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

LOCAL RURAL ROADS

Constituted by the majority of two lane local roads

Design ADT 20 years after the date of completion ofconstruction or 20 years from the current year

Design Speed see Exhibit 5-2

Sight Distance see Exhibit 5-2 for SSDsee Exhibit 5-3 for PSD

Grades Maximum grade see Exhibit 5-4Minimum grade see P242.

Alignment consistent and smooth two-lane alignment

Cross Slope 1.5 –2 for high-type pavement2-6 for low-type pavementsee Exhibit 5-5

Superelevation e no more than 12% generallye no more than 8% at snow and ice conditions

StructureBridges to remain Standard Specifications for Highway BridgesIn place see Exhibit 5-6 and Exhibit 5-7

Vertical Clearance at least 4.3 m

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 HThe ditch bottom and slopes should be rounded.The backslope should not exceed the maximum required for stability.

H. Clearance toObstructions 2-3 m clearance from the ETW

Curbs see curbs in the Local Urban Streets

IntersectionDesign no intersection on a short-crest vertical curve or

on a sharp horizontal curve. More on Chapter 9 on Intersections Design

LOCAL RURAL ROADS

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% General8% for commercial and industrial areasdesirable 0.3% min for streets with outer curbs

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 mcannot be less than 25 m for a 30 km/h design speed

Cross Slope 1.5 – 2 for high-type pavement2-6 for low type pavement

Superelevation Usually superelevation is not needed in residential and commercial areas. When superelevation is used, emax = 4

Number ofLanes At least one unobstructed moving lane must be ensured

even where parking occur on both sides.

Roadway Width 3.0 – 3.6 m/lane

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.

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 CurbRamps 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 WidthsFor Bridges see Exhibit 5-6

H. Clearance toObstructions A min. 0.5 m should be provided between the curb face

and obstructions.

LOCAL URBAN STREETS

Vertical Clearance at least 4.3 m

Border Area A border area should be provided along street for the safety of motorists and pedestrians as well as for aesthetic reasons. 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 5-11Lighting

LOCAL URBAN STREETS

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 road50 km/h – circulation roads40 km//h – area roads

Design Vehicle: Motor homes, vehicles with trailers, PU

SPECIAL PURPOSE ROADS

Recreational Roads

Sight Distance See Chapter 3SSD 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/hf different in Exhibit 5-16.

SPECIAL PURPOSE ROADS

Recreational Roads

Number of Lanes Two-way one lane for < 100 veh/hturnouts 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 5-18cross slope for local rural roads are applicable

Clear Recovery Zone 3 m or more recovery area

Roadside Slope 1v:4 HRoadside Barrier see AASHTO Roadside Design Guide

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.

SPECIAL PURPOSE ROADS