My houston public transportation pipe dream

How hard would it be to replace HOV lanes with rail? I feel like houston could start one highway at a time, I mean they wouldn't have to clear any space or tear down any building for it. Only thing that I feel would be more challenging to do are the stations. They will most likely need some type of over pass for passengers to safely walk over the highway to the stops. Imagine if there was a rail line on every highway in houston. Starting with 45 and 10, then 610 and 8 and 99 to connect them all. That can just be the start, as the trains get more used, more stops and lines could be added like 290, 249, 59 and 288. Ah man that would be nice, i'd say one day but I know it will never happen.