With his presidential campaign in tatters, Mayor Bill de Blasio has returned crestfallen, hangry and seeking revenge on New Yorkers for being unenthused by his attempt to use us as a steppingstone.

This week, despite outrage and legal challenges from neighborhood residents, the mayor will implement the ill-conceived “busway” plan for 14th Street. Starting Thursday, only buses and trucks will be permitted, and cars will essentially be banned between Third and Ninth avenues from 6 a.m. to 10 p.m.

The stated goal is to improve bus service, specifically the M14, one of the city’s slowest routes. Sounds great. Buses should certainly take precedence over passenger cars, and fewer cars should mean faster buses. But the devil is in the details.

The plan limits cars for six blocks, while the M14 runs almost all the way to the East River. After six blocks of car-free travel, on Third Avenue buses will run into the wall of traffic created by several large, unending construction projects on East 14th, likely the cause of the M14’s sloth in the first place.

Bottlenecks created by cars turning off 14th Street east of Third Avenue and west of Ninth will stack traffic for blocks on end, further exacerbating the congestion.

From a safety standpoint, different rules for different vehicles at different times is guaranteed to foster confusion. Every corner ­is festooned with signs and indecipherable road markings, leaving drivers, cyclists and pedestrians befuddled and uncertain of their boundaries.

The benefits to M14 commuters, if any, will be minimal, and the plan has already cost them more than a dozen stops on the route, forcing longer treks and increased exposure to the elements.

Neighborhoods flanking 14th Street will suffer the overflow of cars seeking alternate passage, and traffic from 14th will simply move to other wide cross streets like 23rd, reducing service for M23 riders, whose cries will be answered with a busway of their own. The 23rd Street busway will beget the 34th, the 34th will beget the 42nd and so on.

Which is the real point. Remember, this idea was conceived as a contingency for a complete shutdown of the L train, which never happened. The plan is moving forward nonetheless, only now under the guise of improving bus service.

Who benefits? The greatest, perhaps the only beneficiary of the 14th Street busway appears be the bike lobby.

Though there is not a single mention of bikes or bike lanes relating to the busways on the NYC.gov website, Bloomberg reported Sunday that the plan would create “a corridor of express buses, wide bike lanes and pedestrian-friendly walkways” and referred to the project as a “bike-friendly experiment.”

If the goal of this plot was truly to speed up buses, bike lanes wouldn’t be part of it. The repurposing of vehicular lanes, also known as “road diets,” slows traffic by design. Having fewer cars may have improved speeds for M14 riders — for six blocks of their trip — but the loss of a lane will offset any gains.

Meanwhile, the biggest losers will be pedestrians, who will have to contend with the consequences of turning one of the city’s most traveled cross streets into yet another lawless leg of cyclists’ inter-borough racetrack.

Three weeks ago, the mayor promised increased enforcement, and said he is considering licensing for all bicycles, which surely would have made the streets safer for everyone, but the reaction from bicycle advocates was swift and seething, and Hizzoner has been cowed into silence.

Through fundraisers, endorsements and ideological alignment, the bike lobby’s every wish has become the command of our City Council and Department of Transportation. They have narrowed our streets, choking traffic to a near halt, complicating deliveries and sanitation and dramatically slowing response times for emergency vehicles — all under the false pretense of increased safety.

If congestion were the ultimate cost of safety, so be it, but much like Shakira’s hips, the numbers don’t lie. Fatalities are up 26.7 percent from this time last year, the number of pedestrians injured by bikes is up 14 percent, total injuries have skyrocketed 18 percent since 2014, and 21 cyclists have died this year, compared to 10 in all of 2018.

Allowing bike advocates to ham-handedly reshape our streets for the accommodation of their niche means of conveyance has made the city more dangerous for everyone. Busway? Call it yet another “bikeway.”

Gary Taustine is a writer in New York.