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Hollow Switch Ties (HST®) Frog

In the typical moveable point frog setup, the operating rod, lock rod, and detector are connected to the switch machine through rods that are located in the tie cribs.

While it is the most common way to install the connecting rods, the cribs that contain rods must either have the rods removed for tamping or must be hand tamped.

The HST®, or hollow switch tie, allows for the connecting rods to be placed inside hollow ties. With the HST®, the switch can be surfaced with mechanized tampers. They have the additional benefit of containing non-conducting composite switch rods, which does away with the need for switch rod insulation. The high strength steel ties also serve as gauge plates to hold the track in gauge. The HST® is a multi-function system designed to make life easier for maintainers and other maintenance personnel, as well as to increase the life of the frog.

HST’s can be combined with any Nortrak moveable point frog (MPF) design. The tie profile has been specifically selected for its high strength and modulus. The composite switch rods, commonly called “blue rods”, have higher strength than their steel counterparts, yet they are flexible enough to bend without breaking or deforming. HST’s with have been used with MPF frogs extensively in both heavy haul freight railroads and in transit railroads.


• Allow for mechanized switch tamping
• High strength composite fully insulating “blue” switch rods
• High strength steel tie section w/ heavy duty insulation
• Positive gauge control
• Reduced maintenance
• Improved frog life

Technical Specifications:

• Used with any Nortrak MPF frog
• Compatible with all common switch machines
• Switch rod strength – 100,000 PSI
• Design wheel loads – 39 kips +100% impact
• Electrical resistance – 400 Volts/Mil Min.
• Track modulus is equivalent to concrete ties