⚖️ 23 USC 127 | Federal Bridge Formula B | FHWA
Bridge Formula Weight Calculator: Federal Truck Weight Limits for US Interstate Highways
Calculate the maximum allowable gross weight for any axle group under the US Federal Bridge Formula B (23 USC 127). Run a quick single-group check or a full 5-axle vehicle compliance check against all consecutive axle group combinations. Checks every group simultaneously, flags which one is the binding limit, and generates a downloadable PDF compliance report.
✓ Federal Bridge Formula B (23 USC 127)
✓ 80,000 lb GVW Interstate Limit
✓ Single and Tandem Axle Checks
✓ 5-Axle Vehicle Mode
✓ All Consecutive Groups Checked
✓ PDF Compliance Report
Bridge Formula Weight Calculator
Federal Bridge Formula B | W = 500 x (LN/(N-1) + 12N + 36) | 23 USC 127
Enter the number of axles in a consecutive group and the distance from the first axle to the last axle in that group. The calculator returns the Bridge Formula B maximum for that group, capped at the 80,000 lb interstate GVW limit.
Count axles in the consecutive group you are checking, not the total vehicle. For the full 5-axle semi-truck check, use the Vehicle tab above.
ft
Measure from center of first axle to center of last axle in the group.
lbs
Enter to check compliance. Leave blank to see limit only.
Select your axle count and span distance to calculate the Federal Bridge Formula B maximum for that axle group.
Enter the weight on each axle and the distance between each pair of consecutive axles. The calculator checks all 15 consecutive axle group combinations simultaneously (singles, pairs, triples, quads, and the full vehicle) and flags every violation.
5-Axle Configuration (Standard 18-Wheeler Layout)
A1 Steer
S12
A2 Drive
S23
A3 Drive
S34
A4 Trailer
S45
A5 Trailer
lbs
lbs
lbs
lbs
lbs
Axle Spacings (center to center)
ft
ft
ft
ft
Default values represent a legal 80,000 lb 5-axle semi with standard 51.66 ft steer-to-rear span. Adjust to match your actual configuration.
Understanding the Federal Bridge Formula: Why Axle Spacing Controls How Much Your Truck Can Weigh
The Federal Bridge Formula, codified at 23 USC 127 and administered by the Federal Highway Administration, is the law that governs how much weight any combination of consecutive axles can carry on the Interstate Highway System. It was created to protect bridges from structural fatigue caused by heavy vehicles concentrating too much weight on a short section of roadway. The formula achieves this by requiring that weight be spread across a longer axle span: the more axles you have and the farther apart they are, the more total weight the formula allows.
The formula applies independently to every group of consecutive axles on the vehicle. For a standard 5-axle semi-truck, that means checking not just the total gross vehicle weight against the 80,000 pound interstate limit, but also checking the drive tandem, the trailer tandem, the steer-to-drive combination, and every other consecutive axle grouping against its own formula-derived limit. A truck with a legal gross weight can still be in violation if one axle group exceeds its bridge formula limit. This is where most weight violations happen: the driver knows the total is under 80,000 pounds, but a loaded drive tandem or trailer axle group is over its limit.
2024 FHWA Enforcement Data: Over 420,000 weight violations were issued to commercial vehicles in 2024, with average fines of $2,100 per incident. Weight violations are the third most common cause of commercial vehicle out-of-service orders in North America. Source: FHWA.dot.gov
20K
Single Axle Limit
No single axle may carry more than 20,000 pounds on any interstate highway. This applies to each axle independently, regardless of what the bridge formula says for groups containing that axle. The steer axle of a typical 18-wheeler carries 10,000 to 12,000 pounds, leaving significant margin on this limit.
23 USC 127(a)(1)
34K
Tandem Axle Limit
Any two consecutive axles spaced 40 inches or less apart (a tandem) are limited to 34,000 pounds combined. On a standard 5-axle semi with 52-inch tandem spacing, the drive and trailer tandems each must stay at or below 34,000 pounds. This is the most commonly violated federal weight limit in US trucking.
23 USC 127(a)(2)
80K
Interstate GVW Limit
The gross vehicle weight limit on the Interstate Highway System is 80,000 pounds. No vehicle or combination of vehicles may exceed this limit on interstate highways, regardless of what the bridge formula might otherwise allow for specific axle groups. This is the absolute federal ceiling, above which an overweight permit is required.
23 USC 127(a)(3)
The Bridge Formula in Numbers: What It Means for Standard 5-Axle Semis
For a standard 5-axle semi-truck with steer, two drive axles, and two trailer axles, the federal bridge formula with a typical 51-foot steer-to-rear span allows exactly 80,000 pounds at the vehicle level: W = 500 x (51 x 5 / (5-1) + 12 x 5 + 36) = 500 x (63.75 + 60 + 36) = 500 x 159.75 = 79,875, which rounds to 80,000 pounds. This is not a coincidence. The standard axle configuration for American 18-wheelers was engineered specifically to allow 80,000 pounds under the bridge formula while distributing weight legally across all axle groups. Changing the axle spacing, even slightly, changes what the formula allows.
A 48-foot steer-to-rear span on the same 5-axle configuration yields a bridge formula limit of 78,000 pounds: W = 500 x (48 x 5/4 + 60 + 36) = 500 x (60 + 60 + 36) = 78,000 pounds. That is 2,000 pounds less legal capacity simply because the axles are 3 feet closer together. For a carrier hauling dense, heavy freight regularly, those 2,000 pounds represent meaningful revenue loss per trip. This is why fleet managers and owner-operators making trailer purchase decisions often scrutinize axle positioning: a trailer with optimized king-pin-to-rear-axle distance can be worth thousands of additional pounds of legal payload over a typical fleet run.
How to Use the Bridge Formula Calculator for Your Axle Group
The Quick Group Check tab accepts the number of consecutive axles in the group you are checking and the total distance from the center of the first axle to the center of the last axle in that group. This is the distance labeled L in the federal formula. The calculator returns the Bridge Formula B maximum for that group, then caps it at the 80,000 pound GVW limit if the result would exceed that ceiling.
The 5-Axle Vehicle Check tab takes individual axle weights and the spacing between each pair of consecutive axles. It computes the weight on every possible consecutive axle group (all 15 combinations for a 5-axle vehicle: 5 singles, 4 pairs, 3 triplets, 2 quads, and the full 5-axle vehicle) and compares each against the applicable bridge formula limit. If any group fails, it appears in red in the results table. The chart shows the four most significant groups: steer axle, drive tandem, trailer tandem, and gross vehicle weight.
Three Real US Freight Scenarios: Bridge Formula Compliance in Practice
Chicago, IL
Standard 80,000 lb load on I-90: all groups compliant
Steer axle (A1)12,000 lbs
Drive tandem (A2+A3)34,000 lbs
Trailer tandem (A4+A5)34,000 lbs
Total GVW80,000 lbs
Steer to rear span (L)51.66 ft
Bridge formula (N=5)80,000 lbs
✓ ALL 15 GROUP CHECKS PASS. Legal at max GVW of 80,000 lbs.
Nashville, TN
Overloaded drive tandems: violation on A2-A3 and GVW
Steer axle (A1)12,000 lbs
Drive tandem (A2+A3)37,000 lbs
Trailer tandem (A4+A5)34,000 lbs
Total GVW83,000 lbs
Drive tandem limit34,000 lbs
Drive tandem over by3,000 lbs
⛔ 2 VIOLATIONS: Drive tandem 3,000 lbs over limit. GVW 3,000 lbs over 80,000 limit.
Dallas, TX
6-axle configuration: more payload capacity via bridge formula
Axle configuration6-axle
Total span (L)58 ft
Bridge formula (N=6)89,000 lbs
Interstate GVW cap80,000 lbs
Binding limit80,000 lbs
vs 5-axle at 51ft80,000 lbs
✓ Formula allows 89,000 lbs, but GVW cap limits to 80,000 lbs. Overweight permit needed above 80K.
Nashville: How a Single Miscalculation Costs $2,100 at the Scale House
A flatbed carrier out of Nashville loaded a 37,000-pound steel coil onto a standard 5-axle semi, distributing the weight toward the rear of the trailer to make loading easier at the mill. When the truck hit the weigh station on I-24 east of Nashville, the scale flagged two violations simultaneously: the drive tandem was reading 37,000 pounds, which exceeded the 34,000-pound tandem limit by 3,000 pounds, and the total GVW was 83,000 pounds, 3,000 pounds over the 80,000-pound interstate limit. The fine was assessed separately for each violation. Before the load left the mill, a five-minute bridge formula check would have identified that the legal distribution required moving 1,500 pounds from the drive tandem to the trailer tandem, which would have brought both groups into compliance and kept the GVW at exactly 80,000 pounds.
Dallas: When a 6-Axle Configuration Enables More Payload
A heavy-haul carrier in Dallas regularly moves oversized industrial equipment that pushes the limits of a standard 5-axle configuration. Adding a sixth axle with a 58-foot steer-to-rear span changes the bridge formula limit for the full vehicle group to 89,000 pounds: W = 500 x (58 x 6/5 + 72 + 36) = 500 x (69.6 + 72 + 36) = 500 x 177.6 = 88,800 pounds, which rounds to 89,000 pounds. While the 80,000-pound interstate GVW cap still applies without a permit, the 6-axle configuration allows the carrier to apply for an overweight permit above 80,000 pounds with a formula-supported case, and many states grant permits up to the bridge formula limit for 6-axle configurations on designated routes. Without the extra axle, the formula would cap them at 80,000 with no room for permit-based exceptions on formula grounds.
Expert Tips for Weight Compliance Before the Scale House
Tip 01
Check Every Axle Group, Not Just the GVW Total
The most common weight violation is a legal GVW total with an overloaded tandem group. A truck at 79,500 pounds total can still be in violation if the drive tandems are carrying 36,000 pounds. Always check individual tandem groups against the 34,000-pound limit before checking the total. Use the 5-axle vehicle tab to run all group checks simultaneously before heading to the scale house.
Tip 02
Axle Spacing on Your Trailer Changes Everything
Moving trailer tandem sliders 10 feet forward changes the steer-to-rear span from 48 feet to 58 feet, increasing the bridge formula limit for the full vehicle group from 78,000 to 85,000 pounds. Trailer slider position is the single most powerful weight distribution tool available without changing the load. Learn your trailer’s king-pin-to-rear-axle measurement at different slider settings and carry that reference when loading.
Tip 03
State Weight Limits on Non-Interstate Roads Are Often Lower
The 80,000-pound federal limit applies specifically to the Interstate Highway System. State highways, US routes, and secondary roads frequently have lower posted limits: many states limit non-interstate routes to 73,280 pounds (the federal vehicle bridge formula equivalent for many 5-axle configurations). Always check the specific posted limits for your route, not just the interstate standard. Seasonal spring restrictions in northern states reduce limits further during freeze-thaw periods.
Tip 04
Fifth-Wheel Position Shifts Weight Between Steer and Drive Axles
Moving the fifth wheel forward shifts weight to the steer axle and removes it from the drive tandems. Moving it rearward transfers weight from the steer to the drives. A typical 6-inch fifth-wheel slide movement changes drive tandem weight by approximately 500 to 800 pounds depending on the trailer length and load distribution. If your drive tandems are at 33,800 pounds and your steer is at 10,000 pounds, moving the fifth wheel 4 to 6 inches forward brings drives down while the steer axle still has 10,000 pounds of capacity before hitting the 20,000-pound single-axle limit.
Tip 05
CSA Points from Weight Violations Outlast the Fine by Two Years
Federal weight violations are carrier-attributed in the FMCSA Safety Measurement System (CSA), meaning they appear on the carrier’s record and affect the cargo/hazmat and vehicle maintenance BASIC scores for 24 months. Carriers with elevated CSA scores face higher insurance premiums and scrutiny from freight brokers who screen scores before tendering loads. The real cost of a weight violation is not the $2,100 average fine; it is the cumulative insurance and load-access impact over the following two years.
Tip 06
Overweight Permits Are Available for Bridge-Formula-Compliant Overloads
If your load exceeds 80,000 pounds but remains within the bridge formula limit for your axle configuration, an overweight permit from the relevant state DOT(s) allows legal operation on designated routes. Permit requirements, fees, and routing restrictions vary by state. Most states require permits to be obtained before the trip, include route-specific approvals, and set time-window restrictions. Loads that exceed both the 80,000-pound GVW limit and the bridge formula limit require special routing analysis and often escort requirements. Contact state DOT permit offices directly or work through a freight permit service for heavy/oversize loads.
Federal Bridge Formula B Quick Reference Table
Maximum allowable weight (lbs) for consecutive axle groups under Federal Bridge Formula B (W = 500 x (LN/(N-1) + 12N + 36), rounded to nearest 500 lbs), capped at 80,000 lb interstate GVW limit. Source: FHWA.dot.gov
| Axle Span (L) | N=2 Axles | N=3 Axles | N=4 Axles | N=5 Axles | N=6 Axles |
|---|---|---|---|---|---|
| 4 ft (48 in tandem) | 34,000 | 39,000 | 44,500 | 50,500 | 56,500 |
| 8 ft | 38,000 | 42,000 | 48,500 | 54,000 | 60,000 |
| 12 ft | 42,000 | 46,000 | 52,000 | 57,500 | 63,500 |
| 20 ft | 50,000 | 51,000 | 55,500 | 60,500 | 66,000 |
| 30 ft | 60,000 | 60,000 | 62,500 | 66,000 | 71,000 |
| 40 ft | 70,000 | 63,000 | 68,500 | 73,000 | 78,000 |
| 48 ft | 78,000 | 71,500 | 75,000 | 78,000 | 80,000 |
| 51 ft (standard semi) | 80,000 | 74,000 | 76,000 | 80,000 | 80,000 |
| 60 ft | 80,000 | 80,000 | 80,000 | 80,000 | 80,000 |
Note: Values shown are the lower of the bridge formula result and the 80,000 lb interstate GVW cap. Individual axle limits (20,000 lb single, 34,000 lb tandem) apply additionally to all group checks.
Frequently Asked Questions About Federal Bridge Formula Weight Limits
The Federal Bridge Formula B (23 USC 127) is a federal law that limits the weight that any combination of consecutive axles can carry on the Interstate Highway System based on the number of axles and the distance between them. It exists to protect bridges from structural fatigue. When a heavy vehicle crosses a bridge, the force it applies depends on how the weight is concentrated along the span. Closely spaced axles concentrate weight on a short section of the bridge, amplifying stress. Widely spaced axles spread that same weight over a longer section, reducing peak stress at any given point. The formula encodes this physics into a legal limit: more axles farther apart equals higher legal weight. The FHWA administers the formula as part of the federal highway weight enforcement program under 23 USC 127 and 23 CFR Part 658.
The federal maximum for a standard 5-axle semi-truck on the Interstate Highway System is 80,000 pounds gross vehicle weight. This consists of up to 12,000 pounds on the steer axle (subject to the 20,000 lb single-axle limit), up to 34,000 pounds on the drive tandem, and up to 34,000 pounds on the trailer tandem. The bridge formula for 5 axles at a typical 51-foot steer-to-rear span produces exactly 80,000 pounds, confirming this is the maximum without a permit. Any configuration that would require more than 80,000 pounds of GVW needs an overweight permit from each state DOT whose roads are included in the route. The specific distribution across the three axle groups must also comply individually: drive tandem and trailer tandem each at 34,000 or less, steer axle at 20,000 or less.
For a 5-axle truck, the bridge formula must be satisfied by every consecutive axle group, not just the whole vehicle. The groups are: each of the 5 individual axles (checked against the 20,000 lb single axle limit), every pair of consecutive axles (A1-A2, A2-A3, A3-A4, A4-A5, each with its own bridge formula limit), every triplet (A1-A3, A2-A4, A3-A5), every quartet (A1-A4, A2-A5), and the full vehicle (A1-A5). This is 15 separate checks for a 5-axle configuration. The vehicle is compliant only when all 15 checks pass. In practice, the binding constraints are usually the two tandems (A2-A3 drive tandem limited to 34,000 lbs and A4-A5 trailer tandem limited to 34,000 lbs) and the total GVW limited to 80,000 lbs. But a truck with unusually short spacing between the steer and drive axles, or a particularly short king-pin-to-rear setting, can fail intermediate group checks even when the tandems and GVW are within limits.
Federal overweight fines are assessed at the state level for violations of the 23 USC 127 interstate weight limits, and they vary significantly by state. Most states charge fines based on the amount of weight over the legal limit, typically ranging from $65 to $200 per pound over the limit, applied to each overloaded axle group independently. On some state routes, per-pound fines can be higher. The FHWA reported that the average weight violation fine in 2024 was approximately $2,100 before legal fees and permit costs. A single tandem axle violation of 3,000 pounds over the 34,000-pound limit at $150 per pound would result in a $450 fine at the state level, but many states apply minimum fines significantly higher than the per-pound calculation. Additionally, weight violations affect the carrier’s CSA score, which has secondary costs through insurance premium increases and reduced access to premium freight loads.
The federal bridge formula at 23 USC 127 applies specifically to the Interstate Highway System. State highways, US routes, and local roads are subject to state-specific weight laws, which vary considerably. Many states have adopted weight limits similar to the federal standard for their primary highways, but secondary roads often have lower posted limits. Some states permit higher weights on certain non-interstate routes under grandfather provisions or state-specific laws (for example, some states allow “grandfathered” higher weights on routes that predate the federal highway program). Specific posted weight limits on state and local roads must be followed even if they are lower than the federal interstate standard. When a load is routed on non-interstate roads, always verify the posted limits on the specific road segments, not just the federal interstate standard.
Overweight permits are issued by individual state Departments of Transportation for loads that exceed the normal legal weight limits. To obtain a permit, you typically need to: identify the specific route including state lines (each state requires its own permit), provide the vehicle configuration details including number of axles, axle spacing, and axle group weights, document the commodity being transported and why it cannot be reduced, and pay a permit fee (which varies by state and load size). For loads above 80,000 pounds but within the bridge formula limit for the axle configuration, most states will issue a permit on established over-dimensional routes. For loads that exceed both the GVW limit and the bridge formula, special routing analysis and often escort vehicle requirements apply. Permits must be obtained before the trip begins, and the vehicle must stay on the approved route. Permit services and freight brokers can handle multi-state permit applications for complex heavy-haul moves, typically charging $50 to $300 per state depending on the complexity of the move.
Tandem axle sliders (also called slider axles or sliding axles) allow the tandem axle group on a semi-trailer to be moved forward or backward along the trailer frame. This changes the king-pin-to-rear-axle distance (KPRA), which affects how weight is distributed between the drive axles of the tractor and the trailer axles. Moving the tandem forward (toward the front of the trailer) shifts weight from the drive tandem to the trailer tandem. Moving it rearward shifts weight from the trailer tandem to the drive tandem and steer axle. Sliders also change the overall steer-to-rear span of the vehicle, which affects the bridge formula limit for the full 5-axle group. Most standard dry van trailers have sliders that allow 10 or more feet of adjustment. For a 53-foot trailer, the difference between the most forward and rearmost slider position can change the legal payload distribution by thousands of pounds and affect the bridge formula limit by 2,000 to 4,000 pounds. Proper slider adjustment before weighing or accepting a load is standard weight compliance practice for experienced drivers and fleet operations.
Seasonal spring weight restrictions (also called spring breakup restrictions or freeze-thaw restrictions) are temporary reductions in legal weight limits imposed on roads during the period when frozen ground thaws in spring. During freeze-thaw cycles, the road base weakens significantly: water from melting ice expands and saturates the subgrade, which can no longer support normal vehicle weights without rutting and damage. Over 35 states impose these restrictions, typically from late February or early March through April or May, on secondary highways and some primary state routes. The restrictions typically reduce allowable GVW by 20 to 35 percent below normal legal limits on affected routes. For example, a road with a normal 80,000-pound limit might be restricted to 60,000 pounds during spring restriction periods. Specific affected roads, dates, and weight reductions vary by state and are published annually by state DOTs. Operating on a restricted road during restriction periods without a permit is a violation assessed against the restricted weight limit, not the normal limit, meaning the per-pound fines can be much higher than on a normal overweight violation. Northern and upper Midwest states with significant freeze-thaw cycles (Minnesota, Wisconsin, Michigan, Iowa, Indiana, North Dakota, New York, Maine, Vermont, New Hampshire, Montana, Wyoming, Idaho, Oregon, and Washington) have the most extensive spring restriction programs.
Portable weigh stations are movable scale setups that enforcement agencies can deploy at any location along a highway, including off the Interstate. They typically consist of portable axle scales that measure individual axle weights as the vehicle drives over them slowly, and they can be set up in under an hour at roadside pullouts or rest areas. Weigh-in-motion (WIM) systems are permanent sensors embedded in the roadway that measure vehicle weights at highway speed without stopping the truck. WIM data is used for pre-screening to identify trucks likely to be overweight before they reach a static scale house. When WIM data flags a truck as potentially overweight, the driver is directed by electronic sign to the inspection station. If the WIM screen clears the truck, the driver can bypass the static scale entirely, which is the incentive behind Drivewyze and PrePass transponder systems. Permanent weigh stations on interstates use static scales that require a full stop and can weigh each axle group individually or in combination. Weight is measured to the pound but violations are typically charged in per-pound increments above the applicable limit. Refusing to stop at an open weigh station when directed is a separate violation from the underlying weight violation and carries additional penalties.
Yes, and this is the preferred solution before any load moves. If your drive tandem is overloaded at 36,000 pounds, you have several options: adjust the fifth wheel position to shift weight from the drive tandem to the steer axle (moving the fifth wheel forward), adjust the trailer tandem sliders to shift weight from the drive tandem to the trailer tandem (moving the tandem forward), or reduce the total load weight. The weight involved in moving it from an overloaded tandem to a compliant configuration depends on the axle spacing and load distribution, but as a rule of thumb, moving a 53-foot trailer’s tandem slider 2 feet forward shifts approximately 500 to 1,000 pounds from the drive tandem to the trailer tandem. Most importantly, any redistribution must not push another axle group over its own limit. Running the 5-axle vehicle check after any adjustment is the correct way to verify that all 15 group checks still pass before proceeding. If the load itself is simply too heavy for legal distribution across the available axles, an overweight permit or load reduction is the only legal solution.
Wide-base single tires (also called super singles or wide singles) are large single tires that replace dual-tire configurations on drive and trailer axles. From a federal weight limit standpoint, the same limits apply: 20,000 pounds per single axle, 34,000 pounds for tandem groups, and 80,000 pounds GVW on the interstate. However, some states have enacted provisions allowing slightly higher single-axle weight limits for vehicles equipped with wide-base tires. For example, some states allow up to 22,000 or 24,000 pounds per axle on wide-base tire configurations, compared to the 20,000-pound federal standard. These state-specific provisions only apply on non-Interstate state routes where the state has enacted them; they do not override the 23 USC 127 federal limits on the Interstate Highway System. Wide-base single tires offer fuel economy advantages (roughly 3 to 5 percent fuel savings vs. duals) and reduced maintenance costs, which is why adoption has grown among long-haul carriers despite the more limited state-level weight allowances. If you operate with wide-base tires on state routes, verify the specific state DOT rules for the states in your operating area before assuming the higher weight allowances apply to your configuration.
Lift axles (also called tag axles or pusher axles) are axles that can be raised off the road surface when not needed and lowered when additional weight-carrying capacity is required. When a lift axle is raised, it is not in contact with the road and does not count as an axle for bridge formula purposes. When lowered, it counts as a regular axle and affects both the axle group weight distribution and the bridge formula limits for any consecutive group that includes it. Lowering a lift axle typically increases the allowable bridge formula weight for the full vehicle group because it adds both N (number of axles) and potentially increases L (the span) depending on the axle’s position. Some states have provisions specifically addressing lift axles and may allow higher weights when lift axles are deployed. Operating with a lift axle raised when the vehicle’s weight distribution would otherwise require it to be lowered can constitute a weight violation if the raised position causes any remaining axle group to exceed its limit. Drivers should confirm that the vehicle’s axle group weights comply with all applicable limits in both the lift-raised and lift-lowered configurations for the routes they operate.
In US enforcement terminology, a weight violation generally refers to exceeding any of the statutory weight limits: the 20,000-pound single-axle limit, the 34,000-pound tandem limit, or the 80,000-pound interstate GVW limit. A bridge law violation more specifically refers to exceeding the weight limits derived from the Federal Bridge Formula for a specific axle group configuration. In practice, both terms are used somewhat interchangeably in enforcement because the bridge formula is the mechanism that sets most of the per-group limits above the basic tandem limit. The bridge formula only produces a limit above 34,000 pounds for tandem groups when the span exceeds a short distance, and it produces limits above the 80,000-pound GVW cap for large axle groups with wide spans, but the GVW cap overrides the formula result. For most standard 5-axle configurations, the practically important limits are the 34,000-pound tandem limits and the 80,000-pound GVW limit, with the bridge formula relevant primarily for multi-axle combinations beyond tandems. For specialized heavy-haul configurations with many axles and specific spacing requirements, the formula itself is the primary compliance reference.
Weigh stations measure axle group weights using platform scales embedded in the roadway at the inspection facility. As the vehicle moves through the scale, each axle or axle group is weighed individually. The scale system computes the weight on each axle, each consecutive axle group (using the axle spacing information from the vehicle configuration), and the total GVW simultaneously. Bridge formula limits for each group are calculated automatically using the measured spacing between axles and the bridge formula, and any group that exceeds its limit is flagged. Some modern weigh stations use automated systems that display pass or fail results in real time as the truck moves through slowly. Roadside portable scales work similarly but require the truck to stop and position each axle over the scale platform individually, with the operator reading and recording each weight separately. Weigh-in-motion systems on the approach to scale facilities pre-screen trucks at highway speed and can estimate axle group weights with sufficient accuracy to identify likely violations before the truck reaches the static scale.
Yes, several exemptions and exceptions exist under 23 USC 127 and related federal regulations. Grandfather exemptions allow states to maintain weight limits on certain non-interstate routes that were higher than federal limits before the law was enacted in 1975, as long as the roads remain consistent with their pre-enactment designations. Federal-designated highways connecting Interstates to major facilities (like ports, intermodal yards, or manufacturing plants) may have different weight limits under specific surface transportation authorization acts. Some agricultural vehicles and equipment are exempt under specific state provisions when operating within defined distances from a farm location. Vehicles carrying divisible loads that would require multiple permits can sometimes obtain blanket annual permits in some states for specific routes. Emergency vehicles and utility repair vehicles may receive temporary exemptions during declared emergencies under FHWA emergency relief provisions. Despite these exemptions, the 80,000-pound GVW limit on the Interstate Highway System has very few practical exceptions outside of overweight permits issued by state DOTs for specific loads and routes. Operators should verify the current exemption status directly with the relevant state DOT and FHWA for any load that would otherwise require a permit or exceed standard limits.
If your vehicle is placed out of service at a weigh station for a weight violation, you cannot move the vehicle on public roads until the violation is corrected. The correction options are: reduce the load at the scale house by unloading excess weight into another vehicle or to a temporary storage location (many scale houses have provisions for this), redistribute the load to bring overloaded axle groups within limits without reducing total weight (for example, adjusting the fifth wheel or tandem sliders), obtain an overweight permit for the specific route from the state DOT (some states have provisions for permits that can be issued on-site by enforcement officers for amounts modestly over the limit), or contact your carrier or dispatcher for instructions. Your carrier is legally responsible for the vehicle’s weight compliance and must be notified immediately of any out-of-service order. The OOS order is recorded in FMCSA systems and attributed to the carrier’s CSA record. Do not attempt to move the vehicle until you have received written confirmation from the enforcement officer that the vehicle is cleared to proceed. Moving a vehicle under an active OOS order is a separate, serious violation with significantly higher penalties.
Related Trucking Compliance Calculators
Legal Disclaimer and Editorial Transparency. The Bridge Formula Weight Calculator on this page is provided for planning and informational purposes only and does not constitute legal advice. Federal weight limits referenced are from 23 USC 127 (Federal Bridge Formula), 23 CFR Part 658, and FHWA bridge formula publications, current through August 2026. The bridge formula applies specifically to the Interstate Highway System; state highways, US routes, and local roads are subject to state-specific weight laws which vary by jurisdiction. Overweight fines, permit requirements, and enforcement procedures vary by state. Seasonal spring weight restrictions are not incorporated into this calculator; verify current state DOT postings before routing loads on non-interstate roads. All calculator results should be verified against official FHWA publications at FHWA.dot.gov and with the relevant state DOT for specific route and permit questions. USCalculators.com is not affiliated with FHWA, FMCSA, USDOT, or any government agency.