Two women died in separate single-vehicle accidents as the ACT doubled its road toll for 2013.
In the first incident, a female passenger has died after coming off the back of a motorbike on the Cotter Road early this morning.
Police said a man riding the bike had lost control when approaching a bend on the road about 2.30am.
"A woman pillion has come off the motor cycle and collided with a guard rail," police said in a statement.
"Both were transported to The Canberra Hospital where the man was treated for minor injuries and the woman was treated for serious injuries and later died."
In the second incident, Tuggeranong police found a woman dead in her vehicle while out on routine night patrol about 4am.
"Police believe the collision may have occurred earlier in the morning," they said.
"The vehicle was travelling north on Kambah Pool Road when it left the road and collided with a tree."
They are the third and fourth people to die on ACT roads this year, and the third in four days.
An 84-year-old O'Connor man was killed in a two-car collision in Bruce on Wednesday morning.
The man was the passenger in a blue Toyota Corolla Seca, being driven by an elderly woman.
Police said the Toyota was travelling east along Belconnen Way when it collided with a green Mitsubishi Lancer about 10.10am.
Police are investigating this morning's crashes, and ask anyone who may have seen them to contact Crime Stoppers on 1800 333 000 or at www.act.crimestoppers.com.au.