"If the Eagle helicopter is in the vicinity and is able to provide immediate assistance in emergency situations then they may be asked to attend, as was the case yesterday.
"While it is not a common occurrence, Eagle has previously landed on main roads during critical incidents when required."
The woman, who was two cars behind the van, described the events as "unbelievable".
"It was unbelievable how the man didn't get run over by the truck that was on the left lane as it happened so suddenly," she told the Herald.
All citybound lanes were closed after the man fell from the van, causing lengthy traffic delays from 11.15am to 1.30pm.
The police Eagle helicopter had to land in the middle of the motorway to provide immediate first aid.
A police spokeswoman said the Eagle helicopter was requested to assist because it would be the quickest way to get to the scene.
One witness said a person could be seen lying on the motorway and was being treated by ambulance staff.
Witnesses said drivers were reversing down the motorway to try to avoid the crash scene, with delays stretching back as far as Sylvia Park.