Eyewitness Books Train

This book is mostly too dense, but it has a great cut away of a steam engine.

Trains! by Susan E. Goodman and Michael J. Doolittle

This book has a great diagram of a steam engine.  It also has a good section on freight trains and bullet trains.  Text is about a 2nd grade level.

Trains by Jean Coppendale

This book is visually appealing, with photographs, captions, a table of contents, an index, and a glossary.  Topics include steam engines and freight trains.  Text is about a 2nd grade reading level.  

Trains by Phyllis J. Perry

This book has doable text; not too easy, not too dense.  It includes history, steam engines, and the Transcontinental Railroad. Read the parts you want to use thoroughly ahead of time.  Could be used for close reading.

National Geographic Kids Trains

This simple book has labels and information about steam engines, the Transcontinental Railroad, turn tables, passenger trains, bullet trains, and freight trains.