The allocation of electric power transmission lines in tunnels is a common practice in several applications, like underground lines in urban areas, connections of cables to substations, mining and railway systems. Construction of tunnels requires difficult and costly works. Besides, limitations of external and internal magnetic fields generated by the currents in the cables of the tunnel are needed. The present paper proposes and analyzes different statistical methods for calculation of optimal dispositions of cables and tunnel dimensions for reducing magnetic field and costs, for time varying currents in the cables. The implementation of these methods to a four-circuit real case probes their effectiveness.