=Methods of Taking Traffic Censuses.=--It is well known that the traffic on any road is not constant. A count, then, made on a single day could not be applied for an entire year. Counting every day for the year would, of course, give a correct total, but that is impracticable. It is customary, therefore, to take the count on a limited number of days and consider their average to be the average for the year. There seems to be a seasonal variation in traffic and a weekly variation. The season variation in crops affects all sorts of commercial enterprises, of which the road traffic is one. Sunday traffic is largely pleasure traffic, and is more dense as a rule than week-day traffic, which is partially pleasure and partially business. In France, where more regular and scientific censuses have been made than in any other country, the counting days are divided uniformly between the seven days of the week and the four seasons of the year, in order to eliminate, as far as possible, the periodic variation. The number of counting days per year is therefore, 28, and these are so arranged that each of the days of the week figures once in each quarter. The interval between counting days is, consequently, 13. For 1923, then, the count might be made as follows: -----------+-----------+----------+----------+----------- Days of the| | | | Week |1st Quarter|2d Quarter|3d Quarter|4th Quarter -----------+-----------+----------+----------+----------- Monday | Jan. 1 | Apr. 2 | July 3 | Oct. 2 Sunday | 14 | 15 | 16 | 15 Saturday | 27 | 28 | 29 | 28 Friday | Feb. 9 | May 11 | Aug. 11 | Nov. 10 Thursday | 22 | 24 | 24 | 23 Wednesday | Mar. 7 | June 6 | Sept. 6 | Dec. 6 Tuesday | 20 | 19 | 19 | 19 -----------+-----------+----------+----------+-----------