I remember Scania N113 CAC on 505.
I miss all the former Express buses like 501, 503, 505, 507,
511 and 512 in the early 2000s. Those were the heydays. 
They should re-introduce them back.
501 - Sengkang to Marina Sq. Use the old route of 502 from
Orchard to Sengkang.
505 - Punggol to Clementi via KPE, ECP, MBS, Harbourfront
and Pasir Panjang (West Coast Highway).
507 - Hougang Central via Serangoon, KPE, ECP, MBS, Shenton Way,
Raffles Place, Orchard Rd and loop at Scotts Rd to return to
Hougang Central.
511 - Replace 97e. (Peak Hour service only)
512 - Replace 10e (Peak Hour service only)
513 - Repace 14e (Peak Hour service only)
515 - Repalce 196e (Peak Hour service only)
516 - Replace 174e (Peak Hour service only)
510 - Merge with 74e and 151e and amended to ply from Punggol,
Sengkang, Hougang, Serangoon North, CTE, PIE, Bukit Timah, Ngee Ann
Poly, NUS to Kent Ridge.
518 rename as 508.
502 and 506 remains the same.
I made edits:
501 - Sengkang to Tampines
Ctrl. See Route Details
Above
505 - Punggol to Clementi via KPE, ECP, MBS,
Harbourfront and Pasir Panjang (West Coast
Highway).Good!
507
- Hougang Central via Serangoon, KPE, ECP, MBS, Shenton Way,
Raffles Place, Orchard Rd and loop at Scotts Rd to return to
Hougang Central.
510
- Punggol, Sengkang, Hougang, Serangoon North, CTE, PIE,
Bukit Timah, Ngee Ann Poly, NUS to Kent Ridge.
518
withdraw.
502
and 506 remains the same.
