Detective Acting Senior Sergeant Martin Bourke said when police approached the driver they saw what may have been a bomb strapped to his head.
"Police then observed what appeared to be a suspicious device strapped to this male so we backed right off and tried to negotiate with the male,'' Det Bourke said.
"The device was around his head.''
After negotiation attempts failed, the man drove his truck away from police. They chased the driver for about 4km before he stopped, did a U-turn and started driving into on-coming traffic on the Monash Freeway.
Police stopped the traffic at Toorak Road and evacuated the freeway.
"In his truck, in his prime mover he got up to about 100km/h, accelerating quite quickly towards the oncoming traffic,'' Det Bourke said.
"It was an incredibly risky situation.''
The man stopped his truck just short of vehicles that had been parked on the freeway after their drivers were evacuated. Police again attempted to negotiate with the man, who stripped naked and then surrendered.
The man was arrested and taken to the Alfred hospital for a psychiatric evaluation.
Roads were re-opened about 7am after the area was declared safe. The device was not an explosive device.
The man didn't make any threats, Det Bourke said.
"He spoke to police quite a bit but they couldn't understand him,'' Det Bourke said. "He appeared to have some sort of mental condition.''
The man has not been charged.
- AAP
