calculate single-sided PCB transmission line impedance?

I wondered if trace on a single sided PCB could be optimised to
resemble a 50 ohm transmission line. It will be enclosed largely
between ground areas.

But looking around on the web I have so far only found dual layer
calculators for microstrip or striplines with ground planes.

Does anybody know some calculator, reading material or an simply
example?

Cheers,

Joop
.