Plans are creeping ahead for a centralized Regional Transit Authority hub that would serve numerous bus lines converging on a single downtown location to ease transfers.

But nearly every aspect of the proposal remains up in the air, from its location to the amenities that would be offered, said Tim Reynolds with Parsons Brinckerhoff, the contractor hired to make recommendations on the project.

Reynolds, speaking at a public meeting called last week to lay out the proposals and gather preliminary input, said everything remains up for discussion.

The idea is to find a site that’s already on bus routes and close to the RTA’s streetcar lines, to provide a single location for transfers.

The first step is choosing a location. Four possible sites have been identified: Basin Street near Canal Street; South Rampart Street between Canal Street and Tulane Avenue; the rectangle of green space running from Perdido Street to Gravier Street between Duncan Plaza and the parking garage behind it; and the Canal Street neutral ground.

Each has its own strengths and weaknesses.

Basin Street has room for a potentially expansive hub, though it’s farther from the heart of the Central Business District than some of the other sites.

The 100 block of South Rampart already sees significant bus traffic and would be close to the end of the North Rampart streetcar line that is now under construction, but making it a bus hub would require buses to continue to line the curbs and could cause other traffic issues.

Like Basin Street, the area behind Duncan Plaza has room but is a bit farther from the center of the downtown area, a potentially important consideration for a project that is expected to be a major economic driver because it will bring thousands of travelers — and potential customers — to a centralized location.

The Canal Street location faces a number of challenges. The neutral ground would be the only part of the street that could be used; hotels use the sidewalks for drop-offs and businesses have raised concerns about buses blocking their signs. But that would mean a relatively confined space that would have to be shared with streetcar lines.

Residents at Wednesday’s meeting raised a number of concerns, worrying that a concentration of buses in one location would result in increased exhaust fumes and more trash. There also are worries about increased crime with hundreds of young people from throughout the city gathered at one spot.

At the same time, many argued that a centralized location could be a positive step, making it easier for riders to make transfers, providing a more pleasant wait and potentially increasing ridership.

The proposal is in such an early stage that there are no concrete plans for what the hub might look like, how much it would cost or what amenities would be available.

At the high end of the possibilities would be an actual building, with air conditioning and space for bathrooms, vending machines and shops. At the other end, the hub could be simply a collection of outdoor shelters distinguished from other stops mainly by the number of routes that would converge in the area.

Between those two extremes are numerous other options. The hub could have various levels of lighting, security features such as guards or emergency call buttons, seating areas and different types of signage, perhaps including electronic signs that would state when the next bus is expected.

“This is an opportunity, and its RTA’s desire that it not be a meek facility,” Reynolds said. “It can be a good piece of design, a signature type of facility, that’s an asset to downtown and not just transit riders.”

RTA officials want the transit hub to be completed in time for New Orleans’ tricentennial in 2018.

In addition to the four main sites, the RTA is looking at other locations that could serve as smaller hubs that would feed into the central one. Planners are considering the foot of Canal Street at the river, a location on Galvez Street near the new University Medical Center and Veterans Affairs Medical Center, the Union Passenger Terminal and even a site as far from the city center as South Broad Street and Washington Avenue.

Some or all of those could be developed, depending on how plans for the main center progress.

Beyond minor tweaks, the plans will not involve major changes to present bus routes.

“We’re not looking at restructuring or making any changes to the route network beyond what it would take to get to and from the transit center itself,” Reynolds said.

Follow Jeff Adelson on Twitter, @jadelson.