Who sets Connecticut’s speed limits anyway?

Crawling along I-95 the other day in the usual bumper-to-bumper traffic, I snickered when I noticed the “Speed Limit 55” sign alongside the highway. I wish! Of course, when the highway is not jammed, speeds are more like 70 mph, with the legal limit, unfortunately, rarely being enforced. Which got me thinking: who sets speed limits on our highways and by what criteria?