What’s true is that primary sources don’t count towards notability, so if an article mostly just uses primary sources it’s likely to get deleted.
Which is absolutely absurd. Counting secondary sources and deciding if something is “Notable” from that is completely arbitrary. Furthermore, there’s legitimate reason for secondary sources not to exist on the topic; and the Notability guidelines of the local WikiProject on Roads, which probably contained the people leaving, should have been taken under advisement as notable roads don’t always have secondary sourcing due to lack of local newspapers or publications.
Specifically a highway may be notable because it never appears in the news… often because it rarely if ever sees auto accidents. A source is a source, and I think attacking primary sources and excluding them is problematic if the source in question never was causing issues with NPOV.
Now if someone can prove that a website from the DOT is actually doing some weird POV pushing or is legitimately not behaving like a neutral source; then sure, challenge that citation for that article and get it struck.
But it’s otherwise a waste of time to pretend that roads and highways aren’t notable and not of encyclopedic interest for good reason.