Lanes are implied but not imperative. The most important thing is to get where you are going as fast as possible with the least injury to yourself or others. Speed is essential. Another critical thing is to warn everyone everywhere that you are one the way. This means liberal application of the horn.
Horns are a constant sound in Kathmandu.
They are simply a part of life. If you do not use your horn, you will not get anywhere. People are tuned into horns. If they hear one, they will move to the left or right as appropriate. Whenever I took a cab, from the moment I entered until the moment I exited, the cab driver would be blowing his horn.