Following is an array of questions to test your reasoning ability in different situations. Answer each of them according to the question asked in each of them respectively:

If highways were restricted to cars and only those trucks with capacity of less than 8 tons, most of the truck traffic would be forced to run outside highways. Such a reduction in the amount of truck traffic would reduce the risk of collisions on highways. The conclusion drawn in the first sentence depends on which of the following assumptions?

The correct answer is: Most trucks that are currently running in highway have a capacity of more than 8 tons.

Step-by-Step Explanation:

1. Understand the Premise and Conclusion:
- Proposed Rule: Highways are restricted to cars and trucks with a capacity of less than 8 tons.
- Conclusion (First Sentence): Under this rule, most of the truck traffic would be forced to run outside highways.

2. Identify the Missing Assumption:
For the conclusion to hold true—that restricting highways to trucks under 8 tons will force most truck traffic off the highways—it must be true that most of the trucks currently using the highways actually exceed this 8-ton limit. If most trucks currently on the highway were already 8 tons or less, restricting the highway to trucks under 8 tons would not force "most" of them off the highways.

3. Evaluate the Options:
- Option 1: "The roads outside highway would be as convenient as highway for most drivers of trucks." - This speaks to convenience, not whether traffic will actually be shifted based on capacity.
- Option 2: "Most of the roads outside highways are not ready to handle truck traffic." - This discusses the readiness of alternate roads, which is irrelevant to whether the rule itself forces traffic off the highway.
- Option 3: "Most trucks that are currently running in highway have a capacity of more than 8 tons." - This is the necessary assumption. If current trucks are mostly over 8 tons, the rule directly forces most of them off the highway.
- Option 4: "Cars are at greater risk of being involved in collisions than are trucks." - This relates to the second sentence about collision risks, not the assumption behind the first sentence's conclusion.

Therefore, the conclusion logically depends on the assumption stated in Most trucks that are currently running in highway have a capacity of more than 8 tons.