If I write a training manual for my team, will I have a right to publish any or all of the material in the future?

I am a civil engineer working for a railroad. I have been asked to write a training manual for my small group on construction management. I am currently attending graduate school on the topic, and see technical writing as a future possibility. So far as I know, the manual would not be distributed outside of my group, but if it is worthwhile, they could make it official and distribute it to others of my function within the company. In this case, it may become a product of collaberation. If I want to write anything regarding construction management in the future, what right do I have to the material I have written? If I write it, does it belong to me? Or, does it belong to my employer?