Hi I must say that one of the ways around this problem is to use Current Shunts 
soldered or bolted (or both) to the track. These Current Shunts may be copper 
wire, copper rods or copper bars (square or rectangular.) My favorite are the 
copper common and earth bars used in mains DBs.  
Some of these have holes drilled at regular intervals giving you an ideal way 
of connecting large cables to your PCB. 
This enables hundreds of amps to effectively flow on your PCB with no overheating problems.

Another, not so neat, Current Shunt is old solder wick!

(These Current Shunts also act as great Heat Shunts)

> Richard Ottosen wrote:
> ....
> >>
> >> As a general rule of thumb in electronics, it seems reasonable to
> >> allow 2-3x safety margin on most critical design decisions - especially
> >> those concerning power dissipation levels. It would seem that even so
> >> much as thinking about driving traces to the point where they are
> >> heating up or glowing or discoloring the pcb might be like flying
> >> too close to the sun on waxed wings.
> >
> ....

MikeW