Reducing traffic speed from 50 to 30 km/h in cities is now implemented in the Netherlands. The big issue here is that road design should be in line with the allowed speeds. This means that you can’t have separated bike lanes om 30km/h roads. Many of the 50km/h roads are too congested to allow mingling between cyclists and automobiles. To overcome this paradox Leiden implemented these traffic lights. They turn red when drivers exceed the 30km speed limit. Resulting in an almost serene atmosphere.