1. How Monorail Vehicles Stay on a Single Beam
At a station, the monorail sits on a single beam, not two rails. The relationship between this beam and the vehicle takes two main forms. The first is the "straddle-type" (koza-shiki), where the vehicle rides on top of the beam. The second is the "suspended-type" (kensui-shiki), where the vehicle hangs below it [1]. In the straddle-type, rubber wheels run around the beam. In the suspended-type, rubber wheels run inside the open bottom of a box-shaped beam [1].
Materials from the Japan Monorail Association list "no collisions or derailments on dedicated tracks" as a feature of the straddle-type. The reason given is that the vehicle wraps around the left and right sides of the beam [3]. This is a description of the association's features, so it does not mean accidents are impossible. The question remains: what roles do the wheels playing this wrapping action have?
2. The Three Types of Rubber Tires and How They Protect Against Punctures
The Osaka Monorail vehicles have three types of rubber-tired wheels. There are "running wheels" that support and roll the vehicle. There are "guide wheels" (2 pairs) that clamp the beam from the left and right. There are also "stabilizing wheels" (1 pair). All three types have auxiliary running wheels in case of a puncture [2]. The specific position of each tire on the beam is not detailed in this material, so only the roles are introduced here.
The size of the beam these run on is also known from Osaka Prefecture materials. A standard concrete beam is 22 m long, 1.5 m high, and 0.85 m wide [6]. The width is only about 1/26th of the length (22 ÷ 0.85 ≈ 25.9). Hitachi materials also state that the running path is narrow: 700 mm for small types and 850 mm for large types [4].
This narrowness is a strength in snowy regions. Hitachi materials state that because the running path is narrow, it is easier to take measures against snow damage [4]. But can these narrow beams handle steep slopes and tight curves?
3. How Rubber Tires Let Monorails Climb Steep Slopes and Take Tight Curves
Materials from the Japan Monorail Association state that the steepest gradient on the Tama Monorail is 6%, and the minimum curve radius is 60 m. Because rubber tires and bogie trucks are used, it can run on steep slopes and small-radius curves. This makes it easier to choose routes in urban areas [3].
A 6% gradient means rising 6 m for every 100 m traveled horizontally. Hitachi materials also state that due to the rubber tire method, steep gradients are 60‰ (per mille; 1000ths, so 60‰ is the same as 6%). For small types, curves with a radius of 40 m are possible [4]. A circle with a 60 m radius has a diameter of 120 m. A 40 m radius means an 80 m diameter. These are values from Tama and Hitachi materials, not numbers common to all monorails.
The benefits of rubber tires are not just for slopes and curves. Traffic News articles state that rubber tires are used in both straddle and suspended types. This improves acceleration and reduces noise. The background was the development of high-performance tires capable of supporting heavy railway vehicles [5]. Now that we know how they run, what happens where the track splits?
4. How Monorail Switches Move the Whole Beam Instead of Part of a Rail
For trains, switches move part of the rail to change the path. According to Osaka Prefecture materials, monorail switches use a method where "the track beam itself moves." The standard beam length is 22 m. However, at a switch, four short 5.5 m beams are connected to form a 22 m articulated beam. Because the short beams change angle slightly, they form a smooth curve [6].
The beam is 85 cm wide. So, rather than shifting sideways, it is more natural to bend the long beam at the joints. Imagine lining up four fingers and shifting them slightly to bend them into a gentle curve. Thinking of the switch beam this way helps visualize it. However, the actual beam is much larger and heavier.
How the force is applied to move the beam, and how long the switch takes, are not written in the materials read here. What is certain is that the beam itself moves, and it is an articulated type made of connected short beams. So far, this has been about straddle types. What are the advantages of the suspended type?
5. The Advantages of Suspended Monorails and Their World Records
Traffic News articles summarize the advantages of the suspended type as follows: because wheels run inside a steel beam, it is less affected by rain and snow. It is covered, so noise is low. Support pillars can be spaced widely, so it does not spoil the landscape [5].
The straddle type is the German-born "Alweg system." The suspended type is the French-born "Safège system." These are the two major systems, and they competed in the 1960s [5]. However, in Japan, according to the same article, 6 of the 8 monorail operators use the straddle type. Only 2 use the suspended type: Shonan Monorail and Chiba Urban Monorail. The suspended type is the minority. These figures are from an article dated June 2023 [5].
The world's first monorail was also a suspended type. It was the Wuppertal Schwebebahn in Germany, opened in 1901. It is considered the oldest monorail, with an operating distance of 13.3 km [5][7]. However, this used steel rails like a railway, not rubber tires [5].
The Chiba Urban Monorail exceeded the length of this old line. With an operating distance of 15.2 km (Line 1: 3.2 km, Line 2: 12.0 km), it is said to be the longest suspended-type monorail in the world. Chiba City official materials also state "Longest operating distance in the world (15.2 km)" [7][8]. Now that we know the mechanisms, how can we check them with our own eyes?
6. Things to Try: Ride, Look, and Calculate to Check What You Learned
Things you can do at home today: Place two pencils against the left and right sides of a thin piece of thick paper. Support it with both hands and move it slowly. The paper does not fall. This mimics how guide wheels clamp the beam from the left and right with your fingers. The actual tire action is more complex.
Another activity is calculation. A 6% slope means going up 6 units for every 100 units across. With a 30 cm ruler, lifting one side by 1.8 cm creates a 6% slope. Try making this by stacking books.
Things you can do by going out: If you can ride a monorail, look at the floor inside. The Tokyo Monorail has steps like a small stage (hina-dan) on the floor. The company explains this is because the trucks (wheel assemblies) are under the floor. Raising the body would require a major review of the track structure, so it cannot be changed [10].
The Tokyo Monorail opened on September 17, 1964, between Hamamatsucho and Haneda Airport. It was a transport system to carry tourists visiting the Tokyo Olympics the following October to the city center [9].
Official information: Osaka Prefecture pages titled "How are monorail vehicles structured?" and "Types of monorail rails and pillars" summarize tire and beam dimensions in Japanese [2][6].