Which electric vehicle charging station to upgrade? Biased judgments based on differences in station efficiency

One way of controlling global warming is to substitute fuel driven cars with electric cars. Electric vehicles need to be charged. For maximal efficiency the charging times should be as short as possible. In the US charging stations are classified as Level 1 charging 5-10 miles/h, Level 2 25 miles/h and Fast DCFC stations 150-1000 miles/h. We asked participants to select one of two upgrades of charging stations that would save most charging time for a vehicle. The alternatives were upgrading L1 (5miles/h) to L2 (25 miles/h) or L2 (25miles/h) to Fast (250 miles/h). In all, 86% of the participants wanted to upgrade to a Fast station, which objectively saves less time than L1 to L2. The second study replicated the first study and 91% of the participants wanted to upgrade to the Fast (250) station. The third study offered alternatives with smaller objective efficiency differences than the earlier studies: upgrading L2 (30) to Fast (150) and Fast (150) to Fast (600) and 68% of the participants preferred the second incorrect alternative. Verbal justifications showed that many participants seemed to assume that differences in charging time are proportional to charging time saved. The results have practical implications and illustrate the difficulty to process reciprocal variables leading to incorrect decisions. Finally, we suggest two strategies for counteracting biased intuitive decision making when charging efficiencies are compared.