CHICAGO—A federal agency has issued an emergency bulletin to motorcoach companies about weight limits on tires following investigations into a Megabus fire in northeast Georgia, a deadly Megabus accident in Illinois and other crashes involving tire blowouts.

The Chicago Tribune reported Thursday that the Federal Motor Carrier Safety Administration says fully loaded double-decker buses "may overload tires outside the suggested weight limit."

A Megabus caught fire Aug. 8 after a tire blew out on I-85 near Lavonia.

In a more serious accident, one passenger died in the Megabus crash Aug. 2 near Litchfield in southern Illinois. State Police say a blown tire likely caused the bus to lurch out of control and hit a bridge pillar.

Authorities say the buses in both cases were heavily loaded and running on very hot days. That can cause stress on tires.