HOW do I know my topic is a good one ?

I'm a little bit at a crossroads this year as to what I may pick to be my AP research topic... Over the summer, I've considered doing something chemistry-related, more specifically electrochemistry, but I am not sure if this is a good, decent topic. A more broader topic I've just recently considered is road infrastructure, which could expand in many ways, almost too many. But for both topics I cannot tell exactly how good they may be for AP Research given the things that are needed. How hard could it be to find a gap in heavily scientific fields like electrochemistry, and how should I manage variables in quantitative research... I want to avoid picking a hard topic that I may regret when I have to change it later in the year, yet I want to find an interesting hard science topic in chemistry or a quantitative data-driven topic like road infrastructure... where do i go from here?!?!