My old city rowhouse neighborhood (built 1948, gas heat, hot water, cooking, clothes dryer) had about 70 houses off of one transformer. My present complex (built 1970 and all electric) has one transformer per building serving 14 units.
In the 1948 neighborhood, many homes were rewired from 60 amp to 100 amp service in the 1960s and 1970s. Around 1980 the electric company strung new cables.
I wonder how much the power company had to add to their neighborhood distribution system to accomodate increased needs. In 1948 home air conditoners were rare, by the 1970s almost every house had at least one large window unit (required 220 service). (My family had an early RCA window air conditioner from about 1950 that lasted for 30 years. When it was running we couldn't use other appliances without blowing a fuse).
Likewise, I wonder how much extra capacity was needed for telephone service. I believe everyone in the neighborhood had a phone in 1948, but many had party lines. Into the 1970s party lines were gone and some families had two lines. Into the 1990s multiple lines would be common for computer/home fax/home business use.
(I would love to find any planning documents for the neighborhood. Land was reserved for schools. Streets were usually continuation of the existing grid, but individual blocks were built by many different developers, large and small. I believe the city and private utilities were ready in advance. The new schools built with the neighborhood did suffer from overcrowding from the baby boom. Today the school population is a lot lower than my day.
The power cables were mounted on the back wall of the wall houses near the second story. The telephone cable pipe (also redone around 1980 from lead to heavy rubber) was around the first floor. Around 1990 cable TV came and was hung still lower.