if you go Bruge, Brussels, Achen and in you'll find it is not only fast but a damn sight smoother/better roads.
traffic is not as bad as you may think.
sub 4 hours quay to door
well took some ruuners 8 hours using that route 2 years ago due to hitting loads of traffic passing through brussels
as i said is several ways and is upto the individual to decide which route thay want to take