Question 1187885
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I will guess that the problem is not presented correctly.<br>
With the questions that are asked, the fact that the tunnel cross section is semi-elliptical is irrelevant....<br>
Furthermore, with only the given information, the two lanes closest to the edge of the tunnel will have zero height on their edges, which is absurd....<br>
Nevertheless... to answer the questions that are asked....<br>
i. The width of the tunnel is given: 14.64m.<br>
ii. With a total width of 14.64m, four lanes, and three barriers of 0.6m between lanes, the width available for the 4 lanes is 14.64-3(0.6) = 14.64-1.8 = 12.84m.  That makes the width of each lane 12.84/4 = 3.21m.<br>
Since the picture drawn by that response is nonsensical, I suggest you re-post the problem presenting the information clearly and correctly.<br>