Axle Loads & Pavement formula solvers
Annual ESALs from a Truck Count (Truck Factor)
Axle Loads & PavementYearly equivalent single axle loads from a daily truck count and the ESALs an average truck delivers per pass. The truck factor is the sum of the equivalency factors of all the truck's axles, and it is a property of the LOAD that trucks carry on that road, not of the trucks themselves.
Axle Group Load Against the Legal Cap
Axle Loads & PavementHow close an axle, an axle group or a whole vehicle sits to the weight it is allowed, as a percentage of the cap. The caps are INPUTS, because they are jurisdiction-specific: 20,000 lb single, 34,000 lb tandem and 80,000 lb gross are the US interstate figures, and a spring load restriction can cut them to half overnight.
Cumulative ESALs with Traffic Growth
Axle Loads & PavementTotal equivalent single axle loads accumulated over a design period when traffic grows at a compound annual rate. The growth factor is already a SUM over the whole period, which is why multiplying it by the number of years again — a mistake made constantly — inflates the answer by that many times.
Design Lane ESALs
Axle Loads & PavementThe share of a highway's total equivalent single axle loads that lands in the one lane the pavement is designed for, after splitting the two-way total by direction and then by lane. Pavement is designed for the worst lane, not the average one.
Equivalent Tyre Contact Radius
Axle Loads & PavementThe radius of the circle that carries the same wheel load at the same contact pressure as the real footprint. Layered-elastic pavement analysis is built on circular loaded areas, so every real, roughly rectangular tyre print gets turned into this before anything can be calculated.
Federal Bridge Gross Weight Formula
Axle Loads & PavementThe federal limit on how much any group of consecutive axles may weigh, set by how far apart the outer axles of the group are spread. Written into 23 U.S.C. § 127(a)(2), it is the reason a five-axle semi needs 51 feet from steer to rear trailer axle before it can gross 80,000 pounds.
Kingpin and Bogie Load Split on a Semitrailer
Axle Loads & PavementHow a semitrailer's weight divides between the kingpin at the tractor's fifth wheel and the trailer's own axle group, from one moment balance. No standard governs this; it is plain statics, and it is the arithmetic behind every trailer bogie slid forward or back at a weigh station.
Load Equivalency Factor (the Fourth Power Law)
Axle Loads & PavementHow much pavement damage one axle does compared with the standard 18,000 lb (80 kN) single axle, as a power of the load ratio. The exponent is an INPUT here and defaults to 4, because the famous fourth power is a later curve fit and not a finding of the AASHO Road Test, whose own load exponents were 4.79 flexible and 4.62 rigid.
Structural Number of a Flexible Pavement
Axle Loads & PavementThe single number that stands for the whole strength of a flexible pavement: each layer's thickness multiplied by a coefficient for what it is made of, and by a drainage coefficient for the unbound layers. Layer coefficients are INPUTS — they are regionally calibrated, they live in copyrighted design guides, and no honest tool bakes them in.
Tyre Contact Area
Axle Loads & PavementThe area of the patch a loaded tyre presses onto the pavement, taken as the wheel load divided by the contact pressure. Contact pressure is NOT inflation pressure: van Vuuren measured it as much as 30% lower, and the textbook rule of adding ten per cent was found completely unacceptable.