B+B-B+B
"B+B-B+B" means there are four trucks under the unit. Within each truck, there are two powered axles, and pairs of them are connected by span bolsters. An example would be the General Electric U50, built from 1963 to 1965. The 4500 horsepower (3.4 MW) turbine locomotives built by GE for Union Pacific also used this arrangement. The EFVM railway of Brazil uses narrow gauge GE "BB" locomotives with this arrangement, both with "standard" and wide cabs. A GE BB40-9W, for instance, is a wide cab GE Dash 9-40CW series 4,000 hp (3,000 kW) locomotive with a B+B-B+B wheel arrangement.
Read more about this topic: AAR Wheel Arrangement