CE562 Lecture 21 Collector Roads and Streets

2. Collector Roads and Streets Collectors serve the following functions: collecting traffic between local and arterial roads serving through traffic in local areas providing access to abutting properties Collectors serve a dual function and their level of design intermediates arterial and local road design.

3. Rural Collectors Design traffic volume is an average daily traffic (ADT) predicted for 20 year time horizon or shorter measured from the date of construction completion. Hourly design volume may be needed to analyze collector capacity.

4. Rural Collectors Stopping Sight Distance

5. Rural Collectors Passing Sight Distance

6. Rural Collectors Maximum Grades

7. Rural Collectors Alignment: Horizontal and vertical alignments should be considered in combination Cross slopes: Follow general rules Superelevation: A superelevation rate appropriate for the design speed and the radius. Maximum is 12% without ice and 8% with ice conditions expected. Number of lanes: The collector must accommodate the design volume at the desirable level of service. Two traffic lanes usually suffice. More lanes may be provided if justified by traffic and specific area.

8. Rural CollectorsTraveled Way Widths

9. Rural Collectors Foreslopes rates: Depend on soil stability but not higher than 1:3. Foreslopes 1:4 or flatter foreslopes and well-rounded ditch bottoms are recommended. Vertical clearance: At least 4.3 m with an allowance for future resurfacing. Horizontal clearance to obstructions Design speed 70 km/h or less - Three-meter clear zones Design speed 80 km/h or more - Refer to the AASHTO Roadside Design Guide Right-of-way width: Right-of-way should accommodate the construction, adequate drainage, and should ease a proper maintenance of a highway. Intersections: see Chapter 9

10. Rural CollectorsStructures

11. Urban Collectors The function of urban collectors is equally divided between mobility and access. Sometimes access control restrictions are needed. Design traffic volume is an ADT projected for at least 10 years and preferably 20 years. Hourly design volume is needed to analyze capacity of the collector. Design speed: Design speed of 50 km/h or higher should be used. See Exhibit 6-1. Sight distance: see Exhibits 6-2 and 6-3

12. Urban Collectors Grades: Residential streets should be consistent with terrain. Urban streets are generally depressed below the surrounding terrain to accommodate drainage from the adjacent properties. Minimum gradient for curbed streets is 0.3-0.5% (drainage consideration). See Exhibit 6-8 for maximum values, 5 % for sidewalks Alignment: Alignment of residential streets should fit closely the topography.

13. Urban Collectors Cross slope: Normally, the cross slope ranges between 1.5 and 3%. Superelevation may not be provided for low design speeds (70 km/h and below). Number of lanes: Two moving lanes are typical. In suburban areas, future converting of the shoulders into parking lanes or additional through lanes (curbs). In commercial areas, a continuous two-way left-turn lanes A highway capacity analysis to determine the number of lanes.

14. Urban Collectors Width of roadway: Moving lanes should be at least 3.0 m, where feasible - 3.6 m, in industrial areas - 3.6 m. Additional turning lanes should be preferably 3.0-3.6 wide depending on the percentages of trucks. Parallel parking lanes should be 2.1-2.4 m wide in residential areas, and 2.4-3.3 m wide in commercial and industrial areas. Angle parking only in special cases.

15. Urban Collectors Medians: Used for four or more traffic lanes. Types of medians include paint-striped separation, 0.6-1.2 m wide narrow raised or curbed sections, 0.6 to 1.8 m paint-striped or curbed sections, 3.0-4.8 m for separate left-turn lanes curbed sections, 5.4-7.5 m wide for protecting crossing vehicles and landscape treatment 8-12 m for parking inside the median Openings should be provided if needed where there is an adequate sight distance.

16. Urban Collectors Curbs: Urban collectors are normally curbed. The steep-face curb on the right of traffic should be 15 cm high . The type of a median curb depends on the median type and function. Low curbs where left turns use the median, 2.5-5 cm Vertical curbs to prevent the median crossing No curbs for painted medians Vertical curbs without gutter should be offset from the moving lanes at least 0.3 m , and with gutter - 0.6 m .

17. Urban Collectors Drainage: Surface runoff is gathered by a system of gutters, inlets, catch basins, and sewers. The gutter grade should be at least 0.3% (preferably 0.5%). Inlets or catch basins should be located in the gutter line. Sidewalks: Sidewalks should be situated on both sides of collectors that provide access to schools, parks, commercial areas, transit stops. In residential areas, sidewalks should be provided at least on one side of the collector, although two sidewalks are desirable. Clear sidewalk width should be at least 1.2 m in residential areas, and 1.2-2.4 m in commercial areas.

18. Urban Collectors Horizontal clearance to obstructions: At least 0.5 m of clear distance should be provided between the curb face and the obstruction. Urban collectors without curbs should have clear zones the same as on rural collectors. Right-of-way: The right-of way should be sufficient to accommodate all facilities required. The width should range between 12 m and 18 m depending on the local conditions.

19. Urban Collectors Vertical clearance: 4.3 m with an allowance for future resurfacing. Border area: The border width ranges from 2.4 m to 3.3 m. It should accommodate a buffer space between pedestrian and vehicular traffic, underground and above-ground utilities (traffic signals, parking meters, fire hydrants). Intersections: Type of traffic control, location of traffic control devices, auxiliary lanes, channelization should be considered. The geometric design includes capacity analysis. See Chapter 9