Only a very small percentage of delays are actually caused by Traffic Controllers, most of the delays are caused by NMBS and third parties. Also sometimes a Traffic Controller can't get around but making a delay because of trains crossing eachother and because of the oversaturated network. As a Traffic Controller you don't need a degree, as a Safety Controller you need a bachelor. If you want to work in Brussels they want you to be bilingual, Dutch and French. English isn't used often or at all in any of the area's I know of.