Method and apparatus for monitoring traffic flow

A method for determining the interval between first and second vehicles traveling along a predetermined path, comprising the steps of:

• generating a reference image of a section of said path;
• transducing said reference image into a reference array of pixels;
• generating successive images of said section of said path;
• transducing said successive images into successive arrays of pixels;
• successively comparing pixel intensity information obtained from each one of said successive arrays to pixel intensity information obtained from said reference array;
• generating data indicative of the presence of said first vehicle in said section of said path when the difference in pixel intensity information between one of said successive arrays and said reference array exceeds a predetermined value;
• recording a first reference time when said first vehicle is determined to be present in said section of said path;
• generating data indicative of the presence of said second vehicle in said section of said path when the difference in pixel intensity information between a second one of said successive arrays and said reference array exceeds said predetermined value;
• recording a second reference time when said second vehicle is determined to be present in said section of said path;
• and
• calculating the interval between said first and second vehicles from the difference in said first and second reference times.

A method for determining the length of a vehicle traveling along a predetermined path, comprising the steps of:

• generating a first reference image of a first section of said path;
• transducing said first reference image into a first reference array of pixels;
• generating first successive images of said first section of said path;
• transducing said successive images into first successive arrays of pixels;
• successively comparing pixel intensity information obtained from each one of said first successive arrays to pixel intensity information obtained from said first reference array;
• generating data indicative of the presence of said vehicle in said first section of said path when the difference in pixel intensity information between one of said first successive arrays and said first reference array exceeds a first predetermined value;
• recording a first reference time when said vehicle is determined to be present in said first section of said path;
• generating data indicating that said vehicle has vacated said first section of said path when the difference in pixel intensity information between one of said first successive arrays and said first reference array falls below a second predetermined value;
• recording a second reference time when said vehicle is determined to have vacated said first section of said path;
• determining the difference between said first and second reference times;
• determining the speed of said vehicle;
• and
• determining the length of said vehicle by multiplying said time difference by the speed of said vehicle.

A method for tracking the movement of a vehicle within the field of view of a video camera, comprising the steps of:

• generating successive images of said field of view;
• transducing said successive images into successive arrays of pixels;
• identifying the coordinates of pixels associated with the image of said vehicle for each of said successive arrays;
• electronically determining the centroid of the image of said vehicle from said coordinates;
• and
• recording the coordinates of said centroid for each of said successive arrays.