In places it's remarkably fast and quiet, especially its northernmost stretch which has three lanes running straight and flat across the countryside, making the M18 is one of the police's favourite motorways for speed patrols. It's also surprisingly well-endowed with lanes and motorway connections for such a short and remote route: it is, after all, a shortcut to East Yorkshire from the south and isn't too heavily used.
The only exception is around Doncaster, the busiest section and for reasons that are hard to explain also the narrowest. Two lanes now struggle to cope with rush hour traffic, which promptly evaporates when the road widens out at either end of the bottleneck.
For a little while, the M18 used to have a short spur towards Scunthorpe called the A18(M). The slightly strange phasing of motorway construction projects around Hatfield - which saw a series of very short sections built one after the other - meant that for a few years in the 1970s the whole area was in a constant state of transition. It was very nearly a temporary road, and whether it was meant to last any length of time before being consumed by the M180 isn't known. It was only ever applied to the link between the M18 and the A18, and is now underneath the eastbound exit from the M180.