This is a limited time promotion. The Muni price is a long term price. After a while, lyft and uber will bring their prices back up. It will be a shame if any muni services are lost in the meantime because people stupidly believe that these are long term prices.
Lyft's normal line price is frequently (slightly) cheaper for my wife and I than Muni. Of course, during heavy demand times or for longer rides, muni wins, and I certainly would not want it to go away!
I think long term something like robot driven 6-rider lyft-line style vans is probably the future of public transit (hopefully) :)
