I am not getting 600km/tank :(

[stuffy]

That's good advice, and what hypermilers attempt to achieve in traffic like this. Our term for it is "Driving Without Brakes", or DWB, meaning we try to maintain constant forward movement by picking the right speed to let us not use our brakes at all, or come to a stop. The whole idea is to conserve momentum.

this also lessens the "chain-reaction" effect for the cars behind you that happens when people are stomping on their brakes every 2 seconds.

it's amazing to me how people drive in stop and go traffic, if they just left 3-5 car lengths in front of them they would be applying the brakes much less often and traffic would actually start moving if everyone did this.