Environmental efficiency measures for ports: an application of RAM-Tobit-RAM with undesirable outputs

In this paper, the environmental efficiency of the ports is measured. Labour, fund and infrastructure input are selected as the inputs, container throughput, cargo throughput and main business income are selected as the outputs, CO₂ emission is chosen as the undesirable output. A new model—RAM-Tobit-RAM (Range Adjusted Measure) with undesirable outputs is built to evaluate the environmental efficiency. Ten Chinese ports from 2004 to 2013 are taken as the samples to verify its rationality. The results suggest that it is not necessarily beneficial for environmental efficiency to expand the port scale.