Speed computation (non-kinematic) uses a*v^3 for air resistance

[radim-asamm]

There is this comment explaining how speed for segments ("way segment") is calculated

    // Solves a * v^3 + c * v = d with a Newton method
    // to get the speed v for the section.

Where a represents drag coefficient * reference area for a cyclist. Is the use of cubic term a good model? In many common situations, air resistance (or drag) is modeled as being quadratic with respect to speed, not cubic.