Dead At 44 After Bicycle Crash

Ironman athlete Brian Kozera -- who was also a police officer and cancer survivor -- has tragically died at 44 years old ... after he was involved in a terrifying bicycle crash while he was training for an upcoming competition.

Kozera -- a 16-year veteran of the Norristown Police Dept. -- passed away after he struck a car on Saturday while he was biking in Caernarvon Township, PA.

According to a crash report, obtained by TMZ Sports, at around 9:48 AM ... Brian ran a stop sign and hit the passenger side of a pickup.

Kozera, according to the docs, was thrown from his bike and ended up being caught in the car's rear wheel. Cops say he was transported to a nearby hospital, but died from the…