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98-792: State Route 504 ( SR 504 , designated as the Spirit Lake Memorial Highway ) is a state highway in southwestern Washington state in the United States. It travels 52 miles (84 km) along the North Fork Toutle River to the Mount St. Helens area, serving as the main access to the Mount St. Helens National Volcanic Monument . The highway begins at an interchange with Interstate 5 (I-5) and SR 411 in Castle Rock and terminates at

196-470: A Parker truss or Pratt truss than a true arch . In the Brown truss all vertical elements are under tension, with exception of the end posts. This type of truss is particularly suited for timber structures that use iron rods as tension members. See Lenticular truss below. This combines an arch with a truss to form a structure both strong and rigid. Most trusses have the lower chord under tension and

294-533: A partial cloverleaf interchange with an access road that serves the Coldwater Science and Learning Center , a visitor center that overlooks the mountain and open from autumn to spring. The highway heads west before completing a hairpin turn to travel south around the end of Coldwater Lake . Beyond milepost 45, SR 504 is closed during the winter months due to hazardous conditions for drivers and potential avalanches . It typically reopens in time for

392-510: A rest area . SR 504 continues further into the mountains, crossing Bear Creek and traveling around Elk Rock to a viewpoint on its southeast side. From the Elk Rock area, the highway forms the northern boundary of the Mount St. Helens National Volcanic Monument and encounters more mountainous terrain that results in several hairpin turns between other scenic viewpoints. After crossing several branches of Maratta Creek, SR 504 reaches

490-640: A 0.87-mile (1.40 km) section of the former highway and terminates near the Toutle River Sediment Dam at a viewpoint and WSDOT maintenance facility An average of 50 vehicles use the road on a daily basis, according to annual daily traffic data measured by WSDOT in 2016. State highways in Washington All state highways are designated by the Washington State Legislature and codified in

588-550: A Parker truss vary from near vertical in the center of the span to diagonal near each end, similar to a Warren truss. George H. Pegram , while the chief engineer of Edge Moor Iron Company in Wilmington, Delaware , patented this truss design in 1885. The Pegram truss consists of a Parker type design with the vertical posts leaning towards the center at an angle between 60 and 75°. The variable post angle and constant chord length allowed steel in existing bridges to be recycled into

686-599: A common truss design during this time, with their arched top chords. Companies like the Massillon Bridge Company of Massillon, Ohio , and the King Bridge Company of Cleveland , became well-known, as they marketed their designs to cities and townships. The bowstring truss design fell out of favor due to a lack of durability, and gave way to the Pratt truss design, which was stronger. Again,

784-435: A conventional truss into place or by building it in place using a "traveling support". In another method of construction, one outboard half of each balanced truss is built upon temporary falsework. When the outboard halves are completed and anchored the inboard halves may then be constructed and the center section completed as described above. The Fink truss was designed by Albert Fink of Germany in 1854. This type of bridge

882-427: A few homes, and follows the south side of the narrower valley as the river meanders north and south around various mountains. At a third crossing of the river, SR 504 intersects a short spur route on Sediment Dam Road that leads to a viewpoint overlooking the Toutle River Sediment Dam . The highway continues along the northeast side of the earthen dam and its reservoir, climbing uphill and running through cuts in

980-616: A gap in the middle, and State Routes 35 , 168 , 230 , 276 , and most of SR 171 , 213 , and 704 , have not been constructed. Notable sections of state highways include the six crossings of the Cascade Range - the Columbia River Gorge ( SR 14 ), White Pass ( US 12 ), Chinook Pass ( SR 410 ), Snoqualmie Pass ( I-90 ), Stevens Pass ( US 2 ), and the North Cascades Highway ( SR 20 ). Of

1078-653: A grid, with even-numbered routes running east–west and odd-numbered routes running north–south. Even two-digit routes increase from south to north in three "strips", with SR 4 , SR 6 , and SR 8 in the western part of the state, SR 14 , SR 16 , SR 18 , and SR 20 along the Interstate 5 corridor, and SR 22 , SR 24 , SR 26 , SR 28 , and former SR 30 in the east. Odd numbers similarly increase from west to east, with SR 3 , Interstate 5 , SR 7 , SR 9 , SR 11 , SR 17 , SR 21 , SR 23 , SR 25 , SR 27 , and SR 31 following this general progression. ( SR 19

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1176-565: A higher elevation between Kid Valley and the newly formed Coldwater Lake , crossing over various creeks with ten major bridges. The project's $ 118 million cost (equivalent to $ 278 million in 2023 dollars) was paid from emergency funds from the Federal Highway Administration . Construction of the new highway and its scenic viewpoints began in 1988 and the first section to the Coldwater Ridge visitor center

1274-405: A limited construction window due to weather and elevation as well as the steepness of the terrain, the highway and access to the observatory was to remain closed until 2026. The closure timeline was revised by WSDOT to April 2027, with construction to rebuild the route not slated until April 2026. SR 504 has a short spur route east of Kid Valley that runs along Sediment Dam Road. It follows

1372-481: A limited number of truss bridges were built. The truss may carry its roadbed on top, in the middle, or at the bottom of the truss. Bridges with the roadbed at the top or the bottom are the most common as this allows both the top and bottom to be stiffened, forming a box truss . When the roadbed is atop the truss, it is a deck truss; an example of this was the I-35W Mississippi River bridge . When

1470-477: A lower chord (functioning as a suspension cable) that curves down and then up to meet at the same end points. Where the arches extend above and below the roadbed, it is called a lenticular pony truss bridge . The Pauli truss bridge is a specific variant of the lenticular truss, but the terms are not interchangeable. One type of lenticular truss consists of arcuate upper compression chords and lower eyebar chain tension links. Brunel 's Royal Albert Bridge over

1568-573: A mass evacuation. On May 18, 1980, the north face of Mount St. Helens slid away and triggered a massive eruption that created a lahar that devastated the North Fork Toutle River. The lahar destroyed about 25 miles (40 km) of SR 504, including seven of the highway's eight major bridges, leaving only the Kid Valley bridge standing because of its sufficient clearance . The remaining section between Toutle and Kid Valley

1666-581: A narrower truss bridge . By the 1970s, several new campgrounds, trailheads , and recreation areas had been established along the highway by the Forest Service and logging companies like Weyerhauser to serve tourists visiting the Mount St. Helens area. A major flood in December 1977 left eight sections of the highway washed out and only passable by one lane of traffic until repairs were completed

1764-726: A new span using the Pegram truss design. This design also facilitated reassembly and permitted a bridge to be adjusted to fit different span lengths. There are twelve known remaining Pegram span bridges in the United States with seven in Idaho , two in Kansas , and one each in California , Washington , and Utah . The Pennsylvania (Petit) truss is a variation on the Pratt truss . The Pratt truss includes braced diagonal members in all panels;

1862-459: A pin-jointed structure, one where the only forces on the truss members are tension or compression, not bending. This is used in the teaching of statics, by the building of model bridges from spaghetti . Spaghetti is brittle and although it can carry a modest tension force, it breaks easily if bent. A model spaghetti bridge thus demonstrates the use of a truss structure to produce a usefully strong complete structure from individually weak elements. In

1960-447: A planned ski resort on Mount St. Helens hastened the construction of a modern highway linking Spirit Lake to the timberline on the mountain's northern slopes in the 1950s. Despite support from the state government, the Forest Service, and Bureau of Public Roads, the highway project was put on hold for several years due to funding shortfalls. The state legislature approved funds for the five-mile (8.0 km) extension of SSH 1R into

2058-650: A portion of Chuckanut Drive and a road around the west side of the Olympic Peninsula . Under a 1909 law, the State Highway Board surveyed a connected network of proposed state roads, The legislature added most of these routes to the state highway system in 1913, when they formed a two-tiered system of primary and secondary roads. Primary roads were completely controlled by the state, including maintenance, and received only names, while secondary roads kept their numbers and county maintenance. Unlike

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2156-530: A possible buildup of magma, forcing 2,500 visitors to leave the Coldwater and Johnston centers for several days. The evacuation was later cancelled and other restrictions were relaxed after steam eruptions diffused pressure inside the volcano. A minor mudslide in March 2007 blocked a section of SR 504 near Kid Valley and was removed after a week-long cleanup by WSDOT crews. A mudslide and debris flow, known as

2254-413: A small commercial area before ascending into the hills above Salmon Creek, passing several farms and wineries along the way. The highway follows a minor stream heading southeast into the wetlands around Silver Lake , where the Mount St. Helens visitor center and Seaquest State Park lie. SR 504 continues along the north side of the lake and passes through the town of Toutle at the confluence of

2352-486: A stable foundation. It replaced an original plan to build a forest road that would be used by shuttle buses between Coldwater Ridge and the Johnston Ridge facility. A long-proposed extension of SR 504 to the eastern side of the Mount St. Helens area gained traction in the early 2000s, sparking outcry from scientists and environmentalists. The 7-to-17-mile (11 to 27 km) route, connecting Coldwater Lake to

2450-545: A variant of the lenticular truss, "with the top chord carefully shaped so that it has a constant force along the entire length of the truss." It is named after Friedrich Augustus von Pauli  [ de ] , whose 1857 railway bridge (the Großhesseloher Brücke  [ de ] ) spanned the Isar near Munich . ( See also Grosshesselohe Isartal station .) The term Pauli truss is not interchangeable with

2548-406: Is a bridge whose load-bearing superstructure is composed of a truss , a structure of connected elements, usually forming triangular units. The connected elements, typically straight, may be stressed from tension , compression , or sometimes both in response to dynamic loads. There are several types of truss bridges, including some with simple designs that were among the first bridges designed in

2646-700: Is a Pratt truss design with a polygonal upper chord. A "camelback" is a subset of the Parker type, where the upper chord consists of exactly five segments. An example of a Parker truss is the Traffic Bridge in Saskatoon , Canada. An example of a camelback truss is the Woolsey Bridge near Woolsey, Arkansas . Designed and patented in 1872 by Reuben Partridge , after local bridge designs proved ineffective against road traffic and heavy rains. It became

2744-519: Is a hybrid between a Warren truss and a double-intersection Pratt truss. Invented in 1863 by Simeon S. Post, it is occasionally referred to as a Post patent truss although he never received a patent for it. The Ponakin Bridge and the Bell Ford Bridge are two examples of this truss. A Pratt truss includes vertical members and diagonals that slope down towards the center, the opposite of

2842-832: Is named after the K formed in each panel by the vertical member and two oblique members. Examples include the Südbrücke rail bridge over the River Rhine, Mainz, Germany, the bridge on I-895 (Baltimore Harbor Tunnel Thruway) in Baltimore, Maryland, the Long–Allen Bridge in Morgan City, Louisiana (Morgan City Bridge) with three 600-foot-long spans, and the Wax Lake Outlet bridge in Calumet, Louisiana One of

2940-518: Is partly based on the Howe truss . The first Allan truss was completed on 13 August 1894 over Glennies Creek at Camberwell, New South Wales and the last Allan truss bridge was built over Mill Creek near Wisemans Ferry in 1929. Completed in March 1895, the Tharwa Bridge located at Tharwa, Australian Capital Territory , was the second Allan truss bridge to be built, the oldest surviving bridge in

3038-695: Is practical for use with spans up to 250 feet (76 m) and was a common configuration for railroad bridges as truss bridges moved from wood to metal. They are statically determinate bridges, which lend themselves well to long spans. They were common in the United States between 1844 and the early 20th century. Examples of Pratt truss bridges are the Governor's Bridge in Maryland ; the Hayden RR Bridge in Springfield, Oregon , built in 1882;

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3136-427: Is sufficiently stiff then this vertical element may be eliminated. If the lower chord (a horizontal member of a truss) is sufficiently resistant to bending and shear, the outer vertical elements may be eliminated, but with additional strength added to other members in compensation. The ability to distribute the forces in various ways has led to a large variety of truss bridge types. Some types may be more advantageous when

3234-407: Is supported only at the ends and is fully independent of any adjacent spans. Each span must fully support the weight of any vehicles traveling over it (the live load ). In contrast, a continuous truss functions as a single rigid structure over multiple supports. This means that the live load on one span is partially supported by the other spans, and consequently it is possible to use less material in

3332-525: Is the Victoria Bridge on Prince Street, Picton, New South Wales . Also constructed of ironbark, the bridge is still in use today for pedestrian and light traffic. The Bailey truss was designed by the British in 1940–1941 for military uses during World War II. A short selection of prefabricated modular components could be easily and speedily combined on land in various configurations to adapt to

3430-420: The 2023 South Coldwater Slide , occurred on May 14, 2023, destroying the 85-foot (26 m) Spirit Lake Outlet Bridge and severing SR 504 northeast of Johnston Ridge Observatory at milepost 49. Twelve people were airlifted from the area beyond the mudslide; the observatory's seasonal reopening was postponed and the highway east of Coldwater Lake was closed to all traffic. WSDOT contractors cleared debris over

3528-770: The Australian Capital Territory and the oldest, longest continuously used Allan truss bridge. Completed in November 1895, the Hampden Bridge in Wagga Wagga, New South Wales , Australia, the first of the Allan truss bridges with overhead bracing, was originally designed as a steel bridge but was constructed with timber to reduce cost. In his design, Allan used Australian ironbark for its strength. A similar bridge also designed by Percy Allen

3626-621: The Dearborn River High Bridge near Augusta, Montana, built in 1897; and the Fair Oaks Bridge in Fair Oaks, California , built 1907–09. The Scenic Bridge near Tarkio, Montana , is an example of a Pratt deck truss bridge, where the roadway is on top of the truss. The queenpost truss , sometimes called "queen post" or queenspost, is similar to a king post truss in that the outer supports are angled towards

3724-1316: The Fort Wayne Street Bridge in Goshen, Indiana , the Schell Bridge in Northfield, Massachusetts , the Inclined Plane Bridge in Johnstown, Pennsylvania , the Easton–Phillipsburg Toll Bridge in Easton, Pennsylvania , the Connecticut River Bridge in Brattleboro, Vermont , the Metropolis Bridge in Metropolis, Illinois , and the Healdsburg Memorial Bridge in Healdsburg, California . A Post truss

3822-445: The Howe truss . The interior diagonals are under tension under balanced loading and vertical elements under compression. If pure tension elements (such as eyebars ) are used in the diagonals, then crossing elements may be needed near the center to accept concentrated live loads as they traverse the span. It can be subdivided, creating Y- and K-shaped patterns. The Pratt truss was invented in 1844 by Thomas and Caleb Pratt. This truss

3920-557: The Johnston Ridge Observatory near Spirit Lake . The Cowlitz County government built the Spirit Lake Highway in 1903 and paved it in the early 1930s before it was transferred to state control, becoming Secondary State Highway 1R (SSH 1R) in 1937. SSH 1R initially ended at the boundary of Columbia National Forest (now Gifford Pinchot National Forest ), but was extended in 1961 to

4018-535: The Revised Code of Washington (RCW), namely Chapter 47.17 RCW. These routes are defined generally by termini and points along the route; WSDOT may otherwise choose the details, and may bypass the designated points as long as the road serves the general vicinity. WSDOT's duties include "locating, designing, constructing, improving, repairing, operating, and maintaining" these state highways, including bridges and other related structures. Within cities and towns,

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4116-481: The River Tamar between Devon and Cornwall uses a single tubular upper chord. As the horizontal tension and compression forces are balanced these horizontal forces are not transferred to the supporting pylons (as is the case with most arch types). This in turn enables the truss to be fabricated on the ground and then to be raised by jacking as supporting masonry pylons are constructed. This truss has been used in

4214-625: The Toutle River 's two forks. The highway crosses over the river on the Coal Bank Bridge and continues along the north side of the North Fork Toutle River , following the narrow valley to the east of Beigle Mountain . Near the Riverdale Raceway, SR 504 intersects the east end of SR 505 , which provides connections to I-5 and Toledo . The highway continues northeast into Kid Valley , home to camping sites and

4312-499: The United States , because wood was in abundance, early truss bridges would typically use carefully fitted timbers for members taking compression and iron rods for tension members , usually constructed as a covered bridge to protect the structure. In 1820, a simple form of truss, Town's lattice truss , was patented, and had the advantage of requiring neither high labor skills nor much metal. Few iron truss bridges were built in

4410-552: The Washington State Legislature created the State Highway Board in 1905 and appropriated funds to construct - but not maintain - twelve numbered "state roads" in sparsely settled areas of the state. (Main highways in more populated areas would continue to be entirely under county control, though sometimes built with 50% state aid .) Six of these highways were east–west crossings of the Cascades; others included

4508-564: The timberline of the mountain. It was renumbered to SR 504 in 1964 and remained popular with loggers and tourists, requiring bridges and sections to be rebuilt. A major section of SR 504 was destroyed in the May 18, 1980, eruption of Mount St. Helens and its subsequent lahar on the North Fork Toutle River. The state government rebuilt most of the highway from 1988 to 1997, relocating it further north and connecting to new interpretive centers at Coldwater Ridge and Johnston Ridge. A part of

4606-482: The "blast zone," where trees were felled during the 1980 eruption of Mount St. Helens , located 12 miles (19 km) away. The area has large forests of young fir, pine, and cottonwood trees planted by Weyerhaeuser in the 1980s as part of a regeneration and restoration project. The company also operates the Charles W. Bingham Forest Learning Center , a museum that overlooks the North Fork Toutle River and also includes

4704-678: The 13 public road crossings of the Canada–US border in Washington, nine are on state highways. Major bridges include the Tacoma Narrows Bridge and three floating bridges : the Evergreen Point Bridge , Hood Canal Bridge , and Lake Washington Bridge . The Washington State Ferries , except the route to Sidney, British Columbia , were legally included in the state highway system in 1994; a new State Route 339

4802-499: The 1905 numbering. The state legislature adopted new standards for designating state highways in 1990, following a three-year study from the Road Jurisdiction Committee. Among the changes were recommending highways serving state parks and ferry terminals be added to the system. A major restructure was passed by the legislature in 1991 and took effect on April 1, 1992. Truss bridge A truss bridge

4900-461: The 19th and early 20th centuries. A truss bridge is economical to construct primarily because it uses materials efficiently. The nature of a truss allows the analysis of its structure using a few assumptions and the application of Newton's laws of motion according to the branch of physics known as statics . For purposes of analysis, trusses are assumed to be pin jointed where the straight components meet, meaning that taken alone, every joint on

4998-715: The Loowit Viewpoint and reaches the Johnston Ridge Observatory , the volcano's main visitor center open from spring to autumn and situated at an elevation of 4,314 feet (1,315 m). SR 504 terminates downhill from the observatory at its parking lot, located 5.5 miles (8.9 km) north of the Mount St. Helens crater. SR 504 is maintained by the Washington State Department of Transportation (WSDOT), which conducts an annual survey on state highways to measure traffic volume in terms of annual average daily traffic . Average traffic volumes on

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5096-495: The May 18 anniversary of the 1980 eruption . The highway continues into the National Volcanic Monument and turns east before reaching the border between Cowlitz and Skamania counties. SR 504 follows South Coldwater Creek upstream through a narrow valley to its headwaters near Spirit Lake , passing several trailheads , and turns west to continue its ascent. The treeless landscape is home to winter herds of Rocky Mountain elk and deer . The highway turns east once again near

5194-427: The Pennsylvania truss adds to this design half-length struts or ties in the top, bottom, or both parts of the panels. It is named after the Pennsylvania Railroad , which pioneered this design. It was once used for hundreds of bridges in the United States, but fell out of favor in the 1930s and very few examples of this design remain. Examples of this truss type include the Lower Trenton Bridge in Trenton, New Jersey ,

5292-517: The RCW are "state route number 20 north" (signed as State Route 20 Spur ) and "state route number 97-alternate" (signed as U.S. Route 97 Alternate ). Some other spurs, such as State Route 503 Spur , are defined as part of the main routes, as is U.S. Route 101 Alternate . WSDOT has also defined some spurs that mainly serve to provide full access between intersecting routes. Although most state highways as defined by law are open to traffic, State Route 109 dead-ends at Taholah , State Route 501 has

5390-454: The Spirit Lake Memorial Highway to honor the victims of the eruption. A visitor center was also opened at Silver Lake in 1987 to serve the growing number of tourists to the area, but the highway would remain closed beyond the sediment dam. Preliminary plans for a replacement for the highway to serve the north side of Mount St. Helens were approved by the state government in 1986. The highway would include 23 miles (37 km) of new road built at

5488-423: The United States before 1850. Truss bridges became a common type of bridge built from the 1870s through the 1930s. Examples of these bridges still remain across the US, but their numbers are dropping rapidly as they are demolished and replaced with new structures. As metal slowly started to replace timber, wrought iron bridges in the US started being built on a large scale in the 1870s. Bowstring truss bridges were

5586-461: The availability of machinery, and the cost of labor. In other cases, the appearance of the structure may take on greater importance and so influence the design decisions beyond mere matters of economics. Modern materials such as prestressed concrete and fabrication methods, such as automated welding , and the changing price of steel relative to that of labor have significantly influenced the design of modern bridges. A pure truss can be represented as

5684-632: The bridge companies marketed their designs, with the Wrought Iron Bridge Company in the lead. As the 1880s and 1890s progressed, steel began to replace wrought iron as the preferred material. Other truss designs were used during this time, including the camel-back. By the 1910s, many states developed standard plan truss bridges, including steel Warren pony truss bridges. In the 1920s and 1930s, Pennsylvania and several states continued to build steel truss bridges, using massive steel through-truss bridges for long spans. Other states, such as Michigan , used standard plan concrete girder and beam bridges, and only

5782-406: The bridge deck, they are susceptible to being hit by overheight loads when used on highways. The I-5 Skagit River bridge collapsed after such a strike; before the collapse, similar incidents had been common and had necessitated frequent repairs. Truss bridges consisting of more than one span may be either a continuous truss or a series of simple trusses. In the simple truss design, each span

5880-493: The center, the opposite of the Pratt truss . In contrast to the Pratt truss, the diagonal web members are in compression and the vertical web members are in tension. Few of these bridges remain standing. Examples include Jay Bridge in Jay, New York ; McConnell's Mill Covered Bridge in Slippery Rock Township, Lawrence County, Pennsylvania ; Sandy Creek Covered Bridge in Jefferson County, Missouri ; and Westham Island Bridge in Delta, British Columbia , Canada. The K-truss

5978-435: The center. Many cantilever bridges, like the Quebec Bridge shown below, have two cantilever spans supporting a simple truss in the center. The bridge would remain standing if the simple truss section were removed. Bridges are the most widely known examples of truss use. There are many types, some of them dating back hundreds of years. Below are some of the more common designs. The Allan truss , designed by Percy Allan ,

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6076-418: The cliffs. Further southeast along the river, SR 504 passes the privately owned Eco Park resort, a youth camp, and a heliport near the Hoffstadt Bluffs Viewpoint. The highway then crosses over Hoffstadt Creek on a 2,340-foot (710 m) steel truss bridge that sits 370 feet (110 m) above the valley floor; it is the longest of 13 bridges on SR 504. The bridge also marks the western extent of

6174-414: The compression members and to control deflection. It is mainly used for rail bridges, showing off a simple and very strong design. In the Pratt truss the intersection of the verticals and the lower horizontal tension members are used to anchor the supports for the short-span girders under the tracks (among other things). With the Baltimore truss, there are almost twice as many points for this to happen because

6272-399: The construction of a stadium, with the upper chords of parallel trusses supporting a roof that may be rolled back. The Smithfield Street Bridge in Pittsburgh, Pennsylvania , is another example of this type. An example of a lenticular pony truss bridge that uses regular spans of iron is the Turn-of-River Bridge designed and manufactured by the Berlin Iron Bridge Co. The Pauli truss is

6370-597: The earlier state roads, these primary roads mostly followed existing passable county roads. A 1923 restructuring of the system reassigned numbers to almost all the primary state highways, which were soon marked on signs. In 1937, the old primary/secondary split was abolished, and a new system of primary and secondary state highways was created, all to be maintained by the state in the same manner. The old state roads all kept their numbers as new primary state highways, and secondary state highways were created as alphanumeric branches of those primary highways (for instance SSH 8D

6468-414: The earliest examples is the Old Blenheim Bridge , which with a span of 210 feet (64 m) and a total length of 232 feet (71 m) long was the second-longest covered bridge in the United States, until its destruction from flooding in 2011. The Busching bridge, often erroneously used as an example of a Long truss, is an example of a Howe truss, as the verticals are metal rods. A Parker truss bridge

6566-401: The elements, as in a Vierendeel truss . In the bridge illustrated in the infobox at the top, vertical members are in tension, lower horizontal members in tension, shear , and bending, outer diagonal and top members are in compression, while the inner diagonals are in tension. The central vertical member stabilizes the upper compression member, preventing it from buckling . If the top member

6664-496: The existing Forest Highway 99 near Windy Ridge and beyond to Forest Highway 25, was supported by officials from Cowlitz and Lewis counties as a tourist draw and a potential evacuation route. WSDOT studied several options for the proposed highway, which enjoyed mixed public support, and estimated a cost of $ 18.5 million to construct one option and $ 44 million for another (equivalent to $ 30.4 million and $ 72.3 million, respectively, in 2023 dollars). The proposed highway

6762-438: The following year. In March 1980, Mount St. Helens was struck by an earthquake swarm that indicated potential eruptive activity for the volcano, which had been dormant for over a century. The Forest Service established a roadblock on SR 504 approximately 4 miles (6.4 km) west of Spirit Lake on March 28 because of potential avalanche risks. In the following days, the roadblock was moved to 15 miles (24 km) west of

6860-416: The former Hoffstadt Bluffs Visitor Center, opened in 1995 at milepost 33 and 1996 at milepost 27, respectively. In May 1997, SR 504 was extended 7.5 miles (12.1 km) to its current terminus at the newly opened Johnston Ridge Observatory, named for volcanologist David A. Johnston . Construction of the extension included underground blasting to compact soil and provide one of the highway's bridges with

6958-408: The highway by July and created a temporary gravel road to access Johnston Ridge for vehicle retrieval and to prepare for reopening in 2024, but the interim roadway was washed out in November due to a collapsed culvert caused by heavy rainfall and erosion unrelated to the earlier landslide. WSDOT announced in early 2024 that because of the costs and difficulties in making repairs to the bypass, based on

7056-734: The highway in 2016 ranged from a minimum of 500 vehicles near Coldwater Lake to a maximum of 14,000 vehicles at the I-5 interchange in Castle Rock. SR 504 is the main route for a majority of the 3 million annual visitors to the Mount St. Helens area. It is designated by the state government as the Spirit Lake Memorial Highway, a state scenic byway , and a National Forest Scenic Byway by the United States Forest Service . The Spirit Lake Highway

7154-431: The lake and later 30 miles (48 km) west as the risk of an imminent eruption grew. Many local residents and sightseers violated the roadblock, which was planned to be moved further west by an order from Governor Dixy Lee Ray to take effect on May 19. An exception was made on May 17, allowing for the retrieval of belongings from various buildings during a four-hour period that was monitored by local authorities in case of

7252-408: The local governments are responsible for certain aspects of the streets maintained as parts of a state highway, including their grade and the portion not used for highway purposes. All routes, even Interstate and U.S. Highways, are defined as "state route number" plus the number; for instance, Interstate 5 is "state route number 5" and U.S. Route 395 is "state route number 395". Also included in

7350-443: The national forest, which began in late 1959. The SSH 1R designation was extended onto the new timberline highway, which opened to traffic on September 29, 1962. During the 1964 state highway renumbering , SSH 1R was designated SR 504 under the modern "sign route" (now state route) system. The state highway department completed construction of a new bridge over the Toutle River at Kid Valley in November 1965, replacing

7448-412: The needs at the site and allow rapid deployment of completed trusses. In the image, note the use of pairs of doubled trusses to adapt to the span and load requirements. In other applications the trusses may be stacked vertically, and doubled as necessary. The Baltimore truss is a subclass of the Pratt truss. A Baltimore truss has additional bracing in the lower section of the truss to prevent buckling in

7546-491: The old alignment near the Toutle River Sediment Dam is signed as a spur route . Continued volcanic activity at Mount St. Helens, particularly in the mid-2000s, has resulted in closures and evacuations along the highway at various times. SR 504 begins as an extension of Huntington Avenue at an interchange with I-5 northeast of Castle Rock . The street continues southwest into downtown Castle Rock as SR 411 and I-5 Business . SR 504 travels northeasterly through

7644-574: The short verticals will also be used to anchor the supports. Thus the short-span girders can be made lighter because their span is shorter. A good example of the Baltimore truss is the Amtrak Old Saybrook – Old Lyme Bridge in Connecticut , United States. The Bollman Truss Railroad Bridge at Savage, Maryland , United States is the only surviving example of a revolutionary design in the history of American bridge engineering. The type

7742-451: The simplest truss styles to implement, the king post consists of two angled supports leaning into a common vertical support. This type of bridge uses a substantial number of lightweight elements, easing the task of construction. Truss elements are usually of wood, iron, or steel. A lenticular truss bridge includes a lens-shape truss, with trusses between an upper chord functioning as an arch that curves up and then down to end points, and

7840-454: The standard for covered bridges built in central Ohio in the late 1800s and early 1900s. The Pegram truss is a hybrid between the Warren and Parker trusses where the upper chords are all of equal length and the lower chords are longer than the corresponding upper chord. Because of the difference in upper and lower chord length, each panel is not square. The members which would be vertical in

7938-464: The structure is functionally considered to be a flexible joint as opposed to a rigid joint with the strength to maintain its shape, and the resulting shape and strength of the structure are only maintained by the interlocking of the components. This assumption means that members of the truss (chords, verticals, and diagonals) will act only in tension or compression. A more complex analysis is required where rigid joints impose significant bending loads upon

8036-481: The term lenticular truss and, according to Thomas Boothby, the casual use of the term has clouded the literature. The Long truss was designed by Stephen H. Long in 1830. The design resembles a Howe truss , but is entirely made of wood instead of a combination of wood and metal. The longest surviving example is the Eldean Covered Bridge north of Troy, Ohio , spanning 224 feet (68 m). One of

8134-552: The truss members are both above and below the roadbed it is called a through truss; an example of this is the Pulaski Skyway , and where the sides extend above the roadbed but are not connected, a pony truss or half-through truss. Sometimes both the upper and lower chords support roadbeds, forming a double-decked truss . This can be used to separate rail from road traffic or to separate the two directions of road traffic. Since through truss bridges have supports located over

8232-471: The truss. Continuous truss bridges were not very common before the mid-20th century because they are statically indeterminate , which makes them difficult to design without the use of computers . A multi-span truss bridge may also be constructed using cantilever spans, which are supported at only one end rather than both ends like other types of trusses. Unlike a continuous truss, a cantilever truss does not need to be connected rigidly, or indeed at all, at

8330-428: The upper chord under compression. In a cantilever truss the situation is reversed, at least over a portion of the span. The typical cantilever truss bridge is a "balanced cantilever", which enables the construction to proceed outward from a central vertical spar in each direction. Usually these are built in pairs until the outer sections may be anchored to footings. A central gap, if present, can then be filled by lifting

8428-622: The western boundary of the Columbia National Forest near Spirit Lake. The state government paved sections of the highway in the late 1930s and early 1940s, with only a short section at the east end remaining unpaved by 1944. The remaining section of the highway within Columbia National Forest was improved and paved by the federal Bureau of Public Roads in the late 1930s for $ 1.2 million (equivalent to $ 20.7 million in 2023 dollars). Expanded logging and

8526-430: The wood is employed for compression elements while other types may be easier to erect in particular site conditions, or when the balance between labor, machinery, and material costs has certain favorable proportions. The inclusion of the elements shown is largely an engineering decision based upon economics, being a balance between the costs of raw materials, off-site fabrication, component transportation, on-site erection,

8624-483: Was a branch of PSH 8 ). The final renumbering was authorized by law in 1963 and posted in January 1964, when new "sign route" numbers were assigned that matched the inter-state systems and otherwise formed the present grid. Until 1970, these numbers coexisted with the older primary and secondary state highways, when the legislature adopted the sign route numbers as "state routes", finally eliminating all vestiges of

8722-520: Was added in 1991, and lies west of SR 3; SR 35 and SR 41 are extensions of highways in adjacent states.) Three-digit routes (and SR 92 and SR 96 ) are usually numbered by taking the first one or two digits of a route it connects to and adding another digit or two. In some cases, instead of using the two-digit route's actual number, a number that would fit the grid is used instead. Three-digit routes have been numbered as follows: After passing several early laws designating state roads starting in 1893,

8820-414: Was also easy to assemble. Wells Creek Bollman Bridge is the only other bridge designed by Wendel Bollman still in existence, but it is a Warren truss configuration. The bowstring truss bridge was patented in 1841 by Squire Whipple . While similar in appearance to a tied-arch bridge , a bowstring truss has diagonal load-bearing members: these diagonals result in a structure that more closely matches

8918-427: Was buried in up to 6 feet (1.8 m) of sediment, but was able to re-open by September with temporary Bailey bridges and other structures. Several vehicles on the highway were swept away by the lahar, including those carrying some of the eruption's 57 victims. The highway was closed beyond the town of Toutle , controlled by a roadblock and an existing turnaround loop installed by Weyerhaeuser . Access to Kid Valley

9016-481: Was completed in 1903 by the Cowlitz County government, connecting Castle Rock to the shore of Spirit Lake by following the North Fork Toutle River. The 47-mile (76 km) highway was initially unpaved and characterized as rough and narrow, and several sections were improved or bypassed in the 1910s. It was added to the state highway system in 1937 as Secondary State Highway 1R (SSH 1R), terminating at

9114-502: Was completed on October 16, 1992. The expected influx of tourists and their potential impact on the recovering habitat around the volcano alarmed scientists looking to preserve areas for sensitive research. After finding that elk herds were leaving areas with improved highway access, the Forest Service established restricted zones within the national monument that prohibited off-trail hiking, pets, fires, and camping. Two additional visitor centers, Weyerhaeuser's Forest Learning Center and

9212-583: Was created at that time for the passenger-only Seattle-Vashon Ferry . According to the Washington State Department of Licensing , ocean beaches are legally state highways with a general speed limit of 25 mph (40 km/h), many only open to vehicles between the day after Labor Day and April 14, but state law places the beaches under the control of the Washington State Parks and Recreation Commission and only designates them as " public highways ". Most state routes are numbered in

9310-405: Was named after its inventor, Wendel Bollman , a self-educated Baltimore engineer. It was the first successful all-metal bridge design (patented in 1852) to be adopted and consistently used on a railroad. The design employs wrought iron tension members and cast iron compression members. The use of multiple independent tension elements reduces the likelihood of catastrophic failure. The structure

9408-683: Was popular with the Baltimore and Ohio Railroad . The Appomattox High Bridge on the Norfolk and Western Railway included 21 Fink deck truss spans from 1869 until their replacement in 1886. There are also inverted Fink truss bridges such as the Moody Pedestrian Bridge in Austin, Texas. The Howe truss , patented in 1840 by Massachusetts millwright William Howe , includes vertical members and diagonals that slope up towards

9506-417: Was rejected by state legislators due to its cost, despite attempts at salvaging the cheaper proposal by converting it into a toll road . From 2004 until 2006, increased volcanic activity at Mount St. Helens caused a surge in tourist traffic on SR 504, along with periodic shutdowns of the Johnston Ridge section. An evacuation of the area was ordered in early October 2004 due to seismic activity, indicating

9604-498: Was restored by early September using a temporary Bailey bridge over the Toutle River. The highway was extended to the debris and sediment dam and Weyerhaeuser's Camp Baker site in 1987 at a cost of $ 11 million (equivalent to $ 25.3 million in 2023 dollars). In 1982, the federal government designated the area around the volcano as the Mount St. Helens National Volcanic Monument and the state government designated SR 504 as

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