NEW ORLEANS (AP) — Lines of people waiting for buses to take them out of the city grew longer Saturday and traffic grew heavier on main highways as Hurricane Gustav strengthened into a dangerous Category 4 storm on track for the Gulf Coast.

A line well over a mile long stretched in six loops through the parking lot at Union Passenger Terminal. Under a blazing sun, many led children or pushed strollers with one hand and pulled luggage with the other. Volunteers handed out bottled water, and medics were nearby in case people became heatsick.

Joseph Jones Jr., 61, wore a towel over his head to block the sun. He’d been in line 2 1/2 hours, but wasn’t complaining. During Katrina, he had been stranded on a highway overpass.

‘‘I don’t like it. Going someplace you don’t know, people you don’t know,’’ Jones said. ‘‘And then when you come back, is your house going to be OK?’’

The city had yet to call for a mandatory evacuation, but began ushering out the sick, elderly and those without their own transportation on Saturday. The state has a $7 million contract for more than 700 buses to carry an estimated 30,000 people to shelters.

Many residents said the evacuation was more orderly than Hurricane Katrina, which struck three years ago Friday. But not everyone was happy.

Elizabeth Tell, 67, had been waiting on the corner since 6:30 a.m. for a special needs bus to take her and her dog, Lee Roy, to the station. It was three hours before the first bus arrived, completely full of people in wheelchairs.

‘‘They’re not taking care of us down here!’’ she shouted as the brown-and-white spotted hound mix panted inside his hip-high plastic kennel.

Many residents weren’t waiting for a formal evacuation call.