T/O alternate mins do not include landing mins. T/O alternate mins, as already stated, are published in each airlines Ops Specs. Most are 600 RVR from what I've heard from freinds at other airlines, some are 500 RVR. The only time the T/O alternate comes into play is when the landing mins at the your departure airport are below landing mins. I guess what I'm trying to say is, 121 T/O mins have nothing to do with landing mins at that airport. T/O mins stand alone. And, you can only do the 600 RVR within certain crieteria, such as having RWY centerline lights.