N_C,
Looking at your posts, it sounds like you have everything to you need to write a letter. Why don't you do a draft and post it?
Getting others to support you is critical. So, if half of the local trail association wants to repeal it, ask them to write individual letters. Do you have a cyclist advocacy group, or is a trail association all you have? If you don't have a cyclist advocacy group, this could be the way to start one.
(P.S. People, HH asked a bike lane question and the usual suspects chimed in for and against. Might I suggest that the bike lane debate go back to the
bike lane sticky?)