There is an exponential amount of engineering work that must be taken into account before operating high speed trains, as the track infrastructure, such as rails, ties, and ballast must be properly engineered to accept speeds over 150 mph.
So, what do high speed trains run on? Conventional rail. The rail is reinforced, equipped with special sleepers and fasteners. Furthermore, copious amounts of ballast is utilized to keep track in place.
There are many infrastructural elements that must work together seamlessly in order for a high speed rail network to operate properly, including other technologies that could be utilized to power high speed trains in the future.
Track Infrastructure
Super-elevated Curves
Track infrastructure for high speed networks must be properly prepared, as there are various forces that come into play at such high speeds. One of the most common forces is the centrifugal force, which by definition, is an outward acting force, directing away from the axis of the force. This force comes into play in the context of high speed trains when rounding a curve. When a train makes a left turn, passengers would sway to the right, if a train makes a right turn, passengers would sway to the left.
In order to negate some of the effects of centrifugal forces, high speed rail networks are built with banked turns, where the track is either elevated or super-elevated. The tighter the radius of the curve, the higher centrifugal forces present inside the train. This elevation is made possible through copious amounts of ballast underneath the track, thereby, elevating the outer edge of the rail.
Super-elevated curves are designed to lessen the movement of passengers within the train, as the train’s suspension balances much of the forces encountered within the curve. The most pertinent feature of a banked curve is to balance both the centrifugal forces, pulling the train outward, and the force of gravity, pulling the inner part of the train down, therefore, keeping the train on the track.
Although super-elevated curves offset some of the centrifugal forces at play, choosing the proper radius is perhaps the most important aspect of curves on a high speed rail network. Typically, a high speed railway has a larger curve radius compared to a traditional rail line to further negate the effects of centrifugal forces.
Rail
The manner in which rail is laid on a high-speed line is imperative as well. Since the dawn of rail travel, jointed rail was commonplace, however, beginning in the fifties, welded rail was found to deliver improved ride quality, ease of maintenance, and was more apt to handle high speeds. Continuous welded rail had become particularly advantageous in the sixties, when the world’s first high speed rail line opened in 1964, the Japanese Shinkansen.
High-speed railways have continuous welded rail, which prevents excessive friction, provides a smoother ride for passengers, and is less maintenance heavy. Although welded rail is less maintenance heavy, its installation is increasingly more expensive that its jointed rail counterpart, and various precautions must be taken to prevent inconsistencies in the rail.
Upon its installation, continuous welded rail is installed utilizing a process known as “flash butt welding”, where ends of the rail are heated up to a certain temperature, then pushed together, therefore, welding the two ends of the rails together.
Expansion Joints on a piece of continuous welded rail on the French TGV network. These types of expansion joints are imperative in order to prevent kinks in the rail as a result of expanding or contracting. These are especially important for the safety of high speed running.
A continuous welded rail line could stretch several miles long, and allow for much higher speeds than traditional jointed rail. However, due to the phenomena known as thermal expansion, joint bars or spacers must be placed every few miles to negate rails becoming kinked due to expansion and contraction as a result of changing temperatures.
Furthermore, it is important to ensure the rail is properly restrained in the event of an expansion or contraction. On a high speed line, such as the TGV or Shinkansen, it would be commonplace for specialized clips to be attached to the sleepers or cross ties in order to prevent the track from becoming misaligned.
In addition to restraints such as Pandrol clips, the ballast underneath the track must be properly supporting the track infrastructure. In order to keep sleepers in place, it is ideal that ballast is placed underneath, beside, and in the between the sleepers to ensure the infrastructure is properly in place, and the track bed is secure.
Sleepers or Cross Ties
Sleepers support the rails, and are positioned perpendicular to the rail. When a train passes, the function of the ties is to transfer the load and weight of the train through to the ballast and sub grade on the infrastructure. Furthermore, sleepers assist in maintaining the proper gauge of the rail line, and prevents the rails from falling sideways, or becoming misaligned.
Interestingly, concrete ties are both cheaper and more plentiful than concrete. In addition to being able to handle high speed operation, concrete sleepers are also apt to handle heavier trains than traditional wooden ties. Proper installation of concrete ties is critical to their performance, as they require the ballast to have ample draining capabilities, which is achieved through properly preparing the railway’s sub-grade.
Although concrete sleepers are advantageous on many fronts, one major downfall of utilizing concrete sleepers as opposed to conventional wooden ties is higher pitched sounds when trains pass. Concrete ties amplify the wheels and other sounds of the train, thus, wooden ties are oftentimes utilized in populous areas.
Grade Separated Right-of-Way
The interesting aspect of high speed networks is that oftentimes they are completely separated from conventional railways. Grade separated right-of-way is defined as having different modes of transit separated at a different height from one another. This allows trains to operate at much higher speeds, as slower trains are not present on the same rail line.
This has been extremely advantageous for high speed trains such as the TGV and Shinkansen, as they are able to stay on schedule, and operate at increased intervals. In fact, due to grade separation, when trains such as the Shinkansen are late, it is by only mere seconds, as opposed to other services, which must operate slower due to other trains utilizing the same track.
Maglev Technology
Although most high speed trains operate on conventional tracks, new technology such as Maglev trains have come to fruition in recent years. Maglev trains lack rails, sleepers, and ballast, and instead utilize a guide-way in which the train levitates due to the strength of opposing magnetic forces.
Maglev technology allows passengers a nearly completely smooth ride, as no contact is made with the guide-way, or a rail, such as a conventional train. Maglev trains can utilize either a single or double guide-way, however, they are both elevated above the guideway in a similar manner.
An example of a single guide-way system is the German “Transrapid”, and the Shanghai Maglev, which transports passengers from the city’s airport to the city center. The Shanghai Maglev is the only example in revenue operation, as its German counterpart is not longer operable.
An example of a double guide-way Maglev is JR Central’s experimental SC Maglev MLX01, which holds a speed record of 370 mph (590 kp/h). The Miyazaki test track, the MLX01’s guide-way, resembles a trench, and operates via superconducting magnets placed inside the bogie, guided by two sets of metal coils on each side of the guide-way. The SCMaglev remains in testing phases, however, the train has garnered much interest internationally, in countries such as the United States and Australia.
Related Questions?
What are the fast trains called? Fast trains are oftentimes called “Bullet Trains”. The term bullet train originated in Japan, with the introduction of the Shinkansen in 1964. The name was given due to the train’s speed of 130 mph, and the pointed shape of its nose.
