This year 254 ran a system that could generate and drive along a given spline (not an arc, but close enough). The first step was to derive a set of splines to follow given a set of waypoints (x,y,heading combonations) using quintic hermite spline interpolation (an algorithm to generate a 5th order polynomial using the positions, headings and rate of change in heading at consecutive waypoints). After this, the splines are broken down into encoder position, robot heading, velocity, acceleration, and jerk target profiles over time. Then control loops attempt to match the profiles over time. You can find the source code we used for this project
here