CSSHEGEWISCH
An additional entrance on the Clinton Street side is not an absolute necessity. The existing entrances on Clinton near Adams and Jackson generally serve Metra riders and are quite sufficient for the existing traffic.
Yes so I suspect they want a central entrance for both fire code (panic exit) and so they can market the food court better to sidewalk traffic but I am not 100% sure they are putting one in. I thought I saw one in the artists rendering with a sign above it saying UNION STATION FOOD COURT or something to that effect.