When a wheelchair rider wants to take Caltrain, wheelchair lifts must be used to load and unload that passenger. On trains with a broken wheelchair lift, or without a wheelchair lift (as evidenced by the cars recently removed from service due to product defect), a portable lift would be used for loading and unloading.
Using a portable lift is a time consuming process. As you can see from the picture above, it is not a simple procedure either. The lift must be taken out of the enclosure on the platform and place it by the door. The conductor would have to hand crank the rider on and off the train. The train would generally be late when portable lifts are used.
11 years ago when I first take Caltrain, only portable lifts were used. The newer cars with automatic lifts did not arrive at Caltrain until 2000. However, most stations were not ADA compliant, so Caltrain did not provide lifts at those stops. At that time, very few wheelchair riders take Caltrain as they can only board and exit at some major stations. Eventually, Caltrain slowly add more ADA compliant stops by rebuilding station platforms.