Having read the blogs till now, most of what I will say repeats others.
Lane widths are measured center of line pattern to center of line.
I joined a southern California county in 1963 as their first traffic engineer, and soon after was out on the tarmac laying out a revised striping plan to provide left turn pockets, using a rope and a 4-inch brush, to provide a "Cat Track" for the striper to follow. Since the rope divided the brush spots into two halves, "cat track" was used to define the laid-out line.
The previous responder that commented on the accuracy of the striping machine driver to track the "cat-track" line was spot-on. Often times engineers get overly conscious of dimensions which will need a plus or minus tolerance in the field.
I suggest that the originator of this topic go out in the field and deal with the level of experience of the striping crew, and settle on measuring lane widths from center to center, plus or minus what the striping truck can do.
Maynard Keith Franklin
RCE CA 15487
RTE CA100