Nonstandard Design Features. The project does not propose to change any geometric features. According to Design Information Bulletin 81-02, a Design Standard Decision Document or Memo to File is not required. Per DIB-81-02, Table 5-1 lists the nonstandard design features to remain under the Build Alternative. The table also lists the relevant design standards and the justification for keeping the nonstandard features unchanged. Table 5-1: Nonstandard Design Features to Remain Under the Build Alternative Matrix of Nonstandard Design Features Alternative Design Standard Nonstandard Design Features to Remain Justification for Keeping Nonstandard Features Unchanged Build Alternative HDM Index 301.1 (Lane Standard Width) Lane width is less than 12 feet. The nonstandard lane width originated from the existing roadway cross sections and will remain. Build Alternative HDM Index 302.1 (Shoulder Standard width) Shoulder width is less than 10 feet for the mainline and less than 8 feet for ramps. The nonstandard shoulder width originated from the existing roadway cross sections and will remain. Build Alternative HDM Index 304 (Side Slopes of 4:1 or Flatter) Side slopes are steeper than 4:1. The nonstandard side slopes originated from the existing roadway cross sections and will remain. Build Alternative HDM Index 305.1 (Median Standard Width) Median width is less than 36 feet from PM 0.0 to PM 9.0. The nonstandard median width originated from the existing roadway cross sections and will remain. Notes: HDM = Highway Design Manual PM = post mile Interim Features The project does not involve interim features. High-Occupancy Vehicle Lanes The project is not proposing HOV lanes.
Nonstandard Design Features. The project proposes to maintain the existing nonstandard features. The approval date for the Existing Features to Remain: Memo to File is August 23, 2020. The details of the nonstandard features to remain are discussed below. Stopping Sight Distance (M1) The existing posted speed for the corridor is 65 miles per hour (mph), and the project will maintain this existing speed. The design speed for freeways in urban areas varies from 55 mph to 80 mph. The design speed for the project is 70 mph. The existing horizontal and vertical curves along I-80 within the project limits provide stopping sight distances that vary from 311 feet to greater than 750 feet (40 mph to 70 mph), and the project will maintain the existing vertical curve sight distances. Median Width (M2) Nonstandard median widths of 6 feet to 12 feet are proposed between “WB3” Station (Sta.) 296+00 and “WB6” Sta. 1125+00, where the project conforms to existing conditions. Table 5-1 lists the existing and proposed median widths within the project limits. Table 5-1: Existing and Proposed Median Widths Page Number* Location Existing Median Width Proposed Median Width P12 to P27 "WB4" 548+00 to "WB5" 756+00 6 6 P30 to P41 "WB5" 791+00 to "AM4" 954+00 6 6 P41 to P54 "AM4" 954+00 to "WB6" 1122+00 12 12 * “Page Number” refers to the layout page number; see Attachment C.
Nonstandard Design Features. A Design Standard Decision Document was approved on October 2nd, 2020. The proposed project requires the following nonstandard design features: HDM Section 304.1 titled Side Slope Standards states “In light grading where normal slopes catch in distance less than 18 feet from the edge of the shoulder, a uniform catch point, at least 18 feet from the edge of the shoulder, should be used.” Uniform grading standard is meant for construction production efficiencies for larger production projects. This standard does not address safety or the Federal Highway Administration (FHWA) 10 controlling criteria and will not be classified in the same category because of the proposed nature of improvements.
Nonstandard Design Features. Exceptions from the Caltrans Highway Design Manual (HDM) design standards have been identified for the preferred alternative and it was determined there one bold face design standard and two underlined design standards required written approval. The Design Standard Decision Document (DSDD) was approved on February 9, 2021. The approved cover sheet for the DSDD is provided in Attachment L. The following table summarizes the approved nonstandard design features for the recommended preferred alternative. Design Features with Headquarters Approval Authority (Bold Face) HDM Section Description of Design Standard Minimum Standard Comments 501.3 Local Interchange Spacing to Freeway-to- Freeway Connectors 3 miles The existing nonstandard interchange spacing of 2.15 miles is being maintained to avoid excessive cost, environmental impacts, and opposition from the local agency to close adjacent interchanges. The length between the International Parkway interchange and I- 580/I-205 interchange to the north is an existing condition with a formally executed freeway agreement. Design Features with District Delegated Approval Authority (Underlined) 304.1 Embankment Side Slope 4:1 This nonstandard feature of a 2:1 side slope is to avoid excessive cost to acquire additional right-of-way from an adjacent private property with agriculture land use in the northeast quadrant of the interchange. The existing WB I-580 direct off-ramp proposed to be removed and replaced with the new realigned direct off-ramp has existing nonstandard side slopes steeper than 4:1 in a similar location to the new off-ramp with guard railing systems. Design Features with District Delegated Approval Authority (Underlined) HDM Section Description of Design Standard Minimum Standard Comments
Nonstandard Design Features. The geometrics of the existing and proposed facility will be checked for nonstandard features and a list of mandatory and advisory design exceptions will be identified and submitted to Caltrans for review and comments. GHD assumes that there will be four (4) design exceptions. Geometric refinements will be investigated to assess if any nonstandard features can be eliminated and agree on the advisory and mandatory design exceptions to be requested during the PA&ED Phase. Draft and final versions of advisory and mandatory fact sheets will be submitted to obtain geometrical concurrence from Caltrans.
