In some states it is law to merge into a left lane when a vehicle is in the emergency lane - this means there will be a clear lane between the stationary vehicle and the moving vehicle. This would be especially important when the stationary vehicle is a police car.
Emergency vehicles - you are required to pull to the right and stop when an emergency vehicle is in the vicinity (lights flashing).
Counting Wal-Mart trucks helps to pass the time. FedEx trucks are the most common, if you are going to count those you will be busy. Swift trucks are also common.