At the height of the Cold War, defense analyst Herman Kahn wrote Thinking About the Unthinkable, a book which tried to inform readers about what would happen in a nuclear conflict.

When it comes to mass transit funding, “thinking about the unthinkable” is the idea that Congress might someday cut off money from the Highway Trust Fund (HTF) which has been spent on subways, bus systems, and other forms of mass transit since the 1980s.

Approximately 80 percent of HTF money is spent on highways and 20 percent on mass transit.

Most of the roughly $40 billion a year that goes into the trust fund comes from taxes on gasoline and diesel fuel paid by people who drive cars and trucks.

At a hearing Wednesday of the House Transportation and Infrastructure Committee, some Republican members skeptically quizzed Transportation Secretary Anthony Foxx about why HTF money must go to mass transit, and whether the funds would be better spent on highways.

On Thursday, American Public Transportation Association President Michael Melaniphy fired back.

“There has been bipartisan support for federal investment in public transportation through the federal gas tax since 1983 when, under President Reagan, fuels tax revenues were dedicated to public transportation through the Mass Transit Account of the surface transportation legislation,” he said.

He said that public transportation systems mean fewer cars on the roads, which “reduces congestion and allows our existing highway system to function more efficiently.”

For Congress to end mass transit funding from the Highway Trust Fund, Melaniphy said, would be “catastrophic” and would hurt millions of Americans who use public transportation to get to work.

Public transportation ridership was up by nearly 2 percent in the third quarter of 2014, compared to the same period in 2013, according to APTA.

But it’s also true that according to the Census Bureau, just five percent of Americans who commute to work use public transportation.

In its American Community Survey, the Census reported that in 2013 nearly 143 million Americans traveled to a workplace, and 76 percent of them drove alone in their car, truck or van.

At Wednesday’s hearing, first-term Louisiana Republican Rep. Garret Graves, who represents Baton Rouge and its environs, captured the skepticism of some Republicans when he told Foxx, “Whenever I look at the mandatory split of 20 percent for transit and sometimes see buses passing by with two folks on them, it doesn’t always seem to be kind of I guess best bang for the buck being invested in some cases.”

But my CQ colleague David Harrison reported Thursday that Transportation and Infrastructure chairman Bill Shuster noted the Republicans tried to “pull that [mass transit funding] out before” when the House debated the 2012 highway reauthorization bill “and had a revolt on our hands.”

So for now, thinking the unthinkable is a thought, and not very close to a reality.