you overtake a truck on the inside and now want to change lanes. why is this a problem?

Overtaking a truck on the inside and then wanting to change lanes is a problem primarily because if the overtaking vehicle slows down during the lane change, the truck behind it may not be able to stop in time. Trucks have much longer stopping distances compared to smaller vehicles, so a sudden deceleration close to a truck can increase the risk of a collision. Additionally, the truck driver may not expect a vehicle to suddenly move back into the lane beside them, making the maneuver more dangerous. In summary, the key safety concern is that slowing down after overtaking on the inside puts the truck at risk of not being able to brake safely, increasing the chance of an accident.