Italian to English Tech/Engineering Transport / Transportation / Shipping rail building works

Hello!

Last one for this particular job! :)

We're still talking about a list of works carried out, and this comes from another item on the list:

Sostituzione totale traverse e contemporaneo risanamento su tratte varie linea DD.ma Prato - Bologna

My problem is the DD.ma... anyone know what it stands for?

I've also found DD.ma Roma-Firenze on the internet.

Thank you very much!!
Giuliana