Automobile sales plunged in 2018 as tax increases and higher-than-expected inflation dashed the “cautious optimism” offered by carmakers at the start of the year.

The 16-percent drop to 357,410 units — a reversal from 2017’s record 18.4-percent surge to 425,673 — was lower than the 14-percent contraction estimated by a senior industry executive late last year as car companies mounted a motorshow aimed in part at drumming up yearend sales.