At present there are many car companies with assembly lines. Ford is one of the most famous assembly lines. This assembly line had its beginnings at the beginning of the 20th century, but the technology involved in these processes has changed a lot as can be seen in the video. The sequence of processes and the material flow of these factories must be perfectly synchronized to avoid wasting time and money.
When designing an assembly line, you must take into account the number of activities to be performed and the proximity between activities. If you want to minimize the distances traveled to minimize the cost, you can design a matrix that relates the activities and identify if: 1) It is absolutely necessary that two activities are together, 2) Especially needed, 3) Important, 4) Certain importance 5) Indifferent, or 6) Harmful. So in the case of a car assembly line it is important the proximity of the materials used in each activity.
To improve the assembly line it is necessary to know the initial times and, once the improvements are implemented, to verify that the changes have reduced the time spent on the activity. There are many tools to study times. You can use the timekeeping (the time should be multiplied by a correction factor, prevent that the timed person sees the timekeeping). It can also be used Methods Time Measurement (MTM) that breaks down the movement in micro movements. Another tool used for large magnitudes is sampling.
Here you have some templates to study times: http://www.systems2win.com/c/timeObservation.htm
The improvement of activities is facilitated through the use of process simulation tools. These tools allow you to make changes in the process and see how these changes affect the process. This reduces the costs of testing on the actual process, allows more testing, and reduces the need for pilot plants.