Actually, true 'figure eight' wire is fairly rare, being a kind of 'bar wire' used in specially high wear, high traffic situations. Most 'Light Railways' and railroad electrifications use 'Grooved Wire' for actual contact wire, which is essentially round in cross section but with a continuous grove on either side above the midpoint. screw bolt 'ears' hold the wire without interfering with the running surface, even with trolley poles. Grooved wire is almost an absolute necessity with pantograph or bow trolley. Round wire, seldom seen now was actually of round cross section and the ears were shaped around it
by hand, using special but rather crude tools. Only the bottom of round ware was unobstructed and, when worn, not even that. For us old timers, it was the source of the measured click made by trolley wheels, also now extinct.
Way back, 00 size wire which was if I recall a bit over 1/4 inch in diameter was popular with small, poor lines and 0000 (20% more diameter but geometrically bigger area) was the standard on the 'big' companies.
With todays "light" rail vehicles, 00 might pop like a fuse. There are bigger sizes, defined by circular mils, impossible for trolley shoes, but very nice for today's higher ampereage and, always favoured by railroad electrifications. Trolley wire was almost always Annealed Phospher Bronze. today, there are newer alloys with special conductivity and wear caracteristics.