Example of track with overlapping elements using TnT Board
Modified http://tntvis.github.io/tnt.board/build/tnt.board.min.js to a secure url
https://d3js.org/d3.v3.min.js
https://cdnjs.cloudflare.com/ajax/libs/es6-promise/3.2.2/es6-promise.min.js
https://tntvis.github.io/tnt.board/build/tnt.board.min.js