History of Rim Drive, Crater Lake National Park
Design and Construction of Circuit Roads
NPS Collaboration with BPR
The NPS gained a measure of control over its need to continually upgrade park roads in the face of increased vehicle speeds and a massive increase in automobile ownership with passage of legislation in 1924 authorizing annual appropriations specifically for this purpose. After working to solidify a working relationship with BPR over the next year or so, NPS director Stephen T. Mather signed an inter-bureau agreement on January 18, 1926. Under its terms, the NPS and BPR were to use “every effort to harmonize the standards of construction” they employed with those of the Federal Aid Highway system located outside the parks, while at the same time securing the “best modern practice” in locating, designing, constructing, and improving park roads. The inter-bureau agreement stipulated that the NPS reimburse BPR for overhead expenses from the annual appropriations for park roads. This included various levels of investigation and survey, the preparation of bid documents (derived from the plans, specifications, and estimates, known as PS&E), as well as salaries for engineers to supervise and inspect contracted work.
Once initiated, projects followed a familiar sequence that began with road location. After reconnaissance, engineers did a preliminary survey (or P-line) of the road location to obtain topography for representative cross sections. The P-line allowed for curvature and connecting tangents to be placed by “projection” back in the office, a step resulting in the semi-final location (or L-line). Staking in the field, or final location, necessitated the establishment of benchmarks on the ground, as well as any adjustments to grade or positioning of cross-drainage. All stages of road location were subject to NPS approval, with most of the changes provided by landscape architects.
The process of road design along Rim Drive was shared between the BPR and NPS. At a landscape scale, BPR designed three basic elements of the road: horizontal alignment, vertical alignment, and cross-section. The design of curves and tangents in a planar relationship is horizontal alignment, with preference given to use of spiral transition curves instead of tangents throughout most of the circuit. These made for a sympathetic alignment in relation to the park landscape, but also brought average speed and design speed closer together for the purposes of safety. Vertical alignment or “profile” is how the located line in plan view fits the topography in three dimensions, especially in reference to grade, sight distance, and cross drainage. The banking or “superelevation” of curves represented one particularly significant part of vertical alignment, since adequate sight distance in relation to the design speed needed to be maintained, particularly where a combination of curvature and grade occurred. The third element, cross-section, is a framework in which to place individual features and their relationship to each other. Features such as road width, crown, surface treatment, and slope were usually depicted through drawings of typical sections.
At the scale of individual features, the NPS worked to provide the BPR with standard guidance for the design of road margins (shoulder, ditch, bank sloping), drainage structures (culvert headwalls and masonry “spillways”), and safety barriers (masonry and log guardrails) along Rim Drive. As the lead NPS landscape architect for much of the project, Francis Lange produced planting plans in conjunction with a number of site plans for areas along the road corridor that needed individualized treatment beyond the standard measures described in the contract specifications.
Scott Bluffs parking area with Mount Scott in the distance.
Road construction consisted of three types of contracts beginning with the grading phase. There were numerous items on which contractors bid on the basis of unit prices for each. BPR engineers, in consultation with NPS engineers and landscape architects, provided estimates for the items, starting with clearing vegetation from the roadbed. Removing stumps and other obstacles to rough grading through blasting or burning constituted a separate item called grubbing. The subsequent rough grading with heavy machinery began with excavation, usually divided into separate bid items called “unclassified” and “Class B,” with the latter often specified by the NPS to avoid damage to natural features. Rough grading also included items such as moving excavated material based on estimated volumes needed for cuts and fills, placement of concrete or metal culverts as cross-drainage, as well as the flattening of slopes at prescribed ratios to control erosion. Completing the earth-graded road involved several items under the heading of “finish grading.” This step included fine grading of the sub-base and shoulders, as well as bank sloping. Depending on how much funding was available, subcontractors handled the stone masonry for culvert headwalls, guardrails, and retaining walls at this stage. Other subcontracted items under the heading of finish grading included old road obliteration and special planting once bank sloping had been accomplished.
With the grading phase completed, a separate contract for preliminary surfacing could be let. This next phase of road construction involved laying a base course of crushed rock on the roadway, followed by a top course of finer material to provide a definite thickness and protection for the earthen road underneath. This type of contract might include items, usually subcontracted, such as building masonry structures like guardrails (often on fills created during rough grading that had to settle over the winter) or special landscaping provisions to be completed as part of executing site plans or working drawings provided by the NPS.
Bituminous surfacing, or paving with asphalt, was done through another contract. This phase of road construction involved laying aggregate (crushed stone and sand) along a specified width of roadway as a base, followed by placing a bituminous “mat” as binder. The thin surfacing of bitumens known as a “seal coat” served as the final step. Completion of the paving contract generally signified the end of BPR involvement with construction. Road maintenance and post construction items thus became NPS responsibility.
Reconstructing 3 miles of approach road between Park Headquarters and Rim Village set the NPS/BPR collaboration in motion at Crater Lake. With the location survey completed several months prior to formal approval of the inter-bureau agreement, the grading contract commenced during the summer of 1926. The project reduced the maximum grade (from 10.9 percent to 6.5 percent) of this approach and produced a new roadway 20′ in width. As a precursor to reconstructing the Rim Road, this realignment became known for how visitors obtained their first view of Crater Lake as a spectacular and sudden scenic encounter. Landscape architects with the NPS chose the point of “emergence,” one allowing visitors to enter a new “plaza” developed on the western edge of Rim Village or begin a circuit around the lake.
The initial step in planning for reconstruction of the Rim Road took place once the inter-bureau agreement had been signed. The BPR reconnaissance survey of the park’s road system in 1926 furnished a starting point and allowed Superintendent C.G. Thomson to reference estimated construction costs in a report on his priorities for road and trail projects over the next five years. NPS officials in Washington requested the report in connection with allocating the congressional appropriation for park roads and trails, a separate process from the site development plans of the period that were aimed at facilities for areas like Rim Village.
Rudimentary lists of projects with estimated costs evolved over the next five years into a bound set of drawings by landscape architects showing the proposed site development in the context of projected park-wide circulation. Formal adoption of these “master plans” by the NPS came as appropriations for park development steadily increased, but these documents remained apart from planning for the location and design of roads. BPR accomplished these tasks through its usual process prior to letting contracts for road construction, subject to NPS approval. Master plans contained some information about Rim Drive and other road projects, but only as context for what the NPS landscape architects hoped to accomplish in a “minor developed area” such as the Diamond Lake (North) Junction or at the “parking overlooks” like Kerr Notch, Skell Head, or Cloud Cap.