^Yes, I agree, this is old problem that is repeated at every highway u/c... 
D8 => yes there are only 16km gap, I advice you to follow signs for Prague, gap is filled with quite nice road along the Labe valleyI have a few questions, because i haven't been to the Czech Republic for a few years.
Is the section Usti - Lovosice now the only missing link in the D8?
Will there be a motorway from Brno via Ostrava or so to Northern Slovakia?
Is the D5 now connected with the German A93 motorway near Pfreimd?
Both are tolled, they have same speed limit (130km/h). Only difference is that R-class roads are little bit narrower (D = 26,5m - R = 22,5-26,5m). But that is also relative for example Prague baypass have 3lines in each direction so it is better than most west european highways and it is still marked as R - expressway.What is exactly the difference between a Dalnice (D) and an Expressway (R)? i didn't saw much difference between them. Is it only toll?
I think R (expressways) are allowed to be a bit steeper and have lesser radius of corners than D (motorways). And traffic lanes are a bit narrower IMO.Only difference is that R-class roads are little bit narrower (D = 26,5m - R = 22,5-26,5m). But that is also relative for example Prague baypass have 3lines in each direction so it is better than most west european highways and it is still marked as R - expressway.