Elevators

Elevators permitted increases in height of buildings. In other words, density of people living per square km could go up because elevator permitted multiple floors and hence more people.

More people per square km means that a much larger number of people are using the same available space of roads to move around. Congestion.

What do you do?

a.) Wish that elevators were not invented and instead of vertical growth, the cities would grow horizontally and that instead of pockets of highly developed cities you had continuous stretches of several small cities with mid sized buildings and less congestion on the road due to lower population density.

b.) Wish that somebody invents private-individual flying cars quickly and the somebody also builds lanes of air traffic with different lanes for different levels (heights) paying different charges.