I took the previous Track Worker test back in '06 or so and if it's anything like the one that I took, it's basically a reading comprehension multiple choice test. I remember it also asked several questions about tools(they'll show you a picture and you have to choose the correct one). No book will help you for this exam. They don't expect you to know the stuff beforehand, so there's no need to study for it(maybe brush up on your tools, but that's about it).
If you've never taken a civil service exam, it's all about patience. It takes years to be called after taking the exam, assuming you did well enough to be called and the hiring needs for the position. I waited almost 6 years before I got a letter to start the hiring process for Track Worker. It took 6 years becuase there was a hiring freeze. In that time, I took another MTA exam, scored much better on the test and now I'm working in a different job title. Even that one took about 3 or so years from taking the exam to being sworn in and on the job. I'm pretty sure that if there was no hiring freeze during that period, I would've been working as a Track Worker.
So in the mean time, try to find another line of work. Always have a back up plan. Once it's time to take the exam, relax and don't stress it.