Both can be true. If you have cars coming from all directions that can easily merge with each other, it makes sense that throughput would also be increased sinc

Both can be true. If you have cars coming from all directions that can easily merge with each other, it makes sense that throughput would also be increased since the other 3 directions don't need to stop to make a left turn from any direction. Safety might be factor number 1, but a roundabout will sustain higher traffic loads than a traffic light, assuming that all directions are being fed with equal amounts of vehicles. For this reason, a lot of arterial roads in NL still use traffic lights because they prioritize traffic moving in a single dimension (x or y, but not both). The smaller intersecting roads need to wait on the light during rush hour since the priority is traffic on the larger road. When two roads of a similar size/traffic mix, a roundabout can be used to facilitate changing directions. Here is an example near Eindhoven in the south part of the country: https://maps.app.goo.gl/SYMnP9jwNEj1ytx2A https://maps.app.goo.gl/SYMnP9jwNEj1ytx2A There's also a fairly large roundabout about 1-2km north of that intersection if you're interested. It's increased size provides more throughput and slows down drivers coming from the highway and allows a smooth transition down to the lower speed allowed within the city limits.