INTRODUCTION

1. INTRODUCTION This chapter presents guidance on the application of geometric design criteria to freeways which are arterials highways with full control of access. Control of access refers to the regulation of public access right to and from properties abutting the highway. Access is provided only to selected public roads through ramps and connectors. No crossings at grade and no direct private driveway connections. Elements of freeways include the roadway, medians, grade separations at crossroads, ramps to and from the traveled way at selected locations, frontage roads (optional). This chapter discusses two types of freeways: Rural freeways and Urban freeways.

2. GENERAL DESIGN CRITERIA The general design criteria are applied to both rural and urban freeways. Design Speed Urban > 80 km/h minimum speed = 100 km/h many urban freeways = 110km/h corridor of mainlines Rural 110 km/h Mountainous 80 – 100 km/h Design Traffic Volumes Traffic projections for a 20 year period. LOS For acceptable degrees of congestion, freeways and their auxiliary facilities (ie. Ramps, mainline weaving sections, and C-D roads in urban and developing area) should generally be designed for LOS C D for heavily developed sections of metropolitan areas B for through and auxiliary lanes for rural freeways.

3. GENERAL DESIGN CRITERIA The general design criteria are applied to both rural and urban freeways. Pavement and A minimum of two through lanes for each direction. Shoulder Each lane 3.6 m wide, cross slope 1.5 –2 %. The usable shoulder width is at least 3.0 on both sides. When DDHV for truck exceeds 250 veh/h, the right shoulder width is 3.6 m. Median shoulder is 1.2 to 2.4 m for four lane freeways. Shoulder cross slope 2-6%. Curbs caution should be exercised in the use of curbs on freeways. When used, they should be beyond the outer of edge of shoulder and traversable. Superelevation Full SE rates are generally not applicable to elevated freeways on viaducts. 6-8 % for viaduct. 8-12% for areas that do not have concerns on snow and ice factors

4. GENERAL DESIGN CRITERIA The general design criteria are applied to both rural and urban freeways. Grades see Exhibit 8-1 Structures Standard Specification for Highway Bridges AASHTO LRFD Bridge Design Specification Traffic Load is MS-18. The clear width of bridges as wide as the approach roadway. Vertical at least 4.9 m over the entire roadway width including Clearance auxiliary lanes and the usable width of shoulders. Hor. Clearance see AASHTO Roadside Guide To Obstructions Non-traversable obstacles within the clear zones should be shielded by an appropriate barrier as long as the barrier represents a lower potential for severe crashes.

5. GENERAL DESIGN CRITERIA The general design criteria are applied to both rural and urban freeways. Ramps and Terminals see Chapter 10 Outer Separations An outer separation is defined as the area between Borders the traveled way of the main lanes and a frontage Frontage Roads road or local street. A border is the area between the frontage road or local street and the private development along the road. A border is also the area between the traveled way of the main lines and the ROW limit when no frontage roads exist.

6. RURAL FREEWAYS Alignment and Smooth flowing horizontal and vertical alignments. Profile Medians See Exhibit 8-3 15-30 m is common on rural freeways Median widths in the range of 3.0 – 9.0 m may be needed where ROW restrictions dictate or in mountainous terrain. emergency crossover should be provided when interchange spacing exceeds 8 km. Sideslopes Flat, rounded side slopes, fitting with the topography and consistent with available ROW should be provided on rural freeways. 1 V : 6 H Frontage Roads Frontage roads are usually intermittent and short along rural freeways.

7. URBAN FREEWAYS Urban freeways are classified as depressed, elevated, ground-level or combination-type. Median on urban freeways should be as wide and flat as practical. The min. median width is 3.0 m (1.2 shoulders and o.6 m median barrier) for a four lane urban freeway 6.6 m for six or more lanes. 7.8 m when DDHV for truck traffic exceeds 250 veh/h. Median crossovers for emergency or maintenance purposes are not warranted on urban freeways.

8. URBAN FREEWAYS Depressed Urban Freeways A Depressed freeway is located at approximate depth of 4.9 m in addition to the clearance for structural depth below the surface of the adjacent streets. Drainage is critical in the design of a depressed freeway. Fences should be provided on structures passing over the depressed freeway and retaining walls in order to prevent objects being dropped or thrown onto vehicles below. Slopes and Walls side slopes of a depressed freeway are designed in the same manner as those for cut slopes. Very (see Exhibit 10-6) often fore slopes are not used beyond the shoulder on depressed freeways. When retaining walls are used, they should be located no closer to the roadway than the outer edge of shoulder and should be 0.6 m beyond the outer edge of shoulder.

9. URBAN FREEWAYS Depressed Urban Freeways Typical Cross see Exhibits 8-4 to 8-6. Section Outer separation, medians, and borders can be adjusted to fit with the high-cost ROW. Restricted Cross see Exhibit 8-5A Section Walled Cross Exhibit 8-6 Section

10. URBAN FREEWAYS Elevated Urban Freeways An elevated freeway may be constructed either on a viaduct or an embankment. It may be appropriate in level terrain where restricted ROW, high water table, extensive underground utilities, close pattern of streets to be retained.