The steep terrain means there are lots of tunnels. Some of these are ancient and narrow with terrible sight lines. Occasionally, you’ll see a sign that says you should honk before entering because even the authorities have recognized that no one can see the traffic on the other side. That of course also means you should be listening for a horn before entering a tunnel.
The wider tunnels such as Fort Pitt, Liberty, and Squirrel Hill are two lanes wide, with the lanes separated by double white lines. You cannot change lanes in these tunnels.
The no-lane-change rule is particularly problematic with the Liberty Tunnel.