Correct choice is (a) spot speed
For explanation I would say: Enoscope consists of a simple open housing containing a mirror mounted on a tripod at the side of the road in such a way that an observer’s line of sight turned through 90o. The observer stands at one end of section and on the other end enoscope is placed and measure the time taken by the vehicle to cross the section (fig 6.2). Advantages of this method are that it simple and eliminate the errors due to parallax and considerable time is required to time each vehicle, which lengthen the study period and under heavy traffic condition it may be difficult to relate ostentatious to proper vehicle are the disadvantages of enoscope method.
