Mayor Bill de Blasio once promised that he would replace horse-drawn carriages in Central Park with vintage-looking cars—but now there is confusion and concern about how serious City Hall really is about the proposal that was geared to tourists. There are new developments today amid growing frustration from de Blasio's allies that the mayor is moving far too slowly on his promise to ban the carriages. NY1's Josh Robin filed the exclusive report.

A prototype of a vintage-looking electric car, to replace the Central Park horses, was rolled out fifteen months ago, and Mayor Bill de Blasio appeared to be in gear.

"It is a cleaner, better, more humane approach that, obviously, will also provide employment opportunities and will be good for our tourism industry. So that’s how we’ll proceed," de Blasio said in April 2014.

If the cars are proceeding at all, though, they are stuck in the slow lane.

There is an ongoing environmental review required on the carriage ban.

NY1 obtained documents releated to it, with a line stating: "the non-polluting tourist vehicle is no longer part of the proposed program."

A line below there is a deadline that's a month old. Officials say they expect the report this summer. 

As for the cars, officials say the review looks only at the effects of a bill the City Council is considering. That bill bans the carriages. It doesn't specify a replacement, but confusion remains. 

The documents suggest consultants were looking at the vehicles until a top city economic official called them off. 

City Hall says that's not unusual. Although one thing of note is the call to change the review came four months after the Council bill emerged. 

De Blasio famously promised a ban his first day in office.

"There's obviously a host of different opinions and we're working it through, but I know where I want to get us ultimately," he said Monday.

The bill was first introduced more than seven months ago. In the meantime, 300 carriage workers are in limbo. Anger is also growing among animal rights activists, the very people who helped elect de Blasio.

"He said that he would do it and he would do it quickly," says animal rights activist Donny Moss.

Moss led a protest against de Blasio Monday night. 

The next day, hip hop mogul Russell Simmons tweeted that de Blasio should ride the horseless carriage to pressure the council. 

"Eighteen months have passed and voters will remember when re-election time comes around that he didn't fulfill his promise," Moss says.

Those same activists can help derail candidates. They helped beat Christine Quinn with de Blasio, of course, finishing first.