New toll lanes on I-285 and Ga. 400 could tower 30 feet or higher over neighborhoods on elevated ramps, eat into back yards, and plug major interchanges into such local Sandy Springs streets as Mount Vernon Highway and Raider Drive in a state conceptual design that could start construction within five years.

The “managed lanes” could have massive impacts on neighborhood character, local traffic and mass transit options, but the concepts remain largely unknown to the general public. The city of Sandy Springs is protesting parts of the concepts and suggesting some alternatives, but mostly behind the scenes. The Georgia Department of Transportation’s first public meetings for the Ga. 400 lanes are expected to be held late this year after the conceptual designs are more solid.

A rare public display of the behind-the-scenes tensions about the managed lane plans came at the City Council’s Jan. 23 retreat, where GDOT officials presented the latest concepts and city transportation planners pushed back with counterproposals. One concept: moving the proposed managed lanes interchange from Mount Vernon to Hammond Drive.

“Sometimes the greatest fear is fear of the unknown,” said City Councilmember Chris Burnett to GDOT officials, asking for community meetings, particularly about the Mount Vernon Highway interchange concept. “Can we get out in front of this early on…?” he asked.

The answer was no. GDOT spokesperson Jill Goldberg said the agency will do “aggressive outreach” once it has what it considers to be a more solid plan. The Mount Vernon interchange, for example, was proposed relatively recently and is still being studied by engineers.

The city officials who represent the public had some blunt expressions of concern and objection about the managed lane concepts. Mayor Rusty Paul said he is worried the Ga. 400 concept lacks “common sense” on preserving space and flexibility for a truly functional rapid-transit bus system. And as for the idea of building a highway interchange on residential Raider Drive, “That’s not going to work,” said City Manager John McDonough.

Tim Matthews, a GDOT project manager, said the agency remains in discussion with MARTA and local cities, and that interchange locations and designs remain at least partly open for change. One interchange proposal that the city objected to last year — on Sandy Springs Circle — appears to be removed from the conceptual plan.

GDOT is currently a year into its “Transform 285/400” project, which is essentially reorganizing and rebuilding the I-285/Ga. 400 interchange to make traffic flow faster and safer. That project, set to finish in 2020, has drawn public attention for large-scale tree removal for additional highway lanes and for the reconstruction of the Mount Vernon overpass bridge.

But Transform 285/400 is only the beginning. The managed lanes are a separate project that would add even more lanes — four on each highway — in construction that could take a decade. The concept of the project is to allow toll-paying drivers to speed through the interchange in dedicated, entirely separate lanes.

The Ga. 400 managed lanes are tentatively slated to come first, with a construction start in 2021 and opening in 2024. They would run between I-285 — or possibly a bit farther south at the Medical Center area — and Alpharetta’s McFarland Parkway.

On I-285, the lanes would run between I-75 in Cobb County and I-85’s Spaghetti Junction, with other segments to the east and west extending near I-20. Construction could start in 2022 and opening could come in 2028.

Squeezing even more separate lanes into the interchange has a number of effects that concern the city. At least 300 properties would lose some land along I-285, Matthews said, and the Ga. 400 section would require acquisition of an undetermined amount of property. That is sure to be controversial as highways inch closer to homes.

On stretches where there is not room to add surface lanes — including Ga. 400 between I-285 and Spalding Drive — the lanes would be built on elevated ramps that would be at least 30 to 40 tall and go even higher over interchanges.

That height means “you’re going to have homes that look straight on the managed lanes,” Burnett noted. GDOT officials said sound-blocking walls could be added to such elevated ramps, but there would be no visual screening.

Maintaining right of way for long-desired mass transit is another concern and has been discussed by a new group of leaders from top-end Perimeter cities. GDOT officials have said their designs will not preclude mass transit, but it remains unclear how that will really work in practice.

An example is North Springs MARTA Station, right on Ga. 400, which would be a stop for a proposed bus-rapid transit service. GDOT’s concept puts the buses on the highway’s express lanes, which will be inner lanes there. Matthews said GDOT is working with MARTA on a concept for having a bus platform there that riders can access with a bridge. Even if that works, Paul noted, the plan puts buses in regular highway traffic, meaning it may not be rapid at all, defeating its purpose.

Yet another concern are the additional highway interchanges that the managed lanes require. GDOT says it wants the managed lanes to have entirely separate exits and entrances from regular, existing highway interchanges. That means creating or expanding interchanges.

Possible Sandy Springs interchanges on the latest GDOT map include Johnson Ferry Road, Mount Vernon Highway, Northridge Road, Perimeter Center Parkway and Raider Drive. Dunwoody’s Cotillion and Savoy drives interchange along Chamblee-Dunwoody Road is also on the map.

At Mount Vernon, that could mean adding 20,000 vehicles a day to a street that currently has a lot of homes and could mean widening the overpass bridge to six lanes by 2041, city planners said. It also complicates the city’s plans for other parts of Mount Vernon, including adding “multimodal” lanes and reconfiguring the Johnson Ferry Road intersection.

Paul and McDonough suggested using Hammond Drive instead, as it already has a half-interchange and is a bigger street. The city has a controversial widening study of its single-family residential section coming soon. Matthews said GDOT will examine the idea.

Sandy Springs is not only a critic. Officials suggested another interchange, at Northside Drive, to handle Cobb commuter traffic. Matthews said GDOT likely will not approve that, but said the agency would consider the city’s backup suggestion: an interchange at Powers Ferry Road in nearby Cobb.

For GDOT’s presented to the City Council about Transform 285/400 and managed lanes, click here. For the city’s managed lanes response presentation with alternative suggestions, click here.