Looks good. You've managed to reproduce the Javascript demo version in the tutorial in C++ with SFML rather well!
thanks Hapax, it seems after all, it is easy to change code from HTML5/javascript to c++/SFML. (IMHO), javascript is C/C++ like no extra job needed to convert it. however ,HTML5 is bit harder but it can be managed. it took me 2 days to get familiar with HTML5/javascript synthetics and code's data and strictures, to be able to convert them to C++/SFML.
Now fix the cars so that you can't always see the right-hand side of them
yeah, this is indeed a problem, also, i left the AI implementation it is bit ineffective even in original tutorial, for example, if there is heavy traffic ahead the cars rubberbanding left and then right as they try to squeeze through a gap between 2 other vehicles. this is not good and it gives bad expression of game, it needs to rewrite a new robust AI algorithm.
and for textures unfortunately the origin sprite-sheet has only the right-hand textures of cars, i don't know how make new textures for them. it needs artist, surely i'm not