Terri Austin never expects a quiet ride. For years, Austin has boarded the No. 15 Regional Transportation District bus almost daily. Like many who frequent the always-lively route along Colfax Avenue, Austin shares a sense of pride in having grown to expect anything but normal during her daily commute.

“Everything and anything can happen on the 15 — and it usually does,” Austin said.

Within 48 hours, two different stabbings on RTD buses left one man dead and Denver police officers looking for another man suspected of slashing a female bus rider with a box cutter. Both buses were serving routes along Colfax Avenue in Denver.

Isaiah Moreno, 20, faces charges for stabbing and killing 39-year-old Estevan Ruiz at 2:46 p.m. Tuesday, while aboard a crowded No. 16 bus near Federal Boulevard and West Colfax Avenue. Police are still looking for a man accused of slashing a woman’s back after a fight on a No. 15 bus near East Colfax Avenue and Fillmore Street at 1:43 p.m. Thursday.

The woman is expected to make a full recovery.

“There have been times when I’ve been nervous about a fight and gotten off the bus,” Austin said. “There are definitely moments when you need to get off the 15.”

RTD, which is working with the Denver Police Department in the criminal investigations, will review both incidents once the investigations are complete, said spokesman Scott Reed.

“We are very concerned about these incidents,” Reed said. “We know that our system overall is safe, but even any small incident is something we take very seriously.”

RTD transports about 100 million passengers in Colorado each year. Reed said Route 15 was recently ranked the seventh-busiest bus route in North America.

Only standing room and single seats were available on several No. 15 buses that rolled up and down Colfax on Saturday afternoon. The personalities aboard the buses changed as often as the scenery that lines the avenue they travel.

Many passengers said the stabbings did not deter them from riding the bus but reminded them that they need to be prepared for anything while aboard.

All buses are equipped with video surveillance, Reed said. Security and off-duty police officers frequently patrol RTD stops and buses. RTD also coordinates with the Denver Police Department.

“The level of incidents we’ve seen recently is not a regular occurrence based on the number of buses we have going everyday,” said Sonny Jackson, Denver police spokesman. “We do need the citizens to help us by being additional eyes and ears.”

Tracy sat at the back of a No. 15 bus on Saturday, his eyes moving from the back of one head to another. With each ding of the stop cord, Tracy, who asked that his last name not be used, watched one group of people step off the bus and another take their place.

“It’s all just part of riding the bus,” Tracy said as he listened to the conversations around him. Several riders who stepped on the bus immediately recognized others already seated.

As Tracy explained the importance of paying attention to other riders, he stopped midsentence and shouted toward the front of the bus where two women were arguing about a seat. “Can’t we all just get along!”

Jordan Steffen: 303-954-1794, jsteffen@denverpost.com or twitter.com/jsteffendp