The sentence 

# HAS A TRIVIAL ERROR, PERHAPS JUST A TYPO

It's just that simple. the two "of"s were meant to be "are" (or "is").

"of" is utterly meaningless, might as well have typed "cat" there.

> The total length of the public road's network is 29151 km, out of
> which 1243 km are motorways, 6810 km of national roads and 21098 km of
> regional and local.

should be..

> The total length of the public road network is 29151 km, out of
> which 1243 km are motorways, 6810 km are national roads, and 21098 km
> are regional and local roads.

or, if you prefer,

> The total length of the public road network is 29151 km, out of
> which 1243 km is motorway, 6810 km is national road, and 21098 km
> is regional or local road.

It's **truly incredible** something **so simple** can get so much press here.

---

Regarding the issue asked about in the comment below.

It couldn't be simpler. You can interpret the three references as to **"sections"** (so for example, the first section discussed is a section 1243 kms long), in which case **singular**.

Or you can interpret the discussion as about the various **"kilometer lengths of highway"** in which case **plural**.

What's the question?  It's the norm in English that there are at least three ways to go with anything. You can choose either the plural "way" or the singular "way"; this is totally unsurprising in English: it is the norm, there is nothing, whatsoever, to say about it. Just choose one or the other.

Note also the infuriating apostrophe-s in "road's" - idiotic, or just a typo.