As a matter of fact, road and rail noise is first of all a consequence of the traffic itself, namely its noise emission. Little traffic is less noisy than strong traffic, slow vehicles are less noisy than fast ones, and at the same speed heavy trucks are louder than light cars and freight trains are louder than passenger trains. The traffic, in turn, normally depends on the time of the day. Business peaks are found at morning and evening hours, cargo train traffic concentrates on the night (in Europe). Already this causes a rather variable noise load in the environment. 

• attenuation of sound waves
• refraction of sound waves
• scattering of sound waves
• diffraction of sound waves
• reflection of sound waves