Mexico City began revenue service this week on a trolley-like bus rapid transit (BRT) system that is the nation’s first of its kind.

The system is meant to reduce pollution and improve public transport in the congested, often chaotic streets, which are dominated by privately operated minibuses.

Since the service opened, about 75 articulated buses — using exclusive bus-only lanes — have struggled to accommodate passengers. City officials attribute the crowding to the free introductory period.

Reports of breakdowns, delays, overcrowding and traffic jams caused by the new Metrobuses have been widely publicized in the Mexican media.