What a feat of engineering this road is clinging to the cliffs and passing through numerous tunnels. There are scare stories about the road but it’s 2 full lanes wide so unless you’re driving a bus or truck it’s fine. Just give way to any buses or trucks if you need to because they’re not going to stop for you.
If you’re cycling you need to be aware that there are lots of tunnels and that there is no hard shoulder for you so if the roads busy you’ll have frustrated traffic right behind you trying to pass. You’ll need a rear light to be seen although most tunnels are lit. There’s a long tunnel before Dongyue, don’t ride it.