I'm also not sure what's up with the difference between 50 and 75cm. But being able to see some features that are less than 50cm wide is what you should actually expect, even though it is a bit counterintuitive. Think of it like this: each pixel is the average color of a 50x50cm square. Now a square of black asphalt will have a very dark average. But square of asphalt with a 10cm wide white line running through it will be about 10/50 = 20% lighter. Easily enough to be visible. And many road markings are wider than that.