ST. LOUIS COUNTY, Mo.—Cars parked and crowds formed along Route 66 in Eureka to see Union Pacific's "Big Boy" steam engine roll by. The locomotive is traveling coast-to-coast to celebrate the nation’s 250th birthday.

“In true spirit of the railroad, they're always late,” said Timothy Hammond, life-long train enthusiast. “I love trains and I worked for Union Pacific Railroad in Los Angeles as a yard clerk when I was a youngster.”

As people suffered from the heat, the Meramec Ambulance District called on mutual aid support to help tend to numerous victims of heat-related illnesses. No fatalities occured as 20 to 25 individuals were treated by the 20 ambulances that jointly handled the situation, per the Ambulance District.

The crowd expressed its excitement to see the world's largest operating steam engine.

“I just think it's really neat to see this,” said James Boyster, a local resident who found out about the Big Boy on social media recently. “I mean, one of the biggest man-made moving objects, I was like, ‘Hey, why not see it?’”

Some people are concerned that the rising maintenance costs of the engine may result in the historic locomotive joining the other seven built that are inoperable or destroyed. St. Louis resident and train enthusiast, Dustin Alvarez, tries to see the Big Boy each time it’s around.

“It is not every day that you get to see one coming through Saint Louis,” said Alvarez. “I just wanted a neat little opportunity to see it.”

Big Boy makes its way through the Show Me State and is expected to arrive in Kansas City Tuesday afternoon.