D routes are toll bypasses of the unsuffixed free routes. Often the endpoints are obvious, for example
180D east of Coatzacoalcos. It splits from 180 at both ends, and is all maintained with toll money (compare the length on
#17 in the middle column).
But there can be complications. The portion of
45D bypassing Irapuato to the south is free to travel, but is still toll maintained (
"begin section in charge of Capufe") (and signed as 45D, though there are many errors across Mexico in which the D is erroneously omitted or included). Still it seems clear that this is part of 45D. It's toll maintained, signed as D, and built to freeway standards.
Now I'll give examples of cases where one or more of these is not true.
14D's west end at Uruapan.
Toll maintenance ends where the freeway ends.
A distance sign just beyond does call it 14D, as does
an overhead sign on what is a really a city street. So here we have signage on what's neither a freeway nor maintained as a toll road. Luckily signage is consistent and we have a logical endpoint.
1D's north end at Tijuana.
Toll maintenance ends just past the toll booth, before the interchange where it curves east next to the border. The remainder of the freeway is either federally maintained as a branch of 1 (if I'm interpreting
this source correctly) or locally maintained. There are no northbound signs for 1D past that interchange. Southbound signs exist but are of the "implied to" style that are common in Mexico. In other words, a sign for a route may either be saying that you're on that route or that the road you are on leads to that route. Here are several 1D signs all over the Tijuana area, some far from any route that could actually be 1D:
#1 #2 #3. So do we end 1D where it stops being a toll road (and put the rest of the freeway in mexsf), or where the freeway ends? Or do we keep it going farther east along Calle Segunda/Benito Juarez?
2D's west end at Tijuana. Just like 1D, toll maintenance ends before the freeway ends, in this case at the BC 201 interchange. The freeway continues a bit farther (note that
this freeway predates BC 201). It then feeds into a local boulevard that predates the construction of 2D. As with 1D, there are signs for 2D eastbound but not westbound on this freeway (which is federally maintained according to GIS data) and boulevard. The junction chosen to be the west end of our file is not in fact the westernmost sign for 2D;
here is one farther west on Boulevard de las Americas, and as with 1D there are many signs on other roads pointing towards 2D. So here the options are BC 201 (end of maintenance), end of freeway, or somewhere chosen along the continuing surface road.
