Abstract
At two locations, a total number of 1300 observations were made by use of aerial photography to measure the speed, vR, of entering vehicles, the time-headways, t, in the outside lane of the expressway and the speed, vB, of vehicles in that lane. This data was combined in a function, X =a1. vR + a2. t + a3. vB, such that values of referring to situations in which vehicles did not enter. This kind of statistical method is known as multiple discriminatory analysis. An evaluation of the coefficients ai of the above equation showed that the length of the required time gap, t, decreases sharply with the entering speed, vB. For values of vR=80 km-h, the acceptable time gaps increased: beyond this speed there was again a decrease.