Calculate the percentage by column total and not by the grouped variable

Question

As a follow up to this question, what is the best way if you would like to calculate the percentage not as a share inside of the group, but rather as a share of the column total.

d <- read.table(text="Fuel     Year   Region   Count
Gasoline 2013       GE  169600
                Diesel   2013       GE   46790
                Hybrid   2013       GE    2268
                Electric 2013       GE      85
                Other    2013       GE     532
                Gasoline 2013       VS  149232
                Diesel   2013       VS   50591
                Hybrid   2013       VS    1028
                Electric 2013       VS     268
                Other    2013       VS     261", header = TRUE)


d <- data.table(d)

I would then like to calculate the share of fuels irrespective of the regions. So in a first step I would like to have this:

d[, .(Car.Total = sum(Count)), by = "Fuel"]

Is there a better way to calculate the percentage than this:

d[, .(Car.Total = sum(Count)
    , Car.Share = sum(Count)/sum(d[,Count])), by = "Fuel"]

This seems pretty inefficient, but works. Is there any more efficient way using only data.table methods.