CHICAGO (CBS) — The terrorist bombings in Brussels have caused a ripple effect of travel warnings and increased security around transportation centers.

As spring break gets underway in many areas, the U.S. State Department has issued a travel alert for Europe, warning American citizens of a potential threat throughout the continent after Tuesday’s attacks in Belgium, and other recent bombings in Turkey.

“Terrorist groups continue to plan near-term attacks throughout Europe, targeting sporting events, tourist sites, restaurants, and transportation,” the State Department said. “U.S. citizens should exercise vigilance when in public places or using mass transportation. Be aware of immediate surroundings and avoid crowded places. Exercise particular caution during religious holidays and at large festivals or events.”

The State Department also advised travelers to be prepared for additional security screenings at airports in the U.S. and overseas, and to make sore their families know how to contact them in the event of an emergency.

Cook County Homeland Security Department executive director Ernest Brown said while the main threat now is overseas, there is also risk on U.S. soil.

“Certainly as long as there are people who are willing to try to change our way of life in America … there is a threat,” he said.

Brown said Americans – especially here at home – need to call the police if they see anything suspicious.

“People will do things in front of civilians that they simply won’t do under recognized authority figures,” he said.

The State Department encouraged any American traveling overseas to enroll in the Smart Traveler Enrollment Program (STEP), which is the fastest way to get messages from the federal government, as well as locate a traveler in case of an emergency.

Chicago police have increased security presence at O’Hare and Midway airports as a precaution in response to the bombings in Brussels. Security also has been increased at train stations, bus terminals, and other high-profile locations.

At the Metra station in Oak Lawn on Wednesday, most commuters said they feel a little safer seeing more police officers and K-9 units patrolling stations.

As for the travel alert for Europe, most said you can’t live your life afraid, but Greg O’Sullivan said “I’m not planning to go there anyway, but I do have a daughter that wants to go back to Paris, and we’re trying to talk her out of it right now, because of everything going on. … She still wants to go back.”