Idaho Transportation Department spokesman Jeff Stratten said, "These loads will not exceed the capacity of any bridge on the route. Permits will not be issued if they cannot supply us a configuration that the models show is under the capacity of the bridge." The permit issued, but stayed, for the four ConocoPhillips megaloads proposed for U.S. Highway 12 in north-central Idaho show that the loads will be up to 29 feet wide, 28 feet high, and 227 feet long, and have a gross weight of up to 664,096 pounds; they also show that "helper dollies" will be required for the loads to cross several bridges on the route - with those helper dollies included, the loads will have a gross weight of up to 675,500 pounds.
On Page 2 of the permit, under "Special Bridge Requirements," the permit states, "The load exceeds the normal capacity of all the bridges on the route listed above. The load may travel U.S. 12 from MP 2.45 to MP 174.42 with special requirements. The load must travel down the center of all bridges, be the only vehicle on each bridge, and have front and rear pilot cars while crossing each bridge. Additional requirements apply to the bridges listed in the chart below." That's followed by a chart listing four bridges: Arrow, Maggie Creek, Fish Creek and Squaw Creek, with special requirements for each, from a maximum speed of 5 mph to requirements for helper dollies. The same requirements are repeated later in the permit for the second configuration within the four loads.
Stratten said the helper dollies distribute the weight to bring it within the bridge's capacity. "It is a complex science calculating load ratings on bridges, and each one is unique to the trailer configuration," he said. "(For) every trailer configuration, there is a capacity, but there isn't one single capacity for the bridge. It all depends on how many axles, how wide the axles are, how that's distributed."
Despite the permit's statement that "the load exceeds the normal capacity of all the bridges on the route," Stratten said the department won't permit any loads that exceed the capacity of the bridges over which they'll travel. "We stand by that 100 percent," he said. You can read the full 30-page permit here, in a link that first was posted here on Nov. 10th.
Stratten said that statement in the permit about exceeding the "normal capacity" refers to normal operating conditions, such as at posted speed limits and when multiple vehicles are on the bridge at the same time. "The ConocoPhillips loads are not being allowed to cross the bridges under normal operating conditions. In the permit are the operating requirements for each bridge," he said.