Cars with less than three passengers will be virtually barred from entering Manhattan, Mayor Bloomberg announced today, in a desperate bid to relief gridlocked city streets.

This post-Hurricane Sandy rule will be enforced from 6 a.m. to midnight tomorrow and Friday.

“To reduce the number of cars coming into Manhattan, however, we have to take some steps. The streets just cannot handle the number of cars that have tried to come in,” the mayor said today.

“I know it is inconvenient for a lot of people. But the bottom line is the streets can only handle so much.”

The restrictions will be enforced on the Triborough and Henry Hudson bridges, the Lincoln Tunnel and all four East River bridges. But cars with less than three passengers will have a loophole, on the George Washington Bridge, Bloomberg conceded.

The mayor explained the exemption, saying most eastbound traffic on the GWB hooks up to northbound highways, headed into Connecticut.

But otherwise, anyone entering Manhattan better have at least two passengers in their car.

“If you’re coming in from New Jersey on anything other than the GW … you have to have three people in the car,” said Bloomberg.

Commercial, police, emergency and paratransit vehicles will be able to come into Manhattan at all times.

Taxi cabs with less than three people are good to enter Manhattan between 4 p.m and midnight tomorrow and Friday. The mayor said an exemption had to be made for taxi drivers, as they enter Manhattan for their midday or late shifts.

Anyone who braved Manhattan streets today could see how jam-packed Gotham had become, the mayor said.

Full bus service began today and only partial subway service is set to begin tomorrow.

“Anybody who tried to drive around New York City today realized there are a lot of cars on the road,” Bloomberg said. “Traffic is very heavy.”

The mayor said he hopes motorists will pick up strangers standing near bridges.

“They’ve got a problem of getting in: You’re their solution and they’re your solution as well,” Bloomberg said.

Similar measures were in effect after the Sept. 11 terror attacks.

Additional reporting by David K. Li and Rebecca Harshbarger