What happens on the European mainland with non EU countries which border the EU?
www.bbc.co.uk/news/uk-44054594 Brexit: What can UK learn from other external EU borders?
Norway-Sweden : average wait 20 minutes for one of the most technologically advanced borders in the world. That includes roughly 10 minutes waiting time, three to six minutes of handling time, and the time spent coming off the road to complete the customs process.
It is highly efficient, but certainly not entirely frictionless. 
And that's with Norway in the Single Market 
Turkey-Bulgaria : average wait for HGVs, 24 hours.
And that's with Turkey in the Customs Union 
Switzerland-France : average weight 20 minutes to 2 hours, according International Road Transport Union (IRU), (more than two hours if full inspections have to be carried out).
This is for HGVs.
For people, Freedom of Movement under Schengen and/or the Common Travel Area applies (but not in Turkey's case?). Some MPs (like Daniel Hannan) don't seem to understand the difference between people and goods 