Oversize Load Axle Weight Limits and Heavy Haul Permit Guide

Federal Legal Weight Limits: The Baseline

The Federal Highway Administration (FHWA) sets baseline weight limits for the National System of Interstate and Defense Highways under 23 CFR § 658.17. These are the thresholds that trigger permit requirements:

Any load exceeding these limits on the Interstate system requires an oversize or overweight permit from each state on the route. States have authority to set their own limits on non-Interstate roads, which can be more or less restrictive than federal limits.

The Federal Bridge Formula: Why Axle Spacing Matters

The Federal Bridge Formula (also called Bridge Formula B) is designed to protect road infrastructure by ensuring that heavy loads are distributed across enough axles and sufficient distance to prevent excessive stress on bridges and pavement. The formula is:

W = 500 × [(LN / (N – 1)) + 12N + 36]

Where:

• W = maximum weight in pounds on any group of two or more consecutive axles
• L = distance in feet between the outer axles of the group
• N = number of axles in the group

In practical terms, this means that the more axles you have and the farther apart they are, the more weight you can legally carry. This is why heavy loads use multi-axle trailers with extended wheelbases — not just to carry more weight, but to distribute it in a way that satisfies the bridge formula.

State Variations: Not All States Are Equal

While federal limits apply on the Interstate system, states have significant latitude to set their own rules on state and local roads, and to issue permits for loads exceeding federal limits. Key state variations to know:

• Texas: Allows higher axle weights than federal limits on designated routes — for example, 46,000 lbs for tandem axles (vs. 34,000 lbs federal) and 60,000 lbs for tridem axles. Texas is generally considered one of the more carrier-friendly states for heavy haul.
• Michigan: Historically allowed significantly higher GVWs on approved routes (up to 164,000 lbs on some roads), though recent changes have tightened some of these allowances.
• California: Has strict enforcement and requires permits for loads over 80,000 lbs or 8.5 ft wide. California also has specific restrictions on certain highways and bridges.
• Illinois, Ohio, Indiana: Enforce spring weight restrictions (typically February–April) that reduce allowable axle weights on non-designated routes to protect roads from frost damage.

When Are Oversize/Overweight Permits Required?

Permits are required when a load exceeds any of the federal legal limits listed above. Key points:

• Non-divisible loads only: States generally only issue oversize/overweight permits for non-divisible loads — loads that cannot be reduced in size or weight without destroying their value, compromising their intended use, or requiring more than 8 work hours to dismantle. A single piece of heavy equipment (excavator, crane, dozer) is always non-divisible.
• Route-specific: Permits are issued for a specific route, not a general authorization. Deviating from the permitted route can result in being placed out of service and significant fines.
• State-by-state: There is no federal oversize/overweight permit. Each state issues its own permits, and you need a permit from every state on the route.
• Time-limited: Most single-trip permits are valid for a specific date range (typically 5–10 days). If the move is delayed, the permit may need to be reissued.

What Information Is Required for a Permit Application?

When your carrier applies for oversize/overweight permits, they typically need:

• Vehicle unit number, license plate, and VIN
• Trailer type and configuration (number of axles, axle spacing)
• Load dimensions: length, width, height, and weight
• Individual axle weights when loaded
• Exact origin and destination addresses
• Proposed route (specific highways and city streets)

Providing accurate dimensions and weights is critical. Incorrect information can result in a permit being issued for the wrong configuration, which can lead to fines or being placed out of service during the move.

Pilot Car (Escort Vehicle) Requirements

Pilot cars are required for loads that exceed certain width or length thresholds. Requirements vary by state, but general guidelines:

• One pilot car (front): Typically required for loads over 12 ft wide in most states
• Two pilot cars (front and rear): Required for loads over 14–16 ft wide in most states
• Rear pilot car only: Required for loads with significant rear overhang in some states
• Pole truck: Required for loads over 100 ft in combined length in some states

Spring Weight Restrictions: A Seasonal Complication

Many states enforce spring weight restrictions during the freeze-thaw cycle, typically from February through April. During this period, the ground beneath road surfaces becomes saturated with water as frost melts, reducing the road's load-bearing capacity. States respond by reducing allowable axle weights on non-designated routes — sometimes by 25–35% below normal limits.

Spring weight restrictions can significantly affect heavy equipment moves. Carriers may need to route via designated heavy-haul corridors (which are exempt from restrictions), reduce payload, or delay the move until restrictions are lifted. Plan heavy equipment moves in late fall or early winter if possible to avoid spring restriction complications.

IronHaul Logistics handles all permit procurement, route planning, and pilot car coordination for heavy equipment moves nationwide. Our team knows the permit requirements for every state and ensures your load moves legally and on time. Call (208) 495-2260, email [email protected], or get a free quote at ironhaullogistics.com.