Idaho frost law restrictions 2021.

2021 Idaho winter frost/spring thaw laws and seasonal weight restrictions.

During the spring months when warmer temperatures cause the road surface to break up and generally deteriorate, the highways most affected are restricted to lower axle weights and speed restrictions.
The District will sign and mark affected state highways the day before the weight and/ or speed restrictions are in effect. The weight and/or
speed restrictions will be enforced the day after the Districts sign and mark the state highway.
On those sections of highways which are posted for legal weight, or to less than legal weight, trucks and buses weighing 10,000 pounds or
more will be restricted to 30 mph in critical areas. Speed zones will be marked with red and yellow markers. A red marker will mean speed
is restricted to 30 mph and a yellow marker will mean that legal speed can be resumed.
For information on operating restrictions for state highways posted for spring breakup limits or to check on a route of travel for construction
restrictions etc., go to and the trucking page.
It is important for the trucking industry to cooperate and comply with the load and speed limits. If compliance with the load and speed limits
are adhered to, the need for future, more restrictive, limits may be alleviated. Excessive violations may lead to the implementation of more
restrictive limits.

Live map.

This is a excellent reference and resource point for Idaho chain laws and basic seasonal weight restriction information.


See also:

Tire chain laws.
Tire chain laws by location.
Trucking regulations.
Federal bridge formula.
Exemptions from seasonal restrictions.


Iowa State Shipping Regulations 2021

2021 Iowa state shipping regulations, limitations, rules and laws in the state of Iowa.



Iowa State Trucking Permit Regulations – oversize shipping and transport.

Legal Loads.

Length: 53’ trailer
Weight:  GVW = 80,000 lbs. Steer 20,000 lbs.
Width: 8’ 6”
Height:  13’ 6”

Routine oversize shipping, trucking and transport permits.

Length:  120’
Weight:  5 axles 92,000 lbs., 6 axles., 7 axles 132,000 lbs.,
Width:  18’
Height:  16’

How to apply for trucking permits.

Iowa DOT
Phone: 515-237-3264
Fax: 515-237-3257

Permits are valid for 5 days.  Single trip oversize trucking permit costs $10. Iowa State Trucking information site.

Pilot Car – Escort Car Requirements.

Length: 80’ to 100’ must have revolving lights.  Over 120’ requires 1 rear pilot/escort vehicle. 10’ overhang requires flashing lights.
Weight: Over 80,000 lbs. GVW requires amber lights.
Width: On Primary Road  Over 12’     1 front pilot car escort vehicle is required. On 2 lane over 14’ one rear pilot car escort vehicle is required. On 4 lane over 14’6” one rear pilot car escort vehicle is required.  On Interstate over 16’6” one pilot car escort vehicle or lighting is required.
Height:  Over 14’4” requires 1 front pilot car escort vehicle with height pole.

Travel Restrictions.

Travel is permitted from ½ hour before sunrise to ½ hour after sunset 7 days per week (see holiday and event traffic below). Trucks can travel 24/7 if the shipment is less than 11’ wide, 100’ long and 14’4” wide.

Holidays and event traffic.

Iowa code specifically states the designated restricted movement holidays are Memorial Day, Independence Day, and Labor Day. No movement will be allowed on these holidays or after 12 noon on days preceding these holidays and holiday weekends that include holidays falling on Monday, except as provided for in Iowa Code 321.457.

Note: If you are not in excess of the following weights/dimensions continuous travel may be permitted. 

Width: 11′.
Height: 14′ 6′
Length: 100′
Weight: Under legal limits.

Always refer to your permit first before movement. If you are not specifically clear on the complete instructions contact the Iowa DOT by phone: 515-237-3264.

The information contained in these pages is research information primarily for use by oversize and overweight trucking company drivers, dispatchers and pilot car companies. While every effort is put into maintaining the accuracy of this information you must absolutely verify this information with the Iowa State DOT Permits office before commencing movement.


2021 frost winter frost laws, thaw laws and weight restrictions.

2021 frost laws, thaw laws and seasonal weight restrictions.

Frost/thaw damages to surface.

Frost/thaw damages to surface.

Learn the details of the winter frost laws, spring thaw laws and seasonal weight restrictions. Details for the USA and Canada by State/Province. Many areas incorporate temporary special weight limits and restrictions (frost or thaw laws) during the winter and spring months of the year. These temporary restrictions are usually referred to as “frost laws” or “thaw laws” and implemented typically during the month or March and April. In some Northern States and Provinces frost laws can still be in effect in July as it’s much colder in the North. Since these restrictions are implemented on a “as needed” basis it is possible many of the official government websites may not have published this temporary restriction in a convenient place as frost laws are also subject to change at any moment based on the temperature of the roads core. You want to be certain to check with the appropriate officials to verify the latest changes in the laws.

2021 United States: Restrictions on winter and spring seasonal weight laws.

Idaho   Iowa   Maine   Michigan   Minnesota    Montana   Nevada    New Hampshire    New York   North Dakota  Pennsylvania    South Dakota    Vermont   Washington    Wisconsin    Wyoming

2021 Canada: Restrictions on winter and spring seasonal weight laws.

Alberta   British Columbia   Manitoba   New Brunswick New Foundland & Labrador  Nova Scotia  Nunavut  Ontario    Prince Edward Island   Quebec    Saskatchewan

Why we have these laws and must protect our roads and highways.

In order to keep the trucking industry operating the Northern US states and Canadian provinces rely on engineers and scientific data to determine which dates frost laws will be in effect. With fairly recent advances in science and technology, data is much more reliable. This helps with the implementation of “Frost Laws” or “Seasonal Weight Restrictions” ensuring they are not implemented to early or late. While no State or Province desires to delay the transportation of goods through their territory it is imperative public assets are protected.

In areas that constantly get negative (ie: -10 below zero) temperatures the amount of damages has forced Northern US States as well as Canadian Provinces to create and enact laws that restrict vehicle weights during the spring and winter months (specifically trucking companies) when the roads and bridges are thawing out. There are all kinds of things that can go wrong with different types of roads and pavements. For example the State of Michigan has implemented permanent frost laws that go into effect during the months of March through May (and in some cases even June). Some routes require legal axle weight limits be decreased by as much as 35%. Some areas and local governments may also limit heavy-haul vehicle speeds to a maximum of 35 miles per hour during frost/thaw law months regardless of posted limits.

Oregon hwy. US 1. Photo courtesy of

One of many examples is in Southern Oregon on old US Highway 1 (which follows the coast line from Mexico to Canada) the road is as much as 16 feet thick as years of pavement (even bricks) has been laid down year after year since the early 1900’s. It should be noted that today’s technology is able to provide us with roads that are flexible due to the engineering of the construction process and the materials used. Excessive weight exerted by overloaded axles (or a weakened supporting base) can cause the pavement to bend or deform. The strength of the road combined with its resistance to bending determines the amount of weight the roadway can handle.


See also:

Tire chain laws.
Tire chain laws by location.
Trucking regulations.
Federal bridge formula.
Exemptions from seasonal restrictions.

Iowa frost law restrictions 2021.

2021 Iowa frost laws, seasonal load weight and restrictions.


In previous years the general rule seasonal restrictions typically begin around March 15th each year in Iowa. By no means consider this legal advice. Be sure to consult with the Iowa DOT before attempting to travel.


Current Iowa route restrictions by Iowa counties map.

Iowa DOT office: 515-237-3264

For more information about Iowa regulations and restrictions try our “Trucking regulations” link below.

See also:

Tire chain laws.
Tire chain laws by location.
Trucking regulations.
Federal bridge formula.
Exemptions from seasonal restrictions.


2021 Federal Bridge Formula Weights Explanation.

2021 Easy – Federal Bridge Formula weights explanation.

The Federal Bridge Formula explanation.

Heavy-haul truck drivers should know exactly how to calculate the Federal Bridge Formula. Below is a very simple explanation to ensure compliance.

Explaining the maximum weight any combined set of axles on a truck and trailer can carry to cross a bridge on the Interstate highway system.  The following Federal bridge formula is used for calculating acceptable weights:

W=500 [ LN/N-1 + 12N + 36]

W= the overall gross weight on any group of two or more consecutive axles the the nearest 500 pounds.

L= the distance in feet between the outer axles of any group of two or more consecutive axles.

N= the number of axles in the group that are under consideration.

How do I determine Bridge Formula?

THIS IS A PERFECT EXAMPLE: Bridge formula is 30 times the wheelbase* in centimeters plus 18,000 kg.

*Wheelbase in the above Bridge Formula calculation refers to the maximum axles span (center of the first axle to the center of the last axle of any axle group) in a heavy commercial vehicle.

Axle spacing is another consideration that must be taken into account when looking at the Federal weight compliance laws.  In order to properly protect our bridges the number and the spacing of truck and trailer axles carrying the shipment must be calculated.  So a bridge weight formula applies when the gross weight on 2 or more consecutive axles exceeds the limitations on the formula, except that the 2 consecutive sets of tandem axles may carry a gross weight load of 34,000 pounds each if the overall distance between the 1st and last axle is  over a 36 feet minimum.

Exceptions to the Bridge Weight Formula:

There are exceptions.  Federal law does include an exception to the Federal Bridge Formula and the bridge table. 2 consecutive sets of tandem axles may carry 34,000 pounds each IF the overall distance between the first axle and last axles of these tandems is 36 feet or greater.  For example:  a 5 axle tractor semi trailer combination may carry 34,000 pounds of weight both on the tractor tandem (axles 2 and 3) and the trailer tandem (axles 4 and 5), provided the axles 2 and 5 are spaced at least 36 feet from each other.  Without this exception the bridge formula would allow for actual weight of only 66,000 pounds to 67,000 pounds on tandems spaced 36 feet to 38 feet apart. (References: U. S. Department of TransportationFederal Highway AdministrationFederal Bridge Formula Weights” – FWHA-FBFWHA-FBFF the .pdf)

Note:  In addition to the above formula weights Federal law says that a single axle is limited to a maximum of no greater than 20,000 pounds and that axles that are closer than 96 inches from each other are limited to a maximum weight of 34,000 pounds.  Also that gross vehicle weight be less than 80,000 pounds.

Federal law (23 U.S.C. 127) does include an exception to the Federal Bridge Formula and the Bridge Table—two consecutive sets of tandem axles may carry 34,000 lbs. pounds each if the overall distance between the first and last axles of the tandem axles is 36 feet or more. For example; a five-axle tractor and semitrailer combination may carry 34,000 lbs. pounds both on the tractor tandem (axles 2 and 3) and the trailer tandem (axles 4 and 5), if axles number 2 and 5 are spaced at least 36 feet apart. Without this exception the Federal Bridge Formula would allow an actual weight of only 66,000 pounds up to 67,500 pounds on tandems spaced 36 to 38 feet apart.

2020 Federal Bridge Weight Chart

Less than 8’3″ 34,000 34,000
More than 8’4″ 38,000 42,000
9 39,000 42,500
10 40,000 43,500
11 44,000
12 45,000 50,000
13 45,000 50,500
14 46,500 51,500
15 47,000 52,000
16 48,000 52,500 58,000
17 48,500 53,500 58,500
18 49,500 54,000 59,000
19 50,500 54,500 60,000
20 51,000 55,500 60,500 66,000
21 51,500 56,000 61,000 66,500
22 52,500 56,500 61,500 67,000
23 53,000 57,500 62,500 68,000
24 54,000 58,000 63,000 68,500 74,000
25 54,500 58,500 63,500 69,000 74,500
26 55,500 59,500 64,000 69,500 75,000
27 56,000 60,000 65,000 70,000 75,500
28 57,000 60,500 65,500 71,000 76,500 82,000
29 57,500 61,500 66,000 71,500 77,000 82,500
30 58,500 62,000 66,500 72,000 77,500 83,000

59,000 62,500 67,500 72,500 78,000 83,500
32 60,000 63,500 68,000 73,000 78,500 84,500 90,000
33 64,000 68,500 74,000 79,000 85,000 90,500
34 64,500 69,000 74,500 80,000 85,500 91,000
35 65,500 70,000 75,000 80,500 86,000 91,500
36 66,000 70,500 75,500 81,000 86,500 92,000
37 66,500 71,000 76,000 81,500 87,000 93,000
38 67,500 71,500 77,000 82,000 87,500 93,500
39 68,000 72,500 77,500 83,500 88,500 94,000
40 68,500 73,000 78,000 84,000 89,000 94,500
41 69,500 73,500 78,500 84,500 89,500 95,000
42 70,000 74,000 79,000 84,500 90,000 95,500
43 70,500 75,000 80,000 85,000 90,500 96,000
44 71,500 75,500 80,500 85,500 91,000 96,500
45 72,000 76,000 81,000 86,000 91,500 97,500
46 72,500 76,500 81,500 87,000 92,500 98,000
47 73,500 77,500 82,000 87,500 93,000 98,500
48 74,000 78,000 83,000 88,000 93,500 99,000
49 74,500 78,500 83,500 88,500 94,000 99,500
50 75,500 79,000 84,000 89,000 94,500 100,000
51 76,000 80,000 84,500 89,500 95,000 100,500
52 76,500 80,500 85,000 90,500 95,500 101,000
53 77,500 81,000 86,000 91,000 96,500 101,500
54 78,000 81,500 86,500 91,500 97,000 102,000
55 78,500 82,500 87,000 92,000 97,500 102,500
56 79,500 83,000 87,500 92,500 98,000 103,000
57 80,000 83,500 88,000 93,000 98,500 104,000

84,000 89,000 94,000 99,000 104,500

85,000 89,500 94,500 99,500 105,000

85,500 90,000 95,000 100,500 105,500