The Federal Bridge Weight Formula , also known as Bridge Formula B or Federal Bridge Formula , is the mathematical formula used in the United States by truck drivers and Ministry of Transport (DOT) official to determine the maximum gross weight of a proper commercial vehicle (CMV) based on shaft number and distance. The formula is part of heavy federal regulations and measures concerning interstate commercial traffic (intrastate traffic is subject to state borders). This formula is necessary to prevent heavy vehicles from damage to roads and bridges. CMV most often is a tractor-trailer or bus, but the formula is most attractive to truck drivers because of the heavy loads their vehicles often carry.
The weight limit of the early 20th century was put in place to protect the dirt and gravel roads from the damage caused by the heavy truck's heavy wheels. As time passes, the weight limit of the truck is focused primarily on the gross weight limit (which has no specified length limit). In 1974, the bridge received special protection from the increased weight limit of trucks. The bridge formula formula was enacted by the US Congress to limit the weight-to-length ratio of large trucks, and to protect roads and bridges from damage caused by the heavier weight of trucks. This formula effectively lowers the legal weight limit for shorter trucks, preventing them from causing bridge damage and worsening road infrastructure.
Compliance with the law is checked when the vehicle passes a weighbridge, often located on the border between the state or on the outskirts of major cities, where vehicles can be weighed and measured. One exception to this formula allows the standard five-axle semi-truck configuration to weigh the legal maximum weight. This exception is specifically requested by the American Trucking Association to allow the tanker truck to achieve maximum legal gross weight without violating the bridge formula law.
Video Federal Bridge Gross Weight Formula
Histori
The first truck weight limit was enforced by four states in 1913, ranging from 18,000 pounds (8,200 kg) in Maine to 28,000 pounds (13,000 kg) in Massachusetts. This law was passed to protect earth-covered roads and gravel from damage caused by solid steel and rubber wheels from heavy trucks early. By 1933, all countries had some form of heavy truck regulation. The Federal-Aid Highway Act of 1956 implements the first federal truck weight regulation (set at 73,280 pounds or 33,240 kilograms) and certifies the construction of the Interstate Highway System.
In the late 1950s, the US State Roads and Transportation Association (AASHTO) conducted an extensive field test of roads and bridges to determine how traffic contributed to pavement damage. In 1964, the AASHTO recommended to Congress that the bridge formula table be used in lieu of a gross weight limit for trucks. The Federal-Aid Highway Act Amendments of 1974 set the bridge formula as law, along with a gross weight limit of 80,000 pounds (36,000 kg). The current application of the formula allows up to 7 axles and 86 feet or longer between the axle sets, and a maximum load of 105,500 lbs.
Maps Federal Bridge Gross Weight Formula
Usage
The formula is defined as a law to limit the weight-to-length ratio of commercial motor vehicles (CMV). This formula is necessary to prevent the weight concentrated on the truck's axle from generating pressure on the bridge member (possibly causing the bridge to collapse). In a simplified form, this is analogous to someone walking on thin ice. When standing upright, a person's weight is concentrated at the bottom of their feet, channeling all their weight into a small area. When lying down, a person's weight is distributed in a much larger area. This weight distribution difference will allow a person to cross an ice area during a crawl that may collapse under their weight while standing. For overweight trucks to comply with the formula, more axles should be added, the distance between the axles should be raised, or the weight should be removed.
DOT division, Federal Motor Carrier Safety Administration (FMCSA), regulates security for the US trucking industry. FMCSA imposes limits on the length, width and weight of CMV set by the Federal Highway Administration (FHWA) for commercial traffic interstate . Interstate commercial traffic is generally restricted to the Interstate Highways network, the U.S. Highway, and the state highway known as the National Network (NN). As long as the truck remains in NN, it is not subject to state borders. These limits (which may be lower or higher than the federal limit) apply to commercial traffic intrastate , provided the vehicle is not in NN.
CMV is defined by FMCSA as a vehicle engaged in interstate commerce used to transport passengers or property: vehicles with a gross vehicle weight of 10,001 pounds (4,536 kg) or more; designed or used to carry more than 8 passengers (including drivers) for compensation; vehicles designed or used to carry more than 15 passengers (including drivers) without compensation; or used to transport hazardous substances in quantities requiring vehicles to be marked or signed under hazardous materials regulations.
CMV weight and size are limited for practical and security reasons. CMV is limited by gross weight (total weight of vehicle and cargo), and with axle weight (ie, weight carried by each tire). The federal weight limit for CMV is 80,000 pounds (36,000 kg) for gross weight (except the bridge formula determines the lower limit), 34,000 pounds (15,000 kg) for tandem axle, and 20,000 pounds (9,100 kg) for single axle. A tandem axle is defined as two or more successive axles centered more than 40 inches (102 cm) but not more than 96 inches (244 cm) apart. Axle spaced less than 40 inches (102 cm) apart is considered a single axle.
As a result, the formula reduces the legal weight limit for shorter trucks with smaller axles (see table below). For example, a 25-foot (7.6 m) three-axle truck will have a gross weight limit of 54,500 pounds (24,700 kg) instead of 80,000 pounds (36,000 kg), which is the standard weight limit for 63-feet (19 , 2 m) five-tractor tractor-hoist. The FHWA Regulation Ã,§658.17 states: "The maximum gross vehicle weight is 80,000 pounds (36,000 kg) except where the low gross vehicle weight is determined by the bridge formula."
Bridge collapse
The collapse of the Mississippi River Interstate 35W bridge in August 2007 in Minneapolis brought new attention to the weight problem of trucks and their relationship to bridge stress. In November 2008, the National Transportation Safety Board determined that there were several reasons for the collapse of the bridge, including (but not limited to): damaged plates, inadequate inspections, and additional weight of heavy construction equipment combined with heavy rush hour traffic. The I-35 Trade Corridor Study reports that the Federal Highway Administration (FHWA) expressed concern over the bridge in the I-35 corridor due to the expected increase of international truck traffic from Canada and Mexico, with FHWA listing it as "high priority" in 2005.
In 2007, federal estimates showed truck traffic increased 216% since 1970, shortly before the federal gross weight limit for trucks increased by 30,000 pounds (14,000 kg). This is also a period in which many existing interstate bridges are built. Research shows that increased truck traffic (and therefore, increased stress) shortens the life of the bridge. National Pavement Cost Estimate (NAPCOM) estimates that a truck of 80,000 pounds (36,000 kg) damages the road of 750 3,800 pounds (1,700 kg).
Some small bridges have a weight limit (or a gross weight rating rating) indicated by a sign placed in a position visible in front of the bridge (hence a reference to the "installed bridge"). This is required when the bridge weight limit is lower than the gross or federal gross weight limit for trucks. Driving a truck over a bridge that is too weak to support it usually does not lead to an immediate collapse. Bridges can develop cracks, which over time can weaken the bridge and cause it to collapse. Most of these cracks were discovered during the mandated inspection of the bridge. Most collapsed bridges occur in rural areas, resulting in little injury or death, and receive relatively little media attention. While the number varies from year to year, as many as 150 bridges could collapse in a year. Around 1,500 bridges collapsed between 1966 and 2007, and most were due to soil erosion around the bridge. In 1987, the Schoharie Creek Bridge collapsed in northern New York, due to soil erosion around the foundation, which sparked renewed interest in the design of the bridge in inspection procedures.
In special cases involving extraordinarily overweight trucks (which require special permission), not observing the weight limit of the bridge can lead to catastrophic consequences. Fifteen days after the collapse of the Minneapolis bridge, a heavy truck overthrew a small bridge in Oakville, Washington.
Legal formula
CMV must pass weigh stations on the border of most states and some major cities. The weigh stations are run by state DOT, and the weight of CMV as well as the size enforcement are supervised by FHWA. Weigh stations check the gross weight and axle weight of each vehicle using a series of truck scales in the ground, and usually where the truck compliance with the formula is ticked.
FMCSA rules Ã, 658.17 states:
- No vehicle or combination of vehicles to be moved or operated on an international highway when dirty weights on two or more consecutive axes exceed the limits specified by the following formula:
- w = maximum weight in pounds that can be carried on a group of two axles or more to the nearest 500 pounds (230 kg).
- l = distance in the foot between the outer axles of each axle two or more in sequence.
- n = number of axles to be considered.
Two or more consecutive axles may not exceed the weight calculated by the bridge formula, even if the gross weight of the truck (or weight on one axle) is below the other legal limit. Although this means that every two axles should be in accordance with the formula, experience shows that axles 1 to 3, 1 to 5, and 2 to 5 are very important and should be checked. This means that the axle group consisting of all trucks (known as "outgroups") and the interior shaft groups (known as "tractor groups" and "trailer groups") must also comply with the bridge formula. If this combination is found satisfactory, then all other axle groups on this type of vehicle will usually be satisfactory.
Penalties for breaking heavy borders vary between states (grave formation offenses are treated as gross violations), because states are responsible for enforcement and collection of fines. Some states, such as Connecticut, issue fines on a percentage basis (eg 20% ​​overweight at $ 10 per 100 pounds or 45 kilograms), which means large trucks pay a higher penalty. For example, a truck with a legal limit of 20,000 pounds (9,100 kg) breaking the limit of 5,000 pounds (2,300 kg) would pay a $ 500 fine, while a truck with a legal gross margin of 60,000 pounds (27,000 US dollars). Ã, kg) that breaks the limit by 5,000 pounds will pay a $ 250 fine. Other countries, such as New York, issue penalties on a per pound basis (for example, an excess of 5,000 pounds equals $ 300 fine). Others, such as Massachusetts, impose more complicated schedules where vehicles that break the limit of less than 10,000 pounds ($ 4.500) are fined $ 40 per 1,000 pounds (450 kg), while breaches of more than 10,000 pounds (4,500 kg) pay $ 80 per 1,000 pounds (450 kg) (eg 5,000 pounds or 2,300 kg of overweight equal to a $ 200 fine).
Some states require overloaded trucks to move enough payloads to comply with the limit. In Florida, any vehicle exceeding the limit of more than 6,000 pounds (2,700 kg) shall be reduced until the vehicle is complied with. Florida also includes a scale tolerance, which allows for less than 10% offense to be forgiven, and nothing is issued. Florida also allows to move the load (for example, moving from the front to the rear of the vehicle) so that the vehicle obeys the weight limit of the axle, without penalty.
Exceptions
There is one exception to the formula: two sets of successive tandem drives can carry 34,000 pounds (15,000 kgs) each if the overall distance between the first and last tandem axle is 36 feet (11 m) or more. For example, a five-axle truck can carry 34,000 pounds in both tractor tandem axles (2 and 3) and tandem axles (4 and 5), as long as 2 and 5 are at least 36 feet (11 m) apart.
This exception allows for standard 5-axle semi-truck configurations up to 80,000 pounds (36,000 kg) (legal limit) without violating the bridge formula law. Without it, the bridge formula would allow the actual weight of only 66,000 pounds (30,000 kg) to 67,500 pounds (30,600 kg) on ​​tandems spaced 36 feet (11 m) to 38 feet (11.6 m) apart; compared to 68,000 pounds (31,000 kg) with the exception. These exceptions are sought by the American Trucking Association so the trucking company can use a 40 foot (12.2 m) trailer and weigh 80,000 pounds (36,000 kg). This is the only way tanker truck operators can reach £ 80,000 without adding axle to their already operated trailer fleet.
CMV can exceed the bridge formula limit (or gross weight and axle weight limit) to 400 pounds (181 kg) if the vehicle is equipped with an additional power unit (APU) or idle reduction technology. According to FMCSA, this is allowed "to promote the reduction of fuel use and emissions due to idling engines". To be eligible, the vehicle operator must prove the weight of the APU with a written certification, or - by demonstration or certification - that idle reduction technology is fully functional at all times. APU heavy certification must be available to law enforcement officers if the vehicle is found to be in violation of applicable law. Additional allowable weight should not exceed 400 pounds or a certified weight, depending on the less.
Problem
The bridge formula (also referred to as Formula B) is based on research into a single bachelor bridge, and fails to consider multi-span bridges. The two-span bridge may not be fully protected by Formula B, depending on the length of the truck, the length of the span, and other factors. Shorter wheelbase vehicles (usually special trucks such as garbage trucks and water trucks) have difficulty obeying Formula B.
In 1987, the US Congress passed the Surface Transport Assistance Act and Relocation Uniform, requested the Transport Research Agency (TRB) to conduct research to develop an alternative to Formula B. This study recommends some that have never been implemented. It shows that Formula B is too tight for trucks with shorter axle lengths. One alternative formula (later known as the TTI HS-20 Bridge Formula) was developed in conjunction with the Texas Transportation Institute. The TTI HS-20 allows shorter trucks to have higher weight limits than Formula B. For a 3-axle truck with a 14-foot (4.3 m) shaft length, the weight limit increases from 46,500 pounds (21,100 kg) to 54,000 pounds ( 24,000 kg). TTI HS-20 also failed to overcome the problem of multi-span bridges.
Table bridge formula
- 1 The calculated value reflects the FHWA policy of rounding down when the distance falls exactly between the 6 inch (15 cm) increase.
- 2 The calculated value reflects the FHWA policy of rounding down when the weight drops right between the 500 pounds increase.
- 3 Tandem axle by definition.
- 4 The distance between 8 feet (2.4 m) to 8 feet 11 inches (2.72 m) should not be rounded down.
- 5 __ The maximum legal weight limit is based on the number of axles. This increased shaft length does not increase the maximum weight.
- 6 __ Exceptions to the formula: when four axles under consideration are two tandem axles spaced at least 36 feet (11 m) apart, gross weight of 68,000 pounds (31,000 kg) allowed.
- __ The upper blank area represents an unrealistic configuration.
See also
Vehicle combination length
References
This article incorporates public domain material from a United States Government document "" Ã,§658.17 Weight "Federal Motor Carrier Safety Administration Archived from the original on January 4, 2008 . Retrieved < span> February 3, 2008 . Ã, ".
External links
- The bridge formula calculator uses the calculator
Source of the article : Wikipedia
0 Comments