If, then, there be included under the head of pleasure passenger traffic all not purely business it may with propriety be estimated that three-fourths of all automobile travel is for pleasure. Considering ten million automobiles in use in the United States, that they average 4000 miles per year and carry two passengers each, there results a total passenger mileage of 10,000,000 × 4,000 × 2 = 80,000,000,000 80 billion miles. A number beyond ordinary comprehension. The passenger mileage upon the steam railroads is roughly speaking about 37¹⁄₂ billion miles, a little less than half as much as that by automobile. It is evident that all this travel, even though a large percentage be local, must affect seriously the earnings of the steam and electric railway lines. Since 75 per cent may be estimated to be for pleasure purposes, it will not be possible for the steam and electric lines ever to regain it. The people who do the dancing are perfectly willing to pay the piper, and even though automobile riding cost more than trolley or train riding the people will continue to have it as a means of entertainment.[168] Most men who own cars pay the expenses in lump sums and forget about them. To have the speedometer register in dollars and cents instead of miles, while it might be a deterrent on the use of the automobile, would “take the joy out of life.” =Freight Traffic.=--When it comes to freight traffic cost and time will be the principal factors to determine the type of performance. The element of pleasure is here eliminated and only cold economical features remain. Already horse trucking is rapidly disappearing as it seems to be able to compete with the motor only where many stops are to be made. In large cities motor trucks are utilized to haul packages to certain districts at considerable distances from the store, where they are turned over to small wagons for delivery. Ice and milk are often distributed in the same manner, thus taking advantage of long rapid hauls upon fully loaded trucks and less expensive delivery wagons where many stops are to be made and smaller loads are to be carried. Even in delivery service some merchants have by carefully arranging and timing their routes brought the cost of delivery to below ten cents per parcel. All purchasers of goods at the store whether delivered or not should be interested in reducing this cost because usually in the accounting it is spread out over the entire turnover and charged to the expense of doing business. It may be possible that in a few years horses will be barred from the streets for sanitary reasons; then it will be necessary to use motors for all sorts of deliveries, possibly large ones for hauling to the distant districts and small ones for the house to house delivery in the district.