This is a diesel refueling platform which can also be used for replenishing fuel supplies on oil powered steam engines.
The depot model was originally digitally designed by Lazarus Bricks in 2013 and sold at his store on Bricklink. (It's still being sold today, and is available here: www.bricklink.com/store/home.page?p=lazarus992&itemID... I stripped the model of it's built-up track base, extended the platform and added another fuel tank inspired by the one in set 60052, plus I revised the roof and it's angled awnings.
The platform has been extended to accommodate larger locomotives.