This silver grey section of the mural shows normal daily life on Market Street in the mid 20th Century, as the traffic composition began to shift towards internal combustion vehicles.
The four sets of railway tracks on Market Street are now only two: the outer tracks were removed, and diesel buses were introduced, as the comprehensive railway network of San Francisco was dismantled, a market-driven policy shift that occurred in most major US cities around this time.
San Francisco did retain a few of its rail lines, and the mural shows the PCC-style railway cars that replaced the previous Market Street Railway design. These cars are still (or again) in use on MUNI's F line.
Some of the discontinued railway lines' electric infrastructure was kept for the operation of electric buses.