What type of vehicles are likely to get stuck on railroad-highway crossings?

Answer: B — Low slung units and single-axle tractors

Low slung units and single-axle tractors are indeed more likely to get stuck on railroad-highway crossings due to their design and clearance height. These vehicles often have a lower profile, which means they can more easily encounter elevation changes at crossings. When the road meets the railroad tracks, there can be a dip or a rise, and vehicles that sit lower can bottom out, causing them to become stuck. In contrast, passenger cars and SUVs, while they may also experience issues, typically have a greater clearance than low slung units. Large buses and vans, depending on their size and weight distribution, may handle crossings better. Motorcycles and pickup trucks usually have sufficient clearance and maneuverability to navigate these crossings without difficulty. Therefore, low slung units and single-axle tractors are particularly vulnerable at railroad-highway crossings, making them the correct choice.