MEJS is a mechanical device installed in bridge expansion joint openings. The primary function of the MEJS is to allow vehicle traffic to travel smoothly across large expansion joint openings. It does this by dividing the large expansion joint openings into a series of smaller openings called cells. These cells work together to accommodate the necessary thermal bridge movement (expansion and contraction) while providing a smooth riding surface for bridge vehicle traffic. The MEJS is normally used for expansion joints with a movement range up to 1500m.
MEJS also has the secondary function of protecting the surrounding bridge superstructure and substructure. All MEJS cells are equipped with watertight sealing elements that prevent debris, water and corrosives such as de-icing chemicals from passing through bridge expansion openings and damaging superstructure and substructure components.