The Age of Steam Roundhouse site covers 36 acres and has a 3-acre retention pond. To level-off sloping ground, 115,000 cubic yards of compacted clay fill were dumped to elevate the site by up to four feet. Additionally, 60,000 tons of aggregates (stone, ballast, etc.) were used at the site. The turntable pit was dug 132 feet in diameter to encase the 127-foot diameter, 2.7 million-pound concrete ring wall on which each end of the 115-foot long turntable sits and rotates.
Soft ground caused 178 steel I-beam pilings (5,525 lineal feet) to be driven down to bedrock under the ring wall and center pivot point to provide support for heavy locomotives rotating on the turntable. For added strength, 49,000 pounds of rebar were formed inside the concrete in the turntable pit's 550 cubic yards of ring wall. Nearly 4,500 cubic yards of poured, reinforced concrete are in the site.
Before the 1940 delivery of Western Maryland’s 4-6-6-4 Challenger-type locomotives, a 115-foot long, 400-ton capacity turntable was installed at the Hagerstown roundhouse. Moved to the Age of Steam Roundhouse in 2008, more than 57 tons of new steel was needed for repairs to this 75-year old turntable. The Age of Steam turntable pit is not round. Actually, it is comprised of 196, flat, individual surfaces on the interior concrete ring wall which, when seen together, give the illusion of a perfectly circular wall.
Each roundhouse stall covers an angle of 6 degrees, 47 minutes and 09 seconds. Together, all 18 roundhouse stalls comprise an arc of 122 degrees, or 1/3 of a circle, and cover an area of 48,500 square feet, more than an acre (43,560 square feet). A half-mile of gutters and downspouts carry away rain water. Roundhouse stalls #1 to #7 measure 127 feet long with a track length of 112 feet; stalls #8 to #18 measure 97-feet long with tracks measuring 82-feet. Roundhouse Stall #1 measures about 160 feet long.
Below roundhouse stalls #2, #4 and #5 are 4-foot deep, 100-foot long inspection pits. For employee comfort the floor in roundhouse stalls #1 through #7 is radiantly heated by pumping hot water through a spider web of tubes strategically placed in the 14-inch-thick concrete floor.
To reduce construction costs, ballasted tracks are used underneath short-stall, locomotive exhibit tracks #8 to #18. These 11 tracks are covered with wood planks to provide a continuously flat floor.