Alto and the environment:  Greenhouse gas emissions are actually increased, not decreased, during the time of construction.  

This reflects machines and processes used in the construction.  It also involves pollution and greenhouse gases from production of the rails and other equipment.

(See "Carbon  Footprint Of High Speed Transportation Services", as a PDF, below.)

Once the construction is finished – said to be 2035 or later – there may not be an environmental benefit.  Let's not forget that most cars will be electric by then.  For this reason, Alto's electric trains, replacing cars on the road, will not reduce greenhouse gases by much, if at all. 

Even with non-electric cars, high speed rail studies show that the effect on greenhouse is minimal.

" . . . Benefits from reduced road congestion and environmental betterment are relatively minor."

(see  PDF below - International Transport Forum - The Economics of Investment in High Speed Rail: Summary and Conclusions. 2013. )