The M602 starts at the M60/M62 intersection (jcn 1) in the Irwell Valley, west of Manchester. It runs alongside the A57 and ends at jcn 3, which is the A57 in south Salford.
Any Urban Motorway has an importance which is sometimes hard to define. One aspect is the effective link to all points west via the M62 to Liverpool and beyond. Thus, looking at Central Manchester as a whole, the A5103 takes traffic south to the M56, the A57 to the east, A34 and A6 to the south east; with the M602 taking the western link.
The M602 appears (like many Urban Motorways) to have been carved out of the land, as it is much lower than most of the surrounding area, giving no views whatsoever. It is very easy when travelling eastbound on the M62 to end up on the M602 accidentally, due to the nature of the M60/M62/M602 intersection, see below for info on that.
The M602 has never been renumbered, merely extended to Salford Quays over a period of time.
My first instance of the M602 was of my old man ending up on it after taking a wrong turn at the M62/M60/M602 intersection, mainly due to the fact that the M62 (in those days, now its the M60) was reached by turning left, and to go straight ahead was to end up in Salford, which is what occurred. I loved it of course, Urban Motorways are a particular delicacy. Years later, after picking up a car at Salford Quays, late on a friday afternoon (oh no), I used the M602 to get to the (then) M62 to get back to Goole. It was fun until we hit the big intersection, then it was stop-start-stop until after the M61 jcn. Fab little motorway.