What is a potential risk of not placing the transmission in neutral after uncoupling?

Not placing the transmission in neutral after uncoupling poses a significant risk, primarily because the trailer may roll away. When the tractor and trailer are uncoupled, the parking brake system of the trailer takes over to secure it in place. If the transmission is not in neutral, this can lead to an unstable condition where the trailer might not be fully secured, particularly if the ground is not level or if there are other forces acting upon the trailer, such as wind or vibrations.

When the vehicle’s transmission is not properly positioned, it increases the chance that the trailer's brakes may not hold adequately, which can result in it rolling away. This is a critical safety concern in the operation of vehicles with trailers, especially in situations involving loading or unloading, where personnel could be at risk if the trailer moves unexpectedly.

The other risks mentioned do not adequately address the immediate safety concern that comes from failing to engage the neutral gear, which is why it is crucial to ensure the transmission is in neutral to prevent any risk of the trailer rolling away.