Ahh, I beg to differ: the earliest rapid transit proposals did indeed specify heavy metro running underground. Through 1974, newsletters and other promotional material showed a car similar to the PATH PA3. However, by the summer of 1976 the decision appears to have been made to switch to LRT. (Now why did you have to make me go and look that all up? Now I'm going to have to do the rest of the research, and add it to the article.)