Abstract: A traffic flow change monitoring system is disclosed, which uses data obtained from a vehicle perceiving sensor placed on a road and which can detect a traffic congestion or an unexpected event. Since a change in traffic flow is monitored on the basis of the speeds or the like of individual vehicles and the distances between successive vehicles, it is possible to monitor a positional relationship between successively running vehicles Also, it is possible to make a prompt detection of an unexpected event such as an accident by detecting a change in relative vehicle speed difference between traffic lanes at each measurement spot.

Abstract: Assuming that a given equation representing a quadratic curve is:F(x, y)=ax.sup.2 +bxy+cy.sup.2 +dx+ey+f=0,the method for generating quadratic curve signals repeatedly selects a point close to F (x, y)=0 in only one of either the region of F (x,y).gtoreq.0 or the region of F (x,y)<0. This method allows to generate quadratic curve signals by using only a few parameters and without using complicated calculations. A hardware implementation is also disclosed.