For tolling purposes, how do you differentiate between a large passenger van and a small truck, or between a small truck and a large truck? 

New York State has classified these vehicles as:

• Vans that do not have raised rooflines above the top of the windshield or body modifications extending beyond the driver’s cab are classified and charged as passenger vehicles. These vans maintain their original structure without significant alterations.
• Small trucks, also known as single-unit trucks, include various types of non-articulated trucks. This category encompasses pickup trucks with modified beds, vans that have body modifications behind the driver’s cab, pickup trucks with caps that extend above the roofline or over the sides, and vans with an extended roof above the windshield. Examples of small trucks include vehicles commonly used for grocery or package deliveries.
• Large trucks, or multi-unit trucks, refer to articulated trucks where a power unit is connected to and carries one or more trailers. These trucks are typically used for transporting larger loads over longer distances.