The authority to regulate, restrict, or prohibit access to limited access facilities (tollways) under Republic Act No. 2000, originally vested in the Department of Public Works and Communications, was transferred to the Department of Transportation and Communications (DOTC) by Executive Order 546 in 1979; consequently, subsequent issuances by the Department of Public Works and Highways (DPWH) regulating such access are void for lack of authority, while regulations issued by the predecessor department prior to the transfer remain valid if consistent with the Constitution.

The case arose from the implementation of various administrative orders and regulations issued over several decades by the Department of Public Works and Highways (DPWH) and its predecessors, aiming to regulate traffic on limited access highways, commonly known as tollways or expressways. Specifically, these issuances involved restrictions and prohibitions on the use of motorcycles on these facilities, prompting challenges from motorcycle riders regarding the issuing body's authority and the constitutionality of the restrictions.

• Petitioners James Mirasol, Richard Santiago, and the Luzon Motorcyclists Federation, Inc. filed a Petition for Declaratory Judgment challenging DPWH Administrative Order No. 1, Series of 1968 (AO 1), DPWH Department Order No. 74, Series of 1993 (DO 74), and Art. II, Sec. 3(a) of the TRB's Revised Rules on Limited Access Facilities, arguing they were inconsistent with RA 2000 (Limited Access Highway Act).
• They later amended the petition to include a challenge against DPWH Department Order No. 215, Series of 1998 (DO 215), which declared the Manila-Cavite Toll Expressway a limited access facility, effectively banning motorcycles.
• During the case pendency, on July 18, 2001, DPWH issued Department Order No. 123 (DO 123), amending AO 1 to allow motorcycles with engine displacements of 400cc or more on tollways. Petitioners also challenged DO 123.
• AO 1, issued in 1968 by the Secretary of Public Works and Communications, prohibited various vehicles, including motorcycles, from using limited access highways.
• DO 74 (1993) declared sections of the North and South Luzon Expressways as limited access facilities subject to DPWH/TRB rules.
• DO 215 (1998) declared the Manila-Cavite Toll Expressway sections as limited access facilities subject to DPWH/TRB rules.
• The TRB, under the DPWH at the time, issued Revised Rules implementing these orders.
• The RTC initially granted a preliminary injunction but later dismissed the petition regarding AO 1, DO 74, DO 215, and the TRB Rules, upholding their validity, while declaring DO 123 unconstitutional for violating the equal protection clause.

• The RTC's final decision dismissing their petition was barred by res judicata because the earlier RTC order granting preliminary injunction, which respondents did not appeal, had become a final judgment on the issues.
• DPWH DO 74, DO 215, and the TRB Revised Rules contravene RA 2000 because the DPWH's authority under the Act is limited to designing the physical structure of tollways, not determining user qualifications or prohibiting vehicle types like motorcycles.
• DPWH AO 1 (prohibiting all motorcycles) and DO 123 (allowing only 400cc+ motorcycles) are unconstitutional exercises of police power, lacking scientific basis, creating unreasonable classification discriminating against motorcycles, and violating the right to travel.
• Possession of an LTO driver's license and vehicle registration entitles them to use all public roads, including tollways.

• (Inferred from RTC ruling and Solicitor General's summary) The preliminary injunction order was merely a provisional remedy and did not constitute a judgment on the merits, thus res judicata does not apply.
• Section 4 of RA 2000 grants the relevant department (argued to be DPWH) the authority not just to design but also to "regulate, restrict, or prohibit access" to limited access facilities to best serve traffic, which includes determining permissible vehicles.
• AO 1, issued by the DPWH's predecessor (Department of Public Works and Communications), was a valid exercise of the authority granted by RA 2000 and constitutes a reasonable exercise of police power for public safety and traffic management on tollways.
• The prohibition or regulation of motorcycles on tollways is based on safety considerations and inherent differences between motorcycles and other vehicles, making the classification reasonable and not violative of the equal protection clause.
• The right to travel is not absolute and can be reasonably regulated; restricting the mode of transport on specific facilities like tollways does not unduly curtail this right, especially when alternative routes exist.
• A driver's license and vehicle registration do not confer an absolute right to use any road but are privileges subject to reasonable regulation.

• Whether the RTC's decision dismissing the petition was barred by res judicata due to the prior grant of a preliminary injunction.
• Whether DPWH Department Orders 74 and 215, and the TRB Revised Rules and Regulations implementing them, are invalid for contravening RA 2000 or having been issued without authority.
• Whether DPWH Administrative Order 1 and Department Order 123 are unconstitutional for violating the equal protection clause, the right to travel, or constituting an invalid exercise of police power.

• The Supreme Court PARTLY GRANTED the petition.
• The argument of res judicata was rejected; a preliminary injunction is a provisional remedy, not a final adjudication on the merits.
• DO 74, DO 215, DO 123, and the TRB Revised Rules issued under them are declared VOID because the DPWH lacked the authority to issue them. Executive Order 546 (issued in 1979) split the Department of Public Works, Transportation and Communications into the Ministry (now Department) of Public Works (now DPWH) and the Ministry (now Department) of Transportation and Communications (DOTC), transferring the function of regulating transportation and communications, including the power to regulate access to limited access facilities under RA 2000, to the DOTC.
• Administrative Order No. 1, issued in 1968 by the Secretary of the Department of Public Works and Communications (DPWH's predecessor) before the transfer of functions by EO 546, is declared VALID. The issuing authority possessed the power under RA 2000 at that time.
• AO 1 is constitutional. It is a valid exercise of police power aimed at ensuring public safety and traffic order on limited access highways (tollways), which are special facilities requiring specific regulations. The classification prohibiting motorcycles (along with bicycles, tricycles, etc.) is reasonable due to inherent differences in vehicle stability and safety risks compared to four-wheeled vehicles. It does not violate the equal protection clause.
• AO 1 does not unduly infringe on the right to travel, as it only regulates the mode of transport on specific roads (tollways), not the right to move from one place to another, and alternative routes are available.

• Police Power: The inherent power of the state to enact regulations to promote public health, safety, morals, and general welfare. The Court upheld AO 1 as a valid police power measure, emphasizing that the standard is reasonableness, not absolute certainty or scientific exactitude, and that the prohibition on motorcycles on tollways was a reasonable means to ensure safety.
• Equal Protection Clause: Requires that all persons or things similarly situated should be treated alike, both as to rights conferred and responsibilities imposed; however, it permits reasonable classification. The Court held that the classification in AO 1 (distinguishing motorcycles from four-wheeled vehicles for tollway access) was based on substantial distinctions (stability, safety risks) germane to the purpose of the law (tollway safety and efficiency) and thus did not violate equal protection.
• Right to Travel: The constitutionally guaranteed right of citizens to move freely from one place to another. The Court ruled that regulating the mode of travel on specific facilities like tollways does not equate to an undue restriction of the right itself, especially when alternative routes exist.
• Presumption of Validity/Constitutionality: Laws and administrative issuances are presumed valid and constitutional until proven otherwise. The burden of proof rests on the challenger. This doctrine was applied in assessing the constitutionality of AO 1.
• Res Judicata: A final judgment on the merits rendered by a court of competent jurisdiction is conclusive as to the rights of the parties and their privies and constitutes an absolute bar to a subsequent action involving the same claim, demand or cause of action. The Court clarified that a preliminary injunction is an ancillary, provisional remedy and does not constitute a judgment on the merits that triggers res judicata.
• Statutory Construction (Devolution of Powers): The interpretation of laws governing the transfer of powers between government agencies. The Court analyzed the effect of EO 546, EO 125, and EO 125-A in determining that the power to regulate limited access highways under RA 2000 had been transferred from DPWH's predecessor to the DOTC.
• Delegation of Powers: An administrative agency cannot delegate a power it does not possess. Since DPWH lost the authority to regulate tollways, the TRB (at that time attached to DPWH) could not derive such power from it.

• "The validity of a police power measure does not depend upon the absolute assurance that the purpose desired can in fact be probably fully accomplished, or upon the certainty that it will best serve the purpose intended. Reason, not scientific exactitude, is the measure of the validity of the governmental regulation."
• "A toll way is not an ordinary road. As a facility designed to promote the fastest access to certain destinations, its use, operation, and maintenance require close regulation. Public interest and safety require the imposition of certain restrictions on toll ways that do not apply to ordinary roads."
• "The right to travel does not mean the right to choose any vehicle in traversing a toll way. The right to travel refers to the right to move from one place to another."
• "Clearly, under EO 546, it is the DOTC, not the DPWH, which has authority to regulate, restrict, or prohibit access to limited access facilities."
• "A classification based on practical convenience and common knowledge is not unconstitutional simply because it may lack purely theoretical or scientific uniformity."

• Bautista v. Juinio (1984): Cited for the principles of the equal protection clause, explaining that classification is permissible if based on substantial distinctions, germane to the purpose, not limited to existing conditions, and applies equally to all members of the class. Used to justify the classification in AO 1.
• Ichong v. Hernandez (1957): Cited for the broad scope and fundamental nature of police power as the "most essential, insistent and illimitable" of government powers. Used to support the validity of AO 1 as a police power measure.
• Searth Commodities Corp. v. Court of Appeals (1992) / Urbanes, Jr. v. Court of Appeals (2001): Referenced to explain that a preliminary injunction is a provisional remedy to preserve the status quo and not a final determination of the merits that would trigger res judicata.
• Eslao v. Commission on Audit (1994) / JMM Promotion and Management, Inc. v. Court of Appeals (1996): Cited for the principle that administrative issuances have the force and effect of law and enjoy the presumption of validity/constitutionality.
• Department of Education, Culture and Sports v. San Diego (1989): Cited regarding the reasonableness standard in exercising police power.
• United States v. Toribio (1910): Cited for the principle that the government's act under police power needs only be reasonable and not oppressive, not necessarily proven conclusively by research.
• Taxicab Operators of Metro Manila, Inc. v. Board of Transportation (1982): Cited potentially in relation to classification based on vehicle type (distinguishing old vs. new taxis), supporting the idea that reasonable differentiation between vehicle types is permissible.
• American Motorcyclist Ass'n. v. Park Comm'n. of City of Brockton (1991): Cited as analogous case where prohibiting motorcycles in a park did not infringe the right to travel, as it merely regulated the mode of transport within the area.

• Republic Act No. 2000 (Limited Access Highway Act): Sections 2, 3, and 4 defining limited access facilities and granting authority to the (then) Department of Public Works and Communications to design, establish, regulate, restrict, or prohibit access.
• DPWH Administrative Order No. 1, Series of 1968: Specific issuance challenged, particularly Section 3(h) prohibiting motorcycles.
• DPWH Department Order No. 74, Series of 1993: Challenged issuance declaring NLEX/SLEX sections as limited access facilities.
• DPWH Department Order No. 215, Series of 1998: Challenged issuance declaring Manila-Cavite Toll Expressway sections as limited access facilities.
• DPWH Department Order No. 123, Series of 2001: Challenged issuance amending AO 1 to allow 400cc+ motorcycles.
• TRB Revised Rules and Regulations on Limited Access Facilities: Implementing rules challenged alongside the DPWH orders.
• 1997 Rules of Civil Procedure, Rule 58, Section 9: Referenced regarding the nature of preliminary injunction and the requirement for a final injunction.
• Act No. 2711 (Revised Administrative Code of 1917): Section 75 cited regarding the original structure of executive departments.
• Republic Act No. 4136 (Land Transportation and Traffic Code): Mentioned creation of Land Transportation Commission.
• Presidential Decree No. 458 (1974): Cited for creating the Department of Public Highways.
• Executive Order No. 546 (1979): Crucial order cited for splitting the Ministry of Public Works, Transportation and Communications and transferring regulatory functions over transportation (including tollways) to the Ministry (now Department) of Transportation and Communications (DOTC). Sections 1, 3, 6, 8 referenced.
• Executive Order No. 710 (1981): Cited for merging the Ministry of Public Works and Ministry of Public Highways into the Ministry of Public Works and Highways (now DPWH).
• Executive Order No. 125 (1987) and Executive Order No. 125-A (1987): Cited for reorganizing the DOTC and confirming its authority to administer and enforce laws relative to transportation. Section 5 referenced enumerating DOTC powers.
• Constitution: Equal Protection Clause invoked by petitioners and analyzed by the Court. Right to Travel invoked by petitioners.