Diamond lane on 19th

I looked at Google streetview and see what you mean. I wouldn’t know what they meant either. According to VA DMV they signify an HOV lane (last page). According to Wikipedia, they mean:

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 road. They are usually implemented to provide ways through traffic congestion, for safety reasons, and to encourage environmentally friendly transportation. A diamond lane may be intended for a specific type of traffic, or for several types. The intended use of a diamond lane is marked by traffic signs. In most areas, violating the rules of a diamond lane is punishable by a fine.

Some common examples are:

• High-occupancy vehicle lane, also known as a carpool lane. These are typically freeway lanes intended for multiple occupant or “green vehicles” (such as hybrid or electric cars).
• Bike lane, sometimes referred to as segregated cycle facilities. Separating bicycle traffic from pedestrian or motor vehicle traffic is typically safer and improves traffic flow.
• Bus lane, an uncongested lane for buses to travel, load, or unload in.
• Emergency vehicle lane, to help emergency vehicles get to their destination as fast as possible while avoiding traffic congestion.
• Taxicab lanes, most often found at airports or other transit hubs for passenger loading and unloading.
• Horse and buggy lanes in areas with significant Amish populations

In the case of 19th Street, perhaps it’s for drivers planning on taking the Rte 66 HOV lanes???