Fast, reliable & cost effective Equipment Transport

We set the stage for clear, practical guidance on axle limits and safe transport. Federal regulations set a baseline: 80,000 lbs maximum gross weight on the Interstate System. Single axles are capped at 20,000 lbs when centers are ≤40 inches. Tandem axles can carry 34,000 lbs when spacing is >40 inches and ≤96 inches.

The Bridge Formula ties allowable weights to the number and spacing of axles. That rule affects gross weight and how you configure trailers and loads. Some states allow higher limits under grandfather rights. Dual tandem exception: if two tandems span ≥36 feet, each may carry 34,000 lbs.

We translate these technical limits into simple steps. You will learn how axle spacing, vehicle setup, and load plans interact with state and federal rules. Our aim is to protect equipment, meet schedules, and keep routes compliant. Trust us to balance safety with productivity.

Ultimate Guide Overview: Why Axle Weight Rules Differ Across Regions

Local infrastructure and legacy laws create patchwork limits for heavy trucks across the country. We map how state grandfather rights, LCV corridors, and route-specific caps shape allowable weight and axle use.

Federal regulations set the baseline. State authority then preserves higher maximum weight on some corridors or limits access on non-Interstate roads. That split influences where certain trailers and combinations operate.

We cover practical impacts. Trailer type, axle grouping, and kingpin-to-axle dimensions change how a load clears municipal turns and fits permitted routes. Safety and bridge preservation drive many of those restrictions.

1. Assess route legalities before dispatch.
2. Choose trailer and axle layout to match limits.
3. Plan permits for overweight or LCV corridors.

We translate these variations into clear checkpoints so you can move freight legally and safely. The rest of this guide dives into federal baselines, the Bridge Formula, exceptions, and state highlights with practical steps.

User Intent and What You’ll Learn Today

Begin by validating single-axle, tandem, and gross weight before any route is filed. We show a clear, repeatable order so your team can check weights fast and avoid delays. This sequence forms the backbone of compliant load planning.

We cover how to run group checks for outer-bridge and interior axle groups next. You will see a practical example that applies to typical truck and trailer combinations. That helps you translate numbers into on-road decisions.

What success looks like: compliant loads that meet schedules, protect equipment, and reduce enforcement risk. We focus on safety and operational efficiency.

1. Pre-check single axle, tandem, and gross weight.
2. Apply group checks for outer and interior axle sets.
3. Adjust trailer layout, spacing, or permits based on results.

We also explain which dimensions and number axles influence routing across states. Use our checklists and workflows to make fast, repeatable decisions at the scale house and on the road.

Federal Foundations: Gross, Single-Axle, and Tandem-Axle Weight Limits

We follow federal baselines that set clear expectations for payload planning and route choice. The maximum gross for Interstate travel is 80,000 pounds. That gross weight limit frames how many axles and what trailers we select for a job.

80,000 lbs. maximum gross weight on the Interstate System

The 80,000 lbs. cap is the federal ceiling for most motor vehicles on the Interstate. States must allow this as the minimum on those routes since 1982, though some states keep higher allowances under grandfather provisions.

20,000 lbs. single axle and 34,000 lbs. tandem axle limits explained

Single axle loads must not exceed 20,000 pounds when centers are 40 inches or less. Tandem groups can carry up to 34,000 pounds when spacing is greater than 40 inches and no more than 96 inches. These axle weight limits protect bridges and pavement and support long-term safety.

• Check sequence: verify single, tandem, then gross before any bridge formula calculations.
• Plan loads: configure trailers and axles to match these federal limits and state exceptions.

For more on how spacing and kingpin rules affect routing, review our guidance on kingpin laws.

The Federal Bridge Formula: What It Is and Why It Matters

The federal Bridge Formula sets a math rule that links axle spacing and the maximum legal load. It uses three variables: W (the maximum weight, rounded to the nearest 500 lbs.), L (the feet between the outer axles of a group), and N (the number of axles in that group).

How W, L, and N shape allowable weight

As L grows or N rises, the computed W increases. Short spans or fewer axles lower the allowable load. That protects structures by spreading force across length and more axles.

Practical group checks

Enforcement examines every two or more consecutive axles. On a common five-axle combination, critical checks include 1-3, 1-5 (outer-bridge), and 2-5 (interior group).

When single and tandem caps override the formula

If an axle group has centers ≤40 feet for a single axle, the single axle cap replaces the computed W. Tandem limits apply when spacing is >40 and ≤96 feet. Always apply the lower of computed W or statutory caps.

1. Measure L (feet) between outer axles and count N.
2. Compute W and compare to single-axle and tandem caps.
3. Record values, adjust load or spacing, then validate before dispatch.

For state specifics on permissible loads, see our guide to state-by-state axle limits. We use this formula on every load to keep operations legal and safe.

Bridge Table B in Action: Interpreting Allowable Loads by Axle Count and Spread

Use Table B to turn feet of spacing and the number of axles into a legal load limit. We walk through how to read L (feet) and N (axles) and then apply that W value to practical checks.

Reading L and N to find W

Locate the span L in feet between the outer axles of the group. Count N, the total axles in that group. Move across the table to read W, rounded to the nearest 500 pounds.

1. Example: L = 20 ft, N = 3 → W = 51,000 pounds. This confirms capacity for a short interior group.
2. Example: L = 51 ft, N = 5 → W = 80,000 pounds. That outer‑bridge span aligns with the gross weight ceiling.
3. Violation example: L = 35 ft, N = 4 → W = 65,500 pounds. An actual load of 68,000 would fail and require rework.

Note the pivot at 97 inches. At that spacing two axles can carry 38,000 and three axles 42,000. Two axles placed too close can limit W even when gross weight looks legal.

Practical tip: measure and document L and N before departure. We record these values to speed scale checks and avoid reloading or permit delays under motor truck regulation.

Important Federal Exception: Dual Tandems at 36+ Feet

A narrow federal exception lets two tandem sets each carry full tandem caps when their outer axles span at least 36 feet. This targeted rule can add legal payload for compliant teams.

How it works: two consecutive tandem groups may each carry 34,000 pounds when the distance from the first axle of the forward tandem to the last axle of the rear tandem is 36 feet or more. Without this allowance, the bridge formula would limit combined tandem loads to roughly 66,000–67,500 pounds for spans of 36–38 feet.

Why this matters for five-axle combos

In a typical five-axle tractor‑semitrailer, tandems on the tractor and trailer can both be rated at 34,000 if axles 2 and 5 are ≥36 feet apart. That lets the combination carry higher tandem loads while still meeting federal limits.

• Measure span precisely: document feet between outer tandem axles before departure.
• Verify setup: check fifth‑wheel position, suspension spread, and axle centers.
• Keep records: scales and enforcement expect proof to apply the exception.

This is a narrow regulation, not a blanket gross weight increase. Careful measurement and documentation unlock lawful payload while avoiding costly violations.

Grandfather Rights and Historical Context That Shape Today’s Limits

Some state laws kept higher load ceilings when the federal system changed, creating legacy allowances today.

In 1956 Congress let states retain higher axle and gross limits on defined routes. In 1975 states could preserve larger federal bridge allowances.

The 1982 amendments then set the Interstate as both a floor and a ceiling for many hauls. That move standardized the maximum gross baseline for most motor travel.

Why this history matters now

Research from transportation bodies informed these shifts. Studies balanced productivity against safety and infrastructure costs.

• Check corridors: some states still allow higher legal loads under grandfather clauses.
• Document authority: record which regulation or statute authorizes any higher limit you use.
• Don’t skip checks: preserved allowances do not negate the bridge formula or per‑axle safety checks.

Before dispatch, we verify which corridors allow above‑baseline loads. We also confirm the exact regulation and keep proof to satisfy enforcement and protect infrastructure.

Understanding Regional Differences in Axle Weight Rules

Not all state networks treat heavy hauls the same. Route designations, permits, and corridor programs change the legal weight you may carry.

We map where higher allowances apply and where lower caps bite. Examples matter. Michigan allows up to 164,000 pounds on 11 axles. North Dakota permits 105,500 on seven axles. Nebraska and Louisiana have conditional higher limits for certain trailers.

States that allow higher gross loads

Nevada and South Dakota run LCV corridors by permit. That can let motor vehicles move larger payloads when spacing and number of axles comply.

States with lower or route-limited caps

Other states keep tighter non‑Interstate limits. West Virginia and Illinois restrict some highways to lower totals. That affects last‑mile access and how we route trucks and trailers.

• Plan routes: map each state segment to confirm applicable limits and regulations.
• Match configuration: align axle spacing and trailer setup to the strictest segment on route.
• Document: keep permits, photos, and measurements for quick roadside checks.
• Build margin: allow buffer for scale variance and enforcement practice to protect safety and schedule.

Regional Differences by State Type: Highlights You Need to Know

When planning multi‑state hauls, the legal pounds you can carry often depend on corridor type and axle setup. We map examples so you can pick the right trailer and route.

High-capacity states

Michigan allows up to 164,000 pounds on 11 axles. North Dakota and Idaho permit about 105,500 pounds on seven axles. These states reward additional axles and careful documentation.

Conditional or route-limited states

Nebraska will allow roughly 95,000 pounds on seven axles with proper permits. Louisiana offers tri/quad axle options up to about 88,000 pounds when equipment and route meet requirements.

Restrictive examples

West Virginia limits some highways to 65,000 pounds, though a few segments rise to 73,500. Illinois enforces 73,280 on non‑NN roads. These caps change how we size loads and route trucks.

LCV and uncapped corridors

Nevada and South Dakota run LCV corridors where motor vehicles move larger gross loads by permit. Permits, route notes, and dimensions must match the corridor terms.

• Check each state segment for applicable weight limits and permits.
• Match axle plan to the strictest segment on route.
• Confirm pounds allowed, then secure permits and records.

1. Check lane states and note the strictest weight limits.
2. Match axle and trailer plan to those limits and measure dimensions.
3. Secure permits, then move with documented proof for enforcement.

Trailer Types and Axle Groupings: How Configuration Drives Compliance

We explain how trailer layout changes legal pounds and handling. A trailer’s axle layout sets capacity and route options. That matters for payload planning and safety.

Closed-tandem flatbeds

Closed tandems (40–96″) cap the trailer axle group at 34,000 pounds. Five-axle flatbeds commonly carry about 46,000–48,000 lbs. payload while staying inside an 80,000 gross limit.

Spread-axle flatbeds

Spread-axle trailers with roughly a 10-foot spread can permit up to 40,000 pounds on trailer axles, subject to state KPRA checks and route terms. Use spread axles for concentrated loads that would otherwise overload a narrow tandem.

Concentrated versus distributed loads

Distributed loads favor closed tandems and simplify permits. Concentrated loads often need spread axles or extra axles to meet the maximum weight per group.

• Trade-offs: spread axles boost capacity but add routing limits and tire scrub.
• Recommendation: pre-assign trailers by commodity, lane, and regulatory limits.
• Safety: securement and load placement change with axle layout.

For details on booster setups that affect axle counts, see our booster axles guide.

Kingpin-to-Axle Rules and Route Planning Impacts

Kingpin-to-rear-axle spans drive route access and can block common trailer setups on key lanes. KPRA limits shape which equipment fits a corridor and how we place loads for balance and safety.

California’s 40-ft KPRA implication

California caps the kingpin-to-rear-axle center at 40 feet. Many 53‑foot spread‑axle trailers exceed that span. As a result, those trailers can be denied permits or forced to run with closed tandems.

Why some spread-axle 53-ft trailers are restricted

Spread‑axle 53‑ft trailers often place the axle group farther rearward to raise capacity. That increases the KPRA dimension.

States and provinces use KPRA to limit off‑tracking and protect pavement and curbs. At ports and scales, enforcement checks KPRA along with dimensions and weight.

• Verify KPRA before booking freight on spread‑axle trailers.
• Measure and document dimensions in feet and photograph setups for permits.
• Prefer closed tandems or move kingpin forward when running Western states.
• Place weight to maintain axle balance and reduce rear overhang swing.

We integrate KPRA checks into route plans. That prevents detours, avoids delays at scales, and improves safety during tight urban deliveries.

Permits, Exceptions, and Longer Combination Vehicles

Overweight permits unlock payloads above the 80,000-pound baseline when routes, axles, and spacing meet the state’s requirements. We pursue permits when customers need heavier loads and the route can handle them.

Permits do not waive the bridge formula or per-axle caps. Axle spacing and distribution still govern how many pounds each group may carry. State offices issue OS/OW permits that list approved routes, structure limits, and any season-based restrictions.

When overweight permits apply beyond 80,000 lbs. gross

States grant overweight permits for loads above the maximum gross when structure ratings and route studies allow it. Pounds authorized may vary by corridor and by season. We document axle weights, dimensions, and routes to justify each permit request.

LCV-eligible states and corridor considerations

LCV corridors appear in AZ, CO, IN, KS, MT, NV, ND, OH, OK, OR, SD, UT and a few others. Nevada and South Dakota list permit-based corridors that can be uncapped by route. Each corridor has unique limits, escort rules, and timing windows.

• Documentation: axle-by-axle weights, trailer dimensions, route maps, and safety plans.
• Operational limits: escorts, signage, and restricted travel times often apply.
• Coordination: contact state permit offices early; lead times vary by state and load.
• Compliance: maintain photos and weigh tickets; enforcement expects proof.

Operational tip: build a lane-specific permit matrix for repeat corridors. It speeds approvals and reduces surprises. We treat permits as part of the load plan—not an afterthought.

How Enforcement Works: Scales, Calculations, and Common Violations

Inspectors follow a strict order when they check loads at a public or private scale. We recommend the same pre-check routine before departure to avoid delays and fines.

Pre-check sequence before group math

Start with single axle checks. Each single axle should be ≤20,000 pounds. Next, verify tandems are ≤34,000 pounds. Then confirm the gross does not exceed 80,000 pounds.

Only after those pass do inspectors apply the bridge formula to critical groups such as 1–3, 1–5, and 2–5.

Common violation scenarios and corrective steps

A typical example: L = 35 ft, N = 4 gives W = 65,500 pounds. If the actual group reads 68,000 pounds, a violation exists.

• Corrective actions: re-space movable axle sets, reload to redistribute pounds, or reduce payload.
• Frequent issues: over‑concentrated trailer axles, short interior groups, or a mis-set fifth wheel.
• Onsite fixes: move spread axles, shift cargo, or remove partial loads.

Document axle readings and L measurements before you arrive at scales. Keep photos and scale tickets ready. We always balance safety and regulatory compliance when we decide to rework a load. Communicate promptly with dispatch and the shipper if adjustments are needed to meet state limits and axle weight limits.

Planning and Compliance Workflow for Multi-State Trips

Start each multi‑state haul with a short, verifiable pre‑trip that locks down axle spacing, group math, and permits. We use a simple workflow to reduce surprises on the road. The plan focuses on measurement, permits, and clear responsibilities.

Axle spacing and load distribution checklists

Pre-weigh every axle group. Record single, tandem, and group weights.

Measure L and count N for each critical span. Confirm Bridge Table B allowances for groups that cross state lines.

Align trailer choice to the strictest segment on route. Shift load or add axles when a group exceeds an allowable number or pounds.

Route selection with state weight, KPRA, and seasonal constraints

Vet each segment for state regulations, KPRA limits, and seasonal postings. Map the strictest limits first.

Note dimensions, travel windows, and posted structure restrictions. Build alternate routing if a corridor rejects your trailer or axle setup.

Leveraging state contacts and permit offices before dispatch

Call state permit desks early. Confirm OS/OW permit terms and corridor rules. Get written or emailed approvals when possible.

Prepare a documentation pack: scale tickets, measured spans, permits, and permit office contact names and numbers. Share the pack with dispatch, driver, and compliance.

• Assign roles: dispatch secures permits, compliance logs measurements, driver verifies setup at pickup.
• Communicate: notify the shipper if load changes are needed before tender.
• Safety-first: use margins for scale variance and enforcement practice to avoid roadside delays.

We keep the workflow tight. Small checks before dispatch prevent large delays on the highway.

Safety and Infrastructure Rationale: Why These Limits Exist

Bridges and pavements respond to loads the way thin ice reacts to a crowd: spread weight and the structure holds; concentrate it and failure risk rises. We frame regulation around that simple truth.

Bridge stress, vehicle productivity, and the balance set by federal law

The bridge formula reduces peak force by linking spacing and axle count to legal pounds. More feet between outer axles and more axles mean lower stress per linear foot. That protects structures and keeps corridors open longer.

Federal regulation balances the needs of motor vehicles and commerce with infrastructure health. It preserves productivity for trucks while limiting long‑term damage. Short, heavy combos wear bridges faster than longer combinations with the same gross.

Example: two long tandems spread over 50 feet impose less local stress than the same weight on a 20‑foot span. That difference guides permitted configurations and routing.

• Spreading weight improves overall safety and extends service life for bridges.
• Proactive compliance speeds trips and reduces enforcement risk.
• Good documentation and measurement protect motorists and company assets.

Your Next Steps to Stay Compliant and Move Heavier Loads Confidently

Before you assign equipment, confirm that spacing, group math, and permit windows align with your maximum load goals.

Plan for heavier loads by validating axle spacing, Bridge Table B allowances, and state permits. For payloads above about 55,000 lbs., expect different vehicles and additional axles.

As a standard pack, carry measured spans, scale targets, permit copies, and route notes. Match the maximum load to trailer and truck plans during quoting.

Train teams on quick Table B lookups and state regulations. Pilot one lane with a checklist, then scale the process across similar states.

We will review your routes and trailers to spot risk and opportunity. Contact us to move heavier loads with compliance and safety at the core.