CE562 Lecture 24 Freeways

2. Freeways A freeway is the highest type of arterial highway with full control of access. Freeway elements: medians, grade separations, ramp connections, and frontage roads. Design speed ranges between 80 and 100 (110) km/h for urban freeways and 110 (80-100) km/h for rural freeways. Level of service Level-of-service C is acceptable in urban and developed areas, and level B in rural areas.

3. Design Traffic Volumes and LOS Prediction 20 years ahead Directional Design Hourly Volume (DDHV) for LOS C (D) for urban areas LOS B (C) for rural areas

4. Lanes and Shoulders Lane width is 3.6 m. Side slope between 1.5 and 2%, acceptable is 2.5% , unidirectional or two-way. Right shoulders - 3.0 m at least, 3.6 m where more than 250 trucks per hour (DDHV) Left (median) shoulders - 1.2-2.4 m on four-lane freeways, 3.0-3.6 m on wider freeways. Cross slope of shoulders between 2 and 6 %, at least 1% steeper than the adjacent through lane (on tangents). Superelevation max. 8-12% where snow and ice are not expected. Flatter superelevation rates are recommended. On viaducts should be smaller than 6-8 percent.

5. Maximum Grades

6. Vertical Clearance The vertical clearance should typically be 4.9 m. Smaller clearance of 4.3 m is allowable if larger clearance would be unreasonably costly and there is an alternative route with the 4.9-m clearance. The vertical clearance to sign trusses and pedestrian overpasses should be at least 5.1 m. An allowance should be added for future resurfacing.

7. Horizontal Clearance to Obstructions The clear zone should be consistent with the operating speed. Fixed objects should be relocated beyond the clear zone, or shielded, or made breakaway. Piers and walls should be located beyond the shoulder or better 0.6 m from the edge of the shoulder.

9. Rural Freeways Rural freeways have alignment and cross-sectional elements liberal in design. The design speed is 110 km/h and desirable level-of-service is B Foreslopes are 1:6 or flatter Backslopes are 1:3 or flatter Frontage roads are relatively short, normally with two-way traffic Intersections of frontage and cross roads are generally located as far as practical from grade seperations

10. Rural Freeways

11. Rural Freeways

13. Medians on Urban Freeways Medians should be as wide and flat as feasible. The minimum median width on four-lane freeway is 3.0 m (1.2+0.6+1.2). The minimum median width on freeway wider than four lanes is 6.6 m (3.0+0.6+3.0). If lanes are more than four and truck DDHV is larger than 250, then the minimum median width is 7.8 m (3.6+0.6+3.6). For the minimum widths, median barriers are required.

14. Depressed Urban Freeways Advantage: reduced is the impact on the adjacent areas. Disadvantage: increased is the cost for drainage (pumping stations).

15. Depressed Urban Freeways

16. Depressed Urban Freeways

17. Freeways on Viaducts The freeway may be elevated where the right-of-way is restricted, water table is high, or underground utilities are extensive, etc. Advantages: (1) all cross streets can be left open (frontage roads are not required), (2) existing utilities are hardly affected, and (3) detours during construction are limited, (4) space under the structure can be used for surface streets, parking, transit lines, or other purposes Disadvantages: (1) high cost of maintaining the structure, (2) closed drainage system, (3) icing, (4) poor appearance.

18. Freeways on Viaducts

20. Freeways on Viaducts

23. Freeways on Embankments

24. Ground-level Freeways

25. Ground-level Freeways

26. Combination-type Freeways

27. Combination-type Freeways

28. Combination-type Freeways

29. Combination-type Freeways

30. Combination-type Freeways

32. Public Transit on Freeways

33. Public Transit on Freeways

34. Public Transit on Freeways

35. Public Transit on Freeways

36. Public Transit on Freeways

41. Public Transit on Freeways