Metro's next-generation rail cars won't be the dramatic overhaul riders experienced when they first boarded the stainless steel 7000-series in 2015.

Instead, the agency is indicating it wants to improve on the design of the 7000-series cars when it ushers in the 8000-series beginning in 2024. There would be more handles for riders to hold on to, more screens to support digital advertising and charging ports for electronics. Notably absent, however, are the radical ideas Metro envisioned when it began dreaming up the 8000-series: open gangways to reduce crowding and allow free passage through rail cars, almost like an articulated bus; heated floors to make for a more comfortable ride and onboard WiFi to ensure passengers are always connected.

Compare the exterior concept released in February 2017 to the one Metro issued Tuesday, which looks similar, but bears a much closer resemblance to the 7000-series trains now in operation.

Metro announced Tuesday that is has officially begun the procurement process for the 8000-series, issuing a request for proposals for the design and build of its next-generation rail car. The 8000s would replace the aging 2000- and 3000-series cars, with an option to also scrap the agency's second-most reliable fleet, the 6000-series, which came into service in 2006. Metro could purchase between 256 and 800 of the new cars, depending on whether it decides to retire the 6000s as they reach the midpoint of their 40-year anticipated lifespan.

"Options in the contract would allow Metro to purchase 'up to' 800 cars in all, giving the transit agency the flexibility to support a range of initiatives and scenarios, including expanding all trains to the maximum 8-car length, running trains more frequently during rush hours, and retiring the 6000-series fleet in lieu of a midlife overhaul program," the agency said in a news release.

Metro officials said last spring that the agency would need about 1,200 rail cars to meet future service needs, including the expansion of the Silver Line to Dulles International Airport and into Loudoun County. The agency's current fleet meets that threshold, and Metro has supported six-minute headways on five of six lines with the same number of cars (compared to the current eight minutes across six lines).

The agency has scrapped more than half of its 5000-series cars, it says, and the final of 748 7000-series cars are expected to arrive next year, Metro said.

Echoing comments he made in April, Metro General Manager Paul J. Wiedefeld credited the region's dedicated funding agreements for allowing the agency to plan for its future rail car upgrades.

"Today Metro is beginning the multi-year process of acquiring our next railcar fleet, which will take everything our customers love about 7000-series trains and build upon that success," Wiedefeld said in a statement. "I would take this opportunity to again thank our local jurisdictions -- Maryland, Virginia, and the District of Columbia -- for creating a dedicated capital funding source for Metro that has made this possible."

Though the upgrades represent an incremental change from the 7000-series, Metro says the new cars will be fitted with "the most advanced safety technology available." The agency has also indicated they will be more energy efficient.

Metro says it expects to award the contract in late 2019. The 7000-series rail cars are manufactured by Kawasaki at the company's rail car plant in Lincoln, Neb.