In 4 easy steps!
(bonus cameo appearance)
Step 1: First, you need an old bus. This part is easy - just do a run on the west side, which greatly increases the likelihood that your bus was purchased by TriMet during the Reagan administration.

This is our old bus.
Step 2: Something will probably go wrong with the bus. This is neither your fault, nor especially surprising (see
Exhibit A)
Step 3: Ask everyone to leave the bus.
Then drive away.

Some magical, black-box stuff happens here, involving a nice spotter, some confused tourists, and a frustrated passenger whose transfer expired during this exchange. Then...
Step 4: Yay, a new bus!
Now you have air conditioning AND a wheelchair ramp! It's that easy!
(disclaimer: photographer is not a TriMet employee, therefore the restrictions on the photography of TriMet employees, passengers, equipment, bus stops, roads, plants, and wildlife do not apply)