The compositions were determined by the traffic flow on an eight-lane section of Interstate 5.  Each lane was designated a consecutive note in an octave; when a vehicle in that lane passes by, that note sounds. The lowest note in each composition starts on the outside lane of south-bound traffic, and the highest note is on the outside lane of northbound traffic.  

 

A sustained note indicates the length of time it takes the vehicle to pass the person taking the automobile-dictated notation, so a long drawn out note could possibly be a very long truck at an average speed, or a small car moving very slowly. The longest sustained note in these compositions can be found at 5.37pm, and lasts for 44 seconds.

 

The four pieces on this album are made from the traffic movement at 9.00am on a Monday, 12.00pm on a Tuesday, 5.30pm on a Wednesday and 1.00am on a Thursday. The element of time is represented by a single note playing on the second, every second, this repeating note fades in and out of the compositions.