Yes they can be washed in washing machine.
I love them, they stick well and can be washed in a washing machine. I washed mine after 4 months. Shake them out before washing. I washed them in COLD, Quick wash cycle, regular tide detergent, NO softener. Dry them on medium, no dryer sheets, for 10 minutes and then check every 5 minutes afterward. I damp-dried them and then hung them to dry the rest of the way on a drying rack in my garage. I have also dried them until they were fully dried, but I would keep checking on them so I did not over-dry them. The sticky silicon on the back will probably be covered in sand (dirt particles) and lint after washing and drying. Use a tape lint roller to remove anything stuck to the silicon after washing. This also happened to a couple of my treads while they were on the stairs if we tripped on them. Fur and dust eventually took over the sticky part. We used a tape lint roller on the back and they stuck right back on. These are worth the price, are made well, and stand up well to a crazy dog and kids! We bought the small landing rug also, it's my favorite and makes it all come together and look great!