In reply to Pete Gossett (Forum Supporter) :
EMD also installed radial/steering (BN #6599's set-up was not radial/steering, it was just articulated) B trucks on a GP50, ATSF #3810, for some testing. While it did improve traction, reduce parasitic losses in curves and reduce rail wear, the GP line was pretty much coming to an end at that point. EMD did take the test data and applied it to the HTC-R 3-axle radial trucks introduced on the SD70s.
Span-bolster B+B trucks had appeared before, just not on EMDs. The first and second generations of the big GE-built Union Pacific gas-turbine electrics had used span-bolster B+B trucks front and rear for a B+B-B+B configuration. When UP traded them in on GE U50s and Alco C855s, those span-bolstered B+B trucks were actually reused, since the C855s and U50s used GE electrical systems. EMD just used rigid D trucks on their DD35s, DD35As, and DD40AXs.
EMD did apply B+B trucks to locomotives after BN #6599 though. In 1970, Brazilian mining railroads had come to EMD for a variant of the SD45. The problem was that Brazilian railroads use a 1000mm narrow-gauge layout. The big SD45 had too high of an axle loading, and once the trucks were narrowed down to 1000mm, there wasn't enough room to fit a traction motor that could handle the full 3600hp output. EMD's solution was to build a 1000mm-gauge D truck. The extra axle per truck spread the weight out, and by the 8 traction motors allowed utilization of the full output. The resulting machine was called a DDM45 (two D trucks, M for meter-gauge, 45-series) and worked quite well.
Jump forward a number of years and the DDM45s are starting to get long in the tooth. The Brazilian lines want more EMDs, but more modern. Also, the D trucks had been hard on the rails and EMD also hadn't turned out a D truck in a while, so likely didn't even have the tooling anymore. So they took secondhand SD40-2s, lengthened the frame and then installed span-bolstered B+B trucks under them, resulting in a machine called a BB40-2. Quite a freakish-looking machine, between the 8 axles and the abnormally long "porches" front and rear.
There were also some SD40T-2 "Tunnel Motors" rebuilt into BB40T-2s. Many of the BB40s weren't even repainted, just receiving lettering patches, and this one certainly displays it's D&RGW heritage.
GE also built similar units for Brazil, rebuilding C36-7s, C40-8s, C40-9s, and C40-9Ws into BB36-7s, BB40-8s, BB40-9s and BB40-9Ws respectively.
EMD actually catalogs an SD70ACe-BB, which is a meter-gauge span-bolster B+B-B+B SD70ACe for South American markets.