Route 364, known locally as the Page Avenue Extension, is a freeway that connects St. Louis County with St. Charles County via the Veterans Memorial Bridge over the Missouri River and is a designated auxiliary state route of I-64 that will connect I-64 in St. Charles County to I-270 in St. Louis County.

The current termini are at an interchange with I-270 to the east and at the intersection of Missouri Route 94 and Harvester Rd. to the west. The freeway will eventually be extended another 11 miles (18 km) westward to I-64 (US-40/US-61).

The opening of the freeway increased the number of lanes across the Missouri River in the St. Louis metropolitan area from 23 to 33. It provides an alternate route to the Daniel Boone Bridge, Blanchette Memorial Bridge, and Discovery Bridge crossings.

The East-West Gateway Council of Governments determined there was a need for the freeway in 1969. However, little progress was made until the commissioning of the Page Avenue Bridge Committee in the fall of 1984. An earlier alignment, called the Green Line, bypassed Creve Coeur Lake Memorial Park and took the freeway to Interstate 70, but it could no longer be considered due to the rapid growth of the city of St. Peters and because the park expanded in size and encroached on the proposed alignment anyway. The committee proposed a new alignment called the Red Line and the Missouri Department of Transportation (MoDOT) authorized the project in the fall of 1986. In the spring of 1987 Missouri voters approved a fuel tax increase which included funding for the project. MoDOT held numerous meetings since then, but the alignment was not approved until June 1990. The United States Congress passed legislation in October 1992 authorizing the project as part of the Pipeline Safety Act of 1992. The environmental impact study was completed in November 1992, but just before the project was to received final clearance from the federal government Secretary of the Interior Bruce Babbitt took office and ordered more environmental studies resulting in more land mitigation for intrusion into Creve Coeur Lake Memorial Park. In the fall of 1995 the federal government gave the final clearance for the project 11 years after active planning began. For nearly 27 years the roadway was simply referred to as the Page Avenue Extension, but in February 1996 MoDOT gave the freeway an official designation of MO-364. Construction on the freeway is divided into 3 separate phases and began with the first project in 1997.

Phase I included work from I-270 to Route 94 through the Creve Coeur Lake Memorial Park, but due to concerns with traffic congestion at the proposed terminus with MO-94 it was decided to extended the freeway further west along its concurrency with MO-94 to Harvester Rd. Two major bridge structures were required, which included the Veterans Memorial Bridge and Creve Coeur Lake Memorial Park Bridge which cost $79 million and $74 million respectively. Both structures are designed to withstand seismic activity from the nearby New Madrid Fault. The total cost to construct this phase was approximately $350 million.

This phase also included improvements to the Creve Coeur Lake Memorial Park. The park nearly doubled in size and an existing bike trail there was linked to the Katy Trail in St. Charles County via the Veterans Memorial Bridge. The Creve Coeur Lake was dredged and a siltation lake was added to eliminate the need for future dredging.

A ribbon cutting ceremony occurred on December 13, 2003. The ceremony was held on the east bound lanes of the Veterans Memorial Bridge. Dignitaries that spoke included then Governor Bob Holden and Senator Christopher "Kit" Bond. Following the various speeches and ribbon cutting, a ceremonial first drive occurred between Upper Bottom Rd/Arena Pkwy and Maryland Heights Expwy. Due to inclement weather MoDOT opted to use December 13, 2003 to clear snow off the freeway and delayed opening the freeway until around 10:00 am on December 14, 2003 after the roadway was cleared.

The section of the freeway in St. Louis County has been dedicated the Buzz Westfall Memorial Freeway after former St. Louis County Executive Buzz Westfall who helped get the freeway built. Westfall died in 2003, months before the freeway opened.

A new interchange taking NB I-270 to WB MO-364 opened to traffic on July 22, 2011. This two lane ramp replaced a cumbersome cloverleaf movement which caused frequent backups on I-270.

Phase II work will extend the freeway along its concurrency with Route 94 to Route N/Mid Rivers Mall Dr including a one way outer road system. Work along MO-94 from Portwest Dr to Harvester Rd was completed as part of the Phase I. This phase of construction is expected to completed by 2012.

Completion of Phase II had originally been proposed to happen in segments with each interchange constituting a separate project. Work began on the Harvester Rd interchange with grading and utility relocation in the fall of 2006. In 2008 the Jungermann Rd and Woodstone Dr interchanges had been approved, funded, and scheduled for construction in 2010. However, the American Recovery and Reinvestment Act of 2009 accelerated that project and included funding for the segment to construct the Central School Rd interchange. The final Phase II projects including grade separated interchanges at Kisker Rd and Mid Rivers Mall Dr were approved and funded shortly thereafter.

The Harvester Rd interchange opened to traffic on July 27, 2010. Phase II to Mid Rivers Mall Drive opened on August 30, 2012.

Phase III work will extend the freeway from Mid Rivers Mall Dr/Pitman Hill Rd to I-64 (US-40/US-61) paralleling, but not overtaking the existing Route N. The interchange at I-64 and Route N, which opened in October, 2005, will become the western terminus of the freeway upon its completion. Final approval and funding was granted in August, 2011. A start date for construction is tentatively set for early 2013.

Controversy over the construction of the freeway came from several sources. The freeway's alignment would take it through the Creve Coeur Lake Memorial Park and the floodplain of the Missouri River drawing opposition from environmental groups including the Sierra Club and the Missouri Coalition for the Environment. Its high cost and debate over urban sprawl forced many St. Louis County municipalities to pass resolutions opposing the freeway. A petition to put the freeway up for referendum was submitted in 1998, and enough signatures were collected to force a vote. On November 3, 1998, voters approved right-of-way for the freeway by a 61% margin, and construction continued. In exchange, St. Louis County accepted 1,005 acres (4.07 km2) of land adjacent to the park.