When a new road is being planned, or extensive improvements are to be carried out to an existing road, or a bypass is under consideration, the amount of traffic likely to sue it cannot be ascertained from a simple census and it may become necessary to collect information about the origin and destination of traffic passing through the main area in which the road is situated. The origin-destination survey is normally conducted for three consecutive days, on sample basis, if possible during a representative week in the year and must encompass the weekly market day and one working day. For exceptional cases, in heavy density corridors and where the daily variation in the traffic is not much, at least one day survey may be conducted on a normal working day. Care shall be taken during interpretation of the data keeping in mind the seasonal variation of traffic.