The coal bunker of the 1924 train at the zoo. There are electric locomotives —that either require overhead power lines or a so-called third rail, or new rechargeable battery units.

Ostro explained that when uncovered coal trains travel, the coal particles disperse around the railroad tracks. Levels of PM 2.5 "[spread] almost a mile away," he added.

An increasing number of people are walking or jogging along city-owned railroad tracks in Columbia, ... The power plant stopped burning coal in 2015 as the city pursued renewable energy sources. ...