I wrote this on another thread and, as I went to the trouble of doing it, I thought I would copy it here, in the hope that some people might find it helpful. Apologies for telling you what you already know.
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The Trolley Case (what's that?):

A. I’m the conductor on a runaway trolley which is on a track such that it will kill five innocent workmen unless I switch to a sidetrack, where it will kill only one workman.

This is often coupled with another case,

B. The same scenario but there is no sidetrack. However there is a very fat man on the trolley and if I throw them over the front, his body will brake the trolley, so that it stops before it kills the five.

Many people feel that, though both A and B have the same cost benefit analysis, one dies, five live, A is permissible but B is not. In the first case I’m not trying to hit the lone workman on the sidetrack. He death isn’t part of my plan. His death is the foreseen but undesired side effect of what I do to save the five, namely, switch tracks.

Jeremy Bentham said that a consequence of an act is ‘obliquely intended’ when it is foreseen but not desired. The workman’s death is obliquely intended.

In case B., I’m trying to run over the fat man with the trolley, as a means of saving the five. Hitting him with the trolley is part of my plan. Bentham said that an effect of a voluntary act is ‘directly intended’ when it is foreseen and desired both. The harm I do the fat man is directly intended, not for its own sake, but as a means of saving the five.

This goes to the Doctrine Of the Double Effect, a medieval Roman Catholic doctrine, according to which it is sometimes permissible to bring about by oblique intention what it would be wrong to bring about by direct intention.

A consequence of the doctrine is that A. is permissible, B is not. The doctrine, which is quite controversial, is applied in many practical circumstances, including medical ethics and the Catholic doctrine of The Just War.

The cases also go to the ‘consequentialist’ doctrine that the consequences of actions are all that determine their moral value. Utilitarianism is such a doctrine.  As both A and B have the same Consequences, one dies, five live, if we decide that they have different moral worth, we reject consequentialism.

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I add this:

The force of the doctrine in the trolley case is that switching tracks is permissible. Especially I am not trying to hit the lone workman with the trolley. If somehow he escapes, I saved the five in precisely the way I meant to. There was nothing I was trying to do that I failed to do. His death is desired neither as an end nor as a means. This helps explain why switching tracks is permissible, according to the doctrine. The intentions with which I act make a moral difference.

A Roman Catholic doctor, treating a dying patient whose death is imminent and who is in serious pain, may treat aggressively for pain, even to the point, if it is necessary for pain control, of suppressing breathing and killing the patient. The idea is that as the medical mission of saving life is justly abandoned, because it cannot be accomplished, the mission of relieving pain is all that remains. So she can knowingly kill her dying patient as the foreseen but undesired side effect of giving adequate pain control. But she cannot try to kill him. If she gives the adequate dose of morphine and he doesn’t die but is simply relieved of his pain, there was nothing she was trying to do that she failed to do. His death wasn’t part of her plan though she knew she would kill him.
However the doctor who, in precisely the same circumstances,  gives the same dosage of morphine because he wants to kill the patient to put her out of her misery, is trying to kill the patient, which is forbidden. In short, there may be circumstances where it is permissible to kill the dying patient but there are no circumstances where it is permissible to intentionally kill him.

(As Roman catholic medical ethics became part of professional medical ethics proper, it has long been part of standard medical practice that there can be circumstances where it is permissible to knowingly kill a patient and also to permissibly let a patient die whose life could be saved ( where the treatment would pose a 'grave burden' to the patient), even though killing or letting die with the intention that the patient will die were forbidden. Within the prohibition on euthanasia there has been considerable latitude on killing and letting die.)

In fighting a just war, we may bomb the enemy’s munitions plant which is placed near a day care center. When the munitions plant blows up it will kill the children in the day care center. The deaths are foreseen but not desired, obliquely intended, so permitted. But suppose we learn that the dictator’s child is at the day care center and we know him well enough to know that if the child dies he will lose all will to fight and will sue for peace. We are forbidden to target the day care center itself, because then the death of his child, who is innocent, is directly intended. Knowingly killing innocent people in wartime can be permissible, but intentionally killing innocent people is murder and is strictly forbidden.

In such cases The Doctrine of the Double Effect is combined With the Doctrine of Proportionality. Civilian casualties must not outweigh the value of the military target. The idea is NOT that we can permissibly kill lots of innocent people as long as we do not directly intend their death. Killing must not demonstrate ‘a reckless disregard for human life.’ If it does, killing is murder even if the deaths are not desired. If I use a hydrogen bomb in a crowded city to take out a radar installation, thereby making sure to get it on the first try, not caring one way or another about the million people I kill by oblique intention, I commit murder according to the Doctrine of Double Effect.

Personally I believe it is permissible to switch tracks for precisely the reasons the doctrine captures. I’m not trying to kill anybody, the death is the foreseen but undesired side effect of what I do to save the five. No one is being used as a means, no one is being exploited. I think the intuition to the contrary tends to flow from viewing the killing of the lone workman as if he is being targeted in a way that he isn’t. I'm just trying to get off the main track in the only way I can.

If switching tracks is permitted, I think one can argue that it is what I ought to do, in the following way:
if I’m in a situation in which I will do serious harm no matter what I do, and there is a morally permissible alternative which involves doing far less harm than I will otherwise do, then I ought to take it. All things being equal, I ought to do as little harm as possible.