Pivot table that has subtotals that show sums of averages rather than average of averages

I am creating a pivot table to display the weekly average and monthly average of use different types of buses. The pivot is currently showing averages that I have calculated using an AVERAGEIF in the source data. These include a monthly and weekly average.
The averages all work well however I need the subtotals for each Category. ie BUS CAR VAN, to be a total of the averages rather than an average of the averages.
Screenshots of the pivots and the source data are in the Imgr album below. http://imgur.com/a/qWelT
Any help is greatly appriciated.

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