What is the safest type of pedal for all-weather city cycling? I've been commuting by bike for many years on different types of strapless platform pedal and have always been nervous about clip-in pedals.  Excluding any accidents caused by getting used to a new pedal, what type is safest for all-weather commuting in the city with traffic?

There are lots of different types of pedal:


Platform, no toe clip.
Platform with half toe clip, no straps.
Platform with toe clip and straps.
Clip in, of which there are many types.


It's not obvious to me which ones minimize the risk of causing an accident, or are the safest in the event of an accident.

Is it safer being clipped in to minimize risk of your foot slipping and causing a fall?  Or is it safer to be unclipped so that if you do fall you detach from your bike easily?

Is there much difference between the types of clip-in pedal?  There are road, SPD, and SPD "Click'R" (designed for easier release).

I can't find much online aside from anecdotes, so I'd really like to know if there has been a study done on this.
There is a lot of discussion about this topic (i.e. a lot of anecdotes) because pedals are a very personal matter (cf. LondonCyclist or Zach Gallardo). However, I think that you're over-thinking this in some way: The "safest" pedal is the pedal you're most used to and comfortable with. 

Consider, for example, a hypothetical case where clipless pedals have been "empirically proven" to be The Safest Pedal: You then buy some fancy clipless pedals and have no idea how to clip in and out and then you fall at a stop light and some car behind you runs over your leg.

Of course, this answer wouldn't be complete without me giving my own two cents (i.e. anecdote):


Since biking in the city (esp. "all-weather" cycling) involves dealing with a lot of unexpected obstacles/dangers/stops/etc., you should be able to quickly and confidently dismount your bike and re-mount with little hassle. Perhaps if you've got really good reflexes and you're very used to your own clipless setup then doing this with clipless pedals is no issue at all. However, there still may be some unexpected event which happens just a bit too quickly for you to properly unclip, and that split second which makes the difference between properly unclipping and falling may lead to problems like those described in the preceding paragraph.
Likewise, you should have good contact with the pedals. If you wear leather-soled shoes, then please make sure you have rubberized pedals: Slipping on your pedals can be very painful and this will happen if you're wearing leather soles and your pedals get wet.