Transportation Deployment Casebook/Motorcycles
In transportation planning, analyzing the development of a mode can help predict future implications. There are many motorcycle safety concerns that are debated, so considering the growth of motorcycle use in the United States is worthwhile.
Motorcycles have been around since the late 1800's, and have grown into an important transportation method that can be a primary means of travel for people in many countries. However, in the Untied States, motorcycles almost always serve as an alternative method that shifts the focus to the pleasure of travel from the extra freedom provided. This does not mean that motorcycles are not used for normal everyday trips, but generally they are not nearly as important as cars in the United States (motorcycles are not able to transport much), and not everyone has the ability or desire to learn to ride a motorcycle. Furthermore, states require additional license certification to operate a motorcycle, creating an additional barrier to use. Despite the hinderances, development of motorcycle use has been possible because motorcycles are able to use the existing vehicle infrastructure without additional investments while proving a much different travel experience. Just like in automobiles, motorcycles continue to improve and incorporate new technologies (such as fuel injection).
For transportation issues, only street legal motorcycles are of concern, so racing and off road motorcycles are not considered, while dual sport motorcycles (enduros) are included. The definition of a motorcycle in the United States varies by state (and is also applicable to other issues such as helmet laws), but e-bikes and generally small mopeds (having an engine sizes less than 50 cc and maximum speed around 45 kph typically) are not considered motorcycles, while larger scooters (with engine sizes greater than 70 cc and capable of traveling above 45 kph) are classified as motorcycles. This means that smaller mopeds incapable of traveling on higher speed roads (and therefore only suited to short trips) are not grouped with motorcycles. However, smaller mopeds provide better gas mileage at the cost of lower range, but motorcycles still have nearly twice as high of fuel economy as passenger vehicles. Motorcycles are not often publicized as some of the best fuel efficient alternatives, and this is not surprising considering the safety concerns surrounding motorcycle use in the United States. Furthermore, usefulness is greatly affected by weather, so motorcycles can not be used for portions of the year in many parts of the country or during storms.
To look at adaptation over time, the number of registered motorcycles in the United States for a given year is used to determine ownership and use. The yearly data for registered motorcycles goes back to 1914 and is currently available up through 2010, providing a large time period for analysis.
Life Cycle Model
An S-curve model is used to model the life cycle of motorcycle ownership, the equation:
where is the year, is the inflection year, is the saturation level, is a coefficient, and is the predicted number of registered motorcycles for the year.
The coefficient and saturation level are determined based on a best fit to the recored data. The resulting S-curve generally displays periods of birth, growth, and maturity. However, one curve does not fit the observed data well at all. Therefore, multiple S-curve segments were used to fit different periods of development, and the figure also shows how the continuation of trends differs from the recorded number of motorcycles.
The first period involved growth that lasted to approximately 1985. From 1913 to 1945 there was very little change in the low amount of motorcycles, showing that motorcycles were not yet a developed method. From 1945 to 1962 corresponds to a period birth, followed by rapid growth until 1974. After this there is a slow down of growth and a peak that shows maturity, however, this is a rapid change is the trend. The S-curve fitted to this section has a saturation quantity of 11 million motorcycles, and the inflection year would be 1981. However, a peak occurs instead around the fitted inflection year, followed by a steady decrease in registered motorcycles that follows a trend to a low saturation volume of 3.3 million, with a maturity phase in the decrease visible in the figure between 1993 and 1997. Around 1998 the trend quickly changes once again, and the number of motorcycles in the United States increases rapidly, following an almost linear path that the fitted S-curve predicts would reach 23 million motorcycles (more than double the previous value) with the trend starting to slow by 2016 (inflection year). In this case there is very little discernible birth phase before the new growth phase starts. The table below summarizes the parameters of the three curves.
*Here K is still used in the S(t) equation but represents the range of decrease to the low saturation value. Another parameter was then added to the equation to estimate the low saturation level of 3,300,000 registered motorcycles.
The number of motorcycles registered seems to grow rapidly at times. This may be because motorcycles in the United States are not the most essential expenditure when fluctuations occur. Furthermore, sales of motorcycles tend to fluctuate greatly, as there was a high in 1980, then sales decreased to a low in 1995, then increased to a larger high in 2005, and then decreased again to another low currently as of 2010.  Even though major fluctuations exist in motorcycle ownership in the United States, a general trend towards more registered motorcycles is visible, and the S-curve model predicts that this period of growth will continue for many years, unless another rapid shift interups growth. The available sales data indicates that another change will most likely occur unless motorcycles sales start to grow (the rate of junked motorcycles also has the opposite effect too). Because of the expendability of motorcycles in the United States, predicting ownership trends accurately will likely be more difficult than exploring other transportation methods.
- Morris, C. Motorcycle Trends in the United States. Bureau of Transportation Statistics, May 2009. 
- “Motorcycle and Bicycle Helmet Use Laws.” Highway Loss Data Institute. Insurance Institute For Highway Safety, December 2012.
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- U.S. Sales or Deliveries of New Aircraft, Vehicles, Vessels, and Other Conveyances. Bureau of Transportation Statistics. 
- Motorcycle and Scooter Sales Get Pumped Up in First Half of 2006. Motorcycle Industry Council, 20 July 2006.