Introduction of StreetcarsEdit
Streetcars, also called trams, are a type of rail vehicles used for local public transit. The first streetcar system in the United States was introduced in the 1830s, which was horse-drawn, though in later decades most systems were electric streetcars powered by overhead wire.
The adaptation of streetcar systems improved the mobility of urban transportation, as population in cities grew and demand for short trips in urban areas increased since the early 19th century. Operated across and within certain downtown districts, this mode provides residents who did not own a wagon or carriage an option to easily travel easily to busiest areas and major business centres, either for employment or leisure, with streetcar services.
Streetcar systems are also more favourable in terms of its relative low cost and facilitation of defined urban environment. Compared to fixed light rails which travel to suburban areas, streetcars only operate on downtown streets, thus resulting in a much lower infrastructure cost and can be an ideal combination with fixed light rails. Passengers may take light rails to travel to downtown and use streetcars to explore within downtown areas.
Preceding Transportation ModesEdit
Before electric streetcars, horse-drawn omnibuses and cable cars were two of the main transportation modes in cities in the United States.
Horse-drawn omnibuses, or horsecars, which were used to transport small groups of passengers on defined routes, started running in New York City as early as in the 1820s. They began operating on a fixed rail system in New York City since 1832, which provided passengers with a stable speed, and soon other cities followed. However, due to its high cost (feeding and replacing horses) and poor regulation, this mode of transport started to fade in the late 1880s.
The cable cars were adopted around the above time to substitute horse-drawn omnibuses due to the necessity of reducing horses and ease of removing manure or snow from the tracks.  First introduced in San Francisco, California, they proved to be well suited for hilly routes; however, those cars could only operate at a constant speed and often broke down due to cable damage, causing traffic congestion easily. Beginning from the 1900s, electric streetcars almost replaced all cable cars in the United States. 
Technology of InventionEdit
The invention of electric streetcars was dependent on the preceding transportation modes such as horse-drawn omnibuses and electrical products.
The electrical grid invented by Thomas Edison was essential in enabling the invention of electric streetcars. The power, namely electricity, was transmitted via cables to the cars. The electric streetcars were also superior to the horsecars in other aspects, including using steel instead of wood to create the cars and twice the number of wheels (from 4 to 8 wheels), resulting in greater durability and much larger carrying capacity.
Initially, tracks were not compulsory to enable electric transportation, since later there were rubber-tired and electric trolley buses, though batteries were essential to allow electric transportation off the grid. Philadelphia was one of the first states in the United States to see the trial of battery trolleys (streetcars) in the early 1880s.
Early Market DevelopmentEdit
Tennessee is a South-eastern state of the United States, with major metropolitan areas being Nashville, Memphis, Knoxville and Chattanooga. The streetcar era of Tennessee started in the late 1870s when four of its major cities began adopting streetcars as a transportation mode. In the beginning, those were mostly intercity rails that were powered by mules.
In Nashville, the largest city in Tennessee, the first streetcar company was the South Nashville Street Railroad, which started operating mule-drawn cars in 1866. The city began running electric streetcars in the late 1880s by the Nashville Railway and Cumberland Electric Light & Power Company. A common characteristic of the market in Nashville was that all of the streetcar companies were privately owned since the introduction of streetcars there. In addition to those companies, the Nashville-Gallatin Interurban and the Nashville-Franklin Interurban companies also connected Nashville metropolitan area and its neighbouring places by street railways.
Similar to the change in Nashville, interurban transportation became readily accessible across the state, and more Tennessean residents, especially middle- or working-class groups, relocated their homes to suburban areas that were further from their employment locations or activity centres. This resulted in an emerging number of residential suburbs, which can be seen as an impact brought by transportation developments.
Lifecycle of Streetcars in TennesseeEdit
Policies played an impactful role on the development of streetcar systems since its introduction in Tennessee cities.
Initially, the municipal governments imposed little regulation on the private streetcar companies. However, in 1885, a 20-day strike took place in Memphis, the second largest city in the state, which was to achieve better income for streetcar workers, resulted in horse-drawn streetcars as the mass transit option in the region.
The success of this event triggered similar strikes in other cities in Tennessee. At the beginning, streetcar workers formed labour unions within their own areas. Soon after, they transformed the unions to local chapters of the Amalgamated Association of Street and Electric Railway Employees of America (A.A.S. & E.R.E. of A.), which was founded in 1892. This movement was needed, since in the early stages when transportation demand grew, the street transportation workers were not being treated quite well, however there was an increasing demand for them to transport more urban commuters.
The process of streetcars development in Tennessee mostly includes the introduction of horse-drawn cars and the transition to electric streetcars. A few cities such as Montgomery in Alabama and Richmond in Virginia first applied electric streetcars in 1886. Although not one of the firsts in the United States, both Nashville and Chattanooga soon converted to electric-powered streetcars a few years after, followed by Knoxville and Memphis in the 1890s.
The market of the electric streetcars was to some extent competitive due to the existence of various companies operating the businesses. The competitiveness resulted in negative impacts on society. For example, there were even physical conflicts once between two railway companies, taken place in 1897 in Knoxville, which required armed police to end the conflicts.
Nevertheless, electric streetcars continued to thrive, followed by the growth of the electricity production industry (i.e., public utility companies). The Chattanooga Electric Railway Company, the Electric Light Company in Chattanooga, and the Chattanooga Railway Rapid Transit Company, for instance, merged into one monopoly company, which is the Chattanooga Railway and Light Company in that city. This later evolved to the state-wide company - the Tennessee Power and Light Company (TEPCO), which also annexed the Nashville Railway and Light Company in the early 1900s.
Mature Phase and DeclineEdit
The streetcar systems in Tennessee reached a mature phase in the 1910s when their total length roughly reached 480 miles. Despite this, the post-growth phase of streetcars soon faced challenges from inevitable social and economic reasons. Various strikes took place in Tennessee’s major metropolitan areas, including Nashville, Memphis, Chattanooga, and Knoxville, in the early 20th century, which accelerated the replacement of streetcars by buses.
In addition to labour movements, other emerging transportation modes such as buses and private vehicles also played important roles in the demise of streetcars. Unlike (electric) streetcars, the operation of buses was simpler and less costly, as they did not need railways to be built and their service routes could be extended easily by constructing more bus stations. As for private vehicles, they provided citizens with the option and freedom of reaching a destination at their own pace and at any time. Therefore, starting from the 1930s, streetcar systems began to disappear in many regions in the United States, including Tennessee.
The life cycle of the overall streetcar system can be statistically analysed using observed historical data to determine the date and time for each of the above periods (birthing, growth, maturity, and decline). The raw data is extracted from the McGraw Transit Directory.
Selection of FormulaEdit
In this analysis, a three-parameter S-curve logistic function is used:
S(t) = Smax/[1+exp(-b(t-t0)]
S(t) = status measure (in this case it is the length of the streetcar system in miles), t = time (in years), t0 = inflection time (year when half of Smax is obtained), Smax = saturation status level (in this case it is the maximum length of the streetcar system recorded), b = a coefficient to be evaluated.
For ease of calculations, Smax can be named as K. Thus, the above formula becomes
S(t) = K/[1+exp(-b(t-t0)]
where the value of K varies from the maximum length of the streetcar system recorded to a manually determined maximum value.
Value of ParametersEdit
Approximately 20 different values were selected to perform a regression analysis for each hypothetical K. The final selected K-value was the one that achieved an R-squared result closest to 1, which is recorded in the following table alongside the values of other parameters of the S-curve function.
Substituting the above values for each parameter into the logistic function, the total track lengths (in miles) of all streetcar systems in Tennessee during 1894 and 1920 can be predicted.
The predicted and actual recorded data are tabulated in Table 2 below. The first column represents the year studied, the second column shows the data recorded in the McGraw Transit Directory, and the third column displays the predicted track lengths using the S-curve logistic function.
|Year||Total Track Length
|Predicted Track Length
The actual and predicted life cycle can thus be plotted and compared, as shown in Figure 1 below. The orange line refers to the actual streetcar length extracted from the McGraw Electric Railway Directory, whilst the blue line represents the predictions based on the actual data recorded.
Interpretation and Discussions of ModelEdit
Despite the predicted track lengths plotted (Figure 1) may look like a straight line, it in effect illustrates the approximate lifecycle of the streetcar systems in Tennessee.
From Figure 1, it can be seen that while the actual streetcar length fluctuated, the predicted model implies a positive relationship between year and the total streetcar length. An appropriate estimation is that the birthing phase was between 1894 and 1900, the growth phase lasted from 1900 to 1915, and the mature phase was during 1915 and 1920. There seemed no footprint of the decline phase in the predicted line.
The obtained results also demonstrate that they are similar to expectations. The streetcar mileage was increasing in real life and proved to be similar in predictions. However, the logistic model was not able to capture the most dramatic increases or declines (e.g., 1894 and around 1908 and 1912), and reached a lower value for the state-wide streetcar length in its peak period (1919). Nevertheless, the degree of inaccuracy could have been due to manual errors in data extraction or selection of the range of K values.
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