The impact of speeding:
20 mph - in a car accident involving a pedestrian at this speed there is a one in 40 chance the pedestrian will be killed.
30 mph - in a car accident involving a pedestrian at this speed there is a one in five chance the pedestrian will be killed.
35 mph - in a car accident involving a pedestrian at this speed there is a one in two chance the pedestrian will be killed.
40 mph - in a car accident involving a pedestrian at this speed there is a nine in ten chance the pedestrian will be killed.
Most car accidents resulting in a fatality happen on A and B roads.
If you don't know the speed limit of the road you are on, the clues are there:
If there are street lamps, the speed limit is 30mph, unless there are reminders.
If there are no street lamps, the speed limit is the national speed limit, unless there are reminders (60mph on a single carriageway or 70mph on a dual carriageway or motorway).
Any other speed limit (20, 40 or 50mph) will have regular signs reminding you what it is.
I only know all of this as I was recently caught doing 35mph in a 30mph zone and did a speed awareness course. It has worked on me!