CROSS SECTION ELEMNTS

Roadway - The portion of a highway, including shoulders for vehicular use.

Traveled way - The portion of the roadway for the movement of vehicles, exclusive of shoulders.

PAVEMENT

Surface Type

Surface Type = f(traffic volume/composition, design speed,soil conditions, weather, materials, etc)

Cross Slope

Undivided traveled ways on tangent or flat curve a crown or high point in the middle and a cross slope downward toward both edges

Unidirectional cross slopes for ramps and superelevated section

Breaks should be rounded using a parabolic curve.

Divided roadways: crown could be crowned on each traveled way or unidirectional cross slope is used.

PAVEMENT

Cross Slope

Surface Type Range in cross slope rate %

High 1.5 –2Low 2-6

Skid Resistance

Skid resistance should be a consideration in the design of all new construction and major reconstruction projects. Wet surface has a low skid resistance than dry surface.

Lane Width 2.7 – 3.6 m

SHOULDERSDefinition

A shoulder is the portion of the roadway contiguous with the traveled way that accommodate stopped vehicles, emergency use, and lateral support of subbase, base and surface courses.

Shoulder Graded Width ETW – the intersection of the shoulder slope

and the foreslope planes.

Usable Width see Exhibit 4-5 for the range.

Width of Shoulder 0.6 – 3 mWhere roadside barriers, walls, or other vertical elements are present, a minimum of 0.6 m should be provided from the outer edge of the usable shoulder. For low-volume roads, 1.2 m

SHOULDERSShoulder Cross Sections Concrete shoulder 2-6%

Gravel shoulder 4-6%Turf Shoulder 6-8%

Break of cross slope grades 8% rounded

Shoulder Stability Stable to support occasional vehicle loads in all kinds of weather without rutting

Shoulder Contrast Desirable to have shoulders with color and texture different from those on traveled way

Edge lines should be provided when shoulder use by bikes are expected.

Turnouts Turnouts to replace shoulders are needed for emergency stops in locations where shoulders are not feasible.

HORIZONTAL CLEARANCE

Horizontal clearance to obstructions should be considered. AASHTO Roadside Design Guide should be used for it.

A minimum of 3.0 m clear zone should be provided for low-speed rural collector and rural local roads.

The clear zone for freeways, rural arterials, and high-speed rural collectors should be determined using AASHTO Roadside Guide.

Urban streets, collectors, and arterials should have a min offset distance of 500 mm beyond the face of the curb.

CURBS

Type and location of curbs affects driver behavior and the safety and utility of a highway.

Curbs are used for drainage control, roadway edge delineation, ROW reduction, aesthetics, delineation of ped walkways, reduction of maintenance operations, and assistance in orderly roadside development.

Curbs on all low-speed urban highways. Caution on high-speed rural highways. When curbs are used on high-speed highways, they are placed at the outside edge of the shoulder.

CURBS

Configuration Two types of curbs: vertical and sloping curbs.

Vertical curbs discourage vehicles from leaving the roadway150 mm – 200 mm height.No use on freeways and high-speed highways

Sloping curbs Vehicles can cross the curbs. They are mountable under emergency conditions. Extruded curbs are sloped curbs.

The slope of the curb face is 1:1. Height 150 mm

Median edges or outer edge of shoulder

CURBS

Configuration

Gutter section may be designed along with curbs. Width of a gutter is 0.3 – 1.8 m.

Curb Placement

Curbs may be placed at the edge of the traveled way for low- speed urban streets, preferably with the offset of 0.3 – 0.6 m.

Vertical curbs cannot be placed along freeways or high-speed highways

DRAINAGE CHANNELS AND SIDESLOPES

Drainage Channels

Drainage channels collect and convey surface water from the highway ROW.

Drainage design often involve flat sideslopes, broad drainage channels, and literal warping and rounding.

Drainage channels should be designed along with the sideslopes

Drainage channels have roadside channels, toe-of-slope channels, intercepting channels, and flumes.

DRAINAGE CHANNELS AND SIDESLOPES

Sideslopes

Sideslopes should be designed to ensure roadway stability and to provide a reasonable opportunity for recovery for an out-of-control vehicle.

Three regions should be considered for the design of sideslopes: the top of the slope (hinge point), the foreslope, and the toe of the slope (intersection of the foreslope with level ground or with a backslope forming a ditch)

The hinge point and the toe of the slope should be rounded

TRAFFIC BARRIERS

Traffic barriers are used to prevent vehicles leaving the traveled way from hitting an object that has greater crash severity potential than the barrier itself.

There are two types of traffic barriers: longitudinal barriers and crash cushions.

Longitudinal Barriers Redirect errant vehicles.

Along the roadside and in median

Flexible, Semi-rigid, rigid = f(deflection)

Flexible: dynamic deflection, resistance from the tensile forceSemi-rigid: flexure and tensile Rigid: no deflection, energy dissipated by deformation.

Selection = f(barrier perf., lateral deflection, space availability)

TRAFFIC BARRIERS

Longitudinal Barriers

Roadside Barriers Shield vehicles from obstacles or slopes located along either side of a roadway.

Located beyond the edge of the shoulder to ensure that the full shoulder width may be used.

Median Barriers Minimize the possibility of an errant vehicle crossing into the path of traffic traveling in opposite directions.

Used for medians that separate traveled ways at different elevations or outer separations of 15 m or less where the frontage roads carry two way traffic.

TRAFFIC BARRIERS

Longitudinal Barriers

Bridge Railings Prevent vehicles, pedestrians, or cyclists from falling off the structure. It is a structure extension of a bridge.

Its design = f(geometric highway, design load, max. allowable material stress)

A roadside barrier is often used to tie with bridge railing. If roadside barrier is not used, end treatment with crash cushions should be considered.

Crash Cushions Decelerate errant vehicles to a stop.

At the end of a bridge railing, a gore area, or bridge piers

MEDIANS

A portion of a highway separating opposing directions of the travel way. Its width is measured from the edge of traveled way to the edge of another traveled way and varies fro\m 1.2 to 24 m.

Depressed Median: Median side slope 1:6 on freeways.Drainage inlets should be designed.

Raised Median: Arterial streets where left-turn movements should be regulated.

Flush median Urban Arterials. Now converting flush media to two way left turn lanes are commonly accepted.

FRONTAGE ROADS

Frontage roads control access to the arterials, act as a street road serving adjoining properties, or maintain circulation of traffic on each side of the arterial.

A minimum spacing of about 50 m between the arterial and the frontage roads should be provided in urban area.

Where offramps join a two-way frontage road, the potential for wrong way entry is increased.

Connection between the arterial and frontage road are important design element in an urban highway system

OUTER SEPARATIONS

The area between the traveled way of a through-traffic roadway and a frontage road or street is outer separation.

It is the buffer between the arterial and the frontage road and provides space for a shoulder for the through roadway and ramp connections to or from the through facility.

The cross section and treatment of an outer separation depend on the width and the type of arterial and the frontage road. See Exhibit 4-13 on Page 348.

NOISE CONTROL

Motor vehicles generate traffic noise. Designers should design noise barrier or sound walls to minimize the radiation of noise into noise-sensitive areas along the highway.

Before the sound walls design, designers need to evaluate existing or potential noise levels and estimate the effectiveness of reducing noise using sound walls.

A-scale on a standard sound level meter - dbA

An example of noise evaluation will be provided here.

Noise reduction designs: depressed highways, sound barriers, natural barriers (trees)

ROADSIDE CONTROL

Roadside control is the measure to control access from or to a highway.

Driveways: Design should be taken carefully on the location of driveways on highways.

Driveways used for right turns are desirable where cross section includes a curbed median or a flush median and median barrier.

Driveways = f(ROW, land use, functional classification of highway)

Guidelines for Driveway Design and Location is a good reference book.

Driveway regulations control ROW encroachment, driveway location, driveway design, sight distance, drainage, use of curbs, parking, setback, lighting, and signing.

ROADSIDE CONTROL

Mailboxes: Design should be taken carefully on the location of driveways on highways.

Driveways used for right turns are desirable where cross section includes a curbed median or a flush median and median barrier.

Driveways = f(ROW, land use, functional classification of highway)

Guidelines for Driveway Design and Location is a good reference book.

Driveway regulations control ROW encroachment, driveway location, driveway design, sight distance, drainage, use of curbs, parking, setback, lighting, and signing.

PEDESTRIAN FACILITIES

Sidewalks an integral part of city streets but are rarely provided in rural areas.

Sidewalk widths in residential areas vary from 1.2 m to 2.4 m.

Sidewalks should be constructed along any street or highway not provided with shoulders, even though pedestrian traffic may be light.

Pedestrian facilities such as sidewalks should be designed to accommodate people with disabilities.

AASHTO Guide for the Planning, Design, and Operation of Pedestrian Facilities

PEDESTRIAN FACILITIES

Grade-SeparatedPedestrian Crossings

A grade-separated pedestrian facility allows pedestrian and vehicles to cross at different levels, either over or under a

roadway.

Pedestrian overcrossings are preferable to undercrossings

Pedestrian ramps should be provided at all pedestrian separation structures.

Walkways for pedestrian separations should have at least 2.4 m.

PEDESTRIAN FACILITIES

Sidewalk Curb Ramps

When designing a project that includes curbs and adjacent sidewalks, proper attention should be given to the needs of persons with disabilities whose means of mobility are dependent on wheelchairs and other devices.

Factors for sidewalk curb ramps are :

sidewalk widthsidewalk location with respect to the back face of curbheight and width of curb cross sectiondesign turning radius and length of curve along the curb faceangle of street intersectionsplanned or existing location of sign and signal control devicesstorm water inlets and public service utilitiespotential sight obstructions, street width, border width, roadway grade in combination with the grades of the sidewalk, curb, ramps,

and gutter.

PEDESTRIAN FACILITIES

Sidewalk Curb Ramps

Basic curb ramp types have been established and used in accordance with the geometric characteristics of each intersection.

Width min = 0.9 m and 8.33% max grade

Cross slopes on adjacent sidewalks should be no greater than 2%.A level landing area is required at the top of each curb ramp.

The location of the sidewalk curb ramp should be carefully coordinated with respect to the pedestrian crosswalk lines.

Curb ramps for persons wit disabilities are not limited to intersections and marked crosswalks. They can also be needed at pedestrian concentrations such as loading islands and midblock crossings.

PEDESTRIAN FACILITIES

Sidewalk Curb Ramps

Each intersections will differ with respect to the intersection angles, turning roadway widths, size of islands, drainage inlets, traffic control devices, and other factors. An appropriate plan should be prepared that indicates all of the desired geometries, locations of the ramp.

The location of ramp governs the pedestrian crosswalk patterns, stop bar locations, and regulatory signs.

BICYCLE FACILITIES

AASHTO Guide for the Development of Bicycle Facilities

“Design of Bicycle and Pedestrian Facilities” Training course for Caltrans Engineers

BUS TURNOUTS

Bus turnouts serve to remove the bus from the traveled way. The location and design of the turnouts should provide ready access in the safest and most efficient manner practical.

Freeway Bus Its objective is to design the turnout to allow buses to Turnout decelerate, stand and accelerate in the area clear of and

separated from the traveled way

Arterial Bus A deceleration lane or taper to permit easy entrance toTurnout the loading area, a standing space sufficiently long to

accommodate the maximum number of vehicles expected to occupy the space at one time, and a merging lane to enable easy reentry into the traveled way.

AASHTO Guidelines for the Location and Design of Bus Stops

BUS TURNOUTS

Park and Ride Located adjacent to the streets or highways and visibleFacilities to commuters whom they are intended to attract.

PR lot = f(design volume, land area. Size and number of other parking lots in the area)

20 - 60 spaces.

A drop-off and a pick up facilities are needed.

Free parking

One exit and entrance / 500 spaces

more on AASHTO Guide for the Design of Parking-and-Ride Facilities

ON-STREET PARKING

When on-street parking is considered, parallel parking should be preferred.

A problem is the uneven distribution of off-street parking facilities within urban CBD and the lack of off-street facilities in urban neighborhood commercial area.

Exhibit 4-31 shows parking lane transition at intersection