[What is required of a driver who caused an accident from which his passengers died]

The answer – and Allah is the One who grants what is correct – is that if the driver was the one who caused the accident by mistake, then the diyahs of those killed are obligatory, but they are borne on his behalf by his ʿāqilah (male agnatic relatives).
Mistaken killing (qatl al-khaṭaʾ) is divided into two types: one type in which both diyah and kaffārah (expiation) are required, and another type in which diyah is required but not kaffārah. The type in which both diyah and kaffārah are required is mistaken killing by direct action; and the type in which only diyah is required is mistaken killing by causation. Among its examples is that a person digs a pit in a public right of way and someone falls into it and dies, or that he places a stone in a public right of way and a person dies as a result of it.
In light of this, we look at the car accident:
1 – If the accident resulted from a defect in the car or bus – such as the tyres (wheels) exploding, the brakes failing, or the like, which leads to the driver losing control over the vehicle and being unable to manage it – then such a case is considered killing by causation, and no kaffārah is required.
2 – If the accident was caused by a stone or the like in the road, or another car, or a donkey, or a camel, or the like getting in the way of the bus so that the bus collides with it and deaths result from that, then no kaffārah is required.
3 – If the car’s lights go out, or the lights of other cars dazzle and confuse the driver, or something occurs on the road that causes skidding – all while the speed is the normal, customary speed – and an accident occurs thereby in which someone perishes, then no kaffārah is required.
4 – If two cars collide and deaths occur as a result of that, then there is no kaffārah.
5 – If a fire breaks out in the vehicle because of a car accident, and someone dies because of the fire, then there is no kaffārah.
There remain cases that are as follows: when the bus or car leaves its lane due to an action of the driver and strikes into a ravine, a mountain, or the like. Examples of this include:
1. The driver falls asleep.
2. Leaving the lane due to the driver’s heedlessness, such as being occupied with playing with his child, or searching for something, or the like.
3. Leaving the lane in order to escape from something he sees in his path, such as another car or the like.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2