Re: "There are over 200 roads that cross the border."
But the point is that there aren't external EU/Schengen border crossings without customs posts. Take a look at a map - you won't find thousands of crossings.
I can't get the actual total number, but click though the individual borders listed here. I was very surprised to see how few border crossings there are for each EU/Non EU country interface.
https://en.wikipedia.org/wiki/External_border_of_the_European_Union#Border_status_and_cooperation
For instance, on the 535km Poland Ukraine border (comparable in length to the Irish one, and describe as "the most often crossed eastern border of the EU") there's a grand total of 7 road crossings (11 crossings in total including rail).
Taking the example of the longest border in the Schengen Area, the Sweden/Norway border (1,630km) has 10 road crossings with customs stations, and only a further 30 with none.