Excellent StreetsWiki use by Streetsblog regular ddartley, who added the pic you see below to the entry on 20 mph zones. From author Andy Hamilton:

In July 2008, the British Medical Association called for the
application of 20 mph zones throughout residential neighborhoods, not
just in the vicinity of schools, where they are commonly applied.
Stockport public health director Dr. Stephen Watkins stated that "a
child hit at 20mph has a 5% chance of dying compared to 50% at 30mph."
He noted the difference between a two mile journey at 20mph and a two
mile journey at 40 mph was just three minutes. "We are killing our
children for the sake of a couple of minutes," he said.

And since we’re in stimulus mode, here’s another excerpt:

The UK study of best traffic practices across the Europe and the U.K.
concluded that 20 mph streets also increased pedestrian activity,
bicycling, a sense of safety among residents, and economic activity. 
The study cited evidence from the city of Horsham, U.K., where 20 mph
speed limits, along with a bypass road, public arts, gardens, and other
pedestrian amenities have lead to the opening of new shops and
restaurants, and a higher level of overall economic activity.

Okay, I’m convinced. Let’s get some shovels in the ground on those ped safety plans.