Imperial Oil Module

On the left a standard-size pickup and a worker at the Port of Lewiston, alongside an Imperial Oil/ExxonMobil module planned for transported by shipper Mammoet on U.S. Highway 12. Does it look as if it may cause more highway damage than a standard-size pickup, or Governor Otter's 1-ton pickup, or a standard-size semi-truck/trailer? -- Janice Inghram photo

ITD ALERT #6:  Highway Damage and the Taxpayers’ Tab 

The overlegal loads planned by ConocoPhillips and Imperial Oil/ExxonMobil Canada for transport on U.S. 12 in Idaho will predictably violate state and federal laws designed to protect highway surfaces and bridges and result in future increased expenditure of taxpayer money to repair the damage caused by these transports.

Highway and Bridge Facts

1. Highway surfaces and bridges are designed for a given life span, typically 15 years for asphalt and 50 years for bridges. Normal wear and tear of traffic gradually produces fatigue and failure, requiring new public expenditures for repairs and eventual replacement.

2. In order to protect highways and bridges, the Federal Highway Administration has adopted limits applying to all Federal highways that address tire load, axle load, and total load on U.S. highways:
            a. tire load -             600 lb. per inch of tire width
            b. axle load -            20,000 lb. per axle
            c. total load -            160,000 lb.

3. While tire loads impact small areas of road surface, axle loads are critical to larger areas of road surface, subsurface, and to bridge fatigue and damage. Further, as clearly stated in a Washington State Department of Highways 2006 briefing paper entitled Legal Load Limits, Overweight Loads and Pavements and Bridges, “The relationship between axle weight and pavement damage is not linear, but exponential. A single axle loaded to 40,000 lbs (twice the legal load) causes 16 times more damage than a single axle legally loaded to 20,000 lbs.”
4. As recently pointed out to members of Governor Otter’s 15-member task force investigating the funding of Idaho’s highway infrastructure, one fully loaded axle on a big truck is equal to the pavement damage of 10,000 passenger cars. Any claim to the contrary, according to Batelle Group consultant Patrick Balducci, would contradict “50 years of research of the Federal Highway Administration.”

In summary, then, if tire, axle, and total load limits are adhered to, the public can expect regular maintenance costs to keep the public and commerce moving efficiently on state and federal highways. Overloading highways and bridges causes much greater maintenance and replacement costs and more disruption of both private and commercial travel.

The ConocoPhillips and Imperial Oil/ExxonMobil Canada Planned Shipments

1. The engineering drawings provided in both of the above corporations’ transportation plans submitted to ITD indicate tire pressure loads generally in the 500-600 lbs/inch range, thus leading to the oft-touted IO/EM claim that their loads will be no more damaging to the highway than a logging truck.

2. The listed axle weights for both corporations far exceed the State of Idaho’s legal loads of 20,100 lbs per axle. The IO/EM axle weights are listed at 36,990 pounds.  ConocoPhillips lists axle weights for their Goldhoffer trailers  at 36,491 lbs and for their 6-dolly transporter  at 38,172 lbs. These axle weights will predictably cause damage to road surface and substructure at least ten times greater than a normal axle load.

3. The overweight limit used by ITD for Western Regional overweight permits is the Federal Highway Administration limit of 160,000 lbs. Total weight for the I0/EM loads is 517,866 for the load and trailer alone, or 655,866 lbs for the load plus trailer plus pull and push tractors. The CP total weight for their lighter loads is 493,892 lbs, for their heavier loads from 646,204 – 675,500 lbs. These weights far exceed the 160,000 lbs maximum legal weight.

4. Referring to the report to the governor’s task force as noted in #4 above, legal axle loads of 20,000 lbs per axle cause the same road impact on the highway as 10,000 cars. ConocoPhillips configurations indicate use of from 15-18 axles per load, the vast majority of which are in the 36,000 to 38,000 lbs per axle range. At a legal axle limit of 20,000 lbs, a single CP shipment’s impact on the highway would be equivalent to that of from 150,000 to 180,000 cars. However, as explained above, because of axle weights far exceeding the legal limit, the highway wear of a single CP load will be at least ten times greater, or equal to 1,500,000- 1,800,000 cars according to 50 years of research by the Federal Highway Administration. The IO/EM shipments involve 20 axles per load. Each IO/EM shipment will thus cause wear equivalent to that of 200,000 cars. The 207 IO/EM shipments will thus predictably provide the equivalent wear and tear on U.S. 12 as that of approximately 35-40 million automobiles.

These calculations do not address the structural stress these shipments will place on bridges and unstable road shoulders.  As we explained in our ITD Alert #5, miles of unstable shoulders exist on U.S. 12, many within a few feet of the Clearwater and Lochsa Rivers.

According to the Washington State Department of Transportation briefing report on overweight loads cited above,

“ Tire and axle limits are imposed for a number of reasons; foremost is to ensure that loads carried by trucks are transported safely. Having defined load limits allows engineers to design pavements that will hold up under anticipated truck traffic with minimal maintenance required for fixing cracks, ruts, and potholes. Load limits are also necessary for protecting bridges from structural weakening or fatigue, preventing unsafe conditions and early replacement of bridge structures. Current information shows that even slight changes in load limits have major impacts on pavement and bridge performance.” (emphasis added)

Imperial Oil/ExxonMobilCanada has publicly stated they will pay for any damage they cause to the highway. While this may be true in the case of immediately obvious damage, such as the collapse of a bridge, much of the fatigue and wear of overlegal loads occurs over time. As ITD’s recent pilot project on granting permits for overlegal loads of from 105,500 lbs-129,000 lbs concluded, it is impossible to determine responsibility for the increased wear on the roadway caused by such overlegal loads. Taxpayers, in other words, will pay the long-term tab and, in effect, subsidize the industrial shipments of giant international corporations.

ITD regulations state the following: “The primary concerns of the Department, in the issuance of overlegal permits, shall be the safety and convenience of the general public and the preservation of the highway system.”

We find it difficult to believe ITD is not aware of Federal Highway Administration information and related professional literature on damage to highways and bridges of overlegal loads. We find highly problematic the fact that ITD would even consider the permitting of transports weighing from 493,892- 675,500 lbs for travel on U. S. 12.

We have previously addressed the issues of public safety and convenience. This alert speaks to the preservation of the highway system and to implications of accelerated and unfair costs to taxpayers. If ITD follows its own regulations, no permits will be issued for the transport of these loads of illegal and unprecedented weight on U. S. 12 in Idaho.

Further, if Governor Otter cares about the quality of Idaho’s transportation system and the future expenditure of taxpayer money in support of that system, he will ensure that ITD does not issue any such permits.


Late summer, Gov. Otter imposed a $10 million bond on Imperial Oil and ConocoPhillips for damage to bridges and the roadbed. However, that bond would only be used if obvious damage occurred. ITD's own studies show that longterm wear and tear can not be blamed on any vehicle or series of vehicles because thousands of vehicles travel the highway. Thus, accelerated rates of wear and tear caused by megaloads will not be blamed on the oil company shipments and the bond will not pay for repairs/replacements. At the same time, in essence, by granting permits for the megaloads, ITD is certifying the roadbed and bridges as adequate for megaload travel. Thus, should a megaload collapse a bridge, a road shoulder or the roadbed itself, conceivably the oil company could turn around and sue the state for having certified as safe an unsafe highway.




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Highway Damage and the Taxpayers' Tab

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1 = Imperial/Exxon test shipment, February 2010
4 = ConocoPhillips
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