Manhattan-bound drivers beware: the city’s prohibition against most cars along eight blocks of 14th Street begins Thursday.

In an effort to speed up buses, the city plans to limit access to the busy crosstown corridor between Third and Ninth avenues from 6 a.m. to 10 p.m. to large trucks and vehicles making local deliveries or pick-ups and drop-offs.

Buses on 14th Street travel less than 4 mph, according to MTA data. With the new restrictions on car traffic, officials expect bus speeds to improve by 20 to 30 percent; if all goes according to plan, trips across 14th Street will be five minutes faster.

“We knew we needed to make a drastic change,” MTA bus chief Craig Cipriano told reporters at a press conference with city officials Wednesday.

The new rules require any drivers who use the strip to take the next available right turn — or else suffer financial penalties at the hands of automated bus lane enforcement cameras.

The first offense will cost $50 and each successive violation will cost an additional $50, with $250 as the max penalty. Fines won’t be issued until December 2, however, after a 60-day warning period.

By the end of November, the city’s stationary enforcement cameras will be bolstered by one mounted on the MTA’s buses, which after their own 60-day warning period will issue violations to drivers who block bus lanes for five minutes or more.

In the meantime, the NYPD plans to station officers and traffic agents along the route and on surrounding streets to educated drivers and “keep traffic moving along.”

NYPD officers and traffic agents will not be issuing tickets, officials said.

Plans to launch the 18-month pilot on July 1 were delayed more than three months thanks to a lawsuit from local block associations concerned about gridlock on side streets.

On Wednesday, Transportation Commissioner Polly Trottenberg said cities who tried similar traffic restrictions, such as Toronto, managed to avoid spillover traffic chaos, but that the city will closely monitor the situation on nearby residential streets.

“There will be a little period of settling in here,” Trottenberg said.

“Over time, [drivers will] realize they need to change their routes,” she added. “What we see in other cities is the traffic spread itself out across the grid.”