A couple things I noted:
There are three "soft shoulder" signs. No "Stop ahead" sign.
Shoulder on Google looks soupy. Dropping a wheel in it could easily cause an over-correction yaw.
The sign is as the road intersects while curving right, likely for a 90 degree corner, visibility reasons. Hard to see, and 60mph is 88ft/sec so there's little time to react. Trying to turn left is my guess at the driver's actions.
Curb is clearly busted in one pic, a large curved section, as well as undercarriage scraping. That takes an enormous amount of force, especially from a 3200lb car. It also takes a LOT of forward momentum away. Having hit a median, as a passenger, in a far larger Caprice patrol car, even at a lesser speed, I can attest. I'd envision it was a heck of a boom, and probable spark show. Really short wall, and all...
Black box data retrieval laws vary by state, and I would just about bet that fatal accidents are one time an investigator would prefer to have a signed warrant. Adding the possibility of negligence on the part of LE, I'd loan the judge my good pen.
Speedometer needles are less likely to freeze, than to spring ahead and impact the micro-dust on the dial, leaving a witness mark. Pre-black-box investigating. With the time lapse, seeing any skid/yaw marks would be tough.
Google view shows far less vegetation than the pics. Spring in the area, especially adjacent to marsh, is pretty wild for growth. Small car, well off the road, at night, in the underbrush, could be easy to miss. Day shift, different Officers, dispatch, supervisors, rare to follow up on that, unfortunately.
I had a 3AM crash scene where it appeared that a 70's Olds 88 fell from the sky and landed in the middle lane of an expressway, dead-stop, with a bunch of dirt around it, scaring the Corolla driver coming behind bad enough he hit the divider, crossed 3 lanes, hit a pole, knocked the light down. LSS, it was less alien abduction than Duke Boys, as he'd missed a ramp turn, ditched, cleared a guardrail two tiers up, clipped a light pole, causing an in-flight 90 degree turn, hit sideways, flipped, fell the last tier landing on it's tires. Sober. Distracted by eating mom's spaghetti on the way home from laundry night.
Regardless, the girls were found, families can begin to heal, and we'll all move on to the next mystery.