No one knows when humankind first tamed the ox, the burro, or the horse, or when the first dugout canoe was painfully whittled out of a log with a stone adze; these are chapters of human history that were never written in bone or stone. We do know that American Indians shipped copper, iron oxide (rouge), and other valuables from Minnesota to Alabama on foot over "forest highways", and down rivers such as the Mississippi and the Tennessee. We also know that before written history began, there was extensive commerce by canoe and by log raft along the Danube, the Tigris-Euphrates, the Yellow River, the Nile, the Indus, and the world's other great waterways, and that later in prehistory, the Chinese and the Egyptians traveled by sampan and by barge. The invention of the sailboat and of ocean-going "coasters", brought to a high art by the Chinese and the Phoenicians, must have significantly extended the trading ranges of early civilizations. Combined with oars in biremes and triremes, these ships could make steady progress even on windless seas.
  On land, the principal innovations were the construction of roads, and later, of post roads, where repeated changes of horses and riders could keep a message moving at speeds of two hundred miles a day. Freight was carried by camel, by elephant, by burro, by oxwain, by llama, or by human porter.
  Then came the nineteenth century.
  At the dawn of the nineteenth century, humanity traveled little or no faster than it had in the Neolithic Age: the horse and the fast sailing packet were still the benchmarks of transportation celerity. By the close of the nineteenth century, every speed record in existence had been broken, and sustained transportation speeds nearly an order of magnitude greater than the stagecoach and the sailing ship were commonplace.
  In the year 1800, travel was not only slow, but dangerous, uncomfortable, and undependable. Highwaymen and swollen fords threatened the traveler on land; pirates, storms, and the depredations of hostile governments assailed the voyager at sea. The roads were dusty or muddy, the rides bumpy, and the accommodations at night uncertain. Asleep at an inn, the traveler was vulnerable to cut-purses. Ships were infested with rats and other vermin, and were becalmed or tossed about at the whim of the elements. Inclement weather could impact travelers' schedules on land or at sea.
  The application of steam power to transportation changed all this. Stephenson's first steam train began to operate in 1825 in England, but effective railroad operations didn't began until around 1830. The first railroads were barely faster than stagecoaches, but their speeds rapidly improved: in 1893, locomotive 999 made the world's first 100-mph run. Also, they possessed one striking capability: the ability to carry very heavy loads at high speeds. Thus, in regions where navigable waterways weren't readily accessible, some of the traffic which was too heavy to be transported by dray-wagon could now be shipped by railroad.
  By the end of the century, dining cars and Pullmans were standard on passenger trains, as was steam heating and electric lighting. Fast "flyers" were able to complete the run from Washington to Ohio in about eight hours. Not only were railroads faster than stagecoaches, but they were safer, more comfortable, and more dependable. Punctuality became a railroad tradition (symbolized by the "railroad man", with his engineer's cap and his Hamilton silver watch).
  Meanwhile, at sea, steamships were replacing sailing ships that were subject to the capricious wind. Ships rapidly became larger, faster, safer, and more dependable.
  However valuable these innovations were for long-distance travelers, the speed at which the traveler traveled to and from the train depot was still limited to the speed at which a horse could trot. And since total travel times are portal-to-portal, some of the benefits of the steam djinn were lost because of the slow-moving "feeder systems" that supported local transit. Furthermore, most travel is local, and throughout the nineteenth century, the steam-engine-revolution failed to facilitate the day-to-day transportation of the person in the street.
  If the nineteenth century was the age of the railway and the steamship, the twentieth century was the age of the automobile and the airplane, as the steam engine gave way to the internal combustion engine. Once again, as in the nineteenth century, transportation speeds increased by an order of magnitude. In the United States, automotive progress was exemplified by the Olds Motor Works, which mass-produced 425 cars in 1901, 3,750 cars in 1902, and 5,000 cars in 1903. (Later, Henry Ford would bring the automobile to the masses.) Although the steam locomotive was dubbed "The Iron Horse" by its contemporaries, the "Iron Horse" might more appropriately be said to be the automobile, since it was the "car" which truly replaced the horse. One of the principal consequences of the automotive revolution was the paving of roads. The new motorcars had a distressing tendency to become "stuck in the mud". Also, their higher weights and speeds virtually demanded a more-durable surface than a dirt road could provide. The first concrete road in the United States was built in Detroit in 1908. During the 1920's, most major roads in Europe and America were paved, and the automobile, and its cousin, the tractor, replaced the beasts of burden virtually everywhere in the Western world.
  In the 1930's, the first limited-access highways, the Pennsylvania Turnpike and the German Autobahns pointed the way toward the freeway systems of the post-World War II era. In the United States, during the latter 1940's, turnpikes were begun in several states, and this was soon followed by the Federal Interstate Highway System, completed in 1980. Although early automobiles were capable of speeds up to 100-mph, travel speeds in most populated areas were restrained by traffic lights, local speed limits, and stop signs. Motorists on the U.S. Interstate System were restricted to speeds from 55 to 70-mph, but the Interstates freedom from speed zones and traffic lights significantly reduced travel times below those of secondary roads. Meanwhile, there were no speed limits on most sections of the German Autobahns and the Italian Stradas, and travel on these roads took place at speeds up to 150 mph. Thus, the technology for higher speed automotive travel was already in place in Europe.
  The automobile broke the "feeder system" bottleneck which had restricted the "feeder" portions of most nineteenth century travel to a plodding pace. It also all but eliminated the need for passenger trains, since the automobile could more conveniently provide similar services.
  The other major transportation innovation of the twentieth century was the airplane. The first heavier-than-air flight is generally attributed to the Wright brothers in 1903. The first significant applications of aircraft came in World War I, followed by mail service in the 1920's. The 1920's also saw the inauguration of passenger service at cruising speeds in excess of 100 miles per hour. By the 1930's, transoceanic "flying boats" were plying the oceans of the world at speeds greater than 150 miles an hour. Aircraft played a dominant role in World War II, with the introduction of the first jet aircraft, the Messerschmidt 262, and the first rocket-plane, the Messerschmidt 163V. After World War II, commercial airlines provided passenger service at speeds higher than 300 mph. The first jet passenger aircraft, the DeHavilland Comet, affording speeds in excess of 600 mph, entered service in 1952, with wide spread commercial operations commencing in 1958. The first supersonic transport, the Tupolev-144, made its maiden voyage in 1968.
  For passenger travel, airplanes rapidly took the place of railroads, and once again, a local-travel bottleneck developed, though this time at speeds which were an order of magnitude greater than those of the nineteenth century.
  The first airport-to-orbit aerospace plane made its maiden flight in 2009, a second-generation supersonic transport entered service in 2016, and the first hypersonic military aircraft, using supersonic combustion ramjets (SCRamjets), appeared in 2010. Hypersonic aircraft were initially developed to be "satellite killers", but their skip-glide capabilities endued them with fuel economies comparable to those of supersonic transports. Also, after launch, skip-glide vehicles don't deeply penetrate the Earth's atmosphere until ready to land, all but eliminating sonic booms. Consequently, unlike supersonic transports, they may be used over land. The first hypersonic transport service was established between New York and London in 2036, and between New York and Los Angeles in 2040, affording 2.5-hour transit times to London, and 2-hour transit times coast-to-coast. By 2050, most long distance travel was performed by hypersonic transport. The introduction of sub-orbital transports in the middle-seventies further reduced long-distance travel times, although high fuel/oxidizer costs and limitations on passenger accelerations have made them cost-effective for only the longest trips. Human-ware limitations—people-moving and processing times—and travel delays to and from airports frequently add up to more time than it takes to travel 10,000 miles.
  In the meantime, another revolution in individual transportation was underway, both on the ground and in the air. A crude form of autonomous vehicle control was realized with aircraft autopilots as early as the middle of the twentieth century, but true autonomy had to await the development of computer technology in the first half of this century. The first experimental guideways were implemented in Germany in the third decade of the twenty-first century. Inasmuch as existing roads could be retrofitted easily and at low cost, over half the world's roads were equipped for automatic vehicle control by 2050, a development that revolutionized the trucking industry. In the United States, canopies and snow-screens were provided over the Interstate Guideway System from the beginning. U. S. speed limits were gradually raised, and interstate guideways restructured to support them until, in 2043, speed limits along straight and level sections of the interstate system were elevated to 120-mph. One major limitation to guideways is that safe stopping distances increase as the square of vehicle speeds, doubling the standard guideway speed results in quadrupling the safe spacing between vehicles. As a result, the hourly traffic volume which can traverse a guideway tends to decrease as guideway speed limits are increased. However, this is more than offset by the lightning-fast reflexes of computer-controlled and intercommunicating vehicles, allowing a reduction in inter-vehicle spacings. (The ploy of dynamically establishing bumper-to-bumper "trains" suffers from the all-too-familiar problem that when climbing a hill, the speed of an entire "train" is limited to the speed of its slowest vehicle—suitable for heavily-loaded trucks but not for automobiles.)
  In the meantime, the computer advances which had made guideways feasible also permitted the development of personal air transportation. The introduction of built-in test equipment, and robotic disassembly/re-assembly and inspection greatly reduced aircraft maintenance costs. Early aircraft had required frequent manual disassembly and inspection, which made them expensive to own and operate. The development of low-cost avionics, of adaptive autopilots which can outperform human pilots (an outgrowth of military aircraft programs), and of agile thrust deflection vanes eliminated the frequent crashes caused by pilot error, ground shear, and strong, gusty winds. Finally, beginning in the early 21st century, automated air traffic control, followed by semi-autonomous and then autonomous air traffic control in the first half of this century, permitted airspace management on the scale and with the precision required for household aircraft. Lift/cruise ducted-fan VTOLs, which were developed as early as the 1950's, became popular in kit form at the turn of the century. In 2004, a four-seater Møller Aerobot sold for $1,000,000 in kit form, which was quite expensive for its time. These concepts were first tested in military and commercial aircraft and only gradually approved for autonomous flight. The introduction and acceptance of household and commercial robots probably contributed to the acceptance of autonomous autopilots. The Mitsubishi Aviation Corporation introduced the first autonomously controlled "aircar" in 2033, and most other automotive and light-aircraft manufacturers soon followed suit. The first robotic inspection systems were delivered in 2037. These early rotary-engined, annular-wing aircraft used JP1-fueled, turbo-charged, engines, and were capable of speeds of 350-mph, with a non-stop range of 800 miles. The introduction of active boundary layer control and super-slip surfaces permitted fuel mileages in excess of 60-mpg carrying a 600-pound load. At first, personal aircraft were the province of the wealthy, but prices dropped rapidly until, by 2065, more than 40,000,000 aircars were being produced world-wide each year. Speed and endurance gradually improved until, by 2075, they could routinely make the Gander-to-Azores-to-Lisbon and Attu-to-Petropavlovsk transoceanic flights that have helped to make the global village a reality. By the middle seventies, the first dual-powered turboprops were introduced, supporting 500-mph speeds with 2,000-mile ranges. By now, ranges have been extended to 4,000 miles, and speeds have increased to 600-mph.
  Meanwhile, surface travel had become primarily a means of conveying freight. The replacement of railroads with our current 600-mph maglevs began with experiments in the 1980's in Germany and Japan. The discovery of room-temperature superconductors in 2034 facilitated this trend, and T-tracks were widespread by the 2050's. Since centrifugal force rises as the square of vehicle speed, 600-mph speeds can be attained only where long, straight stretches of rail are possible. Trucks continue to provide to-the-doorstep local service.
  Having reviewed how we got where we are, where can we go from here?
  It seems difficult to imagine exceeding the Terrestial speeds achieved by sub-orbital transports. Major improvements would be irrelevant, anyway, without corresponding improvements in passenger access times. Regarding the latter, with modern robotic parking and baggage transfer, it becomes difficult to envision ways of getting passengers on and off their aircraft in less time than is done today.
  One promising trend is a lowering of the cost of corporate-owned, hypersonic aircraft. Sometime in the twenty-second century, the world's slowly-rising standard of living may cross the declining cost of the robotic production of hypersonic aircars. If this occurs, humanity will probably approach the practical limits on Terrestial transportation speeds, given the laws of physics as we know them today. Flying one's aircar from New York to Moscow would take no longer than the two-and-a-half hours it takes to fly from Miami to Boston today. However, most travel is local, and the high cost of adding exo-atmospheric capability to an aircar might render the exercise of this option questionable.
  As the Space Habitats and the Lunar and Martian colonies continue to expand, and as the traffic to and from them continues to grow, there might come a time when private aerospace-craft will replace aircars, though at the moment, trans-orbital traffic would not appear to warrant such a production effort.
  Evacuated tubes have been suggested from time to time as a transportation strategy, but the limitations on longitudinal and centrifugal accelerations which presently restrict tube train speeds would seem to limit major improvements in transit times. Since tube train traffic is largely confined to freight shipping, anyway, would evacuated tubes be worth the cost and effort? Perhaps this question is one which only our great-grandchildren will be able to answer.
 
 
 
 
 
 
 

The following paragraphs, which might be of interest, are notes which were made in preparing the preceding fantasy.
 
 
 
 
 
 

Transportation seems to me to fit into two major categories: transportation within the atmosphere, and transportation in vacuum.

The development of magnetically-levitated "tube trains" or "tube cars" running in evacuated tubes could certainly come about, but there are bottlenecks that would need to be eliminated in order to take full advantage of super-fast transportation systems. For public transit systems, speeds are limited by the need to stop often in order to pick up passengers. For private transportation, the times required to walk to and from one's parking place could become comparable to the time required to go a hundred miles, so that fast people-movers would be needed to remove that particular bottleneck. (At one gee, one could go 100 miles in 4 minutes, with a peak speed of 2700-mph, or at half a gee, one could go 100 miles in 6 minutes, reaching 2,000 mph. at the midpoint...or it could be done in 9 minutes, reaching a speed of 1,000 mph. and "coasting" for 6 minutes, or in 11 minutes at 600 mph., with a 9-minute "coast", or in 21 minutes at 300 mph., with a 20-minute "coast". Of these, the 11-minute trip would seem to be a reasonable compromise, which is similar to what a jet aircraft manages and which doesn't generate sonic booms. Allowing for 10 or 15 minutes to reach and return from a 600-mph road, the 300-mph speed would probably become a more-reasonable compromise, yielding an ulimate total travel time of perhaps 30 minutes on the ground, or perhaps, 15-to-20 minutes by air.)

Table 1 shows the times and distances required to accelerate to, and then to decelerate from various speeds.

Table 1 - Accel-Decel Times/Distances (Seconds/Miles)

Peak Speeds:

Gees 60-mph 150-mph 300-mph 600-mph

1 0.1/.05 0.23/.09 0.46/1.14 .92/4.5

1/2 0.18/.09 0.46/.57 0.92/2.3 1.8/9

1/4 0.36/.183 0.92/1.14 1.8/4.6 3.7/18

1/8 0.73/.37 1.8/2.3 3.7/9.2 7.3/36.2

The left-hand term in each column is the time, in minutes, required to accelerate to a given speed for the four accelerations listed, plus the time required to decelerate again to zero. The right-hand term in each column is the required distance, in miles. For example, accelerating at 1/8th gee, it takes more than 7 minutes and 36 miles to reach 600-mph and then to decelerate again to zero.

Table 2 contains travel times, in minutes, for travelling different distances (shown in the left-hand column) assuming different peak speeds (across the top) and an acceleration of 1/4th gee.

Table 2 - Travel Times vs. Speeds at 1/4th Gee Accel.

Peak Speeds:

Miles 60-mph 150-mph 300-mph 600-mph

10 10.5 4.5 3 -----

20 20.5 8.5 5 4

50 51 11 11 7

100 101 41 21 12

Table 3 contains travel times, in minutes, for travelling different distances (shown in the left-hand column) assuming different peak speeds (across the top) and an acceleration of 1/8th gee.

Table 3 - Travel Times vs. Speeds at 1/8th Gee Accel.

Peak Speeds:

Miles 60-mph 150-mph 300-mph 600-mph

10 11 5.5 3.7 -----

20 21 9 5.7 -----

50 51 21 12 9

100 101 41 21 14

Going to the opposite end of the spectrum is informative, too. Before you can go anywhere else, you first have to get out of your driveway. There would seem to be three approaches to accomplishing this: travelling underground in drilled, or cut-and-cover tunnels; travelling on-the-ground, as we do now; and travelling in the air, using "aircars". Looking at ground-based transportation first, the limitations on neighborhood speeds would appear to be established by

1) the need to slow down or stop and turn corners at intersections;

2) the need to drive slowly because of other cars backing out of their driveways;

3) the need to drive slowly because of children and pets straying into the streets;

4) the presence of parked cars along the streets.

Dealing with the first topic, I don't see any way in which a web of streets with slow corners can be avoided. Cities are two-dimensional, with traffic flow in both x and y directions. Before reaching a through traffic artery, there will be corners to negotiate. It will take at least a few minutes to get out of such a neighborhood.

With respect to the second topic, an acceleration lane on either side of a through street would seem to be both a requirement and a solution.

Blocking children and pets from the street won't be easy because driveways must be able to access streets, and people and pets must be able to cross streets, but let's suppose it can be done. Turning neighborhood streets into freeways with cloverleaf interchanges at every corner is obviously impractical in terms of the real estate involved. If neighborhood streets were made one way, then freeways would be possible, but they would either have to traverse over- or under-passes at every other corner, which would make for a Memorial Parkway kind of roller-coaster, or one set of streets in the wicker-work would have have to be elevated, or below-ground. The streets would have to be at least three lanes wide, with accel-decel lanes on both sides of one or more through lanes. The streets would have to be large enough to accommodate construction equipment and moving vans.

The problem of car-parking space for neighbors of entertaining is also real if you no longer allow street parking. For the sake of argument, let's assume that guest-parking can be accomplished in some other way; the problem of slowing down to turn corners would remain. Since it takes 500 feet to accelerate to 60 mph. at one-fourth gee, and five hundred feet to decelerate again, you probably couldn't much exceed twice the current speeds on residential streets. Cars can accelerate a lot faster than must of us do now, but usually, we choose not to do so, in order to save fuel and wear and tear on the car and us.

Some advantages to running roads underground are that it frees up the surface for other purposes, it insures that pedestrians and animals won't stray into the road, and it protects the road from the weather. Some of the disadvantages are the high costs of underground roads, the requirement that something other than internal combustion engines must be used underground, the fact that they can't easily be used in places where there's no drainage or where only solid rock prevails, the susceptibility of tunnels to seismic activity, the need for active underground lighting and ventilation, the fact that the tunnels must be made large enough that air can pass around high-speed vehicles moving through the tunnels, and the need to provide stranded mo,torists easy access to the surface. One can see them being used in large cities where real estate is sufficiently valuable to offset their liabilities, but their advantages can probably be realized at much lower cost on the surface.

Coming to a traffic artery like BobWallace, things can be different. For thoroughfares of this caliber, one-way freeways might be feasible. Accelerations might be the limiting factor in speed-versus-distance relationships on these streets. Accelerating at one-fourth gee, it would take about half a mile to accelerate to 125 mph. and then half a mile to decelerate again, so you virtually wouldn't reach these kinds of speeds unless you were going more than a mile. (Actually, an acceleration of one-eighth gee is probably more realistic and more comfortable, which means that it wouldn't be profitable to reach 125 mph. unless you were going more than two miles. This would require an accel-decel time of 44 seconds, which would have to be added to the minute or so required to leave a neighborhood.)

(It's interesting to note that the new Jaguar XMG-200 is capable of speeds in excess of 200-mph.)

To summarize, people will probably never be running to the corner grocery store in less than a couple of minutes. Under non-emergency conditions, they'll probably never travel from their houses to a room 10 miles away in less than 4 minutes, or to a room 20 miles away in less than 6 minutes, or 50 miles away in less than 10 minutes, or 100 miles away in less than 15 minutes. On the other road, if they can they can order something by computer for automatic delivery from a store a few minutes later, a lot of the running around that we do now won't be necessary.

For travelling longer distances, 650-mph will be a watershed-speed, because travel at speeds up to 650-mph can be realized without generating sonic booms. Insofar as one could imagine today, travel at higher speeds on the ground or within the atmosphere would require very-expensive evacuated tunnels which would also have to be very straight, both horizontally and vertically, in order to minimize centrifugal accelerations. For the foreseeable future, public air transportation, with all its delays and inconveniences, would seem to be the only viable option for supersonic flight, and right now, only over open water. – —