In the
 United States Court of Appeals
              For the Seventh Circuit
                         ____________

No. 07-1402
AUX SABLE LIQUID PRODUCTS, a Delaware
Limited Liability Company,
                                     Plaintiff-Appellee,
                           v.


KENNETH MURPHY, Individually and as
Monee Township Highway Commissioner,
MONEE TOWNSHIP, and MONEE TOWNSHIP
HIGHWAY DEPARTMENT,
                                Defendants-Appellants.
                  ____________
            Appeal from the United States District Court
       for the Northern District of Illinois, Eastern Division.
             No. 06 C 1227—Charles P. Kocoras, Judge.
                         ____________
     ARGUED DECEMBER 5, 2007—DECIDED MAY 19, 2008
                         ____________


 Before FLAUM, EVANS, and WILLIAMS, Circuit Judges.
  FLAUM, Circuit Judge. This case concerns to what degree
the Surface Transportation Assistance Act (“STAA”),
which governs access to and from the federal Interstate
system, preempts local weight restrictions on bordering
roads. Since 2001, loaded trucks leaving a propane
loading facility (“the Terminal”) owned by Plaintiff Aux
2                                              No. 07-1402

Sable Liquid Products reached Interstate 57 (“I-57”) via
Ridgeland Avenue in Monee Township, Illinois. In 2006,
the Monee Township Highway Commissioner, in order
to protect Ridgeland Avenue from damage, limited the
truck weight on the road to 14 tons, a weight less than
that of an unloaded propane truck. Aux Sable then
brought suit seeking injunctive relief under the STAA,
as codified at 49 U.S.C. § 31114, and under the Illinois
Vehicle Code, 625 ILL. COMP. STAT. 5/15 et seq., against
Defendants Kenneth Murphy (the Monee Township
Highway Commissioner), Monee Township, and the
Monee Township Highway Department. Aux Sable also
claimed that Defendants should be estopped from chang-
ing the weight limits on the road. The district court
granted Aux Sable’s motion for a preliminary injunction
and later granted Aux Sable’s motion for summary judg-
ment, finding that the STAA preempted the local weight
restrictions placed on Ridgeland Avenue. For the reasons
discussed below, we affirm.


                      I. Background
  Plaintiff Aux Sable Liquid Products is the beneficial
owner of a propane loading terminal located at the south-
east corner of West Steger Road and South Ridgeland
Avenue in Monee Township, Will County, Illinois. See
Mapquest, Maps, http://www.mapquest.com/maps/
23313+S+Ridgeland+Ave+Monee+IL+60449-9293/ (last
visited April 28, 2008). The Terminal was constructed in
2000 and began operating in October 2001, and from the
outset, Aux Sable devoted attention to how the propane
trucks coming to and from the Terminal would access I-57,
which runs north and south just east of the Terminal. One
route from the Terminal to I-57 is to exit the Terminal onto
No. 07-1402                                                3

Steger Road and reach I-57 via the Sauk Trail Road inter-
change north of the Terminal. A slightly longer route,
but still within five miles of I-57, is to leave the Terminal
on Ridgeland Avenue proceeding south, entering I-57 on
the Monee Manhattan Road interchange. Which route the
propane trucks would take, however, depended upon
weight restrictions on the roads, since unloaded
propane trucks weigh approximately 39,000 pounds, and
when fully loaded, can weigh up to 80,000 pounds, the
maximum vehicle gross weight permitted on the Inter-
state system. 23 C.F.R. § 658.17(b). Interstate access via
the first route was restricted due to weight limits enforced
by Cook County on Steger Road, where loads up to 80,000
were not permitted unless each truck applied for and
received a permit for each trip. With respect to the
second route, Aux Sable maintains that in June 2000, then-
Monee Township Highway Commissioner Wayne Stessen
signed a Resolution permitting trucks weighing up to
80,000 pounds to use Ridgeland Avenue. Although Defen-
dants contest the validity of this Resolution, Aux Sable
claims that the Terminal was designed with the under-
standing that unloaded trucks could enter from Steger
Road while loaded trucks could exit onto Ridgeland
Avenue. Once the Terminal began operating in October
2001, this is in fact what occurred, with loaded trucks
leaving the Terminal onto Ridgeland Avenue and en-
tering I-57 via the Monee Manhattan Road interchange.
  Truck traffic between the Terminal and I-57 continued
in this manner until Ken Murphy became the new
Monee Township Highway Commissioner in 2005. In the
fall of that year, Murphy informed Aux Sable that he
intended to restrict truck traffic on Ridgeland Avenue
due to damage the trucks were causing to the road. Then,
4                                              No. 07-1402

in February 2006, signs that had been posted in 2004
designating Ridgeland Avenue as a Class II truck route
(which under 625 ILL. COMP. STAT. 5/15-111(f) permits
loads up to 80,000 pounds) were replaced with signs
limiting the truck weight on Ridgeland Avenue to 14
tons. On March 1, Murphy himself instructed the driver
of a propane truck on Ridgeland Avenue of the weight
limit on the road.
   These events spurred Aux Sable to take legal action. On
March 3, 2006, Aux Sable brought suit in the Circuit
Court for the Twelfth Judicial Circuit, Will County,
Illinois. The suit, which sought injunctive relief, claimed
that the weight restriction on Ridgeland Avenue was
preempted by the STAA, 49 U.S.C. § 31114, and violated
the Illinois Vehicle Code, 625 ILL. COMP. STAT. 5/15 et seq.
Aux Sable also claimed that Defendants should be
estopped from changing the weight limits on Ridgeland
Avenue since the Terminal was allegedly constructed
with the understanding that loaded trucks would be able
to exit onto that road. Four days later, Defendants Kenneth
Murphy, Monee Township, and the Monee Township
Highway Department removed the case to the Northern
District of Illinois under 28 U.S.C. § 1441, since the pre-
emption issue concerning the STAA gave rise to federal
question jurisdiction pursuant to 28 U.S.C. § 1331. The
district court then granted Aux Sable’s motion for a pre-
liminary injunction on March 14, and the parties subse-
quently filed cross-motions for summary judgment. On
December 20, 2006, the district court ruled on these mo-
tions, finding that the weight restriction was preempted
by the STAA. Based on this finding, the district court
enjoined Defendants from prohibiting the Terminal’s
truck traffic and found it unnecessary to address Aux
Sable’s estoppel claim or argument that Defendants had
No. 07-1402                                                5

violated the Illinois Vehicle Code. Defendants then brought
a motion to amend the judgment under Fed. R. Civ. P.
59(e), arguing that the district court’s ruling made the
State of Illinois a necessary party to the suit. The district
court denied this motion, after which Defendants appealed
the district court’s summary judgment decision to this
Court.


                       II. Analysis
  On appeal, Defendants challenge the district court’s
grant of summary judgment for Aux Sable on the preemp-
tion issue, as well as the district court’s denial of sum-
mary judgment in Defendants’ favor with respect to Aux
Sable’s claim under the Illinois Vehicle Code and Aux
Sable’s estoppel argument. This Court reviews a district
court’s ruling on cross-motions for summary judgment
de novo. Metro. Life Ins. Co. v. Johnson, 

, 561
(7th Cir. 2002). Summary judgment is proper “if the
pleadings, the discovery and disclosure materials on file,
and any affidavits show that there is no genuine issue as
to any material fact and that the movant is entitled to
judgment as a matter of law.” Fed. R. Civ. P. 56(c). “With
cross-motions, our review of the record requires that
we construe all inferences in favor of the party against
whom the motion under consideration is made.” Hess
v. Reg-Ellen Mach. Tool Corp., 

, 658 (7th Cir.
2005) (quoting Tegtmeier v. Midwest Operating Eng’rs
Pension Trust Fund, 

, 1045 (7th Cir. 2004)).
Thus, with respect to the preemption claim, all inferences
will be construed in favor of Defendants, while for the
other two claims, all inferences will be drawn in favor
of Aux Sable.
6                                                 No. 07-1402

  We first turn to the question of whether the local weight
restriction on Ridgeland Avenue is preempted by the
STAA pursuant to the Supremacy Clause of Article IV
of the Constitution. Under the Supremacy Clause, “state
laws that ‘interfere with, or are contrary to the laws of
congress, made in pursuance of the constitution’ are
invalid.” Wisconsin Pub. Intervenor v. Mortier, 

,
604 (1991) (quoting Gibbons v. Ogden, 

(1824)). The
federal law at issue in this case, the STAA, governs,
among other things, access to and from the national
Interstate system. 49 U.S.C. § 31114. The relevant text of
the statute provides:
    (a) Prohibition on denying access. A State may not
    enact or enforce a law denying to a commercial
    motor vehicle subject to this subchapter [49 U.S.C.S.
    §§ 31111 et seq.] or subchapter I of this chapter [49
    U.S.C.S. §§ 31101 et seq.] reasonable access between—
        (1) the Dwight D. Eisenhower System of Interstate
        and Defense Highways . . .; and
        (2) terminals, facilities for food, fuel, repairs, and
        rest, and points of loading and unloading for
        household goods carriers, motor carriers of passen-
        gers, or any truck tractor-semitrailer combina-
        tion in which the semitrailer has a length of not
        more than 28.5 feet and that generally operates
        as part of a vehicle combination described in
        section 31111(c) of this title [49 U.S.C.S. § 31111(c)].

    (b) Exception. This section does not prevent a State or
    local government from imposing reasonable restric-
    tions, based on safety considerations, on a truck trac-
    tor-semitrailer combination in which the semi-
    trailer has a length of not more than 28.5 feet and that
No. 07-1402                                                        7

    generally operates as part of a vehicle combination
    described in section 31111(c) of this title [49 U.S.C.S.
    § 31111(c)].

thus guarantees commercial motor vehicles1
“reasonable access,” free from State interference, between
the Interstate and terminals,2 although state and local
governments can place “reasonable restrictions, based
on safety considerations,” on certain truck tractor-semi-
trailer combinations. 49 U.S.C. § 31114. The question
then is whether § 31114, which cabins the degree and
manner in which state and local governments may re-
strict commercial vehicles’ access to and from the Inter-
state, preempts Monee Township’s weight restriction on
Ridgeland Avenue.
   Preemption can take on three different forms: express
preemption, field preemption, and conflict preemption.
Hoagland v. Town of Clear Lake, 

, 696 (7th Cir.
2005) (citing Boomer v. AT&T Corp., 

, 417
(7th Cir. 2002)). “Express preemption occurs when a fed-
eral statute explicitly states that it overrides state or local
law.” 

field preemption, it exists “when federal
law so thoroughly ‘occupies a legislative field’ as to make
it reasonable to infer that Congress left no room for the


1
  It is undisputed that the propane trucks traveling to and
from the Terminal are “commercial motor vehicles” under
§ 31114, see also 23 C.F.R. § 658.5 (defining “commercial motor
vehicle”)
2
  Defendants do not contest that Aux Sable’s propane loading
facility qualifies as a “terminal” under § 31114(a)(2). See 23
C.F.R. § 658.5 (defining “Terminal” as including “any location
where . . . [f]reight either originates, terminates, or is handled in
the transportation process”).
8                                                  No. 07-1402

states to act.” 

v. Liggett Group, Inc.,

, 516 (1992)). The district court, however,
limited its finding of preemption to the third type, con-
flict preemption, which “exists if it would be impossible
for a party to comply with both local and federal require-
ments or where local law ‘stands as an obstacle to the
accomplishment and execution of the full purposes and
objectives of Congress.’ ” 

Corp. v.
Myrick, 

, 287 (1995)). We similarly focus
our attention on this third form of preemption, since
Aux Sable does not argue on appeal that express or field
preemption applies.3
  To determine whether state and federal law are in
conflict, it is necessary to “examin[e] the federal statute
as a whole and identify[ ] its purpose and intended ef-
fects.” Crosby v. Nat’l Foreign Trade Council, 

,


3
   We observe that express preemption is present in the STAA,
since the very language of the Act provides that “[a] State
may not enact or enforce a law denying to a commercial
motor vehicle . . . reasonable access between” the Interstate and
certain specified destinations. 49 U.S.C. § 31114. The district
court, however, based its holding on conflict preemption in
order to avoid determining whether the express limits placed
upon “[a] State” in § 31114 similarly extend to local govern-
ments such as Monee Township. We similarly decline to
decide whether the language in § 31114 expressly preempts
local governments, rather than just “[a] State,” from denying
“reasonable access.” Instead, we rest our analysis on con-
flict preemption principles. See Sprietsma v. Mercury Marine,

, 65 (2002) (“Congress’ inclusion of an express
pre-emption clause ‘does not bar the ordinary working of
conflict pre-emption principles’ ”) (quoting Geier v. American
Honda Motor Co., 

, 869 (2000)).
No. 07-1402                                                9

373 (2000). This analysis requires that we “consider the
relationship between state and federal laws as they are
interpreted and applied, not merely as they are written.”
Frank Bros. v. Wis. Dep’t of Transp., 

, 894 (7th
Cir. 2005) (quoting Mite Corp. v. Dixon, 

, 493
(7th Cir. 1980)). Furthermore, “mere differences between
state and federal regulation of the same subject are not
conclusive of preemption . . . the crucial inquiry is whether
[state law] differs from [federal law] in such a way
that achievement of the congressional objective . . . is
frustrated.” 

).
  Under this analytical framework, it is first necessary
to establish the congressional objective for the STAA,
specifically § 31114. The parties are strongly divided on
this issue. Aux Sable draws upon prior cases from other
jurisdictions for its position that “it is manifest that the
STAA reflects a congressional interest in establishing
uniform regulations governing the size, weight, and
arrangements of trucks used in interstate commerce.”
United States v. Connecticut, 

, 576 (D. Conn.
1983). Furthermore, Aux Sable maintains that this con-
gressional interest in uniformity reaches beyond regu-
lating the Interstate itself, and also extends to local
roads that may be miles away, for the purpose of guaran-
teeing reasonable access to the Interstate and other
roads part of the federal National Network. See 23 C.F.R.
§ 658.19; see also New Hampshire Motor Transp. Ass’n v. Town
of Plaistow, 

, 330 (1st Cir. 1995) (“guarantee
of reasonable access [under 49 U.S.C. § 31114] thus has a
formidable reach, extending to local regulatory measures
that operate miles away from any interstate or national
network highway.”). Aux Sable does recognize that
states still have some regulatory authority in this area,
10                                                No. 07-1402

but argues that this power is limited in that states are
mandated to provide reasonable access, and that any
exercise of state authority must be done “reasonably and
in the interest of public safety.” Consolidated Freightways
Corp. of Delaware v. Larson, 

, 1484 (M.D.
Pa. 1986) rev’d on other grounds, 

((3d Cir. 1987).
  Defendants offer a different understanding of Con-
gress’s purpose in enacting the STAA. They contend that
contrary to Aux Sable’s claims, Congress was not con-
cerned with uniformity, but rather, Congress aimed to
ensure commercial vehicles’ access to the Interstate
system, while permitting states to determine the circum-
stances under which such access would be available. In
reaching this conclusion, Defendants rely heavily on
Consolidated Freightways Corp. of Delaware v. Larson, a
case out of the Middle District of Pennsylvania, and that
decision’s review of the STAA’s legislative history. 

(M.D. Pa. 1986). In Consolidated Freightways,
the court emphasized that when Congress amended the
Act in 1984, it declined to more specifically define “reason-
able access,” despite Congress’s awareness of the lack of
uniformity from state to state with respect to the degree
of access being provided to the National Network. 

(citing Senate Committee Report of the Tandem
Truck Safety Act of 1984, S. REP. NO. 505, 98th Cong., 2d
Sess., reprinted in 1984 U.S.C.C.A.N. 4769). Defendants,
mirroring the district court’s reasoning in Consolidated
Freightways, argue that Congress’s failure to modify the
definition of “reasonable access” when the law was
amended, given Congress’s awareness of states’ varia-
tions in interpreting this provision, reflects a con-
gressional intent that states be permitted to define “reason-
able access” on their own. 

While Defendants
No. 07-1402                                                  11

do recognize that federal regulations provide that “[n]o
State may enact or enforce any law denying access
within 1 road-mile from the National Network using
the most reasonable and practicable route available
except for specific safety reasons on individual routes,”
23 C.F.R. § 658.19(d), Defendants argue that Congress in-
tended that states themselves determine whether other
restrictions not covered by this particular regulation
still provide for “reasonable access” to the National
Network.
  These divergent interpretations of Congress’s objective
regarding the STAA lead to different conclusions as to
whether the local Monee Township ordinance over
Ridgeland Avenue is preempted. According to Aux Sable,
because of Cook County’s preexisting weight restriction
on Steger Road, Monee Township’s new weight restric-
tion on Ridgeland Avenue does not just deny “reasonable
access” to the Interstate, but in fact denies all access to I-57
for fully loaded propane trucks leaving the Terminal.
Furthermore, Aux Sable argues that because the local
weight restriction was only imposed to protect Ridge-
land Avenue, the local ordinance cannot be construed as
a reasonable restrictions based upon safety considera-
tions. Defendants, in contrast, argue that because Ridge-
land Avenue is not subject to the regulation in 23 C.F.R.
§ 658.19(d), Congress intended that the State of Illinois
have the authority to determine what constitutes “rea-
sonable access” to the Interstate. Accordingly, Defend-
ants contend that so long as the weight restriction on
Ridgeland Avenue comports with the Illinois Vehicle
Code, no conflict between the local ordinance and the
STAA can be said to exist.
 We are unwilling to accept Defendants’ argument that
Congress intended that each state be permitted to deter-
12                                             No. 07-1402

mine for itself how “reasonable access” in § 31114(a) is
to be defined. If states were truly left to define this term
on their own, the express preemption language in
§ 31114(a) would be rendered effectively meaningless,
since states would be able to define “reasonable access”
so as to allow state and local authorities to severely
impede commercial motor vehicles’ access to the Inter-
state. Indeed, Consolidated Freightways, the case which
Defendants rely upon so heavily, does not in the end
adopt the view advanced by Defendants. Although the
opinion in Consolidated Freightways does state that Con-
gress “left it up to the states themselves to determine
what is reasonable,” the opinion also provides that this
authority came with “the caveats that reasonable access
must be available, and that states may only exercise their
police powers reasonably and in the interest of public

(emphasis in original)—caveats
that Defendants gloss over. Moreover, the court in Con-
solidated Freightways clearly rejected any notion that
states, aside from the restriction in 23 C.F.R. § 658.19(d),
are unchecked in their ability to define “reasonable
access,” since the court ultimately found that the Pennsyl-
vania access route approval scheme at issue in the case
was preempted by the STAA “to the extent it denie[d]
reasonable access” between the Interstate and the loca-
tions discussed in § 31114(a)(2) (then codified at 49 U.S.C.
§ 2312). 

  Instead, we agree with the district court that Congress’s
primary objective in passing the STAA was to create
uniform standards for commercial motor vehicles utilizing
the Interstate and other federal highways. Congress
also recognized that this goal would be frustrated if
commercial motor vehicles validly permitted on the
No. 07-1402                                                    13

Interstate were barred by state and local governments
from entering the Interstate on local roads or exiting
the Interstate for purposes of refueling or delivering
goods. Thus, § 31114 prohibits states from denying com-
mercial motor vehicles “reasonable access” to and from
the Interstate. Congress’s decision not to define “reasonable
access” more specifically does not mean that states
are permitted to define the term however they see fit.
Rather, this broad language can be viewed as reflecting
a recognition on Congress’s part that the manner and
degree of access to and from the Interstate necessary to
protect Congress’s overarching goal of uniformity for
commercial motor vehicles utilizing the Interstate will
vary across the country depending on factors such as
whether the Interstate is cutting across rural or metro
areas, traffic density on the road, and other considera-
tions. See New Hampshire Motor Transp. 

(opining that it would be within a state or local
government’s discretion, in accord with the “reasonable
access” provision under § 31114(a), to impose “a restric-
tion that routed heavy traffic on a detour of a few miles
to assure quiet in a hospital zone”). Under this frame-
work, states are still free to exercise their police powers
over state highways and local roads, so long as these
regulations do not impede “reasonable access” for commer-
cial motor vehicles traveling between the Interstate and
places such as terminals.4


4
  We note that some courts have held that any state or local
restrictions on access to and from the Interstate must be
based on safety concerns. See A.B.F. Freight System, Inc. v.
Suthard, 

, 341 (E.D. Va. 1988); see also New York
State Motor Truck Ass’n v. City of New York, 

                                                    (continued...)
14                                                  No. 07-1402

   We next turn to whether this congressional objective is
frustrated by Monee Township’s weight restriction on
Ridgeland Avenue. When viewed on its own, it is dif-
ficult to see how Ridgeland Avenue’s weight restriction
could be said to deny reasonable access between the
Terminal and the Interstate, since the Terminal also
abuts Steger Road, thus providing propane trucks with
another means of accessing I-57. The STAA, after all, does
not prohibit states from denying any form of access to and
from the Interstate, but rather, preemption only occurs


4
  (...continued)
(S.D. N.Y. 1987), aff’d 

(2d Cir. 1987); Consolidated
Freightways Corp. of 

; see also
Keck v. Commonwealth ex rel. Golden, 

, 16-18 (Ky.
Ct. App. 1999). The First Circuit, however, is the only circuit
court to have fully addressed this issue, and we agree with its
determination that under § 31114(a), states may limit access
to the National Network for reasons other than safety. New
Hampshire Motor Transp. 

. As discussed
by the First Circuit, there is no reason to think that § 31114(b),
which provides an exception from the “reasonable access”
provision in § 31114(a) for reasonable restrictions on certain
truck tractor-semitrailer combinations imposed by state or
local governments for safety reasons, serves to limit any
state restriction to one based on safety considerations. 

Instead, a more proper reading of § 31114(a) is that
states may exercise their police powers for any number of
reasons, so long as reasonable access is provided. Although the
federal regulations provide an exception in that “access within
1 road-mile from the National Network must us[e] the most
reasonable and practicable route available except for specific
safety reasons on individual routes,” 23 C.F.R. § 658.19(d) (em-
phasis added), these extra qualifications do not apply beyond
the 1 road-mile mark.
No. 07-1402                                              15

when reasonable access is denied. Analysis for conflict
preemption, however, requires that we look at the
Ridgeland Avenue weight restriction and the STAA as
applied, and here, Cook County has already refused to
permit fully loaded propane trucks weighing 80,000
pounds to access I-57 via Steger Road. Thus, the subse-
quent weight restriction on Ridgeland Avenue does not
merely deny one method of access, but in effect denies
all methods of access to the Interstate from the Terminal
for fully loaded propane trucks. Under any calculus, the
denial of all access cannot constitute reasonable access.
Accordingly, as applied, Monee Township’s weight
restriction on Ridgeland Avenue conflicts with § 31114(a)
and is thus preempted by the STAA.
  In reaching this holding, we offer no opinion as to
whether the same outcome would occur if the weight
restriction on Ridgeland Avenue were imposed due to
safety considerations, rather than solely for the protection
of the road. See supra note 4. Additionally, because we
have found Monee Township’s weight restriction on
Ridgeland Avenue to be preempted by the STAA, there
is no need for this Court to address whether the road
ordinance is valid under the Illinois Vehicle Code or
whether Defendants should be estopped from enforcing the
weight restriction.


                     III. Conclusion
  For the foregoing reasons, we AFFIRM the district court’s
grant of summary judgment for Plaintiff and denial
of Defendants’ cross-motion for summary judgment.

                   USCA-02-C-0072—5-19-08