A monorail carries passengers along a single beam or rail, using rubber tires for traction and electric motors for propulsion. Unlike conventional trains that run on two parallel steel rails, a monorail’s entire support, guidance, and drive system wraps around or hangs from one elevated guideway. This design lets monorails navigate tight curves, climb steeper grades than traditional rail, and run above street level without massive infrastructure.
Two Basic Designs: Straddle and Suspended
Every monorail falls into one of two categories based on how the vehicle relates to its beam. The distinction determines how the system handles weight, stability, and passenger comfort.
In a straddle-type monorail, the vehicle sits on top of the beam and wraps around it like a saddle. The center of gravity is above the track. This is the more common design worldwide, used in systems like the ones in Tokyo, Kuala Lumpur, and Walt Disney World. The beam is typically a large concrete or steel structure, and the vehicle’s wheels grip its top and sides.
In a suspended-type monorail, the vehicle hangs beneath the track from a wheeled bogie that rolls along the top of the beam. The center of gravity sits below the track, which makes the car swing slightly on curves, similar to a gondola. The Wuppertal Schwebebahn in Germany, operating since 1901, is the most famous example. Suspended systems are less common but offer the advantage of a completely unobstructed view from the cabin and a narrower footprint at ground level.
How the Wheels Keep It Stable
Balancing on a single beam sounds precarious, but monorails use multiple sets of specialized rubber tires working together. A typical straddle monorail has three distinct wheel types, each performing a different job.
- Load tires sit on top of the beam and carry the vehicle’s weight, functioning like the wheels on a car. A single vehicle may have four or more load tires per bogie.
- Guide tires press horizontally against the sides of the beam. These prevent the vehicle from drifting left or right, especially on curves. They’re what keep the monorail from tipping.
- Traction tires (or drive tires) are connected to the electric motors and provide the forward push. In some designs, the load tires themselves serve double duty as traction tires.
All of these are rubber-tired, not steel. Rubber on concrete is quieter than steel wheels on steel rail, which is one reason monorails are popular in urban and resort settings. The trade-off is that rubber tires wear faster and create slightly more rolling resistance, but the noise reduction and climbing ability make up for it in elevated transit applications.
Electric Propulsion
Monorails are electrically powered. The vehicle doesn’t carry fuel; instead, it picks up electricity from conductor rails (often called “power rails” or “bus bars”) mounted along the guideway beam. Contact shoes on the vehicle’s bogie slide along these energized rails to draw current, typically at 600 to 750 volts DC. This is similar in principle to how subway trains collect power from a third rail, except the power rails on a monorail are built directly into the beam structure rather than sitting on the ground.
That electricity feeds onboard motors, which turn the traction tires. Most monorails use conventional rotary electric motors. Some newer or experimental systems use linear induction motors, which generate thrust through electromagnetic fields between the vehicle and the beam rather than through spinning wheels. Linear induction motors eliminate mechanical contact for propulsion, reducing wear and maintenance.
How Monorails Brake
Stopping a monorail involves layered systems that work in sequence. The primary method is dynamic braking: the electric motors reverse their function and act as generators, converting the vehicle’s forward motion into electrical energy. That energy is fed into resistor banks, where it dissipates as heat. On the Disney/Bombardier monorail system, dynamic braking handles roughly three-quarters of normal stopping, slowing the train down to about 13 miles per hour on its own.
Below that speed, mechanical disc brakes take over. Each load tire has its own disc brake, providing the final stop. These are similar in concept to the disc brakes on a car. The mechanical system generally handles less than a quarter of the braking effort during a normal stop, but it can bring the train to a complete halt independently in an emergency. Some systems also include emergency grip brakes that clamp directly onto the beam as a last-resort failsafe.
The Guideway Beam
The beam is the monorail’s equivalent of both the track and the bridge. It must support the full weight of loaded vehicles while also serving as the surface for traction, guidance, and power delivery. Most modern systems use precast prestressed concrete beams, which are manufactured off-site and lifted into place by crane. Spans typically range from about 25 to 30 meters between support columns. Cairo’s monorail project, for example, uses precast concrete beams with individual spans of 26 and 30 meters.
Steel beams are used in some systems, particularly where longer spans or curved sections are needed. The beam’s cross-section is carefully shaped to accommodate the wheel arrangement. On a straddle system, it’s usually a wide, flat-topped shape with vertical sides that the guide wheels press against. The power rails, communication cables, and sometimes emergency walkway brackets are all integrated into or mounted onto this single structure. This consolidation is a key advantage: one beam replaces the two rails, ties, ballast, and overhead wires that a conventional train needs.
Climbing and Turning
Rubber tires on concrete give monorails significantly more grip than steel wheels on steel rail. A conventional freight train struggles with grades above 2 percent (a rise of 2 feet per 100 feet of track). Monorails routinely handle grades of 6 percent or more, which lets them climb over roads, buildings, and terrain changes without long, gradual ramps. This is why monorail routes can follow existing streets and weave between buildings in ways that conventional elevated rail cannot.
Turning works through the guide wheels. As the beam curves, the guide tires on the inside and outside of the turn press against the beam’s sides, steering the bogie along the path. The vehicle itself is often articulated, meaning adjacent cars connect through flexible joints that allow each section to follow the curve independently. Switches (the equivalent of railroad track switches) are more complex on a monorail. Instead of moving a small rail tongue, an entire section of beam must physically shift sideways to direct the vehicle onto a different route. This is one of the engineering challenges that has limited monorail networks from becoming as flexible as conventional rail.
What Happens in an Emergency
Because monorails run on elevated guideways, evacuation is more complicated than stepping off a stopped subway car. The preferred approach is always to move the train under its own power (or a rescue vehicle’s power) to the nearest station. Emergency response vehicles with independent power sources, such as diesel engines, can reach a stranded train on the guideway and push or tow it to a platform.
When that isn’t possible, passengers exit through the train’s doors onto emergency walkways built along the guideway beam. These walkways run along one side or down the center of the elevated structure, ideally at the same height as the vehicle’s door sills. From there, passengers walk to the nearest station or emergency exit staircase. Some systems equip trains with deployable ladders or inflatable slides as a secondary option, though walkways are the standard approach for high-capacity evacuation. Federal transit guidelines require that monorail operators have detailed procedures for total power failure and between-station evacuation scenarios.