Vehicle presence, speed and length detecting system and roadway installed detector therefor

A highway vehicle sensing and communication system comprising:

• a transceiver for transmitting extremely low frequency (ELF) signals to a remote location and receiving ELF signals from the remote location, said transceiver including first and second matched induction coil magnetic sensors maintained at or near a roadway surface, each of said sensors having a longitudinal axis aligned normal to the roadway surface, said sensors being separated from one another by a known distance in a direction substantially aligned with a direction of traffic flow, each of said sensors further generating a differential magnetic field signature with respect to time to indicate the passing vehicle's leading and trailing edge magnetic signatures;
• a triaxial magnetometer maintained at a location in close proximity to said first and second sensors, for measuring a DC magnetic field at said location, said DC magnetic field having vertical and horizontal magnetic field components with said horizontal components including a component substantially aligned with the direction of traffic flow and a component substantially perpendicular to the direction of traffic flow;
• and
• processing means for determining a first, second and third time interval, said first time interval occurring between the passing vehicle's leading edge magnetic signatures detected by said first and second sensors, said second time interval occurring between the passing vehicle's trailing edge magnetic signatures detected by said first and second sensors, and said third time interval occurring between the passing vehicle's leading and trailing edge magnetic signatures detected by one of said first and second sensors, wherein vehicle speed is determined by a time-distance relationship using one at least of said first and second time intervals and said known distance, vehicle length is determined by a time-speed relationship using said third time interval and said determined vehicle speed, and vehicle presence is determined by said vertical and horizontal components caused by the passing vehicle.

A highway vehicle sensing and communication system comprising:

• first and second matched induction coil magnetic sensors maintained at or near a roadway surface, each of said first and second sensors having a longitudinal axis aligned normal to the roadway surface, said first and second sensors being separated from one another by a known distance in a direction substantially aligned with a direction of traffic flow, each of said first and second sensors further generating a differential magnetic field signature with respect to time to indicate the passing vehicle's leading and trailing edge magnetic signatures;
• third and fourth matched induction coil magnetic sensors maintained at or near the roadway surface in close proximity to said first and second sensors, each of said third and fourth sensors lying in a unique horizontal plane and having a longitudinal axis aligned substantially parallel to the roadway surface, said third and fourth sensors forming an orthogonal crossing pattern when viewed with respect to a direction normal to the roadway surface, said orthogonal crossing pattern arranged so that each of said third and fourth sensor's longitudinal axis bisects the direction of traffic flow by an angle of approximately 45°, wherein said third and fourth sensors transmit extremely low frequency (ELF) signals to the passing vehicle and receive ELF signals from the passing vehicle;
• a triaxial magnetometer, maintained at or near the roadway surface in close proximity to said first through fourth sensors, for measuring a DC magnetic field thereat, said DC magnetic field having vertical and horizontal magnetic field components with said horizontal components including a component substantially aligned with the direction of traffic flow and a component substantially perpendicular to the direction of traffic flow;
• and
• processing means for determining a first, second and third time interval, said first time interval occurring between the passing vehicle's leading edge magnetic signatures detected by said first and second sensors, said second time interval occurring between the passing vehicle's trailing edge magnetic signatures detected by said first and second sensors, and said third time interval occurring between the passing vehicle's leading and trailing edge magnetic signatures detected by one of said first and second sensors, wherein vehicle speed is determined by a time-distance relationship using at least one of said first and second time intervals and said known distance, vehicle length is determined by a time-speed relationship using said third time interval and said determined vehicle speed, and vehicle presence is determined by said vertical and horizontal components caused by the passing vehicle.

In a highway vehicle detection system for determining vehicle presence, vehicle speed and vehicle length, an improved detector for installation in a roadway surface comprising:

• first and second matched induction coil magnetic sensors maintained at or near the roadway surface, each of said sensors having a longitudinal axis aligned normal to the roadway surface, said first and second sensors being separated from one another by a known distance in a direction substantially aligned with a direction of traffic flow, each of said first and second sensors generating a differential magnetic field signature with respect to time to indicate a passing vehicle's leading and trailing edge magnetic signatures, wherein first, second and third time intervals associated with said leading and trailing edge magnetic signatures are used in conjunction with said known distance to determine vehicle speed and vehicle length, said first time interval occurring between the passing vehicle's leading edge magnetic signatures detected by said first and second sensors, said second time interval occurring between the passing vehicle's trailing edge magnetic signatures detected by said first and second sensors, and said third time interval occurring between the passing vehicle's leading and trailing edge magnetic signatures detected by one of said first and second sensors, wherein said vehicle speed is determined by a time-distance relationship using at least one of said first and second time intervals and said known distance, and wherein said vehicle length is determined by a time-speed relationship using said third time interval and said determined vehicle speed;
• and
• a triaxial magnetometer maintained at a location in close proximity to said first and second sensors, for measuring a DC magnetic field at said location to determine vehicle presence, said DC magnetic field having vertical and horizontal magnetic field components with said horizontal components including a component substantially aligned with the direction of traffic flow and a component substantially perpendicular to the direction of traffic flow, wherein said vertical and horizontal components caused by the passing vehicle are used to determine vehicle presence.