The Engineer Expansion Pack contains 4 single-die unique expansions:

Construction (1 die)
Renovation (1 die)
Separation (1 die)
Special (1 die)

Use the special dice of the Engineer Expansion in addition to or in place of your regular Route dice to change the core foundations of the game. Increase the challenge of your games with the tricky Separation Expansion and its never-connecting routes! Build Special Routes in a whole new way with the Special Expansion! Modify pre-existing routes and add more connections to them with the Renovation Expansion! Perform special actions and restructure your networks with the Construction Expansion!