In the FAA's document about standards for airport markings, it says:
Width. The taxiway centerline marking width, which is either 6 inches (15
cm) or 12 inches (30 cm), is based on the type of taxiing operation as described below. Uniform
width must be maintained for the entire length of the taxiway except under the following
The taxiway or part of the taxiway is designated as a SMGCS taxi
route. Under this designation, the width of the taxiway centerline must be 12 inches (30 cm)
wide and, on light-colored pavement, further outlined in black. The taxiway centerline width of
any remaining section of the taxiway that is not part of the designated SMGCS taxi route may
change abruptly at that point or at the intersection with other taxiway centerline markings, for
example, reduced from 12 inches (30 cm) to 6 inches (15 cm).
Source, chapter Taxiway Center Lines, page 43
For the taxiway edge lines, following rules apply:
The outermost edge of both marking schemes must be painted along the
edge of the usable pavement.
The continuous taxiway edge marking consists of dual, continuous lines
with each line being at least 6 inches (15 cm) in width and spaced 6 inches (15 cm) apart (edge to edge) [...]
Source, chapter Taxiway Edge Lines, page 48
This really is a great question, I have never thought about airport markings being such a complex thing.