1. What Are Ballast Tracks, the Stone Tracks Used on Most of the Tokaido Shinkansen?
On most sections of the Tokaido Shinkansen where passenger trains run, the tracks use "ballast track." This is a traditional style where crushed stones are spread out, sleepers are placed on top, and rails are mounted on the sleepers. Every time a train passes, the stones shift slightly, causing the track’s height and straightness to become uneven. A machine called a Multiple Tamping Machine, or "Maruta," is used to correct this unevenness[1]. JR Central stated in March 2026 that they use about 50 sets of maintenance vehicles every night for track and electrical equipment upkeep[2]. This number represents the scale of nighttime maintenance, including both tracks and electrical systems. The daytime trains that reach speeds of 285 km/h (about 177 mph) rely on this quiet, hard work at night. So, why do stone tracks need so much maintenance?
2. What Are the Strengths and Weaknesses of Stone Tracks?
Stone tracks are not bad. The angular stones fit together, creating friction that makes them hard to move. They spread out the weight of the train and absorb vibration and noise. Crushed stone is said to be cheap, easy to lay, and good for drainage, which is why it is still used on many railways[5]. However, the weakness is repeated heavy loads. Every time a train passes, the stones sink a little, their corners become round, or they break. This makes regular maintenance essential[5]. A 1987 paper explains that residual displacement in the track bed accumulates as trains pass, distorting the track shape, and most repair work is spent fixing this[4]. In 1970, a Japan National Railways engineer wrote that traditional tracks made of rails, sleepers, and gravel are a "structure premised on destruction" because they absorb running energy through their own deformation[3]. He also noted that the Shinkansen required about three times the maintenance labor of conventional lines, and it was becoming very difficult to gather enough workers[3]. Engineers began to ask: Can we build a track that does not need this kind of maintenance?
3. How Does Slab Track Attach Rails Directly to Concrete Slabs?
Slab track is a type of railway where rails are attached directly to reinforced concrete slabs made in a factory. In the early design for the Sanyo Shinkansen, these slabs were 4.95 m (about 16.2 ft) long, 2.34 m (about 7.7 ft) wide, and 16 cm (about 6.3 in) thick. Under the slabs, a material called Cement Asphalt Mortar (CA mortar) is packed in, and the slabs are supported by the hard roadbed of viaducts or tunnels. Lateral forces are received by protrusions at both ends of the slabs[4]. The idea itself was not new. In Japan, research into non-ballast tracks in tunnels began around 1929 (Showa 4). The concept took shape in the early Showa 40s (the mid-1960s), and from 1965 (Showa 40), a specialized research group at the Japan National Railways Railway Technical Research Institute began work. They conducted model experiments at the Tsudanuma laboratory and tests on bridges on the Kisei Line and inside Nagoya on the Tokaido Shinkansen[3]. On the Sanyo Shinkansen, the section from Shin-Osaka to Okayama used stone tracks like the Tokaido Line. However, to test structures west of Okayama, slab tracks were planned for tunnels and parts of viaducts, totaling about 12 km (about 7.5 miles) in the plan[3]. A 1987 paper records about 16 km of test laying, so the figures differ by source[4]. What were the results of these tests?
4. Did Slab Track Really Lower Maintenance Costs on the Sanyo Shinkansen?
In March 1975 (Showa 50), the Sanyo Shinkansen opened between Okayama and Hakata. Slab track was fully adopted in sections with viaducts and tunnels. It was laid on 545.2 km (about 338.8 miles) of track length, which accounted for 68% of the main line track length between Okayama and Hakata. This is the total length of slab track laid, not the total distance of the section[4]. For the first 10 years after opening (Showa 50 to 59), the average cost to fix height irregularities was about 14% of the cost for stone tracks, or about one-seventh. The cost to fix lateral misalignment was about 20%, or about one-fifth. The paper states that the original goal of saving labor was confirmed[4]. The number of places where height irregularities of 7 mm or more exceeded management targets decreased to about 0.1 per km by 1984 (Showa 59) and stabilized[4]. However, it was not all smooth. Fastening devices that hold the rails sometimes loosened or fell off, the CA mortar under the slabs was crushed, and signal insulation in tunnels weakened. Right after opening, retightening loose devices made up 24% of all maintenance work on slab tracks. There were also times when lateral alignment was worse than on stone tracks[4]. These problems were addressed and used in later designs[4]. But another challenge, one that does not show up easily in numbers, was found.
5. Why Is Slab Track Noisier, and How Was the Noise Improved Later?
During test runs on the Sanyo Shinkansen, it was found that high-frequency noise was louder in slab track sections than in stone track sections. Stones absorb sound and vibration, but hard slabs are not good at this. However, this result was based on comparing high-frequency noise at speeds around 210 km/h (about 130 mph). It is not accurate to say "slab tracks are noisy" without qualification[4]. For the Tohoku and Joetsu Shinkansen, a target was set to keep noise along the line below 80 dB(A) at opening. To achieve this, vibration-damping slabs were created by placing a "slab mat" under the concrete slab. Tests were conducted on Tohoku Shinkansen viaducts in 1973 (Showa 48). The durability of the CA mortar and slabs was also improved for areas with cold and snow[4]. Later, for new Shinkansen lines, slab track became the standard structure due to ease of construction and reduced maintenance. In sections needing vibration control, elastic sleeper direct-fastening tracks are used. On the Nishi Kyushu Shinkansen (Takeo Onsen to Nagasaki), a "elastic sleeper embedded slab track" was laid to combine the advantages of both types, and its vibration-damping effect was confirmed[6]. Improvements have also been made to widen the spacing between rail fastening devices, reducing their number and significantly lowering costs[7]. There are two paths: maintaining stone tracks with regular care, or reducing care with slab tracks. Both have strengths and weaknesses, and engineers continue to refine both methods.
6. What Can You See of the Track From a Station Platform Today?
Today, you can observe the ground under the tracks from a station platform. Stay inside the white line and do not lean out. Just look at what you can see. Is it stones or a concrete slab track? Compare them. Never enter the tracks. If you ride the Shinkansen, try looking for these differences from the station or through the train window. If you want to read more, the 1987 paper in the Journal of the Japan Society of Civil Engineers is available for free in Japanese on J-STAGE. It contains numerical results about slab tracks on the Sanyo Shinkansen[4].