I am riding through Thu Thiem Tunnel going under the Saigon River from District 2 to District 1 on my Kawasaki Z300. I pass through this tunnel at least twice a week now. It is an interesting ride.
Going through the Thu Thiem Tunnel is the fastest way to get from District 1 / District 4 to District 2. I always go this route to Thao Diem. It can be packed. This video the traffic was actually quite good.