I saw him drive through the tunnel.
I saw him driving through the tunnel.
I saw him walking along the road.
I saw him walk along the road.

Please correct my sentences.
User_garyI saw him drive through the tunnel. I saw him driving through the tunnel.
The first is: He drove through the tunnel, and I saw that (saw the whole event; saw him go in one end and come out the other end).
The second is: He was driving through the tunnel when I saw him. (I don't know if he ever came out the other end!)
User_garyI saw him walking along the road.
He was walking along the road when I saw him. (I don't know where he came from or where he was going. He was just walking there.)
User_garyI saw him walk along the road.
Walking along a road has no goal. It's an activity. You never see the end of an activity that has no defined end point, so this one is a bit anomalous.

Compare with "go through a tunnel". Once you've come out the other end of the tunnel, the event is finished. There's an end point. Therefore, you can see the whole event.


I saw ... [state verb]. - No. *I saw the bottle contain wine.
I saw ... [state verb + ing] - No. *I saw Jack having a brother.
I saw ... [activity]. No. *I saw her work in the garden. *I saw them shop at the mall.
I saw ... [activity + ing] OK. I saw her walking. I saw them playing in the garden.
I saw ... [event] OK. I saw the dog jump over the fence.
I saw ... [event + ing] OK. (can focus on part of the event before it finishes) I saw the car going through the tunnel.

All of your sentences are correct. The difference between them is that the -ing endings give the idea that the action was of a longer duraction in comparison to the other events that were happening. If you were mentioning to a friend that you saw him doing the activity during your drive home, and that was all you sw him doing, you would probably use the -ing ending.
However, if you were telling a story in which you saw the person do many things, and so the duration of this specific activity was not as long when a bigger picture is given, you may choose to use the infinitive root alone. For instance, if someone asked you what you saw him do after he drove out of the parking lot, you might choose to say, "I saw him drive through the tunnel." If you went on to tell another detail, it might be, "Then I saw him drive down the highway." Then the part of the story about the tunnel is much shorter in comparison to the entire story.

So really, the only difference is context. Most of the time, I'd expect the progressive (-ing) verb to work better, just because both of these activities can have a long duration. For the tunnel example, it actually could also depend on how long the tunnel was. If it was a very short tunnel, it would be more likely to be said with the root verb (no -ing). We could assume the road is long, and so the -ing would be even more likely for that sentence.
I know, it is not a straightforward answer, but little of English is perfectly clear.
Let me know if I just made it more confusing!

~Miss Mandy
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You are quite right about the duration. However, the explanation is a little bit confusing. the sentence " I saw him walking along the street " gives the idea that I saw the whole process of him walking. And the sentence" I saw him walk along the street" states just the fact, no duration is involved.
 CalifJim's reply was promoted to an answer.