In Ireland, the majority of commercial forests are located in remote areas on predominantly peat soils. These roads exhibit rapid deterioration when traversed by logging vehicles or other heavy machinery. A study of the attributes of forest access roads in Ireland was published in the International Journal of Forest Engineering (July 1999). One measure of the strength of pavement is transient surface deflection— the higher the surface deflection, the weaker the pavement. The type of pavement (mineral subgrade or peat subgrade) was determined for a sample of 72 forest access roads, then each was analyzed for surface deflection (measured in millimeters). The results are summarized in the next table.

a. Compare the two pavement types with a 95% confidence interval. Which pavement subgrade, mineral or peat, is stronger?

b. Compare the surface deflection variances of the two pavement types with a 95% confidence interval. Which pavement subgrade, mineral or peat, has the largest surface deflection variance?

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Pavement Subgrade Mineral Peat Number of roads 32 40 Mean surface deflection (mm) 1.53 3.80 Standard deviation 3.39 14.3