Nearly all cable networks use a low split, cutting off around 42Mhz for upstream bandwidth. Not all bandwidth from 0 to 42Mhz is usable due to external interference, most cable systems are able to get 4 full sized 8Mhz Docsis 3.0 channels into this space and one partial channel of 3 to 4Mhz.

Certain ISPs like Cox have started using OFDMA (Docsis 3.1) upstream channels as it is 50% more efficient than classic Docsis channels and you can operate it closer to spectrum with interference since it can run subchannels at lower modulation