The geometry includes consideration of such things such as cross section, gradient, curvature, sight distance, and clearances. The aesthetics includes consideration of such things as channelization, signs, and markings. All three are components of what is called capacity , a quantitative term.
Volume is the most important item of measurement in traffic engineering.
There are different ways to calculate it, but it generally refers to the number of vehicles passing a given point during a specific period of time. Another important item is density , calculated by dividing volume by the average speed. Vehicles are not manufactured to run for any significant length of time at speeds in the 25 mph range without damage from the jerky stops and starts that sometimes require ignition restarts. Before building a new road is considered, however, qualitative analysis is done. This goes beyond looking at capacity measures and at a concept called level of service .