9 Preliminary Road Design Process
In the preliminary setting design process potential landings were identified. The next step in the design process was to connect these landings to existing roads in a logical fashion. This process is called "pegging in" the roads. During the preliminary analysis one must follow some general guidelines. These guidelines are outlined below.
9.1.1 Side Slope Considerations
Full Bench Road Prism
The HCP states that all roads constructed on side slopes in excess of 40% must be designed with a full bench road prism. On roads with side slopes between 40%-55% a full bench road prism is required, but the excess material can be sidecast and compacted. Any road that is constructed on side slopes over 55% must have a full bench road prism and any excess material endhauled to a suitable disposal site.
Balanced Cut/Fill Road Prism
On all roads constructed on side slopes of less than 40% a balanced cut/fill road prism may be used.
9.1.2 Road Grade Considerations
Favorable road grades are defined as the downhill travel of a loaded log truck. Truck performance, safety, and DNR road standards limit the favorable grade to 18%.
Adverse road grades are defined as the uphill travel of a loaded log truck. Truck performance and DNR road standards limit the adverse road grade to 12%.
9.1.3 Alignment Considerations
Horizontal Alignment
The minimum curve radius used in the preliminary design of horizontal curves was 60 feet. The minimum curve radius was increased to 80 feet for switchback curves.
Vertical Alignment
The maximum vertical break that our critical vehicle can negotiate is plus or minus 10%. Our preliminary designs were constrained to a maximum vertical break of plus or minus 6%.
Overall, an effort was made to minimize stream crossings. The HCP states that all crossing structures must be capable of passing the 100 year flood. Type 1, 2, and 3 streams were only crossed when absolutely necessary. During preliminary analysis, any Type 1, 2, or 3 crossing structure was assumed to be a bridge. In most cases, an alternate route was found as an alternative to a bridge. All Type 4 and 5 stream crossing structures were assumed to be corrugated metal pipes.