Nowadays, Sundays are not as quiet as they used to be many years ago, and transport usage has increased and isn't too far off the usage on Saturdays now. The Sunday service on a lot of routes is very poor, and on some routes results in buses being much busier than on a Saturday. Improving this isn't too difficult as it obviously doesn't require any PVR increases.
I think Sunday frequencies should not go below a certain level of the Monday to Saturday frequency:
>9bph Mon-Sat no less than 6bph on Sunday.
7-8bph Mon-Sat no less than 5bph on Sunday.
5-6bph Mon-Sat no less than 4bph on Sunday.
4bph Mon-Sat no less than 3bph on Sunday.
3bph Mon-Sat no less than 2bph on Sunday.
Therefore these routes should have frequency increases on Sundays:
33, 35, 80, 212, 248, 450, 468, D6, EL2 - Sunday frequency increased from 4bph to 5bph (these routes run at 7.5 or 8bph on Monday to Saturday).
66, 103, 126, 151, 175, 193, 247, 256, 307, 368, 433, EL3, U2, W19 - Sunday frequency increased from 3bph to 4bph (these routes run at 6bph on Monday to Saturday).
47, 50, 89, 95, 116, 118, 128, 130, 150, 152, 157, 165, 179, 186, 194, 196, 197, 198, 206, 217, 226, 232, 234, 251, 255, 275, 284, 286, 289, 294, 306, 312, 320, 325, 330, 340, 358, 365, 394, 403, 407, 415, 419, 487, 490, 493, D8, E5, E7, E9, H2, H20, H22, P12, R11, U3, U5, W5 - Sunday frequency increased from 3bph to 4bph (these routes run at 5bph on Monday to Saturday).
314, 376, R9 - Sunday frequency increased from 2bph to 4bph (these routes run at 5bph on Monday to Saturday).
20, 258, 296, 299, 357, 370, 379, 382, 401, 405, 413, 428, 462, B16, U1, W9, W13 - Sunday frequency increased from 2bph to 3bph (these routes run at 4bph on Monday to Saturday).
117, 203, 423, 482 - Sunday frequency increased from 2bph to 3bph (these routes run at 3bph on Monday to Saturday but are by far the most used routes that run at 3bph).
246, 481, R4, U9 - Sunday frequency increased from 1bph to 2bph.
K4, K5, S3, S4 - Sunday service running at 2bph added.
470 - Evening and Sunday service running at 2bph added.