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Why Use Linear motors

Washington Senate People Mover


Force Engineering was briefed with developing a Linear Induction Motor (LIM) drive for a Personal Rapid Transport (PRT) system to connect the U.S. Capitol building with the Dirksen and Hart Senate buildings in Washington, DC.


The route is a double track loop of 945m (3,100ft) and accommodates up to four three-car trains at speeds up to 14mph with each train weighing an estimated maximum of 6,800kg (15,000lbs) when fully loaded.

Mounting the motors in the track, with a reaction plate fitted to the vehicles in each train, was the first choice for the drive system reducing the size and duty cycle of the drive motors whilst still allowing for the accurate speed and positioning control required.

Force Engineering designed motors capable of providing consistent thrust across the variable passenger load using sensors mounted in the each vehicle and control equipment fitted in each LIM junction box to control the vehicle speed in real time via an inverter driven bus bar system.

The system efficiency is high compared to alternative drive methods and running on electricity negates the need for an exhaust system on the vehicle or in the tunnels further reducing overall complexity and costs.

Being an indoor track no special protective finish was required for the more than 500 motors supplied for the system but a resilient epoxy resin was specified by Force Engineering to ensure the low maintenance and long working life demanded.

Key Benefits of using Force Engineering's Linear Induction Motor for the project:

  • Good operational reliability
  • Quiet system operation
  • Reduced maintenance
  • Overall system efficiency


The goal of a long term and reliable public transport system with smooth, quiet operation requiring little maintenance was achieved with bespoke LIMs from Force Engineering. The original LIMs are still functioning as intended over 15 years after installation.