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INTRODUCTION

INTRODUCTION. This chapter presents guidance on the application of geometric design criteria to facilities functionally classified as local roads and streets.

krystyn-norb
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INTRODUCTION

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  1. INTRODUCTION This chapter presents guidance on the application of geometric design criteria to facilities functionally classified as local roads and streets. Local roads and streets constitute a high proportion of the roadway mileage in the United States. They provide access to farms, residences, businesses or other abutting properties. Traffic volume greater than 400 veh/day is one of the design criteria for design of local roads and streets. Roads less than 400 veh.//day are not applicable to the design criteria in this chapter. AASHTO is working on the design of these types of roads. This chapter discusses three types of roadways: Local Rural Roads, Local Urban Streets, and Special Purpose Roads

  2. LOCAL RURAL ROADS Constituted by the majority of two lane local roads Design ADT 20 years after the date of completion of construction or 20 years from the current year Design Speed see Exhibit 5-2 Sight Distance see Exhibit 5-2 for SSD see Exhibit 5-3 for PSD Grades Maximum grade see Exhibit 5-4 Minimum grade see P242.

  3. LOCAL RURAL ROADS Alignment consistent and smooth two-lane alignment Cross Slope 1.5 –2 for high-type pavement 2-6 for low-type pavement see Exhibit 5-5 Superelevation e no more than 12% generally e no more than 8% at snow and ice conditions Structure Bridges to remain Standard Specifications for Highway Bridges In place see Exhibit 5-6 and Exhibit 5-7 Vertical Clearance at least 4.3 m

  4. LOCAL RURAL ROADS ROW Width Should be acquired to accommodate construction, adequate drainage, and proper maintenance of a highway Foreslope Not steeper than 1V:2 H The ditch bottom and slopes should be rounded. The backslope should not exceed the maximum required for stability. H. Clearance to Obstructions 2-3 m clearance from the ETW Curbs see curbs in the Local Urban Streets Intersection Design no intersection on a short-crest vertical curve or on a sharp horizontal curve. More on Chapter 9 on Intersections Design

  5. LOCAL URBAN STREETS A local urban street is a public roadway for vehicular travel including public transit and refers to and includes the entire area within the ROW. It also serves pedestrians and bike traffic and accommodate public utility facilities in the ROW. Design ADT 2 or 4 lanes = f(traffic volume) 10 or 20 years after the date of completion of construction Design Speed 30 –50 km/h. Not a controlling factor in design. In the typical street grid, the closely intersections limit travel speeds, making the design speed less important. Sight Distance 30 – 60 m depending on design speed (see Exhibit 3-1) Grades < 15% General 8% for commercial and industrial areas desirable 0.3% min for streets with outer curbs

  6. LOCAL URBAN STREETS Alignment fit with the existing topography to minimize the needs for cuts or fills; discourage through traffic Min. Radius of a horizontal curve 30 m cannot be less than 25 m for a 30 km/h design speed Cross Slope 1.5 – 2 for high-type pavement 2-6 for low type pavement Superelevation Usually superelevation is not needed in residential and commercial areas. When superelevation is used, emax = 4 Number of Lanes At least one unobstructed moving lane must be ensured even where parking occur on both sides. Roadway Width 3.0 – 3.6 m/lane

  7. LOCAL URBAN STREETS Parking Lanes A parallel parking lane a min. 2.1 m wide should be provided on one or two sides in residential areas. 2.4 m for commercial and industrial areas. Medians Median openings should be located with adequate sight distance. Shape and length of the median openings = f(median width, and vehicle type to be served) Curbs Streets normally are designed with curbs. The curbs are 100 mm to 150 mm high. Vertical curbs with 150 mm high or more should be offset at least 0.3 m. Drainage gutter min. grade = 0.3%. Surface water are collected by curbs, gutters, and ditches and conveyed to a drainage system Cul-De-Sac and Turnaround Min. outside radius 10 m – 15 m. See Exhibit 5-8.

  8. LOCAL URBAN STREETS Alleys Alleys provide access to the side or rear of individual land parcels. They are a narrow ROW and range from 5-6 m (width) in residential areas and up to 10 m in industrial areas Sidewalks Desirably on both sides of streets. Min. width is 1.2 m. Sidewalk Curb Ramps See AASHTO Guidelines for the Planning, Design, and Operation of Pedestrian Facilities. Driveways Driveway returns should not be less than 1 m in radius. Roadway Widths For Bridges see Exhibit 5-6 H. Clearance to Obstructions A min. 0.5 m should be provided between the curb face and obstructions.

  9. LOCAL URBAN STREETS Vertical Clearance at least4.3 m Border Area A border area should be provided along street for the safety of motorists and pedestrians as well as for aestheticreasons. It is the area between the roadway and ROW. 1.5 m to 3.0 or wider ROW Width varies in order to accommodate planned roadway. Intersection Designs see Chapter 9 Street and Roadway see Exhibit 5-11 Lighting

  10. SPECIAL PURPOSE ROADS Special purpose roads include recreational roads, resource recovery roads, and local service roads. Recreational Roads Criteria are to protect and enhance the existing aesthetic, ecological, environmental, and cultural amenities. Recreational roads involve three types of roads: primary access roads, circulation roads, and area roads. See Exhibit 5-12. Design Speed: 60 km/h – primary access road 50 km/h – circulation roads 40 km//h – area roads Design Vehicle: Motor homes, vehicles with trailers, PU

  11. SPECIAL PURPOSE ROADS Recreational Roads Sight Distance See Chapter 3 SSD should be measure with an eye height of 1080 mm and an object height of 1300 mm. The SSD is doubled for a two-way single lane road. See Exhibit 5-13. PSD see Exhibit 5-14. Grades see Exhibit 5-15 for max grade Vertical Alignment see Exhibit 5-1. SSD doubled on two-way, one lane road. Horizontal Alignment emax = 6% no SE on roads with design speed of 30 km/h f different in Exhibit 5-16.

  12. SPECIAL PURPOSE ROADS Recreational Roads Number of Lanes Two-way one lane for < 100 veh/h turnouts at max. interval of 300 m should be provided when two-way and one lane is considered. Turnouts should be >3 m wide, 15 m long and a taper of 8 m at two ends. See Exhibit 5-17 Cross Section See Exhibit 5-18 cross slope for local rural roads are applicable Clear Recovery Zone 3 m or more recovery area Roadside Slope 1v:4 H Roadside Barrier see AASHTO Roadside Design Guide

  13. SPECIAL PURPOSE ROADS Resource Recovery Roads Mining and logging roads are the resource recovery roads. Criteria are same as those for recreational roads. SE emax = 6% Grades considering the requirements of large loaded vehicles Design Speed See Exhibit 5-19 Local Service Roads Those serving isolated areas that have little or no potential for further development. Criteria are same as those for recreational roads.

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