const Axle &get_fixed_axle(unsigned) const;
const Bogie &get_bogie(unsigned) const;
const Axle &get_bogie_axle(unsigned, unsigned) const;
const Axle &get_fixed_axle(unsigned) const;
const Bogie &get_bogie(unsigned) const;
const Axle &get_bogie_axle(unsigned, unsigned) const;