View source for Federal Bridge Gross Weight Formula

{{Use mdy dates|date=June 2015}}
[[Image:Bridge formula 2.svg|thumb|This diagram illustrates the difference in weight concentration between a short and long [[wheelbase]] truck. The shorter truck causes more wear and tear because all of its weight is concentrated in a smaller area.<ref name=bfw/>]]

The '''Federal Bridge Gross Weight Formula''', also known as '''Bridge Formula B''' or the '''Federal Bridge Formula''', is a [[mathematical formula]] in use in the United States by [[truck drivers]] and [[United States Department of Transportation|Department of Transportation]] (DOT) officials to determine the appropriate maximum gross weight for a [[commercial motor vehicle]] (CMV) based on [[axle]] number and spacing. The formula is part of federal weight and size regulations regarding interstate commercial traffic (intrastate traffic is subject to state limits). The formula is necessary to prevent heavy vehicles from damaging roads and bridges. CMVs are most often [[tractor-trailer]]s or buses, but the formula is of most interest to truck drivers due to the heavy loads their vehicles often carry.

Early 20th-century weight limits were enacted to protect dirt and gravel roads from damage caused by the solid wheels of heavy trucks. As time passed, truck weight limits focused primarily on [[gross weight]] limits (which had no prescribed limits on length). By 1974, bridges received special protection from increasing truck weight limits. The bridge formula law was enacted by the [[U.S. Congress]] to limit the weight-to-length ratio of heavy trucks, and to protect roads and bridges from the damage caused by the concentrated weight of shorter trucks. The formula effectively lowers the legal weight limit for shorter trucks, preventing them from causing premature deterioration of bridges and highway [[infrastructure]].

Compliance with the law is checked when vehicles pass through a [[weigh station]], often located at the borders between [[U.S. states|states]] or on the outskirts of [[List of United States cities by population|major cities]], where the vehicle may be weighed and measured. The one exception to the formula allows a standard five-axle semi-truck configuration to weigh the maximum legal gross weight. This exception was specifically requested by the [[American Trucking Associations]] to allow [[tank truck]]s to reach the maximum legal gross weight without violating the bridge formula law.

==History==

The first truck weight limits were enacted by four states in 1913, ranging from {{convert|18000|lb}} in [[Maine]] to {{convert|28000|lb}} in [[Massachusetts]]. These laws were passed to protect earth and gravel-surfaced roads from damage caused by the steel and solid rubber wheels of early heavy trucks. By 1933, all states had some form of truck weight regulation. The [[Federal-Aid Highway Act of 1956]] instituted the first federal truck weight regulation (set at {{convert|73280|lb|disp=or}}) and authorized the construction of the [[Interstate Highway System]].<ref name=fhwa8>{{cite web |url=http://www.fhwa.dot.gov/reports/tswstudy/Vol2-Chapter2.pdf |title=Chapter 2: Truck Size and Weight Limits |work=Comprehensive Truck Size and Weight Study |volume= Volume 2: Issues and Background |format=PDF |access-date=May 3, 2008 |publisher=Federal Highway Administration }}</ref>

In the late 1950s, the [[American Association of State Highway and Transportation Officials]] (AASHTO) conducted a series of extensive [[AASHO Road Test|field tests]] of roads and bridges to determine how traffic contributed to the deterioration of [[Pavement (material)|pavement materials]]. In 1964, the AASHTO recommended to Congress that a bridge formula table be used instead of a single gross weight limit for trucks. The [[Federal-Aid Highway Act Amendments of 1974]] established the bridge formula as law, along with the gross weight limit of {{convert|80000|lb}}.  Current applications of the formula allow for up to 7 axles and 86 feet or more length between axle sets, and a maximum load of 105,500&nbsp;lbs.<ref name=fhwa8/>

==Usage==
[[File:Concrete pumper truck, Denver.jpg|thumb|The back of the concrete mixer truck carries a 'booster axle', which can be lowered to extend the wheelbase of a fully loaded truck to comply with regulations.<ref>{{cite AV media|url=https://www.youtube.com/watch?v=PlkDcFvK0Ac|title=Booster Axle: Ultimate Weight Lifter|publisher=NRMCA}}</ref>]]
The formula was enacted as law to limit the weight-to-length ratio of a [[commercial motor vehicle]] (CMV).<ref name="FHA1">{{cite web |url=http://ops.fhwa.dot.gov/freight/sw/brdgcalc/calc_page.htm |title=Bridge Formula Weights Calculator |access-date=February 3, 2008 |publisher= Federal Highway Administration }}</ref> The formula is necessary to prevent the concentrated weight on a truck's axle from producing stress on bridge members (possibly causing a [[bridge collapse]]).<ref>{{cite web |url=http://www.mne.psu.edu/ifrtt/ConferenceProceedings/ISHVWD_9_2006/docs/pdfs/session%2011/s11-2%20152.pdf |title=Federal Bridge Formula: How It Influences Vehicle Dynamic Behavior |first=John |last=Woodrooffe |publisher=University of Michigan Transportation Research Institute |location=Ann Arbor |access-date=March 8, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090324233721/http://www.mne.psu.edu/ifrtt/ConferenceProceedings/ISHVWD_9_2006/docs/pdfs/session%2011/s11-2%20152.pdf |archive-date=March 24, 2009 |df=mdy-all }}</ref> In simplified form, this is analogous to a person walking on thin ice. When standing upright, a person's weight is concentrated at the bottom of their feet, funneling all of their weight into a small area. When lying down, a person's weight is distributed over a much larger area. This difference in weight distribution would allow a person to cross an area of ice while crawling that might otherwise collapse under their body weight while standing up. For an overweight truck to comply with the formula, more axles must be added, the distance between axles must be increased, or weight must be removed.<ref name=bfw/><ref>{{cite web |url=http://www.mdt.mt.gov/publications/docs/manuals/truckers_handbook.pdf |title=2006 Montana Commercial Vehicle Size and Weight and Safety Trucker's Handbook |access-date=March 9, 2009 |publisher=[[Montana Department of Transportation]] |format=PDF}}</ref>

A division of the DOT, the [[Federal Motor Carrier Safety Administration]] (FMCSA), regulates safety for the [[Trucking industry in the United States|U.S. trucking industry]].<ref>{{cite web|url=http://www.fmcsa.dot.gov/about/what-we-do/strategy/strategy.htm |title=FMCSA's Strategy |access-date=February 3, 2008 |publisher=[[Federal Motor Carrier Safety Administration]] |url-status=dead |archive-url=https://web.archive.org/web/20080124194531/http://www.fmcsa.dot.gov/about/what-we-do/strategy/strategy.htm |archive-date=January 24, 2008 |df= }}</ref> The FMCSA enforces the length, width, and weight limits of CMVs set by the [[Federal Highway Administration]] (FHWA) for ''interstate'' commercial traffic. Interstate commercial traffic is generally limited to a network of [[Interstate Highway System|Interstate Highways]], [[U.S. Highways]], and [[state highways]] known as the [[National Network]] (NN). Provided the truck remains on the NN, it is not subject to state limits. These limits (which can be lower or higher than federal limits) come into effect for ''intrastate'' commercial traffic, provided the vehicle is not on the NN.<ref name=FHA2>{{cite web |url=http://ops.fhwa.dot.gov/freight/publications/size_regs_final_rpt/size_regs_final_rpt.pdf |title=Federal Size Regulations for Commercial Motor Vehicles |access-date=March 27, 2008 |publisher=Federal Highway Administration |format=PDF }}</ref>

CMVs are defined by the FMCSA as vehicles engaged in interstate commerce that are used to transport passengers or property: vehicles with a gross vehicle weight of {{convert|10001|lb}} or more; those designed or used to transport more than 8 passengers (including the driver) for compensation; vehicles designed or used to transport more than 15 passengers (including the driver) without compensation; or those used to transport [[hazardous materials]] in quantities requiring the vehicle to be marked or [[placard]]ed under [[hazardous materials]] regulations.<ref name=def>{{cite web |url=http://www.fmcsa.dot.gov/rules-regulations/administration/fmcsr/fmcsrruletext.asp?rule_toc=778&section=658.5&section_toc=2129 |title=§658.5 Definitions |access-date=March 27, 2008 |publisher=Federal Motor Carrier Safety Administration |url-status=dead |archive-url=https://web.archive.org/web/20080305123637/http://www.fmcsa.dot.gov/rules-regulations/administration/fmcsr/fmcsrruletext.asp?rule_toc=778&section=658.5&section_toc=2129 |archive-date=March 5, 2008 |df=mdy-all }}</ref>

The weight and size of CMVs are restricted for practical and safety reasons. CMVs are restricted by gross weight (total weight of vehicle and cargo), and by axle weight (i.e., the weight carried by each tire). The federal weight limits for CMVs are {{convert|80000|lb}} for gross weight (unless the bridge formula dictates a lower limit), {{convert|34000|lb}} for a tandem axle, and {{convert|20000|lb}} for a single axle.<ref name=weight/> A tandem axle is defined as two or more consecutive axles whose centers are spaced more than {{convert|40|in|cm|0}} but not more than {{convert|96|in|cm|0}} apart.<ref name=def/> Axles spaced less than {{convert|40|in|cm|0}} apart are considered a single axle.<ref name=randmcnally>{{cite web |url=http://www.randmcnally.com/pdf/tdm/Federal_Bridge.pdf |archive-url=https://web.archive.org/web/20030308203728/http://www.randmcnally.com/pdf/tdm/Federal_Bridge.pdf |archive-date=March 8, 2003 |title=Federal Bridge Gross Weight Formula |access-date=March 8, 2009 |publisher=[[Rand McNally]] }}</ref>

In effect, the formula reduces the legal weight limit for shorter trucks with fewer axles (see [[Federal Bridge Gross Weight Formula#Bridge formula table|table]] below). For example, a {{convert|25|ft|adj=on}} three-axle [[dump truck]] would have a gross weight limit of {{convert|54500|lb}}, instead of {{convert|80000|lb}}, which is the standard weight limit for {{convert|63|ft|1|adj=on}} five-axle tractor-trailer.<ref name=bfw/> FHWA regulation §658.17 states: "The maximum gross vehicle weight shall be {{convert|80,000|lb}} except where lower gross vehicle weight is dictated by the bridge formula."<ref name=weight/>

==Bridge collapse==
[[File:Ohio MUTCD R12-H5.svg|thumb|right|upright|A bridge weight limit sign that drivers must heed before crossing a bridge in [[Ohio]]. The weight limit increases with the number of axles for single-unit trucks. The weights are in [[short ton]]s.]]
The August 2007 collapse of the [[Interstate 35W Mississippi River bridge]] in [[Minneapolis]] brought renewed attention to the issue of truck weights and their relation to bridge stress.<ref name=mpr>{{cite web |url=http://minnesota.publicradio.org/display/web/2007/08/10/bridgetruckweight/ |title=Heavy Trucks Strain Roads and Bridges |access-date=March 28, 2008 |publisher=Minnesota Public Radio |first=Dan |last= Gunderson |date=August 10, 2007 }}</ref> In November 2008, the [[National Transportation Safety Board]] determined there had been several reasons for the bridge's collapse, including (but not limited to): faulty [[gusset plate]]s, inadequate inspections, and the extra weight of heavy construction equipment combined with the weight of rush hour traffic.<ref>{{cite web |url=http://www.ntsb.gov/publictn/2008/HAR0803.htm |title=Highway Accident Report: Collapse of I-35W Highway Bridge |access-date=December 31, 2009 |publisher=[[National Transportation Safety Board]] }}</ref>  The I-35 Trade Corridor Study reported that the [[Federal Highway Administration]] (FHWA) expressed concern over bridges on the [[I-35]] corridor due to an expected increase of international truck traffic from [[Canada]] and [[Mexico]], with the FHWA listing it as "high-priority" in 2005.<ref>{{cite web |url=http://publications.iowa.gov/2975/1/i35study.pdf |title=I-35 Trade Corridor Study |access-date=March 8, 2013 |publisher=I-35 Trade Corridor Study |author=I-35 Trade Corridor Study |date=Winter 1998}}</ref>

As of 2007, federal estimates suggest truck traffic increased 216% since 1970, shortly before the federal gross weight limit for trucks was increased by {{convert|30000|lb}}. This is also the period during which many of the existing interstate bridges were built. Research shows that increased truck traffic (and therefore, increased stress) shortens the life of bridges.<ref name=mpr/> National Pavement Cost Model (NAPCOM) estimates indicate that one {{convert|80000|lb|adj=on}} truck does as much damage to roads as 750 {{convert|3800|lb|adj=on}} cars.<ref>{{cite web |url=http://www.oregon.gov/ODOT/CS/EA/policy_notes/03_policy_notes/0603_New_Resrch_on_Pavement_Damage.pdf |title=New Research on Pavement Damage Factors |access-date=March 31, 2008 |publisher=[[Oregon Department of Transportation]] |date=June 2003 |author=John Merriss |url-status=dead |archive-url=https://web.archive.org/web/20080625110812/http://www.oregon.gov/ODOT/CS/EA/policy_notes/03_policy_notes/0603_New_Resrch_on_Pavement_Damage.pdf |archive-date=June 25, 2008 |df=mdy-all }}</ref>

Some smaller bridges have a weight limit (or gross weight load rating) indicated by a sign posted in a visible position in front of the bridge (hence the reference to a "posted bridge"). These are necessary when the weight limit of the bridge is lower than the federal or state gross weight limit for trucks.<ref name=fldot>{{cite web |url=http://www2.dot.state.fl.us/proceduraldocuments/procedures/bin/850010035.pdf |format=PDF |title=Bridge Load Rating, Permitting and Posting |access-date=March 28, 2008 |publisher=[[Florida Department of Transportation]] |url-status=dead |archive-url=https://web.archive.org/web/20080625110814/http://www2.dot.state.fl.us/proceduraldocuments/procedures/bin/850010035.pdf |archive-date=June 25, 2008 |df=mdy-all }}</ref><ref>{{cite web |url=http://www.pacode.com/secure/data/067/chapter191/chap191toc.html |title=Chapter 191: Authorization to Use Bridges Due to Condition of Bridge |access-date=March 21, 2009 |publisher=[[Pennsylvania Department of Transportation]] }}</ref> Driving a truck over a bridge that is too weak to support it usually does not result in an immediate collapse. The bridge may develop cracks, which over time can weaken the bridge and cause it to collapse. Most of these cracks are discovered during mandated inspections of bridges. Most bridge collapses occur in rural areas, result in few injuries or deaths, and receive relatively little media attention. While the number varies from year to year, as many as 150 bridges can collapse in a year. About 1,500 bridges collapsed between 1966 and 2007, and most of those were the result of soil erosion around bridge supports.<ref>{{cite news |url=https://query.nytimes.com/gst/fullpage.html?res=9B0DE6DA1F3EF931A25757C0A961948260&sec=&spon=&pagewanted=all |title=Bridge Failures |access-date=March 28, 2008 |work=[[The New York Times]] |date=April 12, 1987 |first=Martin |last= Tolchin }}</ref><ref>{{cite news |url=http://www.heraldnet.com/article/20070803/NEWS02/708030384 |title=Many Clues to Collapse |access-date=March 3, 2009 |work=The Daily Herald |location= Everett, WA |date=August 3, 2007 }}</ref> In 1987, the [[Schoharie Creek Bridge collapse]]d in [[upstate New York]], due to erosion of soil around the foundation, which sparked renewed interest in bridge design in inspection procedures.<ref>{{cite web |url=http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JPCFEV000021000004000320000001&idtype=cvips&gifs=yes |title=Fault Tree Analysis of Schoharie Creek Bridge Collapse |publisher=[[American Society of Civil Engineers]] |first1=Keary H. |last1= LeBeau |first2= Sara J. |last2=Wadia-Fascetti |date=July–August 2007|access-date=March 8, 2009}}</ref>

In special cases involving unusually [[Oversize/overweight load|overweight trucks]] (which require special permits), not observing a bridge weight limit can lead to disastrous consequences. Fifteen days after the collapse of the Minneapolis bridge, a heavy truck collapsed a small bridge in [[Oakville, Washington]].<ref>{{cite web |url=http://www.komotv.com/news/9187062.html |title=Truck Collapses Bridge in Grays Harbor County |access-date=March 31, 2008 |location=Seattle |publisher=[[KOMO-TV]] |agency=[[Associated Press]] |date=August 15, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070818022735/http://www.komotv.com/news/9187062.html |archive-date=August 18, 2007 |df=mdy-all }}</ref>

==Formula law==
CMVs are required to pass through [[weigh station]]s at the borders of most states and some large cities. These weigh stations are run by state DOTs, and CMV weight and size enforcement is overseen by the FHWA. Weigh stations check each vehicle's gross weight and axle weight using a set of in-ground [[truck scales]], and are usually where a truck's compliance with the formula is checked.<ref>{{cite web |url=http://ops.fhwa.dot.gov/freight/sw/overview/index.htm |title=Commercial Vehicle Size and Weight Program |access-date=March 27, 2008 |publisher=Federal Highway Administration }}</ref>
[[Image:Axle groups.svg|thumb|300px|Truck axle groups are used to calculate compliance with the formula. Any two axles must comply with the results of the formula, but axle groups 1–5, 1–3, and 2–5 are most critical. This truck is not in violation of the formula.<ref name=bfw/>]]
FMCSA regulation §658.17 states:<ref name=weight>{{cite web |url=http://www.fmcsa.dot.gov/rules-regulations/administration/fmcsr/fmcsrruletext.asp?rule_toc=778&section=658.17&section_toc=2135 |title=§658.17 Weight |access-date=February 3, 2008 |publisher=Federal Motor Carrier Safety Administration |url-status=dead |archive-url=https://web.archive.org/web/20080104024439/http://www.fmcsa.dot.gov/rules-regulations/administration/fmcsr/fmcsrruletext.asp?rule_toc=778&section=658.17&section_toc=2135 |archive-date=January 4, 2008 |df=mdy-all }}</ref>
* No vehicle or combination of vehicles shall be moved or operated on any interstate highway when the gross weight on two or more consecutive axles exceeds the limitations prescribed by the following formula:
::<math>w = 500 \left ( \frac{\ell  n}{n-1} + 12n + 36 \right ) </math>
* ''w'' = the maximum weight in pounds that can be carried on a group of two or more axles to the nearest {{convert|500|lb}}.
* ''ℓ'' = spacing in feet between the outer axles of any two or more consecutive axles.
* ''n'' = number of axles being considered.

Two or more consecutive axles may not exceed the weight computed by the bridge formula, even if the gross weight of the truck (or the weight on one axle) is below otherwise legal limits.<ref name="FHA1"/> Although this means that any two axles must comply with the formula, experience has shown that axles 1 through 3, 1 through 5, and 2 through 5 are critical and must be checked. This means that the axle group which comprises the entire truck (known as the "outer group") and the interior axle groups (known as the "tractor group" and "trailer group") must also comply with the bridge formula. If these combinations are found to be satisfactory, then all of the other axle groups on this type of vehicle will usually be satisfactory.<ref name=bfw/>

Penalties for violating weight limits vary between states (bridge formula weight violations are treated as gross weight violations), as the states are responsible for enforcement and collection of fines. Some states, such as [[Connecticut]], issue fines on a percentage basis (e.g. 20% overweight at $10 per {{convert|100|lb|disp=or}}), which means larger trucks pay higher fines. For example, a truck with a legal gross limit of {{convert|20000|lb}} that violates the limit by {{convert|5000|lb}} would pay a fine of $500, while a truck with a legal gross limit of {{convert|60000|lb}} that violates the limit by 5,000&nbsp;pounds would pay a fine of $250. Other states, such as [[New York (state)|New York]], issue fines on a per-pound basis (e.g., 5,000&nbsp;pounds overweight equals a $300 fine). Others, such as [[Massachusetts]], impose a less complicated fine schedule whereby a vehicle that violates the limits by less than {{convert|10000|lb}} is fined $40 per {{convert|1000|lb}}, while a violation over {{convert|10,000|lb}} pays $80 per {{convert|1000|lb}} (e.g. {{convert|5,000|lb|disp=or}} overweight equals a $200 fine).<ref>{{cite web |url=http://www.cga.ct.gov/2007/rpt/2007-R-0214.htm |first=Zachary|last= Schurin |title=Criminal Penalties for Overweight Trucks |access-date=April 23, 2009 |date=March 20, 2007 |publisher= [[Connecticut General Assembly|State of Connecticut General Assembly]] }}</ref>

Some states require overweight trucks to  offload enough cargo to comply with the limits. In [[Florida]], any vehicle that exceeds the limits by more than {{convert|6000|lb}} is required to be unloaded until the vehicle is in compliance. Florida also includes a scale tolerance, which allows for violations of less than 10% to be forgiven, and no fine issued. Florida also allows for a load to be shifted (e.g., moved from the front towards the rear of the vehicle) for the vehicle to comply with axle weight limits, without penalty.<ref>{{cite web |url=http://www.leg.state.fl.us/statutes/index.cfm?App_mode=Display_Statute&Search_String=&URL=Ch0316/Sec545.HTM |title=316.545 Weight and Load Unlawful; Special Fuel and Motor Fuel Tax Enforcement; Inspection; Penalty; Review |access-date=April 23, 2009 |publisher= [[Florida Legislature]] }}</ref>

==Exception==
There is one exception to the formula: two consecutive sets of tandem axles may carry {{convert|34000|lb}} each if the overall distance between the first and last axles of these tandems is {{convert|36|ft|m}} or more. For example, a five-axle truck may carry 34,000&nbsp;pounds both on the tractor tandem axles (2 and 3) and the trailer tandem axles (4 and 5), provided axles 2 and 5 are spaced at least {{convert|36|ft|m}} apart.<ref name=bfw>{{cite web |url=http://ops.fhwa.dot.gov/freight/publications/brdg_frm_wghts/index.htm |title=Bridge Formula Weights |access-date=February 3, 2008 |publisher= [[Federal Highway Administration]] }}</ref>

This exception allows for the standard 5-axle semi-truck configuration to gross up to {{convert|80000|lb}} (the legal limit)<ref name=weight/> without being in violation of the bridge formula law. Without it, the bridge formula would allow an actual weight of only {{convert|66000|lb}} to {{convert|67500|lb}} on tandems spaced {{convert|36|ft}} to {{convert|38|ft|1}} apart; compared to {{convert|68000|lb}} with the exception. This exception was sought by the [[American Trucking Associations]] so trucking companies could use {{convert|40|ft|1|adj=on}} trailers and weigh {{convert|80000|lb}}. It was the only way [[tank truck]] operators could reach 80,000&nbsp;pounds without adding axles to their fleets of trailers already in operation.<ref>{{cite web |url=http://www.clermontengineer.org/PlanBridgeFormula.htm |title=Living With The 'Bridge' |access-date=March 27, 2008 |publisher=Clermont County Engineers Office |date=January 2, 2002 |archive-url=https://web.archive.org/web/20071010175926/http://www.clermontengineer.org/PlanBridgeFormula.htm |archive-date=October 10, 2007 }}</ref>

A CMV may exceed the bridge formula limits (or gross weight and its axle weight limits) by up to {{convert|550|lb|0}} if the vehicle is equipped with an [[Auxiliary power unit#Commercial vehicles|auxiliary power unit]] (APU) or [[idle reduction]] technology. According to the FMCSA, this is permitted "in order to promote reduction of fuel use and emissions because of engine idling". To be eligible, the vehicle's operator must prove the weight of the APU with written certification, or—by demonstration or certification—that the idle reduction technology is fully functional at all times. Certification of the APU's weight must be available to law enforcement officers if the vehicle is found in violation of applicable weight laws. The additional weight allowed cannot exceed 550&nbsp;pounds or the weight certified, whichever is less.<ref>{{cite web |url= http://uscode.house.gov/view.xhtml?hl=false&edition=prelim&req=granuleid%3AUSC-prelim-title23-section127&num=0&saved=%7CZ3JhbnVsZWlkOlVTQy1wcmVsaW0tdGl0bGUyMy1zZWN0aW9uMTI3%7C%7C%7C0%7Cfalse%7Cprelim |title=23 USC 127: Vehicle weight limitations-Interstate System}}</ref>

==Issues==
The bridge formula (also referred to as Formula B) is based on research into single-[[Span (architecture)|span]] bridges, and fails to consider multiple-span bridges. Two-span bridges may not be fully protected by Formula B, depending on the truck length, span length, and other factors.<ref name=fhwa11>{{cite web |url=http://www.fhwa.dot.gov/reports/tswstudy/Vol3-Chapter6.pdf |title=Chapter 6: Bridge |work=Comprehensive Truck Size and Weight Study |volume= Volume 2: Issues and Background |format=PDF |access-date=March 17, 2009 |publisher= Federal Highway Administration }}</ref> Shorter wheelbase vehicles (usually specialized trucks such as [[garbage trucks]] and water trucks) have trouble complying with Formula B.<ref name=trb/>

In 1987, the [[United States Congress|U.S. Congress]] passed the [[Surface Transportation and Uniform Relocation Assistance Act of 1987|Surface Transportation and Uniform Relocation Assistance Act]], requesting the [[Transportation Research Board]] (TRB) to conduct a study to develop alternatives to Formula B. The study recommended several that were never implemented. It suggested that Formula B was too strict for trucks with shorter axle lengths. One of the alternative formulas (later known as the TTI HS-20 Bridge Formula) was developed in conjunction with the [[Texas Transportation Institute]]. TTI HS-20 allowed shorter trucks to have higher weight limits than Formula B. For a 3-axle truck with an axle length of {{convert|14|ft}}, the weight limit increased from {{convert|46500|lb}} to {{convert|54000|lb}}.<ref name=trb>{{cite book |url=https://books.google.com/?id=c2MVl5782ucC&dq=Truck+weight+limits+By+National+Research+Council+(U.S.).+Committee+for+the+Truck+Weight+Study&printsec=frontcover |title=Truck Weight Limits: Issues and Options |access-date=March 9, 2009 |year=1990 |publisher=[[United States National Research Council|National Research Council]] |isbn=978-0-309-04955-9 }}</ref> TTI HS-20 also failed to address the problem of multiple-span bridges.<ref name=fhwa11/>

{| cellpadding="5" border="0" cellspacing="1"
|-
! style="background:#B0C4DE;" rowspan="2"| Distance in feet between any<br/>group of two or more axles <sup>1</sup>
! style="background:#B0C4DE;" colspan="6"| Gross weight in pounds  (kilograms) <sup>2</sup>
|-
| style="background:#ADD8E6;" |'''2 axles'''
| style="background:#ADD8E6;" |'''3 axles'''
| style="background:#ADD8E6;" |'''4 axles'''
| style="background:#ADD8E6;" |'''5 axles'''
| style="background:#ADD8E6;" |'''6 axles'''
| style="background:#ADD8E6;" |'''7 axles'''
|-
| style="background:#D3D3D3;" | Less than 8 <sup>3</sup>
| style="background:#98FB98;" | {{convert|34,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|34,000|lb|kg|0|abbr=on}}
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
|-
| style="background:#D3D3D3;" | More than 8 <sup>4</sup>
| style="background:#98FB98;" | {{convert|38,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|42,000|lb|kg|0|abbr=on}}
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
|-
| style="background:#D3D3D3;" | 9
| style="background:#98FB98;" | {{convert|39,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|42,500|lb|kg|0|abbr=on}}
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
|-
| style="background:#D3D3D3;" | 10 
| style="background:#FFFF00;" | {{convert|40,000|lb|kg|0|abbr=on}}<sup>5</sup>
| style="background:#98FB98;" | {{convert|43,500|lb|kg|0|abbr=on}}
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
|-
| style="background:#D3D3D3;" | 11
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|44,000|lb|kg|0|abbr=on}}
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
|-
| style="background:#D3D3D3;" | 12
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|45,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|50,000|lb|kg|0|abbr=on}}
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
|-
| style="background:#D3D3D3;" | 13
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|45,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|50,500|lb|kg|0|abbr=on}}
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
|-
| style="background:#D3D3D3;" | 14
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|46,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|51,500|lb|kg|0|abbr=on}}
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
|-
| style="background:#D3D3D3;" | 15
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|47,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|52,000|lb|kg|0|abbr=on}}
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
|-
| style="background:#D3D3D3;" | 16
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|48,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|52,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|58,000|lb|kg|0|abbr=on}}
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
|-
| style="background:#D3D3D3;" | 17
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|48,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|53,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|58,500|lb|kg|0|abbr=on}}
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
|-
| style="background:#D3D3D3;" | 18
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|49,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|54,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|59,000|lb|kg|0|abbr=on}}
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
|-
| style="background:#D3D3D3;" | 19
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|50,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|54,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#BDB76B;" |
| style="background:#BDB76B;" |
|-
| style="background:#D3D3D3;" | 20
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|51,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|55,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|60,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|66,000|lb|kg|0|abbr=on}}
| style="background:#BDB76B;" |
|-
| style="background:#D3D3D3;" | 21
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|51,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|56,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|61,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|66,500|lb|kg|0|abbr=on}}
| style="background:#BDB76B;" |
|-
| style="background:#D3D3D3;" | 22
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|52,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|56,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|61,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|67,000|lb|kg|0|abbr=on}}
| style="background:#BDB76B;" |
|-
| style="background:#D3D3D3;" | 23
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|53,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|57,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|62,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|68,000|lb|kg|0|abbr=on}}
| style="background:#BDB76B;" |
|-
| style="background:#D3D3D3;" | 24
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|54,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|58,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|63,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|68,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|74,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 25
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|54,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|58,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|63,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|69,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|74,500|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 26
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|55,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|59,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|64,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|69,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|75,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 27
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|56,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|65,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|70,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|75,500|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 28
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|57,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|60,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|65,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|71,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|76,500|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 29
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|57,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|61,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|66,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|71,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|77,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 30
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|58,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|62,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|66,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|72,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|77,500|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 31
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|59,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|62,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|67,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|72,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|78,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 32
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#FFFF00;" | {{convert|60,000|lb|kg|0|abbr=on}}<sup>5</sup>
| style="background:#98FB98;" | {{convert|63,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|68,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|73,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|78,500|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 33
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|64,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|68,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|74,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|79,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 34
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|64,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|69,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|74,500|lb|kg|0|abbr=on}}
| style="background:#FFFF00;" | {{convert|80,000|lb|kg|0|abbr=on}}<sup>5</sup>
|-
| style="background:#D3D3D3;" | 35
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|65,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|70,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|75,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 36
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#3CB371;" | {{convert|66,000|lb|kg|0|abbr=on}}<sup>6</sup>
| style="background:#98FB98;" | {{convert|70,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|75,500|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 37
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#3CB371;" | {{convert|66,500|lb|kg|0|abbr=on}}<sup>6</sup>
| style="background:#98FB98;" | {{convert|71,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|76,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 38
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#3CB371;" | {{convert|67,500|lb|kg|0|abbr=on}}<sup>6</sup>
| style="background:#98FB98;" | {{convert|71,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|77,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 39
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|68,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|72,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|77,500|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 40
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|68,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|73,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|78,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 41
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|69,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|73,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|78,500|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 42
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|70,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|74,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|79,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 43
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|70,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|75,000|lb|kg|0|abbr=on}}
| style="background:#FFFF00;" | {{convert|80,000|lb|kg|0|abbr=on}}<sup>5</sup>
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 44
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|71,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|75,500|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 45
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|72,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|76,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 46
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|72,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|76,500|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 47
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|73,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|77,500|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 48
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|74,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|78,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 49
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|74,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|78,500|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 50
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|75,500|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|79,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 51
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|76,000|lb|kg|0|abbr=on}}
| style="background:#FFFF00;" | {{convert|80,000|lb|kg|0|abbr=on}}<sup>5</sup>
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 52
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|76,500|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 53
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|77,500|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 54
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|78,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 55
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|78,500|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 56
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#98FB98;" | {{convert|79,500|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
| style="background:#D3D3D3;" | 57
| style="background:#F0E68C;" | {{convert|40,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|60,000|lb|kg|0|abbr=on}}
| style="background:#FFFF00;" | {{convert|80,000|lb|kg|0|abbr=on}}<sup>5</sup>
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
| style="background:#F0E68C;" | {{convert|80,000|lb|kg|0|abbr=on}}
|-
|}
* <sup>1</sup> Calculated values reflect FHWA policy of rounding down when distances fall exactly between {{convert|6|in|cm|2|adj=on}} increments.<ref name=qna>{{cite web|url=http://vsw.fhwa.dot.gov/qa/qa.jsp?category=23%20CFR%20658.17 |title=Questions and Answers about Vehicle Size and Weight |access-date=March 27, 2008 |publisher=Federal Highway Administration |location=US |archive-url=https://web.archive.org/web/20080315090620/http://vsw.fhwa.dot.gov/qa/qa.jsp?category=23%20CFR%20658.17 |archive-date=March 15, 2008 |url-status=dead |df= }}</ref>
* <sup>2</sup> Calculated values reflect FHWA policy of rounding down when weights fall exactly between {{convert|500|lb|0|adj=on}} increments.<ref name="FHA1"/>
* <sup>3</sup> Tandem axle by definition.<ref name=randmcnally/>
* <sup>4</sup> Distances between {{convert|8|ft|m|2}} to {{convert|8|ft|11|in|m|2}}  may not be rounded down.<ref name=qna/>
* <sup>5</sup> <span style="color: #FFFF00; background-color: #FFFF00;">__</span> Maximum legal weight limit based on number of axles. Increased axle lengths beyond these do not increase maximum legal weight.<ref name=randmcnally/>
* <sup>6</sup> <span style="color: #3CB371; background-color: #3CB371;">__</span> Exception to the formula: when the four axles under consideration are two tandem axles spaced at least {{convert|36|ft|2}} apart, a gross weight of {{convert|68000|lb|0}} is allowed.<ref name=randmcnally/>
* <span style="color: #BDB76B; background-color: #BDB76B;">__</span> Upper blank areas represent unrealistic configurations.<ref name=FHA1/>

==See also==
* [[Long combination vehicle]]

==References==
{{Reflist|colwidth=30em}}

==External links==
* 
* [http://ops.fhwa.dot.gov/freight/sw/brdgcalc/calc_page.htm Bridge formula weights calculator]

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