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The trolley would get stuck after a couple of people.
The closer they are bundled together, the more efficient the obstacle.
So, option B. 
However people that close together can probably help each other out. Just one needs to be able to free an arm by chewing on the rope next to him to release someone else and once two are out everyone is.
Placing them further apart makes sure that they can't reach out to each other to help.
Sure you could pull out all the teeth and cut off the hands but that would make the whole endeavor far less efficient and more costly.
There are 7,530,000,000 people on the planet.
The avg. arm span is 5.6ft or 168cm. Let's make that 6 for a safety margin.
You would need 45,180,000,000 ft. of rail or 8,556,818 miles.
Assuming no one is able to break free their hands, you could do half that to prevent people with long necks from freeing each other.
You could probably also greatly reduce the number if you look further into demographics such as age and height.
