"It is a really bad road."

Translation: Det er en virkelig dårlig vej.

[lauraa.wagner]

Why cant it be den?

[ms.zirly]

why isn't there vigtigT/rigtigT when it seems like an adverb?

[deactivated user]

See here: http://www.elkan.dk/sprog/t_eller_ej.asp

3) Valgfrit t

a) Biord, der betegner grad og forstærker et tillægsord:

Han blev forfærdelig/forfærdeligt vred

Det er jeg ikke særlig/særligt interesseret i

Den er frygtelig/frygteligt sød

Firmaet har klaret sig virkelig/virkeligt godt

In short, it is correct both with and without -t.

[Tamoxifen]

"virkelig" sounds ok but how about "ret"?

[DragonNights]

It's a matter of degrees with "ret" and "virkelig"... consider the difference between these sentences:
"It is a pretty bad road." / "It is a really bad road."
"He is quite handsome." / "He is really handsome."
The difference is the same in Danish. "Ret" is saying "pretty much/quite/relatively" and "virkelig" is "really".