The commonly quoted survival rate of a pedestrian hit by a car can be found on the World Health Organisation website.
"....pedestrians have been shown to have a 90% chance of survival when struck by a car travelling at 30 km/h or below, but less than 50% chance of surviving an impact at 45 km/h. Pedestrians have almost no chance of surviving an impact at 80 km/hr."
For those more familiar with miles: 30km = 18.6 miles and 45km = 24.8 miles and 80km = 49.7. Rounded up these then give a close to 90% chance of survival when hit by a car travelling at 20 miles per hour, less than 50% chance at 30 miles per hour and almost no chance at 50 miles per hour.
In recognition of these statistics some cities are putting slow zones in place particularly around schools that keep the speed limit down to 20 miles an hour through enforcement and traffic taming designs and devices. Here's a link about some in New York including a mention that in London "the introduction of 20 mph zones was associated with a 42% reduction in injuries, as compared to untreated areas. In the UK, average speeds in 20 mph zones were reduced by 9 mph".
And now the good news!
The National Highway Traffic Safety Administration, part of the US Department of Transportation published a National Pedestrian Crash Report in June 2008 containing some wonderful statistics that show that the risk of being hit and killed is low. One of the key findings was that "a pedestrian crash death occurred every 70 million miles walked". I like those odds!
I'll leave you with a couple of questions I asked my husband a while ago:
"If you knew that today, while you are out driving around, you would without a shadow of a doubt save a life by keeping your speed at 20 miles and hour or less, would you do it?"
Second question: "Would you travel at no more than 20 miles an hour on city streets consistently from now on knowing that if you happen to have a crash with a pedestrian it could save a life?"