A transport system for transporting carriers between load ports of equipment, comprising: overhead travelling vehicles provided with a first hoist (34, 35, 36) configured to raise and lower carriers and a lateral transfer mechanism configured to laterally move the first hoist (34, 35, 36); a first travelling rail for the overhead travelling vehicles provided in a ceiling space of a building and passing over a load port; a local vehicle provided with a second hoist configured to raise and lower carriers; a second travelling rail for the local vehicle, provided at a position below the first travelling rail for the overhead travelling vehicles and over the load port; at least one slidable buffer configured to slide between a forward position under the second travelling rail for the local vehicle and a rearward position laterally separated from the position under the second travelling rail for the local vehicle and to support a carrier thereon; and a buffer controller configured and programmed to control the local vehicle and the slidable buffer, wherein a space above the slidable buffer at the rearward position is open for a transfer of carriers, wherein the overhead travelling vehicles are configured and programmed to transfer carriers between the load port and the slidable buffer located at the rearward position, wherein the local vehicle is configured to transfer carriers between the load port and the slidable buffer located at the forward position, wherein the second travelling rail for the local vehicle extends from the position over the load port to a waiting position for the local vehicle shifted from the position over the load port, wherein the local vehicle is configured to wait at the waiting position, wherein first terminals (100, 102) are provided along the first travelling rail for the overhead travelling vehicles for a communication between the overhead travelling vehicles and the buffer controller, wherein second terminals are provided along the second travelling rail for the local vehicle for a communication between the local vehicle and the buffer controller, wherein a sensor (83, 84) configured to detect the slidable buffer located at the rearward position is provided, wherein the overhead travelling vehicles are configured and programmed to request the buffer controller via the first terminal (100, 102) for a transfer permission to transfer to the load port prior to the transfer, and wherein the buffer controller is configured and programmed to permit via the first terminal (100, 102) the overhead travelling vehicles to transfer to the load port if there is no interference with an entrance of the local vehicle and if the slidable buffer is located at the rearward position. overhead travelling vehicles provided with a first hoist (34, 35, 36) configured to raise and lower carriers and a lateral transfer mechanism configured to laterally move the first hoist (34, 35, 36); a first travelling rail for the overhead travelling vehicles provided in a ceiling space of a building and passing over a load port; a local vehicle provided with a second hoist configured to raise and lower carriers; a second travelling rail for the local vehicle, provided at a position below the first travelling rail for the overhead travelling vehicles and over the load port; at least one slidable buffer configured to slide between a forward position under the second travelling rail for the local vehicle and a rearward position laterally separated from the position under the second travelling rail for the local vehicle and to support a carrier thereon; and a buffer controller configured and programmed to control the local vehicle and the slidable buffer, wherein a space above the slidable buffer at the rearward position is open for a transfer of carriers, wherein the overhead travelling vehicles are configured and programmed to transfer carriers between the load port and the slidable buffer located at the rearward position, wherein the local vehicle is configured to transfer carriers between the load port and the slidable buffer located at the forward position, wherein the second travelling rail for the local vehicle extends from the position over the load port to a waiting position for the local vehicle shifted from the position over the load port, wherein the local vehicle is configured to wait at the waiting position, wherein first terminals (100, 102) are provided along the first travelling rail for the overhead travelling vehicles for a communication between the overhead travelling vehicles and the buffer controller, wherein second terminals are provided along the second travelling rail for the local vehicle for a communication between the local vehicle and the buffer controller, wherein a sensor (83, 84) configured to detect the slidable buffer located at the rearward position is provided, wherein the overhead travelling vehicles are configured and programmed to request the buffer controller via the first terminal (100, 102) for a transfer permission to transfer to the load port prior to the transfer, and wherein the buffer controller is configured and programmed to permit via the first terminal (100, 102) the overhead travelling vehicles to transfer to the load port if there is no interference with an entrance of the local vehicle and if the slidable buffer is located at the rearward position.