CUSTER — A 79-year-old man died in a collision Thursday night when his vehicle left the roadway traveling north on I-5 at the Birch Bay Lynden Road exit about four miles north of Ferndale.

The man was pronounced dead at the scene. Authorities believe the accident was the result of a medical emergency, said Trooper Heather Axtman, Washington State Patrol public information officer, on Twitter.

The man was driving a 2005 Kia sedan at approximately 5:05 p.m when the vehicle struck the left guardrail on the offramp then left the roadway to the right, heading down an embankment and into a ditch, according to a memo from the Washington State Patrol.

It is unknown whether drugs or alcohol were a factor and the cause is still under investigation, according to the memo. The man’s identity has not yet been released pending notification of next of kin.