Thanks! For high-speed rail in EU, following gradients are applied: - 3.5% for dedicated high-speed lines with homogeneous high-speed traffic. That restricts traffic of other type of rolling stock, for example freight or regional trains; - 2.5% for lines with mixed traffic - including freight, regional etc.
In EU currently only in France high-speed network gradients higher than 2.5% is introduced while designing new lines, according to my knowledge. In other countries, gradients are kept lower in order to integrate with train traffic on conventional network. As exception, 4.0% was used on Cologne-Frankfurt - that means for example old rolling stock (ICE 1, ICE 2) are not permitted to use.