Two companies took part in the construction of the subway system in New York City. The Interbourough Rapid Transit corporation and the Brooklyn-Manhattan Transit corporation set up dual contracts in order to work together to connect all areas of New York City including Brooklyn, Queens, the Bronx, and Manhattan.

There was much debate and discussion that went into who would put forth the investment to fund the building of the extensive subway system. The government decided, at first, to let the private sector be the driving force in constructing the subway. However, the two construction companies did not want to lay out an enormous amount of capital without knowing how long it would take to make the money back. In response, the city made the decision to issue bonds for individual investors who were willing to invest in the subway system.

Jobs flooded the market during the construction of the subway. Because technology was not as advanced as it was today, many engineers and architects had to make precise calculations without essential tools of today such as the calculator or computer. Since these tools weren't in existence, people who were able to do in such calculations were in such high demand that the wages were extremely high. In addition, construction workers such as driller helpers and timber handlers were paid an average wage. For instance, the median annual salary in the United States of America during `1915 was approximately $680 dollars, or around $2.00 per day. Engineers and architects were paid double that annual salary, or about $4.00 per day. To compare compensation with the cost of living, a hat cost $2 and a movie cost $.09.

Electricians were a newly found specialised work corps that dealt with wiring the subway systems. High voltage cables and large uncovered copper bars were used in the power houses and substations. They played a major role in electrifying the rails and complex systems that provided a structured pathway for electrons to flow, producing the movement of the trains.

Contractors brought in foremen, who were paid approximately $3.50-$4.00 per day, to lay down rails and to lead labourer crews. Rails were placed into wooden "sleepers" or "ties" with spikes or bolted down to the concrete floor. They had to design the rails with a curve and gradient so that the train would stay connected to the actual copper rails while moving, requiring these foreman to be specially skilled. Here is a link describing the education involved in becoming a foreman.
Foreman Training

Population density played a vital role in developing the subway system. In 1900, 80 percent of the population in New York City lived on 25 percent of the land. Sanitation became a major problem, and disease easily spread throughout the island. One reason the subway was built was to disperse the population in lower Manhattan to the surrounding areas. As a result, sanitation became better and people's health improved drastically. The standard of living and life expectancy grew significantly.
The speed of the subway was 400 percent faster than any other transit-technology during that time period. In addition, the cost was extremely cheap. For instance, a subway ticket, adjusted for inflation, costed between 84 cents and $1.18. In comparison, a horse and buggy costed around 20 dollars. Adjusted for inflation, the worth of the buggy was $1,388. That is around 4 years worth of subway tickets for a significantly slower way of transportation.