A "diamond lane" is another name for a "HOV (High Occupancy Vehicle) Lane," so named because they are typically marked with diamonds painted on the pavement (and sometimes on lighted signs above them).
A high-occupancy vehicle lane (also known as an HOV lane, carpool lane, diamond lane, 2+ lane, and transit lane or T2 or T3 lanes) is a restricted traffic ...
A special driving lane reserved for specific types of traffic.
In the United States and Canada, a diamond lane is a special lane
on a street or highway that is reserved for specific types of traffic.
These lanes are usually marked with white diamonds or lozenge, hence
their name. Diamond lanes are generally the right-most or left-most
lane on the ...