Re: How fast trains could posibly run. What are the limiting factors.

Greetings:

Your question is a very interesting and important one.

At the turn of the century steam engines were able to pull trains in excess 
of 175 km/hour (110 miles/hour). The concept of increasing a trains speed 
and efficiency by reducing a trains air resistance, later called  
“streamlining”, was proposed in the late 1860’s and by 1900 the  Adams Wind 
Splitter steam powered locomotive was fabricated in a shape like the prow 
of a ship and the train ended with a fish tail. The Windsplitter was put in 
service on the B&O railroad in the USA.  At the same time the Paris-Lyon-
Mediterranean Railway streamlined their “locomotive a’ Bec" (shaped like a 
beak) to reduce air resistance. However, these early streamlined features 
added  manufacturing cost and maintenance time to the locomotives with 
minimal improvement in the regular scheduled time between cities.

 By the mid 1930s the advent of  diesel electric locomotives enabled long 
distance streamlined trains to average 100 km/hour (60 miles /hour), 
including station stops, in regularly scheduled service. However, while the 
streamlining was good for advertising trains to the public, the reduced 
schedule times were determined more by the elimination of coal and water 
stops for steam engines rather than by an increase in speed. From the 1940s 
through 1960s locomotive power increased by a factor of 10; however, the 
speed of trains was not increased, mainly because of the condition of the 
roadbed, and the design of the tracks, especially the curves, and by the 
large number of grade crossings for the ever increasing automobile road 
traffic. 

For the past 30 years In Japan and Europe and more recently in the USA, new 
railroad tracks were designed to eliminate grade crossings, reduce grades 
and make curves  for trains running in the UK at 200 km/hour (125 miles/
hour) in Japan at 210km/hour (130 miles/hr) and the TGV in France running 
at 270 km/hour (165 miles/hour).

In the USA during the 1970s special test locomotives shaped like aircraft 
and powered by two turbojet engines reached speeds up to 400 km/hr (250 
miles/hour). These locomotives were never put in service because no current 
roadbed in the USA can sustain those speeds. 

In 1990 the TGV set a world speed record of 515.3 km/ hour (320 miles/
hour). However, roadbed  and track design continues to be 
the limiting factor for conventional trains running on rails as evidenced 
by the numerous papers on the subject given at international railroad 
conferences. Many of these papers are available on the Internet. Today, the  
European Community is extending costly high speed track roadbeds throughout 
Europe so that commercial operation up to 300 km/hour (185 miles/hour) will 
be possible.

Recently turbojet powered automobiles designed similar to aircraft were 
able to exceed the speed of sound (1000 km/hour , 750 miles /hour) on  flat 
dry lake beds of the type used here in California to land the Space Shuttle 
and the world’s fastest  aircraft. Also, recently my laboratory along with 
many other university and government participants, conducted a 
demonstration of an intelligent highway vehicle system near San Diego, 
California. During the demonstration  a  platoon (train) of automobiles 
with radar interconnection (couplers) automatically traveled at 100 km/hour 
(60 miles/hour) with only one meter spacing between vehicles. This 
efficient use of expensive, in place highways (roadbed) and hands off 
transportation has many desirable features. Automatic joining and leaving 
of single cars from the platoons at preprogrammed locations are now being 
researched. This concept combines many of the advantages of rail travel and 
personal automobiles.

To improve current high speed trains such as the TGV, to achieve the 
greatest speed at the lowest cost, both shape and weight are being studied. 
The TGV uses only one bogey per car reducing the track noise and  the 
number of pantographs are being reduced and redesigned to reduce noise.  
Noise from the wheels on the track and from the air flow are becoming more 
of a problem as speed is increased above a "critical speed" between 300 and 
350 km/hour for the TGV. Painful shock waves to human ears can arise when a 
high speed train enters a tunnel and studies are underway to minimize this 
problem. Clearly reducing or eliminating wheels and air resistance and much 
improved roadbed are needed for major increases in speed and efficiency. 
One approach to these problems is Mag-lev.

Magnetically levitated (Mag-lev) trains are under development in Japan, 
Europe and the USA. in which the cars  float on a magnetic field 
eliminating rail drag and drive mechanisms and bearings spinning at 
supersonic speeds.Magnetic levitation uses magnetic waves to suspend and 
propel vehicles along a guide way. It is an American technology created in 
the mid-1970s and is now being developed by the Japanese and Germans, who 
have built short mag-lev lines. Mag-lev is still primarily a laboratory 
experiment and has almost never been used commercially. The Mag-lev system 
has an estimated maximum speed of 580 km/hour (300 miles/hour) and would 
require only 40% as much fuel per passenger mile as an average automobile, 
and only 33% as much as the average airplane. A Mag-lev train is quieter 
than a car, airplane or train. It can be built along-side or even in the 
median strips of existing highways. Mag-lev requires its own road-bed and 
cannot be used on existing rail lines, but it requires far less room than 
either regular train tracks or highways, and it can be elevated above the 
ground. The trains would run on electricity. Currently the extra power 
required to produce magnetic fields strong enough to Mag-lev an entire 
train remains a major problem. 

The discovery in the mid 1980s of high temperature super conducting 
materials that can operate at liquid nitrogen temperatures may be the 
breakthrough needed to make Mag-lev practical. Super conducting magnets are 
already revolutionizing the design of Magnetic Resonance Imaging (MRI) 
machines in medicine.  Only a few Mag-lev trains have been used 
commercially such as at the  Birmingham airport in the UK (600 meter 
distance) which because of maintenance  problems has been shut down after 
11 years in service.

For many years a number of concepts have been proposed for running trains 
in evacuated tunnels or tubes to reduce air resistance; also, many designs 
to eliminate the use of wheels at high speed have been proposed. One 
interesting concept that I recall was published in the Scientific American 
magazine: "High speed tube transportation", L.K. Edwards, August 1965, 
pp30-40. The article described a train traveling in an evacuated tunnel. 
The proposed tunnel was curved deep under the earth so that the train 
became a pendulum which used the force of gravity (with differential air 
pressure assist) to propel it between distant cities . 

Gravity and air compression ahead of the 
train is used for slowing and braking at the end of the trip. Also trains 
in a near free fall at the start of a run are able to supply energy to 
trains going uphill at the end of a run by acting as pistons in an air 
pumping/transfer system.  I have do not remember what the proposed 
maximum velocity of the train was ; however, it was very fast (Our library 
does not have issues of Scientific America before 1972). In all cases the 
cost of tunneling is a major problem for all tube concepts. The higher than 
proposed cost in digging the English Channel tunnel and the recent large 
cost over runs in tunneling for the new Los Angeles subway (underground) 
system, discourage the future consideration of tube systems. Also fires in 
both the Channel tunnel and during the Los Angeles construction, with loss 
of life, do not help the situation.  Here in Los Angeles they are now 
considering abandoning the half completed subway in favor of ground level 
track.

I do hope that railroad transportation here in the USA will catch up to the 
technology that is being used daily in Europe and Japan. Meanwhile we are 
designing and building much larger and more efficient aircraft. Also; new 
high precision satellite based navigation systems offer more efficient and 
safer use of the skyways. Rail transport will have a more difficult 
challenge in the future to be cost effective.

Best regards, your Mad Scientist
Adrian Popa