Federal Bridge GrossBridge Formula Weight Formula Table

1 Federal Bridge GrossWeight FormulaBridge FormulaTableDistance in feetMaximum load in pounds carried on any group of 2 or more consecutive axles*between the extremes of any group of 2 or 23456789more consecutive axlesaxlesaxlesaxlesaxlesaxlesaxlesaxles axlesPermissible Federal gross loads for vehicles in regular operation is basedon Weight Formula W = 500(LN + 12N + 36)N - 1W = the maximum Weight in pounds that can be carried on a group oftwo or more axles to the nearest 500 poundsL= spacing in feet between the outer axles of any two or more consec-utive axlesN = number of axles being considered*The permissible loads are computed to the nearest 500 pounds Tandem axle by definition Exception to Bridge Formula Table and Law.

2 See text for explanationWeights shown in red are over the Federal gvw on the InterstateSystemSource: DOT Federal Highway Administration, Bridge FormulaWeights,January, 19944 34,0005 34,0006 34,0007 34,0008 and less 34,00034,000more than 838,00042,000939,00042,5001040,00043,500 1144,0001245,00050,0001345,00050,5001446 ,50051,5001547,00052,0001648,00052,50058 ,0001748,50053,50058,5001849,50054,00059 ,0001950,50054,50060,0002051,00055,50060 ,50066,0002151,50056,00061,00066,5002252 ,50056,50061,50067,0002353,00057,50062,5 0068,0002454,00058,00063,00068,50074,000 2554,50058,50063,50069,00074,5002655,500 59,50064,00069,50075,0002756,00060,00065 ,00070,00075,5002857,00060,50065,50071,0 0076,50082,0002957.

3 50061,50066,00071,50077,00082,5003058,50 062,00066,50072,00077,50083,0003159,0006 2,50067,50072,50078,00083,5003260,00063, 50068,00073,00078,50084,50090,0003364,00 068,50074,00079,00085,00090,5003464,5006 9,00074,50080,00085,50091,0003565,50070, 00075,00080,50086,00091,50036 66,00070,50075,50081,00086,50092,00037 66,50071,00076,00081,50087,00093,00038 67,50071,50077,00082,00087,50093,5003968 ,00072,50077,50082,50088,50094,0004068,5 0073,00078,00083,50089,00094,5004169,500 73,50078,50084,00089,50095,0004270,00074 ,00079,00084,50090,00095,5004370,50075,0 0080,00085,00090,50096,0004471,50075,500 80,50085,50091,00096,5004572,00076,00081 ,00086,00091,50097,5004672,50076,50081,5 0087,00092,50098,0004773,50077,50082,000 87,50093,00098,5004874,00078,00083,00088 ,00093,50099,0004974,50078,50083,50088,5 0094,00099,5005075,50079,00084,00089,000 94,500100,0005176,00080,00084,50089,5009 5,000100,5005276,50080,50085,00090,50095 ,500101,0005377,50081,00086,00091,00096, 500102,0005478,00081,50086,50091,50097,0 00102,5005578,50082,50087,00092,00097,50 0103,0005679,50083,00087,50092,50098,000 103,5005780,00083,50088,00093,00098,5001 04,0005884,00089,00094,00099,000104,5005 985,00089,50094,50099,500105,0006085,500 90,00095.

4 000100,500105,500 The following definitions are used in con-junction with the Bridge Formula Weight :The Weight of a vehicle combinationwithout load plus the Weight of any loadthereon (The Federal gross Weight limiton the Interstate System and reasonableaccess thereto is 80,000 pounds.)Single Axle Weight :The total Weight transmitted to the roadby all wheels whose centers may beincluded between two parallel transversevertical planes not more than 40 inchesapart, extending across the full width ofthe vehicle (The Federal single axle weightlimit on the Interstate System and reason-able access thereto is 20,000 pounds.)

5 Tandem Axle Weight :The total Weight transmitted to the roadby two or more consecutive axles whosecenters may be included between parallelvertical planes spaced more than 40 inches and not more than 96 inches apart,extending across the full length of thevehicle (The Federal tandem axle weightlimit on the Interstate System and reason-able access thereto is 34,000 pounds.)Consecutive Axle Weight :The Federal law states that any consecu-tive two or more axles may not exceed theweight as computed by the Formula eventhough the single axles, tandem axles, andgross weights are within the legal Formula definitionsThe purpose of the Federal bridgeweight Formula is to protect bridges on theInterstate System by controlling the num-ber and spacing of truck axles.

6 For a step-by-step way to check vehicle Weight andexceptions to the Formula , go down-load the Federal Bridge Gross WeightFormula page. It s available as a PortableDocument Format (PDF) Weight of groups of two or more axlesmust be checked against the Bridge formulato ensure that they meet Federal Weight limitrequirements and that the allowable grossand axle weights are correlated with thespacing and number of axles to preventsevere overstressing of highway with Bridge Formula weightlimits may require axle weights lower thanthe standard Interstate System Weight limitsof 20,000 pounds for a single axle and34,000 for a tandem axle set.

7 It may alsorequire a gross Weight lower than the stan-dard 80,000-pound Interstate System allowed under the Bridge formulacan be increased up to these limits by addingaxles or positioning them farther states may retain higher bridgeformula Weight limits than were in effect in1975 ( , grandfathered Bridge formulaweight limits), the limits may be higher insome states than in others. Questions aboutthe Bridge Formula can be directed to theFederal Highway Administration, Office ofFreight Management & Operations,HOFM-1, 400 Seventh St., , Wash-ington, DC a vehicleA tractor-semitrailer combination is used toillustrate a Bridge Formula check.

8 The exam-ple vehicle has a 12,000-pound steering axle(axle 1), a 34,000-pound tandem axle seton the tractor (axles 2 and 3), and a second34,000-pound tandem axle set on the trailer(axles 4 and 5).Before beginning to check your vehicle, besure that single axle 1 and any other singleaxle Weight does not exceed 20,000 pounds,that tandem axles 2 3 and 4 5 do notexceed 34,000 pounds each, and that the gross vehicle Weight does notexceed 80,000 pounds If these weightrequirements are satisfactory, the followingcombinations should be checked as follows:Check axles 1 through 3 using the illustration and (actual Weight )= 12,000 + 17,000 + 17,000= 46,000 = 3 axlesL = 20 feetW maximum= 500 (+ 12N + 36)= 500 (+ (12 x 3) + 36)= 51,000 x 33 1 LNN 1 The actual Weight of axles 1 through 3 in theexample combination is 46,000 pounds sothe Bridge Formula requirement is use the Bridge Formula Table to obtainthe maximum load allowed on axles 1 3,read down the left column (Distance in ) to L = 20 and across thenumber of axles to the right to N = 3 (axles).

9 Now check axles 1 through 5 using the illustration and (actual Weight )= 12,000+17,000+17,000+17,000+17,000= 80,000 = 5 axlesL = 51 feetW maximum from the Table for L of 51 feetand N of 5 axles = 80,000 pounds. This axlespacing is check axles 2 through 5 using the illustration and (actual Weight )= 17,000 + 17,000 + 17,000 + 17,000= 68,000 = 4 axlesL = 35 feetW maximum from the Table for L = 35 feetand N = 4 (axles) = 65,500 pounds. Thismeans the illustration shows a violation; theactual Weight of 68,000 pounds exceeds themaximum allowable Weight of 65,500pounds for the given axle spacing.

10 To correctthe situation, some load must be removedfrom the vehicle or the 35-foot axle spacingmust be to formulaThere is one exception to the use of theformula and Table : two consecutive sets oftandem axles may carry a gross load of34,000 pounds each providing the overalldistance between the first and last axles ofsuch consecutive sets of tandem axles is 36feet or more. For example, a 5-axletractor-semitrailer may be used to haul a full 34,000 pounds on the tandem of thetractor (axles 2 and 3) and the tandem of thetrailer (axles 4 and 5), providing there is aspacing of 36 or more feet between axles 2and 5.