It does however they are not allowed speed camera's but they bypass this by siting on the bridges over the M6 with camera's and all private roads are subject to police control over speeding.
The speed limit is 70 mph as on all motorways. the police seem to have a fairly heavy presence on the road so be careful - it's often better to go via the public M6, you can ton it up and down there with few problems if you're a reckless idiot. Otherwise stick to the speed limit and avoid hospitals / mortuaries for a few more years.
It's NOT a private road. It's only privately operated under a 50 year concession from the government.
It has the same 70mph limit as other motorways except for the special case of the toll booths where the limit is much lower.