The Dow Jones Industrial Average (^DJI 0.04%) is just one of several Dow Jones market trackers. The secular index will never invite any tickers from the railroading, airline, or electrical utilities industries -- because there are separate Dow indexes for these sectors.
If you want to track these industries, you'll have to look for the Dow Jones Transportation Average (DJINDICES: DJT) or Dow Jones Utility Average (DJINDICES: ^DJU) instead. There's even a composite index that brings all 65 tickers together.
In the video below, Fool analyst Anders Bylund explains why you'll never see Duke Energy (DUK -0.46%) and its $48 billion market cap on the DJIA, nor the even larger Union Pacific (UNP 0.11%) railroad.