This is the tunnelbak where the main protests are. The speed limit is actually 70 km/h as shown by the sign visible in the street view. It is about 500 meters from where the A12 ends at the corner of the Malieveld.

I think it is unfair to describe “holding a pre-announced protest” as “jumping into traffic”. I imagine they take care to do it safely.

I think it should also be noted that the road is located directly between parliament and the ministry of economic affairs and climate.