Most attractions are wheelchair and
ECV accessible. They will be marked on the park maps and a sign outside of the attraction that shows a wheelchair symbol. For those, a wheelchair or ECV can be taken all the way to the boarding or show area.
For some of those, you will need to leave the wheelchair or ECV and board a ride vehicle. Those are marked in the maps and signs with an icon showing a person getting up from the wheelchair.
There are a few attractions where the lines is not ECV accessible, but is wheelchair accessible. Those attractions are marked on the park maps with a symbol of a person getting out of the
ECV and getting into a wheelchair. For those, the ECV will be parked with the strollers as was already mentioned. Those attractions do have wheelchairs available for use in line if you need one - just ask the greeter CM.
You can also choose to park the wheelchair or ECV with the strollers and walk in line. Just be sure that you know how long the wait will be and what the distance is. For example, you can't see the line from outside of Soarin, but by the time you walk through the whole lune to get on, you will have walked 1/4 mile. The way out is a similar distance.
The Safari and Bug's Life at AK have similarly long lines. Even if the wait is short, you will still be walking that same distance.