The original is a little underexposed in the background beyond the yellow cab, therefore, there is not a lot of detail in these areas. This translates to dark areas in the B&W with no detail in them. This is a case of a bright foreground and a darker background, where your camera's meter is unable to resolve enough of the dark/light range to expose everything properly. I think either of them would be a good shot, if you could "ring" some more detail out of the shadows in the background. Did you shoot this in raw? If so, then there maybe enough information in the image to produce this detail. My 0.02¢ FWIW.
WesternGuy