only when you need brand new roads and high tech traffic lights. I simply don't value that stuff but I don't make the rules here. The belgium system works far better for me. Less tax and bad roads. Works fine.
An additional car needs >100m additional road lane, except in unusual and uninteresting cases. Try comparing the tax you pay with the cost of acquiring >300m² of land in the areas where you want to drive and building road on it.
I lived in Brussels for two years. Traffic is crippling and the infrastructure is terrible. Brussels has the worst traffic in Western Europe. It's horrible. That's what you get when you don't invest properly in infrastructure and alternatives to driving.