Two months of paid leave for MTA bus drivers to recover from “assault” by spit? News that this is routine, thanks to a contract clause, has outraged New Yorkers. But MTA Chairman Jay Walder’s drive against such wasteful practices has the unions spitting mad.

One of the nicer things transit workers recently called Walder in an online forum is a “tightwad micromanager . . . who manages through fear rather than respect.” Others wish the union had “taken action months ago with rule book slowdowns, mass protests at Walder’s house.”

In other words, ending even the most blatant abuses will be a major battle.

Overtime kicks in by eight-hour day rather than 40-hour week. So employees earn full pay while working less by calling out sick and then making up the lost wages through (premium) overtime.

Over the last few weeks, MTA officials have steadily begun to uncover what Walder calls “the shame of the system” — wasteful work rules that prevent its various agencies from running bus, subway, rail and maintenance operations more efficiently.

For example, many bus drivers clock a 12-hour shift for driving four hours in the morning rush and four in the evening rush. For the four hours in between, they’re paid for being available — but with no work to do. Some have become pretty good pool players, Walder has noted, thanks to free time and recreational equipment at the bus depots.

The union’s response? “The MTA has agreed to these terms for 50 years — and it’s fair,” insists John Samuelson, president of Transport Workers’ Union Local 100. Fair to whom? Surely not to the tax- and fare-paying public.

Walder has begun to end some of the insanity. Maintainers of the Brooklyn-Battery Tunnel, Verrazano-Narrows Bridge and other crossings traditionally clocked an 8 am to 4 pm shift — with the first couple of hours wasted as they waited out the morning rush before starting work. Now, maintenance crews will work an 11 pm to 7 am shift for a 10 percent bonus — rather than traditional overtime wages.

Then there’s the LIRR, with its legendarily obsolete work rules. As The Post reported earlier this month, whenever crew members are switched from one train to another, they get another day’s full pay. That may have made sense back in the coal-shoveling days of railroading; in today’s world it’s a golden giveaway.

For decades, union intransigence has blocked technological advances. Real-time bus arrival information is finally being tested on Manhattan’s 34th Street — more than a decade after technology had made it possible. Union drivers didn’t want to be tracked, so union bus mechanics refused to service wheels with the rotation-counting device needed to supplement GPS in its early days.

And while the new system on the Canarsie line can run trains with no crew aboard, L trains still operate with crews of two — thanks to union work rules.

Of course practices like these are just the tip of the MTA labor-cost iceberg. The agency also faces huge pension and benefit liabilities.

And transit workers who labor in dirty, dangerous and even deadly, conditions deserve fair compensation for the work they do and the risks they take. But that doesn’t mean pay for time not worked.

In fact, work-rule waste jacks up costs for everything in New York:

* The union representing crane operators insists on having full-time “oilers” at construction sites every day. But unlike the steam-driven equipment of old, modern cranes don’t need constant lubrication.

* On building sites across the city, union operators must staff elevators — even when they have normal push-buttons for each floor.

* Told it would cost $1,000 to have a union electrician plug a laptop into the wall of a Midtown hotel, one smart customer ran out and bought a spare battery for $70 instead — and then noted it would be cheaper to buy a whole new computer than to pay the hotel electrician.

* Another Midtown hotel just lost out on hosting the Sidney Hillman Foundation awards dinner after its unionized workers said they’d refuse to serve the foundation president — because he also heads up a rival union.

* Tavern on the Green is about to become a Central Park visitor center, snack bar and retail shop because the demands of the Hotel Trades Council derailed the last attempt to renovate and reopen it. The city’s soliciting new bids, but it’s hard to see how the landmark will ever again operate as a restaurant as long as the unions refuse to accept change.

It’s hard to imagine the city’s transit system going the way of Tavern — but the fact is that outrageous work rules are slowly strangling the entire city economy. New Yorkers need to wake up and realize how often unions now fight to protect unfair pay and other privileges — at the expense of the rest of us.

Hope Cohen is associate director of Regional Plan Association’s Cen ter for Urban Innovation. She spent more than a decade at the MTA, fo cusing on new technologies for the city’s subway and bus systems.