A 400-foot-long big rig hauling a radioactive steam generator continued its journey on Monday through the North County on its way to Utah.On the first day of a three-week drive, the generator only made it 25 miles before it had to stop at about 3 a.m. on the eastbound side of Oceanside Boulevard, just east of El Camino Real, according to police.The truck, which is carrying the generator from the San Onofre Nuclear Generating Station to another plant in Utah, was parked in that location because it is only allowed to travel at night and there wasn't enough time to get to the next checkpoint before daybreak, Lt. Leonard Mata said.The truck, which has 192 large wheels to move and had two other rigs pushing it along, was heading east on surface streets in order to get to Interstate 15.San Diego State University professor Murray Jennex said Southern California Edison had no choice but to transport it by truck because a train is not wide enough. "Oh, it's huge," said spectator Kimberley Edgar, as she got an up-close look at the rig on Monday afternoon. Late-morning traffic was not greatly affected by the lane closures caused by the rig. However, by 5 p.m., traffic was a lot heavier, as the three lanes were condensed into one. "We went just a little slower than we had panned for which is okay," said Scott Andresen of Southern California Edison. "We did it for safety reasons, for the public." Andresen said slower means the rig never reached speeds over 20 mph Sunday night as it made its way to Oceanside from the San Clemente area of Orange County. The maximum speed the rig can reach with its load is 25 mph. The nuclear canister was once used to generate steam at San Onofre, but 10News was told it's not hazardous anymore. "If you stand next to it for one hour, you'd get about the same amount (of radiation exposure) as you would get in a dental X-ray," added Andresen. Murray told 10News, "It's been out of the plant for over a year sitting there decaying, so all the heavy radiation that was there was very short-term. It's gone." Experts said even if someone tried to create chaos by slamming into it the only danger would be to the driver. "It won't release any radiation it won't be a problem," said Jennex. "The vehicle that hits it will probably suffer by far the most damage."