I guess I should know better but I tried to transfer the .elv, .typ, and .tra files, with and without .trb, directly into a new version of a map I'm building and got a CTD.
I removed the .tra files and tried to place a road before adding the fields, again CTD.
I then added a field and tried adding a road. At first it CTD but eventually, I clicked on the field tile before selecting the road tab and then I was able to get the road and drag it around normally.
Yeah, I know, we don't normally install the roads first but...