My first ever attempt to post a video. Please excuse the amateur effort. Taken with a Flip camera (h/t Milepost154). First lesson learned; my monopod isn't steady enough. I need to use the tripod. Second lesson is learning how to edit!
This is the UP 844 pulling the Cheyenne Frontier Days train Southbound from Brighton, CO at about 7:45 p.m. 7/20/13. Please skip to around :55 where you can start to hear the whistle. At around 1:00, you can start to see the headlight.
The diesel behind the steam locomotive is a UP Centennial, the largest single diesel locomotive ever built.
According to the UP sites, they use a diesel unit for safety. The breaking effort far exceeds the steam design.