police District, where his brother, Manuel, is assigned, followed by 15 years with the highway patrol unit. He was an instructor for the patrol's drill team, an elite group that performs tricks at shows to raise scholarship money for the children of fallen officers.
"They have to try out for the drill team, they have to be very, very good riders," Ross said, "and he was an instructor."
Lorenzo received five commendations of merit for superior police work and four commissioner's letters praising his performance.
He was born in the Bronx, N.Y., and moved to Philadelphia with his family when he was in elementary school. He graduated from Frankford High School and married his high school sweetheart, Linda. They have three children, ages 24, 22, and 4.
McNesby said it was normal for officers to ride their police motorcycles home. In 1997, Officer Leddie Brown died after he was hit on his cycle while headed to the Thanksgiving Day parade.
Hours after Sunday's accident, the sellout crowd at the Phillies-Braves game observed a moment of silence for Lorenzo.
Mayor Nutter ordered all city flags lowered to half-staff for the next 30 days.
"As citizens of this great city, we will never forget the sacrifice that our police officers make every day," Nutter said in a statement, "nor will we forget Brian Lorenzo, a decorated officer who exemplified the very best qualities of law enforcement.
City Council President Darrell Clarke took to Twitter to express his thoughts, calling Lorenzo's death "terrible and sad."
Lorenzo was "a "great family man and a true gentleman," said McNesby, the FOP president.
"He raised money for fallen officers. Now, his brother officers will be doing that for him."
Contact Bill Reed at 215-801-2964, firstname.lastname@example.org, or @breedbucks on Twitter. Read his blog, "BucksInq," at www.philly.com/bucksinq.
James Osborne contributed to this report.