Imagine this space ... but entirely for pedestrians and cyclists. File Photo/DOT Ain’t it Grand! Grand Army Plaza will become a grander plaza that’s fully connected to Prospect Park, Mayor Mamdani said on Monday — embracing a 20-year-old plan for a safer, more people-first space. On Monday, Mamdani and Department of Transportation Commissioner Mike Flynn unveiled a familiar-looking redesign to connect the plaza containing the ceremonial Soldiers’ and Sailors’ Arch and the adjacent Bailey Fountain to Prospect Park’s northern entrance. The design eliminates motor vehicle traffic between Union Street and Eastern Parkway to allow for much safer, calmer and more rational pedestrian experience. If the project actually breaks ground this time, Mamdani and Flynn will be delivering on an idea that Brooklyn advocates — including a young Mike Flynn — began discussing in earnest in 2006, when Park Slope and Prospect Heights residents formed the Grand Army Plaza Coalition. DOT’s latest plan simplifies the traffic flow in and around the plaza by removing drivers’ ability to travel all the way around the inside of its traffic circle (to view the current layout, click here). Northbound and southbound drivers on Flatbush Avenue would use the east side of the inner circle. Southbound drivers coming from Vanderbilt Avenue and northbound drivers coming off of Union Street would occupy the west side of the circle: Besides unifying the plaza and park, DOT will also add and upgrade bike lanes in the area. Painted bike lanes on Plaza Street East and Plaza Street West will become raised and parking-protected, while DOT will also add raised and parking-protected northbound and southbound bike lanes on the Vanderbilt-to-Union segment. The redesign will dramatically simplify where and how people can cross the street: DOT will entirely eliminate the notorious concrete triangle on Flatbush Avenue between the park and