What Are STAA Truck Routes and How Do They Work?

STAA truck routes are the highways covered by the National Network created under the Surface Transportation Assistance Act of 1982, where states must allow commercial vehicles that meet federal size and weight standards to operate without imposing stricter local limits. The network is defined in 23 CFR Part 658 and includes the entire Interstate Highway System plus specific non-Interstate segments that were part of the Federal-aid Primary System as of June 1, 1991.¹ If a road is on the list, your compliant equipment is legal on it; if it isn’t, the federal preemption doesn’t reach that pavement.

Which Roads Are on the Network

The National Network has two components. The first is every mile of the Interstate System. The second is the group of non-Interstate highways designated from the former Federal-aid Primary System, frozen as of June 1, 1991. The Federal Highway Administration publishes the full list state by state in Appendix A to 23 CFR Part 658, so carriers can check any specific segment before dispatching.¹

Designation matters because federal preemption is a one-way ratchet. On a designated road, a state cannot impose dimension limits below the federal standards. On a road that isn’t designated, a fully STAA-compliant vehicle has no federal right to be there except through the reasonable-access provisions covered below. The FHWA also controls what enters and leaves the network: removing an Interstate segment requires FHWA approval, a safety justification, an analysis of the impact on interstate commerce, identification of alternative routes, and publication in the Federal Register for public comment.² The high bar for deletion is intentional; it keeps the network from fragmenting under local pressure.

Vehicle Dimensions the Network Protects

Federal law sets minimum allowances that function as a floor. States can permit larger, but they cannot restrict compliant vehicles below the following limits on the National Network.

Width. Under 49 U.S.C. § 31113, states may not impose a width limit other than 102 inches (8.5 feet) on commercial vehicles operating on the Interstate System and qualifying Federal-aid highways with lanes designed to be at least 12 feet wide.³ Blanket bans against 102-inch vehicles are also prohibited on reasonable-access routes off the network.⁴

Semitrailer length. No state may impose a length limit below 48 feet on a semitrailer in a tractor-semitrailer combination, and no state may impose an overall length limitation on tractor-semitrailer or tractor-semitrailer-trailer combinations.⁵ In practice, 53-foot trailers are the industry standard, and many states set their own maximums at or above 53 feet. Any longer trailer allowance that was legal in a state on December 1, 1982, is preserved under 23 CFR 658.13.⁶

Twin trailers. States must allow semitrailers and trailers of at least 28 feet each in tractor-semitrailer-trailer combinations, and they cannot ban twin operations outright.⁵ Trailers that were 28.5 feet and in lawful operation on December 1, 1982, are grandfathered.⁶

Weight Limits and the Bridge Formula

Federal weight limits on the Interstate System are established by 23 U.S.C. § 127. States that deviate risk losing up to 50 percent of their federal highway apportionment, which keeps the caps uniform nationwide.⁷ The basic caps:

Single axle: 20,000 pounds
Tandem axle: 34,000 pounds (axle centers spaced more than 40 inches but not more than 96 inches apart)
Gross vehicle weight: 80,000 pounds for combinations of five or more axles

Meeting the 80,000-pound cap alone is not enough. The Federal Bridge Formula sets the maximum weight any group of two or more consecutive axles may carry, based on the number of axles and the spacing between them. The formula is W = 500 × [(LN / (N−1)) + 12N + 36], where W is the maximum allowable weight in pounds, L is the distance in feet between the outermost axles in the group, and N is the number of axles.⁷ A rig can sit under 80,000 pounds gross and still violate the formula if too much weight rides on a short axle group.

In practice, three axle groups matter most: the tractor bridge (steering axle through the tractor rear axles), the trailer bridge (tractor rear axles through the trailer rear axles), and the outer bridge (first axle to last axle). If all three pass, the interior combinations almost always will too.⁸ One useful exception: two consecutive sets of tandem axles may each carry 34,000 pounds if the distance between the first and last axles of the combined group is at least 36 feet.⁹

Getting Off the Network to Load and Unload

STAA vehicles cannot deliver freight on Interstates alone, so federal law includes a reasonable-access provision. States may not deny STAA-dimensioned vehicles access between the National Network and terminals, food and fuel stops, repair facilities, and rest areas.¹⁰ The implementing regulation draws a bright line: no state may deny access within one road-mile of the National Network, using the most reasonable and practicable route, except for documented safety reasons on specific routes.⁴

A “terminal” under these regulations means any location where freight originates, terminates, or is handled during transportation, and any location where a carrier maintains operating facilities.¹¹ That definition is broad on purpose. It covers warehouses, distribution centers, manufacturing plants, and carrier yards.

States can restrict specific routes on safety grounds, but the restrictions must be route-specific and grounded in engineering analysis. A city can close a road because a bridge on it is weight-rated too low. It cannot ban all large trucks from a neighborhood as a general policy.¹²

For destinations beyond the one-mile zone, states must maintain a formal access review process. Federal regulations require the process to include at least one of three evaluation methods: test-vehicle runs on the proposed route, application of vehicle templates to route plans, or a general provision allowing automatic access for trailers with a kingpin distance of 41 feet or less.¹² A key safeguard: if a state fails to act on an access request within 90 days, the request is automatically approved. The FHWA has also stated that absolute geometric standards, such as requiring 12-foot lanes or 4-foot shoulders on every access route, are unacceptable, because many states safely allow STAA vehicles on narrower roads.¹³

Kingpin Distance: The Common Trap on 53-Foot Trailers

Kingpin-to-rear-axle distance (KPRA) is the measurement that trips carriers most often. The kingpin is where the trailer connects to the tractor’s fifth wheel; KPRA runs from there to the center of the rear axle group. A longer KPRA moves the rear axle back, which changes how the trailer tracks through turns and shifts weight distribution.

Under the federal access framework, states must provide automatic access, without a special request, for semitrailers with a kingpin distance of 41 feet or less.¹² Trailers with a longer KPRA can face route-by-route review. Some states set their own KPRA cap for permit-free 53-foot trailer operation at distances like 38 or 40.5 feet, which is stricter than the 41-foot federal access threshold.¹⁴ Exceed the state limit and you may need a permit or find yourself restricted to specific routes even on the National Network.

For fleets running 53-foot trailers across state lines, the practical rule is simple. Keep KPRA at or below 41 feet unless you have confirmed that every state on the route allows a longer setting. A few inches can be the difference between clean transit and a permit requirement at the border.

When You Need a Permit

When a load exceeds standard STAA dimensions or the federal weight limits, you need a permit, and that permit comes from the state rather than the federal government. Each state runs its own permitting program with its own fees and conditions.¹⁵

The most important distinction is between nondivisible and divisible loads. A nondivisible load is one that cannot be broken down without destroying its value, compromising its function, or requiring more than eight work hours to dismantle. Nondivisible loads qualify for permits that can exceed the bridge formula, axle limits, and gross weight caps. The carrier bears the burden of proving the load qualifies. Divisible-load permits are more limited and depend on state-specific grandfathered allowances or congressional authorization for particular commodities or routes.¹⁵

States may also grant width permits for vehicles exceeding the 102-inch standard, such as manufactured housing. Single-trip fees vary widely, and some jurisdictions add per-mile charges. There is no single federal permit; every state on the route is a separate transaction.

Longer Combination Vehicles

Longer Combination Vehicles (LCVs), such as triple trailers or turnpike doubles that exceed 80,000 pounds on the Interstate, are frozen where they were. The Intermodal Surface Transportation Efficiency Act of 1991 locked LCV operations at whatever each state legally permitted as of June 1, 1991. No state can expand its LCV program beyond that baseline, and states that did not allow LCVs then cannot start now. The freeze covers weights, lengths, routes, and operating conditions, and about a dozen western states permit some form of LCV operation under grandfathered rights documented in Appendix C to 23 CFR Part 658. The same freeze applies to twin-trailer combinations on the National Network where either trailer exceeds 28.5 feet: legal only where the configuration was authorized before June 1991.¹⁶ Assumptions based on neighboring states are a reliable way to get a ticket.

Confirming a Route Before You Dispatch

Signing of National Network routes is optional under the Manual on Uniform Traffic Control Devices. When a state chooses to sign, it uses a designated sign for National Network routes and a separate sign for roads where STAA trucks are prohibited.¹⁷ Because signing is optional, a missing sign tells you nothing. Do not assume a road is off the network because you don’t see a marker, and do not assume it’s on the network because you do.

The reliable source is the FHWA’s route list in Appendix A to 23 CFR Part 658. State DOTs also publish their own truck route maps, most of them online, and states are required to make information about their reasonable-access provisions available to commercial vehicle operators.¹² Treat the official listings as the definitive reference, and build the route check into your dispatch process rather than the driver’s windshield.

1
eCFR. 23 CFR Part 658 – Truck Size and Weight, Route Designations-Length, Width and Weight Limitations
2
eCFR. 23 CFR 658.11 – Additions, Deletions, Exceptions, and Restrictions
3
Office of the Law Revision Counsel. 49 USC 31113 – Width Limitations
4
eCFR. 23 CFR 658.19 – Reasonable Access
5
Office of the Law Revision Counsel. 49 USC 31111 – Length Limitations
6
GovInfo. 23 CFR 658.13 – Length and Width Limitations
7
Office of the Law Revision Counsel. 23 USC 127 – Vehicle Weight Limitations – Interstate System
8
Federal Highway Administration. Bridge Formula Weights
9
Federal Highway Administration. Bridge Formula Weights
10
Office of the Law Revision Counsel. 49 USC 31114 – Access to the Interstate System
11
eCFR. 23 CFR 658.5 – Definitions
12
eCFR. 23 CFR 658.19 – Reasonable Access
13
Federal Highway Administration. Non-Regulatory Supplement for Part 658
14
Federal Highway Administration. Semitrailer Length Limitations on the National Network by State
15
Federal Highway Administration. State Oversize/Overweight Load Permit Contacts
16
Federal Highway Administration. Questions and Answers About Vehicle Size and Weight
17
Federal Highway Administration. Chapter 2B Regulatory Signs – MUTCD