I occasionally travel with someone who has limited mobility so let me add my 2 cents.

1) Call United airlines accessibility desk 800-228-2744. Tell them you have limited mobility and are unable to walk between gates. Depending on the distance, location, length of time between flights, they will make the necessary arrangements to transport you from point A to B. Whether with a wheelchair or a cart, when a long distance is involved, we are rarely transported through the normal pedestrian walkways but rather through the "back door" and the bowels of the airport to get to our gate.

2) In the last few years it seems that airlines are fearful of complaints filed with the DOT regarding transportation issues of passengers who need assistance. We recently had a problem with a Delta flight where we had to wait more than one hour after landing for a wheelchair. By the time we got home, we had an email from Delta with sincere apologies and they threw 25,000 miles into the account as a gesture of goodwill - we had not filed any complaints, however, the pilot would not leave the plane until all passengers were off the plane and I know he was making phone calls and was not happy that we were made to wait as long as we did.