Are there any data on the safety rate of gliders vs single-engine GA aircraft?
I had three days to burn so I took a look.) 

Comparative data was very difficult to find beyond accident counts, so determining relative safety is problematic. No one that I could find tracks or estimates the number of flights/hours for gliders, even the Soaring Society of America, so this is all interesting but essentially meaningless. Even if such data existed, the difference in use models would cause problems making a fair comparison. So now that I've told you this was a waste of my time to compile, I will make you waste your time to read.

If you could extrapolate single mode pilot certificate counts to a common usage basis, flying a glider is 2.5x safer than flying an airplane, but of course you can't.

NTSB accident count for 2017 shows 56x more airplane accidents and 90x more fatal airplane accidents than glider accidents.


271 fatal and 972 non-fatal GA airplane accidents, total 1243
3 fatal and 19 non-fatal GA glider accidents, total 22


US Civil Airmen Statistics shows 18x more airplane only pilots than glider only pilots, with 40-80% of both numbers muddied by multiple certificate pilots.


14k registered glider only pilots
24k registered glider pilots with multiple certificates
260k registered airplane only pilots, excluding ATPs
190k registered airplane pilots with multiple certificates, excluding ATPs


AOPA had a report for 2009 for all general aviation where the accident rate per 100k hrs is 7.2, and a fatal rate for the same of 1.33.