An overhead traveling vehicle system for transporting articles to and from a load port (16, 17) provided in a front surface of a processing device, the system comprising: overhead traveling vehicles that have a hoist for raising and lowering an article; an overhead traveling vehicle track for said overhead traveling vehicles; a local carriage track provided at a position that is over the load port (16, 17) and directly under the overhead traveling vehicle track; a local carriage that includes a hoist for raising and lowering an article and is arranged to travel along the local carriage track; a buffer, wherein both the overhead traveling vehicles and the local carriage are configured to carry an article to and from the buffer by means of the hoists (22, 27); a first sensor attached to the local carriage track and configured to monitor an obstacle that is in a vicinity of the load port (16, 17) and in a passageway-side area on a side opposite to the processing device; and a communication terminal (56, 64) that is configured to transmit an obstacle detection signal from the first sensor to the overhead traveling vehicles and the local carriage, wherein both the overhead traveling vehicles and the local carriage are configured to carry articles to and from the load port (16, 17) by means of the hoists (22, 27), wherein the buffer is suspended from the local carriage track by vertical supports that extend vertically downward, and is configured such that, in use, no part of the buffer exists directly over the load port (16, 17), and wherein the overhead traveling vehicles and the local carriage are configured and programmed to stop the hoists (22, 27) when, in use, the obstacle detection signal from the first sensor is received via the communication terminal (56, 64), characterized in that the overhead traveling vehicles have a second sensor for monitoring an obstacle below; the overhead traveling vehicles are configured and programmed such that, in use, when downward monitoring is not necessary for load ports (16, 17) provided with the first sensor, the second sensor is switched off or the signal therefrom is ignored, and obstacles in the passageway-side area are not monitored by said second sensor. overhead traveling vehicles that have a hoist for raising and lowering an article; an overhead traveling vehicle track for said overhead traveling vehicles; a local carriage track provided at a position that is over the load port (16, 17) and directly under the overhead traveling vehicle track; a local carriage that includes a hoist for raising and lowering an article and is arranged to travel along the local carriage track; a buffer, wherein both the overhead traveling vehicles and the local carriage are configured to carry an article to and from the buffer by means of the hoists (22, 27); a first sensor attached to the local carriage track and configured to monitor an obstacle that is in a vicinity of the load port (16, 17) and in a passageway-side area on a side opposite to the processing device; and a communication terminal (56, 64) that is configured to transmit an obstacle detection signal from the first sensor to the overhead traveling vehicles and the local carriage, wherein both the overhead traveling vehicles and the local carriage are configured to carry articles to and from the load port (16, 17) by means of the hoists (22, 27), wherein the buffer is suspended from the local carriage track by vertical supports that extend vertically downward, and is configured such that, in use, no part of the buffer exists directly over the load port (16, 17), and wherein the overhead traveling vehicles and the local carriage are configured and programmed to stop the hoists (22, 27) when, in use, the obstacle detection signal from the first sensor is received via the communication terminal (56, 64), characterized in that the overhead traveling vehicles have a second sensor for monitoring an obstacle below; the overhead traveling vehicles are configured and programmed such that, in use, when downward monitoring is not necessary for load ports (16, 17) provided with the first sensor, the second sensor is switched off or the signal therefrom is ignored, and obstacles in the passageway-side area are not monitored by said second sensor.