The CTA said that it has reported to the federal government an average of about 30 driver assaults per year that are bad enough for the driver to go to the hospital — at 35 in 2014, 29 in 2015, 27 in 2016, 26 in 2017 and 12 through June of this year. The CTA employs about 4,000 operators, which shows that the incidents are rare.