I disagree Rod, SSDAB is spectrally efficient compared to FM. The London N SSDAB is less than 2MHz wide and carries 26 stations, 26 stations on FM would take up nearly half the band, over 8MHz if you have 400Khz spacing.
The London SSDAB trial used just 500w to cover London inside the boundary of the North and South Circular roads for 26 stations with noise free stereo signal, that's the equivalent of 19w per station, 19w would not be enough power for a noise free stereo signal covering the same area on FM. However I do agree that SSDAB only works well in urban areas.