To the Editor:

Re “Rather Than Shrink Subway Delays, M.T.A. Adds Funds for Expansions” (news article, May 25):

Transit system ridership will soon be severely curtailed by self-driving taxis. In response, the Metropolitan Transportation Authority needs to update its existing infrastructure rather than expand it.

Our research group at Columbia University projects that if autonomous vehicles continue to improve at their current rate, but M.T.A. technology remains rooted in the 20th century, the system will be forced to close altogether within two decades. This is mostly because cab fares will drop in price, closing in on the cost of a subway or bus ride for shorter trips.

Declining ridership, coupled with tens of billions of dollars in debt, is probably not going to be sustainable. Cheap, efficient train transit is possible if the latest signaling and on-train self-conducting technologies are put in place. Technology can both reduce fares and reduce journey times for passengers.

Even then, large subsidies from the government are needed if we are to keep our most valuable asset. The transit system keeps our air clean and our citizens healthy. We need to act soon or all will be lost.