Worked for me. Thank you @Norfolk_Chris

Doesn't work

The Steam workshop is not working for CIM2, but you can still download maps manualy as described below.
You can find your subscribed maps on your PC (you must subscribe to the maps in the normal way). They are located in a folder on your PC (Windows 7, 8 & 10) [C:\Program Files (x86)\Steam\userdata\79832872\ugc\referenced]. They are updated when you start CIM2, so start CIM2 and exit before you start (stay logged into Steam).
The maps are located in numbered folders. Look in the folders to find the map files. Only copy the files ending *****.map. (They have very long names, the city names are included somewhere in the name.)
Copy the map into your maps folder [C:\Users\chris\AppData\LocalLow\Colossal Order\Cities in Motion 2\Maps]. You will then want rename the files to a sensible name.
The bonus is that you can open the maps in your map editor and edit their content to suit your personal preferences (eg. You may want to adjust the 'car factor' to control traffic levels.).

How do you install it?

Love it

Very impressive! I recognized the road layout almost immediately :)