# Transportation Deployment Casebook/History of the Automobile: Ownership per Household in U.S.
## Technology Description

The automobile is a four-wheeled vehicle used for transporting passengers with its own internal combustion engine. Although latest automobiles may be completely electric or use a hybrid power of both electricity of gasoline, the majority of them generate power solely from burning gasoline. It is usually capable of running at around 80 mph nowadays, subject to road conditions and speed limit.
As one of the major transportation modes, automobiles are suitable for traveling at a distance beyond the reach of walking and biking. They are often compared with public transit including buses, trains and subways. The most significant advantage of automobiles over public transit is its high level of freedom. Automobile drivers are not constrained by fixed timetables, bus stops, and train stations. In contrast, they can stop and go wherever whenever they want. They can avoid the frustration of waiting. The freedom and better mobility create more job opportunities and recreational travelling for the owners. Automobiles also provide more comfortable ride than the public transit with private space and radios while public transit can be very crowded thus uncomfortable during rush hours. There are disadvantages associated with automobile as well. Automobile drivers may experience frustrations with congestion while subway and train riders are not affected. Public transit also saves the time and energy in searching for parking spots. In addition, automobiles usually raise greater safety and environmental concerns.
With its high upfront capital cost and continuing spending in fuel, repair, and maintenance, automobiles are much more expensive than public transit. From the U.S. Bureau of Transportation Statistics data for the year 2000, transportation accounts for 19%, or $7,417 of the entire average household expenditure. Of that, private vehicles consume $6,990 (94%)($1,291 in gasoline and $3,418 in vehicle purchases). The data not only show the high cost associated with purchasing and owning an automobile but also show the predominant place automobile is in people's daily life. The target market of it aims at middle and upper class who can afford a car and those who have no access to public transit but live far away from their work or school. In terms of travel distance, extremely short distance that can be done by walking or biking does not require an automobile. Despite the fact that people do drive long distance for recreational purpose from time to time, airplanes provide a better service regarding speed and comfort at this realm. Therefore, automobiles serve somewhere in between, which is a range of distance that is too far to walk and too short to fly.

## Identification of Developmental Phases
### Method

In order to find the S-curve and developmental phases for automobiles in the United States, data of the number of private vehicles in the United States were obtained from the Federal Highway Administration, U.S. Department of Transportation's document “Highway Statistic Summary to 1995”. Yet since the population is growing in the United States, the increase in vehicle ownership in the States does not tell much about the development phases of this transportation mode. Thus, data of the population of the United States were also obtained from the U.S. Census Bureau for the period from 1925 to 1995. With the assumption that the average number of people per household is four, the data for average vehicle ownership per household (VOH) were obtained by dividing the total number of private vehicles by the population of the United States each year multiplied by a factor of four. And the VOH vs. year were plotted. To fit the real data, the following equation was used:
    S(t) = K/[1+exp(-b(t-t0)]
where
    K: saturation level, which in this case, highest average number of vehicles owned per household in the United States
    b: adjustment parameter
    t0: the time when the growth rate reaches maximum and starts to slow down
The three parameters were adjusted to fit the existing plot as good as possible. The linear regression analysis was utilized. Because the guess function is not linear, it was rewritten into a linear form. The derivation is shown below:
* S(t) = K/[1+exp(-b(t-t0)]
* 1+exp(-b(t-t0))=K/S(t)
* exp(-b(t-t0)=K/S(t) – 1
* LN(EXP(-b(t-t0)))=LN(K/S(t)-1)
* -b(t-t0)=LN(K/S(t) - 1)
In a linear format, we have:
* Y=LN(VOH/(K-VOH))=bt-bt0.
Several different K values were used to carry out a set regression analysis aiming to get R as close to 1 as possible. b is the X variable 1 value given in the regression analysis report. And the value of t0 can be calculated by dividing the intercept value by minus b. The tool Solver in Microsoft Excel was also used to minimize sum of square differences between the predicted and actual values to obtain the optimal parameters. The results were same.

### Data

Table 1: Population and the Number of Vehicles in the U.S. (1925–1995) :
| Year | Population | Total Vehicle | Vehicle per person | Vehicle per Household* |
| 1925 | 115,829,000 | 17,439,701 | 0.150564202 | 0.60225681 |
| 1926 | 117,397,000 | 19,220,885 | 0.163725521 | 0.654902084 |
| 1927 | 119,035,000 | 20,142,120 | 0.169211744 | 0.676846978 |
| 1928 | 120,509,000 | 21,308,159 | 0.176817989 | 0.707271955 |
| 1929 | 121,767,000 | 23,060,421 | 0.189381532 | 0.757526128 |
| 1930 | 123,076,741 | 22,972,745 | 0.186653829 | 0.746615317 |
| 1931 | 124,039,648 | 22,330,402 | 0.180026325 | 0.720105301 |
| 1932 | 124,840,471 | 20,632,357 | 0.165269779 | 0.661079114 |
| 1933 | 125,578,763 | 20,586,284 | 0.163931253 | 0.655725013 |
| 1934 | 126,373,773 | 21,472,078 | 0.16990929 | 0.679637159 |
| 1935 | 127,250,232 | 22,494,884 | 0.176776762 | 0.707107049 |
| 1936 | 128,053,180 | 24,108,236 | 0.188267375 | 0.753069498 |
| 1937 | 128,824,829 | 25,390,773 | 0.197095336 | 0.788381345 |
| 1938 | 129,824,939 | 25,167,030 | 0.193853586 | 0.775414345 |
| 1939 | 130,879,718 | 26,139,526 | 0.199721748 | 0.79888699 |
| 1940 | 132,122,446 | 27,372,397 | 0.207174465 | 0.828697858 |
| 1941 | 133,402,471 | 29,524,101 | 0.221315998 | 0.885263992 |
| 1942 | 134,859,553 | 27,868,746 | 0.206650144 | 0.826600575 |
| 1943 | 136,739,353 | 25,912,730 | 0.189504553 | 0.758018213 |
| 1944 | 138,397,345 | 25,466,331 | 0.184008812 | 0.736035247 |
| 1945 | 139,928,165 | 25,694,926 | 0.183629407 | 0.734517629 |
| 1946 | 141,388,566 | 28,103,880 | 0.198770529 | 0.795082114 |
| 1947 | 144,126,071 | 30,722,855 | 0.213166534 | 0.852666136 |
| 1948 | 146,631,302 | 33,218,261 | 0.226542768 | 0.906171071 |
| 1949 | 149,188,130 | 36,316,972 | 0.243430707 | 0.973722829 |
| 1950 | 152,271,417 | 40,190,632 | 0.26394075 | 1.055763 |
| 1951 | 154,877,889 | 42,530,935 | 0.27460947 | 1.09843788 |
| 1952 | 157,552,740 | 43,659,062 | 0.277107602 | 1.108430409 |
| 1953 | 160,184,192 | 46,258,306 | 0.288781967 | 1.155127867 |
| 1954 | 163,025,854 | 48,293,457 | 0.296231891 | 1.184927564 |
| 1955 | 165,931,202 | 51,960,532 | 0.313145035 | 1.252580139 |
| 1956 | 168,903,031 | 54,013,753 | 0.319791496 | 1.279165985 |
| 1957 | 171,984,130 | 55,704,636 | 0.323894048 | 1.295576191 |
| 1958 | 174,881,904 | 56,664,435 | 0.324015428 | 1.296061713 |
| 1959 | 177,829,628 | 59,213,993 | 0.332981594 | 1.331926376 |
| 1960 | 180,671,158 | 61,419,948 | 0.339954361 | 1.359817442 |
| 1961 | 183,691,481 | 63,156,647 | 0.34381914 | 1.37527656 |
| 1962 | 186,537,737 | 65,801,946 | 0.35275407 | 1.411016281 |
| 1963 | 189,241,798 | 68,738,853 | 0.363232931 | 1.452931725 |
| 1964 | 191,888,791 | 71,675,906 | 0.373528363 | 1.494113452 |
| 1965 | 194,302,963 | 74,909,365 | 0.385528681 | 1.542114723 |
| 1966 | 196,560,338 | 77,752,487 | 0.395565493 | 1.582261972 |
| 1967 | 198,712,056 | 79,998,511 | 0.40258509 | 1.610340361 |
| 1968 | 200,706,052 | 83,189,008 | 0.414481811 | 1.657927246 |
| 1969 | 202,676,946 | 86,414,179 | 0.426364126 | 1.705456505 |
| 1970 | 205,052,174 | 88,775,294 | 0.432940028 | 1.731760113 |
| 1971 | 207,660,677 | 92,221,291 | 0.444096072 | 1.776384289 |
| 1972 | 209,896,021 | 96,553,073 | 0.460004304 | 1.840017215 |
| 1973 | 211,908,788 | 101,412,229 | 0.478565471 | 1.914261885 |
| 1974 | 213,853,928 | 104,228,856 | 0.487383407 | 1.949533627 |
| 1975 | 215,973,199 | 106,064,579 | 0.491100653 | 1.964402611 |
| 1976 | 218,035,164 | 109,513,168 | 0.502272964 | 2.009091855 |
| 1977 | 220,239,425 | 111,566,433 | 0.506568853 | 2.026275414 |
| 1978 | 222,584,545 | 115,824,891 | 0.520363581 | 2.081454326 |
| 1979 | 225,055,487 | 117,615,166 | 0.522605192 | 2.090420768 |
| 1980 | 227,224,681 | 120,743,495 | 0.531383714 | 2.125534858 |
| 1981 | 229,465,714 | 122,241,488 | 0.532722235 | 2.13088894 |
| 1982 | 231,664,458 | 122,767,091 | 0.529934942 | 2.119739766 |
| 1983 | 233,791,994 | 125,489,216 | 0.536755831 | 2.147023324 |
| 1984 | 235,824,902 | 127,161,802 | 0.539221265 | 2.15688506 |
| 1985 | 237,923,795 | 126,425,301 | 0.531368882 | 2.125475529 |
| 1986 | 240,132,887 | 128,519,551 | 0.53520179 | 2.140807161 |
| 1987 | 242,288,918 | 129,980,193 | 0.53646776 | 2.145871038 |
| 1988 | 244,498,982 | 132,343,515 | 0.541284524 | 2.165138095 |
| 1989 | 246,819,230 | 133,009,695 | 0.538895187 | 2.155580746 |
| 1990 | 249,438,712 | 132,164,330 | 0.529846907 | 2.119387627 |
| 1991 | 252,127,402 | 126,764,419 | 0.502779222 | 2.011116888 |
| 1992 | 254,994,517 | 125,087,687 | 0.490550497 | 1.962201987 |
| 1993 | 257,746,103 | 125,843,591 | 0.488246338 | 1.952985353 |
| 1994 | 260,289,237 | 126,396,989 | 0.485602057 | 1.94240823 |
| 1995 | 262,764,948 | 126,899,713 | 0.482940034 | 1.931760137 |
* Data taken from the USDOT Federal Highway Administration and U.S. Census Bureau
* Assume the average number of people per household is four.

### Results

Table 2: Predicted Value and Procedure :
| S(t) = K/[1+exp(-b(t-t0)] | Difference | Diff^2 | K=2.54 |
| 0.511096303 | 0.091160507 | 0.008310238 | -1.169006906 |
| 0.530386832 | 0.124515252 | 0.015504048 | -1.057672384 |
| 0.550208083 | 0.126638895 | 0.01603741 | -1.013008345 |
| 0.570559854 | 0.136712101 | 0.018690199 | -0.952580781 |
| 0.591440752 | 0.166085376 | 0.027584352 | -0.856146894 |
| 0.612848131 | 0.133767186 | 0.01789366 | -0.876754623 |
| 0.63477804 | 0.085327261 | 0.007280741 | -0.927574699 |
| 0.65722517 | 0.003853945 | 1.48529E-05 | -1.045003839 |
| 0.680182811 | -0.024457798 | 0.000598184 | -1.05598015 |
| 0.703642811 | -0.024005653 | 0.000576271 | -1.007396458 |
| 0.727595544 | -0.020488495 | 0.000419778 | -0.952903901 |
| 0.752029882 | 0.001039616 | 1.0808E-06 | -0.864543418 |
| 0.776933183 | 0.011448163 | 0.00013106 | -0.798768979 |
| 0.802291274 | -0.026876929 | 0.000722369 | -0.822725624 |
| 0.828088457 | -0.029201467 | 0.000852726 | -0.779518406 |
| 0.854307518 | -0.02560966 | 0.000655855 | -0.725620255 |
| 0.880929744 | 0.004334248 | 1.87857E-05 | -0.625992826 |
| 0.907934953 | -0.081334378 | 0.006615281 | -0.729378509 |
| 0.935301537 | -0.177283324 | 0.031429377 | -0.855221526 |
| 0.963006511 | -0.226971265 | 0.051515955 | -0.896906254 |
| 0.991025577 | -0.256507948 | 0.065796328 | -0.899810807 |
| 1.019333192 | -0.224251078 | 0.050288546 | -0.786474435 |
| 1.047902652 | -0.195236516 | 0.038117297 | -0.683009547 |
| 1.076706184 | -0.170535113 | 0.029082225 | -0.589941592 |
| 1.105715047 | -0.131992218 | 0.017421946 | -0.475839333 |
| 1.13489964 | -0.07913664 | 0.006262608 | -0.341174416 |
| 1.164229618 | -0.065791738 | 0.004328553 | -0.272391481 |
| 1.193674017 | -0.085243609 | 0.007266473 | -0.256383561 |
| 1.223201383 | -0.068073516 | 0.004634004 | -0.181972617 |
| 1.252779901 | -0.067852337 | 0.00460394 | -0.134761776 |
| 1.282377537 | -0.029797399 | 0.000887885 | -0.028053999 |
| 1.311962175 | -0.03279619 | 0.00107559 | 0.01380239 |
| 1.341501751 | -0.04592556 | 0.002109157 | 0.039642092 |
| 1.370964401 | -0.074902689 | 0.005610413 | 0.040406759 |
| 1.400318591 | -0.068392215 | 0.004677495 | 0.096939157 |
| 1.429533253 | -0.06971581 | 0.004860294 | 0.14100563 |
| 1.458577914 | -0.083301355 | 0.006939116 | 0.165486521 |
| 1.487422823 | -0.076406542 | 0.00583796 | 0.222286026 |
| 1.516039066 | -0.063107341 | 0.003982537 | 0.289365431 |
| 1.544398677 | -0.050285225 | 0.002528604 | 0.355905707 |
| 1.572474742 | -0.030360019 | 0.000921731 | 0.434472555 |
| 1.60024149 | -0.017979518 | 0.000323263 | 0.501203885 |
| 1.627674379 | -0.017334018 | 0.000300468 | 0.548524604 |
| 1.654750169 | 0.003177076 | 1.00938E-05 | 0.630144966 |
| 1.681446985 | 0.02400952 | 0.000576457 | 0.713747832 |
| 1.70774437 | 0.024015743 | 0.000576756 | 0.76104819 |
| 1.73362333 | 0.042760959 | 0.0018285 | 0.843226512 |
| 1.759066361 | 0.080950854 | 0.006553041 | 0.965335503 |
| 1.784057476 | 0.130204409 | 0.016953188 | 1.116881437 |
| 1.808582212 | 0.140951415 | 0.019867301 | 1.193082704 |
| 1.832627634 | 0.131774976 | 0.017364644 | 1.226150106 |
| 1.856182328 | 0.152909526 | 0.023381323 | 1.329347657 |
| 1.879236383 | 0.14703903 | 0.021620476 | 1.370715729 |
| 1.901781369 | 0.179672957 | 0.032282371 | 1.511024084 |
| 1.923810302 | 0.166610466 | 0.027759047 | 1.535035773 |
| 1.945317611 | 0.180217246 | 0.032478256 | 1.632867054 |
| 1.96629909 | 0.16458985 | 0.027089819 | 1.648359896 |
| 1.986751848 | 0.132987918 | 0.017685786 | 1.616278155 |
| 2.006674257 | 0.140349067 | 0.019697861 | 1.696059545 |
| 2.026065894 | 0.130819167 | 0.017113654 | 1.726005313 |
| 2.044927479 | 0.08054805 | 0.006487988 | 1.632696281 |
| 2.063260812 | 0.077546349 | 0.006013436 | 1.6774973 |
| 2.081068708 | 0.06480233 | 0.004199342 | 1.692600726 |
| 2.098354931 | 0.066783164 | 0.004459991 | 1.751555974 |
| 2.115124127 | 0.04045662 | 0.001636738 | 1.722008742 |
| 2.131381755 | -0.011994128 | 0.000143859 | 1.615276049 |
| 2.147134026 | -0.136017139 | 0.018500662 | 1.334170913 |
| 2.162387832 | -0.200185844 | 0.040074372 | 1.221218588 |
| 2.177150682 | -0.224165329 | 0.050250095 | 1.200706659 |
| 2.191430643 | -0.249022414 | 0.062012163 | 1.177441994 |
| 2.205236277 | -0.27347614 | 0.074789199 | 1.154306897 |
| | Sum | 1.024115074 | |
Table 3: Optimal Parameter Values :
| Variable | Value |
| K | 2.540797708 |
| b | 0.046598155 |
| tnought | 1954.595291 |
| b*tnought | 91.08053387 |
Table 4: Regression Results Summary :
| Multiple R | 0.963422775 | | | | |
| R Square | 0.928183443 | | | | |
| Adjusted R Square | 0.927142623 | | | | |
| Standard Error | 0.269459424 | | | | |
| Observations | 71 | | | | |
| | df | SS | MS | F | Significance F |
| Regression | 1 | 64.750791 | 64.750791 | 891.7812249 | 3.43875E-41 |
| Residual | 69 | 5.009978293 | 0.072608381 | | |
| Total | 70 | 69.76076929 | | | |
| | Coefficients | Standard Error | t Stat | P-value | |
| Intercept | -91.08053387 | 3.058576644 | -29.7787319 | 4.11903E-41 | |
| X Variable 1 | 0.046598155 | 0.001560413 | 29.86270626 | 3.43875E-41 | |
| | Lower 95% | Upper 95% | Lower 95.0% | Upper 95.0% | |
| Intercept | -97.18222725 | -84.9788405 | -97.18222725 | -84.9788405 | |
| X Variable 1 | 0.043485216 | 0.049711093 | 0.043485216 | 0.049711093 | |
* Figure 1: Vehicles per Household vs. Year
The K value is approximately 2.54 when the error is minimized, which means that the model estimate the maximum number of vehicles per household in the United States will not exceed 2.54. t0 is about 1955, representing the year at which the growth rate reached maximum and started to decline. With the optimal parameters, if the prediction line is extended into the future, VOH will reach the maximum around the year of 2100.

## Analysis
### Before the Advent of Automobile

Prior to the advent of the automobile, people took animal powers for granted for short-distance travel. Shorter trips were made via horse driven wagons and carriages. The most important disadvantage of such travel mode is that it is very slow. Horses need rest, thus making long endured trip impossible. Although trains are much faster, railroads primarily only go through and stop at large cities. They don't offer convenient service to go to smaller towns and take shorter trips.
The slow speed of the existing carriage was obviously constricted by the limitation of horses’ strength. With the rise of the steam engines by James Watt, engineers have attempted to apply the technology to small vehicles as early as 1769, though limited by technological issues. As people have seen the rise of motorized trains, the desire for higher speed travelling not just limited on tracks but wherever they can grew. When the internal combustion engines came along in the beginning of the 1800s, engineers have been trying to motorize vehicles with them in order to achieve high speed. The successful results have led more and more engineers working to incorporate combustion engines with wheels to make a horseless carriage.

### Invention

Automobile is a combination of various type of technology. During its early period, it was basically a horseless carriage: similar kinds of wheels and shape. The biggest different is the power source where animal power is either replaced with steam powered engine or internal combustion engine or electricity, which all require technological expertise in physics and chemistry. In addition, without pulling the rope to tell horses to turn, automobiles were steered with a tiller. Steering wheels were invented later and became standard. The process of combining all the pieces together to make the automobile to work as a unity requires even more advanced mechanical expertise.
Early innovations with steam powered vehicles were hindered by a lack of capital. British engineer Richard Trevithick's steam powered vehicle was capable of running at a speed up to 12 mph reliably. But he did not have financial support from investors to do further research and development. Similarly, the American engineer Oliver Evans obtained the exclusive rights to operate steam-powered vehicles from Maryland Legislature. Yet he couldn't raise the $3,000 startup fund to launch his steam-powered wagon company because the onlookers thought the vehicle would be too slow. Electric automobiles were quite popular for some time around the 1900. But soon the requirements for charging facilities, which were virtually nonexistent at that time and the excessive weight of the batteries outweighed the advantages. In comparison, gasoline can be supplied by any stores and was cheap then. As a result, gasoline automobile was adopted as standard.
Many minor shifts from the original design came from practical experience. The first long-distance travel was made by Karl Benz's wife, Bertha Benz. Karl Benz, who was generally considered as the inventor of the first modern automobile, was trying to perfect everything before the next step, which made his wife frustrated enough to take the first trip with the her husband's design. Her experience during the trip provided great insights into how to improve the initial design: she needed to buy gasoline to finish the trip; she needed to push the car uphill because it didn't have enough horsepower; she needed to use her hatpin to unclog the fuel line; she improvised an insulator to solve the short-circuited ignition problem; she also needed to replace the leather on a brake shoe. All these incidents contributed to improvements in various aspects including gears, material, engine, ignition, and etc. It was exactly these small improvements that added up to the existing predominant technologies such as new ignition technology, brake system, fuel tank, low gear for climbing hills and so on.
Initially automobiles were only meant for the wealthy as they were expensive to make. Henry Ford applied the supply chain production process to his Model T automobile, which significantly cut both cost and production time down to the point that everyone can have an automobile. And the improvements were sustained: in 1913, the cost of the Model T Touring car was reduced to $600 with 250,000 production that year; The cost was reduced further to $360 and the year's production exceeded 700,000 during 1916; By 1927 when Ford stopped making model T, the cost was below $300 and over fifteen millions were sold. Automobile manufacturers all over the world quickly adopted and further improved this process. For example, Japan modified the mass production to a more flexible one. The dramatic improvements in production process contributed to the quick growth that came later.

### Early Market

According to Flink, the major competition for automobile at its birth phase came from the cheaper and more reliable railroad and water transportation in the United States, which were heavily subsidized by the government. Also the improvement progress for public roads was very slow. In addition, the automobiles were quite expensive at first. Only the wealthy people can afford it. It was not until Ford introduced the supply chain mass production method to dramatically decrease the cost and time that his Model T became readily available for purchase at an affordable price to more people.
With more improvements in speed and efficiency, more and more people began to appreciate the advantages of travelling in an automobile: it provided great freedom with much higher speed than the old carriage so that they can travel a decent amount of distance quickly and continuously. During the 1920s, a lot of refinements took place to make automobile ride more comfortable. The introduction of ethyl additive for gasoline in 1923 boosted both performance and fuel economy. Some sedans even began to load a heater. Automatic chokes, easy-shifting synchromesh transmissions and etc. made driving easier. Better technology attracted more customers and more drivers in turn spurred the demand for improving roads and constructing new roads. Enhanced infrastructure for automobiles served the existing market in return while making the automobile an even more appealing transportation mode.

### Policy in the Birthing Phase

The policies regarding the birth of automobiles were not all pleasant, especially in England. Under the horse-drawn transportation interests, the turnpike trusts that were in charge of the highways charged discriminatory tolls against motorized vehicles. In 1865 Parliament passed representing the railroad owners the notorious Locomotive Act, the Red Flag Act. It limited the speed of what they referred to as “road locomotives” to 2 mph in towns and 4 mph on the highway.
When automobiles became more accepted, policies regarding the operational standard began to emerge. To ensure safety, the American adopted drive-on-the-right-side policy to avoid collision, which would be hard to change once the habit had been established. Speed limit was also introduced, varying by road types and states. Toll roads were applied to automobiles as well in order to finance part of the road construction and maintenance. Traffic signs were adopted and standardized using minimal words and mostly symbols to convey ideas easier. Any change in the existing acknowledged commonsense would arouse confusion to the drivers and may cause accidents.
The government also promoted automobiles by investing in transportation infrastructure, building new roads and improving existing ones. Such emphasis on automobiles would attract more demand for automobile while making the country “run on gasoline”.

### Growth Phase

In the growth phase, people's perception towards automobiles has been clearly established. The wait-and-see mentality switched to reasoning of the necessity of owning an automobile as the primary transportation mode. Meanwhile, the government invested massive amount of money in infrastructure construction including the interstate highway system, which to some extent provided an indirect subsidy to the automobile industry. The technology established itself a convenient and efficient way of travelling, drawing huge demand. In addition, there weren't much competition to it. The airplanes were still at its birth phase. The automakers all over the world were spending extravagantly into improving the technology and marketing. All the conditions contributed to the predominant place automobiles stand in the U.S transportation system. The federal government also provided generous funding into automobile-related university research programs aiming to further advance the technology.
The drawbacks associated with such quick expansion in the auto industry were significantly increased carbon emission and fatality in the United States. In the 1970s, the federal government began to control automobile design by implementing tight laws to control emissions and to improve safety, which caused a bit of chaos in the automobile industry in the mid 1970s. This act led to researches in both the industry and universities to improve automobile's fuel economy with the determination for sustainable development.

### Mature Phase and Future

After the growth phase, the automobile almost reached its peak as a transportation mode in the United States, as what was shown in the simulation. The results showed that there is still space for growth yet slow and minimal. In this period, dramatic improvements are highly unlikely while only polishing of the existing system can be achieved. However, in this specific case, because I measured the number of automobiles per household, there still exists demand for automobiles with the population growth. The industry will not die unless that there comes an alternative that will replace automobiles entirely.
Automobile companies all over the world are pouring in huge amount of capital to improve fuel performance. Among them, the Japanese automaker giants Toyota, Honda and Nissan are especially notable. Toyota's Prius has been the most popular hybrid vehicle that touted a 50 plus MPG. Nissan also rolled out its electric car Leaf recently. Alternative energy such as solar power can be taken into consideration as the future power source for the automobiles. The U.S. transportation infrastructure is so heavily dependent on gasoline that people often raise concern for the fuel run-out in the future and they also propose the possibility of using public transit to replace parts of the interstate highway system, especially the high speed rail technology. However, the lock-in effect made the possibility of using the new high speed rail technology widely in the United States quite slim.
During the economic depression from 2007, the government nationalized General Motors and Chrysler in order to save the American auto industry and protect the existing markets and customers based on the reasoning that automobiles have become an indispensable part of the American daily life. The future of automobile in the United States may not change much in terms of design and technology, yet new type of uses such as Zipcar may change the way we think of automobile ownership and the future trend of it.

## References

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