Violence on buses and light-rail trains is "rare" in metro Phoenix, but riders need to be aware of potential for trouble, according to Valley Metro.

The issue became national news last week after two Good Samaritans were murdered, and a third person wounded, by a white supremacist who had been yelling at a woman on a Portland, Oregon, commuter train.

Violence on or related to Phoenix-area buses or light-rail trains does occur sporadically.

On Tuesday, a woman sitting at a bus stop in Mesa was sexually abused by a man who then broke her cellphone.

The woman was on the bus at about 9:15 p.m., court records state, when Anthony Corcios, 22, randomly took the seat next to her and began abusing her.

He put his hands under her bra, "grabbing each breast twice." When she tried to call 911, he allegedly slapped the phone out of her hand, breaking it.

Mesa police officers quickly arrived at the scene after the bus driver called 911 and arrested Corcios, who was "heavily intoxicated." Police accuse him of felony sex abuse and two misdemeanors.

The incident follows the tragic murder of a Phoenix bus rider last month, who was stabbed to death in a random attack. Another man was wounded.

Edgar Dominguez, 33, was arrested and later charged with first-degree murder.

"Incidents on buses are very rare," Valley Metro spokeswoman Susan Tierney said. "Every passenger should feel comfortable when boarding a bus or train and we have tools in place to support safe travel to their destinations ... Operators are trained to provide assistance if a rider is feeling unsafe at any time."

The safety system is augmented by cameras on buses and light-rail trains, plus emergency call boxes at light-rail stations.

But as the above examples show, attacks can occur quickly, and can occur despite Valley Metro's precautions.

Tierney also agreed that the national safety slogan, "if you see something, say something," doesn't mean "say something" directly to an attacker, as in the Portland incident, but rather to inform a bus driver or other authority.

Local public-transportation officials realize the need for more security to help deter street crime or terrorism.

Valley Metro recently hired sworn officers from Phoenix to help patrol the light-rail line, and Tempe and Mesa officers will soon be joining them, Tierney said.

For now, 69 security officers patrol the line and check for fares, along with three Phoenix K-9 teams that randomly board trains searching for explosives.

Residents 21 and older can also choose to pack their own security: Firearms and other weapons aren't banned on Arizona buses or light-rail trains.

Here's the breakdown on Valley Metro crime for October through December 2016, the last period for which statistics were available. Some of the incidents, like disobeying traffic signals, took place just outside of a bus or light-rail train, on a station, or at a bus stop:

Buses:

Assaults on drivers: 6
Assaults on passengers: 1
Threats against drivers: 2
Criminal damage: 7
Disorderly conduct: 4

Light Rail:

(No reported instances of violence, disorderly conduct, or criminal damage in this period.)

Riding without paying fare: 158
Riding without proof of fare: 61
Disobeying traffic signals: 40

The reality is that public transportation can never be 100 percent safe. One reason is that, even in Phoenix, the public transportation system is expansive, providing 32 million miles of service annually. About 250,000 passengers ride the system each day.

Anyone worried about public transportation should consider the alternatives, too. Besides the benefit to the environment, buses and trains are statistically the safest mode of ground-level transportation.

"Very few" criminal incidents disrupt riders during any given year, but transportation users still need to mindful of their surroundings at all times,  Phoenix Police Sergeant Jonathan Howard said.

"Despite the positive safety record, it remains important to our entire community that suspicious behavior is reported to police or transit security," Howard said.