E 300 Roadway Design Controls and Criteria

In making a study for a new highway or the improvement of traffic conditions in existing streets, traffic data must be made available and included in the design considerations. (Pertinent traffic data for this purpose are available from either the Department of Traffic of the City of Los Angeles or the Division of Highways of the State of California.)1 Pertinent traffic data for this purpose are available from the City of Los Angeles Department of Transportation (LADOT). A subset of readily available traffic data can be accessed by activating the 'LADOT' layers when using the NavigateLA map data application. Additionally, the State of California Department of Transportation (Caltrans) provides access to traffic counts on the State Highway System only through the Traffic Census Program webpage. This data will indicate the level of service which the improvement is expected to provide, and such provisions as geometric features: width, alignment, grades, etc.

This chapter also covers the application of design criteria to the determination of grade. The term “grade” as used here will apply both to the vertical relationship between the road surface and the terrain and to the longitudinal rate of grade. The vertical alignment of grade line of a street in general is a series of straight lines and curves. The length of these lines is measured on the horizontal plane. For flat streets, using these horizontal lengths results in no practical errors. In steep grades, corrections may be necessary for calculations that require true lengths. For example, the true curb length on a 15 percent grade for a horizontal distance of 100 feet is 101.119 feet. For general criteria, vertical curve computations, and sight distances see Section E 420, Vertical Alignment, and Section E 440 Sight Distance.

The final location of the grade is affected by such factors as the street classification, terrain, topography, right-of-way, drainage, economics, available financing, etc. These factors are all interrelated and almost all apply in every design. Most of these factors have been discussed elsewhere in this Manual. Another controlling factor in grade location is the City’s specific policies in the application of the design criteria.

Footnotes

  1. The text in parenthesis is from the legacy Street Design Manual text and has been superseded by the italicized text that follows.
E 310 Traffic Data
E 320 Design Vehicle Physical Characteristics and Minimum Clearances
E 330 Speed
E 340 Highway (Street) Capacity
E 350 Drainage Controls and Criteria
E 360 Other Elements Affecting Geometric Design
E 370 Terrain and Land Development
E 380 Intersection Grades Controlled by Street Classification