Sorry, but I have to call you out on that one...Houston would most defintely NOT have cleaner air with a mass transit system.
1) Houston is too close to huge oil and gas refineries in the surrounding areas. They put out a huge amount of pollution..as they say, "The air is always greener in Pasadeener".
2) Houston has the 8th largest seaport in the world and has two major airports plus loads of private fields.
3) Houston has loads of factories around town
4) Houston (and the surrounding Metro area) is a huge area and you are not going to be able to stop all the cars from being on the road.
To make mass transit work in Houston, you would have to get Harris County and ALL of the surrounding counties to agree...and then pass the needed bonds to get the funding. Good luck on that. The problem is that Houston is very spread out. Texans love their space. That's just how we are.
They would need to build and ELEVATED mass transit system. Let me repeat that...ELEVATED. The rail system they have downtown is a JOKE. You have car accidents and delays with this system almost each and every week. If they elevated the train, you wouldn't have those problems. Unfortunately, we live in a city where we have problems with pot-holes an road buckling. The reason why we have these problems is that the entire city was built on flood plains and old rice fields. So, you would need to engineer a very good foundation for the trains.
Do we need mass transit. Absolutely. Do we have the funds for it. NO. Do people want their taxes raised for such a huge project. NO.
It would be a logistical nightmare to make this happen. You think traffic is bad now?
You would need to build both an elevated train system and one with numerous branches, not merely parallel with the existing highways (to account for the huge urban sprawl). You would need branches going beyond Beltway 8, possibly out to the proposed Grand Parkway Corridor. Yes, if you want to plan for the future and do it right, plan for urban sprawl to go past the Grand Parkway Corridor (all the way around). That, in and of itself, will encompass Harris County, Ft. Bend County, Liberty County, Brazoria County, Waller County, Montgomery County.
Or, the city of Houston could just do a half-assed, bureacracy-bloated, crappy rail system...Oh wait, they've done
that already!!