geometric review and design (grad) 5median width is 60-84 feet. 84-foot wide median allows for a...

Geometric Review and

Design (GRAD)

Cross Sections

5

52 | Module 5 – Cross Sections

ODOT L&D Vol. 1 – Section 300

▪ Understand the

elements comprising

the roadway cross

section

▪ Recognize the grading

options outside of the

roadway limits

▪ Understand the various

barrier options

available

Learning Objectives



▪ Section 301

▪ Assists the designer in determining lane and shoulder width and pavement cross slope.

▪ Number of lanes required is determined through use of capacity analysis

▪ Pavement type determined by volume and composition of traffic, soils, availability of materials, initial costs, maintenance costs

Roadway Criteria



The Typical Section

Traveled WayMedian Backslope

Shoulder –treated and

graded

Foreslope and Ditch



▪ Lane Width (Sect 301.1.2)

▪ Lane width in RURAL areas is dependent upon functional classification, traffic volumes, and design speed

▪ Refer to Section 105.3 for the National Network** lane width requirements

Pavement

** National Network is comprised of all Interstate Routes and Federal Aid Primary Routes – refer to TIMS for locations



▪ Lane Width (Sect 301.1.2)

▪ Lane width in URBAN areas is dependent upon functional classification and locale

▪ Refer to Section 105.3 for the National Network lane width requirements

Pavement



▪ Traveled Way widening on curves

(Sect 301.1.3)

▪ Used to accommodate WB-62 truck tracking

▪ Based on design speed, curvature, and traveled way width

▪ Placed on inside of curve

▪ Develop within the superelevation transitions

Pavement



▪ Pavement Transition / Taper

Rates (Sect 301.1.4)

▪ High Speed (≥ 50 mph)

▪ 𝐿 = 𝑊 𝑥 𝑆

▪ Low Speed (< 50 mph)

▪ 𝐿 =𝑊 𝑥 𝑆2

60

▪ Transition length for INCREASES in Traveled Way maybe more abrupt (i.e. 5:1 ratio)

Pavement

L = Taper Length (feet)

W = Offset width (feet)

S = Design Speed (mph)



▪ Pavement Cross Slope (Sect 301.1.5)

▪ Normal Crown (NC) = 0.016 ft/ft

▪ Can increase to 0.02 ft/ft

▪ Drainage issues or pavement type

▪ 3 or more lanes sloped in same direction on high speed roadway –

first two lanes sloped at 0.016; additional lanes are at 0.02

Pavement



▪ Pavement Cross Slope (Sect

301.1.5)

▪ Example Problem

Pavement




301.1.5)

▪ Example Problem

Pavement



▪ Pavement Cross Slope (Sect 301.1.5)

▪ General Guidance:

▪ Crowns located between lanes (on a lane

line)

▪ 3 or 4 lane roadways, lanes can be

sloped in same direction as shown in

previous example

▪ Undivided roadways – crown at the

middle (even number of lanes) and at

the left or right edge of center lane (odd

number)

▪ Narrow raised median sections crowned

to outside as much as possible

Pavement



▪ Adjacent to Traveled Way

▪ Used to accommodate stopped

vehicles, emergency use,

maintaining traffic during

construction, lateral support of

the pavement, and to generally

improve the safety of the

highway

▪ Available for pedestrians and

bicyclists

Shoulders



▪ Definitions (Sect 301.2.1)

▪ Graded Shoulder Width – The area located between the edge of traveled way and the foreslope begin point

▪ Treated Shoulder Width – The portion of the graded shoulder which has some type of surface treatment

Shoulders



▪ Types (Sect 301.2.2)

▪ Paved

▪ Bituminous surface treated

▪ Stabilized aggregate

▪ Turf

▪ Refer to Pavement Design Manual

(Office of Pavement Engineering) for

structural design of shoulders and

shoulder typical sections

ShouldersPaved

Bituminous Aggregate

Turf



▪ Width (Sect 301.2.3)

▪ Shoulder widths in RURAL areas

vary depending on functional

classification, traffic, and locale.

▪ High truck volume could

necessitate wider shoulders

▪ If Treated Shoulder width is

increased, Graded Shoulder width

should be increased by the same

amount (MOT condition typically)

▪ Treated Shoulder width can be

reduced without impacting Graded

Shoulder width

Shoulders




▪ Shoulder widths in URBAN areas vary depending on functional classification and locale.

▪ For ADTs of 400 or less, may

be beneficial to use

AASHTO’s Guidelines for

Geometric Design of Very

Low-Volume Local Roads

publication

Shoulders




▪ Sometimes a wider paved shoulder is provided for MOT or to accommodate HSSD.

▪ Paved shoulder width reduction of less than 2 feet (at signs or lighting) will not require design exception; 4-foot minimum lateral clearance must be provided

Shoulders



▪ Right Turn Lane (Sect

301.2.3.1)

▪ Desirable to maintain the required mainline shoulder width throughout the length of right turn lane

▪ Shoulder may be reduced, but to no less than 4 feet paved and 6 feet graded (constrained R/W limits and low truck volumes)

Shoulders



▪ Shoulder Taper Rate (Sect

301.2.3.2)

▪ 25:1 should be used to reduce the shoulder width

▪ Transition length for INCREASES in shoulder width maybe more abrupt (i.e. 5:1 ratio)

Shoulders



▪ Shoulder Cross Slope (Sect

301.2.4)

▪ Depends on the shoulder type and pavement cross slope

▪ If the bridge shoulder cross slope is different than the approach roadway shoulder cross slope, then the transition shall occur on the roadway section (off of bridge and approach slabs) within a distance of 100 feet.

Shoulders



Shoulders



▪ Shared Lanes (Sect. 308.3) and Paved

Shoulders (Sect. 308.4)

▪ Lane width of shared bicycle/vehicle lanes should be 14 feet minimum

▪ When utilizing paved shoulders on uncurbed roadways, provide minimum 4-foot wide shoulders

▪ Provide 5-foot wide shoulders to the face of vertical obstructions such as guardrail, curb or other roadside barrier

▪ Refer to Multi-Modal Design Guide *

Bicycle Facilities

*currently in development



▪ Bicycle Lanes (Sect. 308.5)

▪ Along two-way streets, should be provided on both sides to discourage wrong-way use.

▪ Along one-way streets, should be on the right-hand side of the roadway unless significant number of left-turning bicyclists or large number of potential conflicts (drives, sidestreets, etc.) on the right side.

Bicycle Facilities



▪ Bicycle Lane Widths (Sect.

308.5.4)

▪ Minimum lane width is 4 feet; 5 feet against curb/vert surface

▪ Preferred lane width is 5 feet

▪ Adjacent to a parking lane, a wider bicycle lane (6-7 feet) provides space to avoid impacting opening vehicle doors

▪ Areas of high bicycle use, width of 6 to 8 feet is preferred to promote side-by-side riding

Bicycle Facilities



▪ Section 702

▪ Multi-use paths designed primarily for

use by bicyclists and pedestrians;

physically separated from vehicular

traffic by an open space or barrier

▪ Fall under accessibility requirements

of the ADA

▪ Paths within public R/W that function

as sidewalks should meet PROWAG

guidelines

▪ Paths outside of public R/W should

meet ANPRM draft guidelines

Shared Use Paths



▪ Elements of Design (Section 702.2)

▪ Determine the Design User

▪ Width – min of 10 feet for two-directional path;

widths generally range from 10-14 feet

▪ Design Speed – 18 mph is typical

▪ Horizontal Alignment – “lean angle” method

should be used

▪ Cross Slope – 2% maximum

▪ Grade – shall not exceed adjacent roadway; 5%

when not adjacent

▪ SSD – eye height = 4.5 feet; object height = 0

inches

Shared Use Paths

Horizontal Alignment –Lean Angle Method.



▪ Sect 302.1

▪ Provides overall bridge

dimensions

▪ Width

▪ Lateral clearance at underpasses

▪ Vertical clearance over roadways

▪ Defined by the scope of work

being completed for the bridge

▪ Refer to Bridge Design Manual for

additional design information

Bridge Criteria

STRAHNET Requirement of 16 ft for military



Bridge Criteria

This definition is required because of a federal requirement tied to funding



Bridge Criteria



▪ Sect 303

▪ Composed of various elements

▪ Ramps

▪ One and two-lane directional roadways

▪ Accel/Decel lanes

Interchange Elements

Acceleration lane

Single-lane ramp

One-lane directional roadway

Deceleration lane

Multilane ramp



▪ Shoulder Widths to use on ramps –

1-lane vs 2-lane

▪ Look at the number of lanes on the ramp that engage the mainline

▪ Single-lane exit that widens to a multi-lane ramp – use single-lane ramp shoulder widths

▪ Multi-lane entrance ramps that reduce to a single lane by the entrance gore – use single-lane ramp shoulder widths

Interchange Elements – A Common Mistake



▪ Sect 304

▪ Portion of highway separating opposing

directions of the traveled way

▪ Principal functions

▪ Prevent interference of opposing traffic

▪ Provide a recovery area for errant vehicles

▪ Provide areas for emergency stopping and left-turn lanes

▪ Minimize headlight glare

▪ Provide width for future lanes

Medians



▪ Width (Sect 304.2)

▪ The distance between the inside edges of the traveled way

▪ Depends upon the type of facility, cost, topography, and right-of-way

Medians



▪ Rural Width (Sect 304.2.1)

▪ In flat or rolling terrain, desirable

median width is 60-84 feet.

▪ 84-foot wide median allows for a future

12-foot wide lane in each direction,

resulting in a 60-foot wide median.

▪ Minimum median width is normally 40 feet

▪ In rugged terrain, 10-30 feet median

widths may be used.

▪ Constant-width medians not necessary

▪ Independent profiles can be

established for the two roadways

Medians



▪ Rural Type (Sect 304.3.1)

▪ Normally depressed to a swale in the center

▪ Typically constructed without curbs

Medians



▪ Urban Width (Sect 304.2.2)

▪ Barrier medians are normally used in urban areas

▪ Dependent on the width of the barrier and the shoulder width required in Figure 301-4.

▪ Minimum widths▪ 10 feet (4-lane urban freeway)

▪ 22 feet (6-lanes or more urban freeway)

▪ Do not take into account extra width needed for median piers; may require a design exception if not able to widen median throughout the section.

Medians



▪ Urban Type (Sect 304.3.2)

▪ Type depends on traffic volumes,

speed, degree of access, and available

right-of-way.

▪ Median consisting of a TWLTL is

desirable on major streets with

numerous business drives

▪ 6-inch high concrete median, minimum

width of 4 feet, may be used on low-

speed roadways; increases safety by

eliminating left turns

▪ Barrier medians are normally

recommended for high-speed roadways

Medians



▪ Sect 601.2

▪ Based on the ADT and the Median Width

▪ Guidance is provided regarding whether a barrier should be evaluated, whether it is optional, or whether it is not normally considered

Median Barrier Warrants



▪ Sect 305

▪ Used mainly in low-speed urban areas

▪ Reasons to justify use of curbs/curbs

and gutters:

▪ Where required for drainage

▪ Where needed for channelization, control of access, or to improve traffic flow and safety

▪ To control parking where applicable

▪ To reduce right-of-way requirements

Curbs



▪ Types of curbs (Sect 305.2)

▪ Refer to SCD BP-5.1 for approved curb types:

▪ Type 1 – used mostly for temp situations

▪ Type 2, 2-A, 2-B, 6 – widely used along edges of traveled way in urban areas on low-speed roadways

▪ Type 3, 3-A, 3-B; Type 4, 4-A, 4-B, 4-C – used for channelization islands and occasionally along medians

▪ Type 7 – protection at bridge approaches

▪ Type 9 – used along truck aprons in roundabouts to assist trucks with an easier path through the roundabout and to help prevent truck overturns

Curbs



▪ Position of curbs (Sect 305.3)

▪ Low Speed Urban

▪ Curbs should be offset at least 1 foot and preferably 2 feet from the edge of traffic lane

▪ High-Speed Roadways

▪ Curbs should be avoided because of hydroplaning and vaulting concerns

▪ If used, should be placed at edge of treated shoulder or no closer than 4 feet from traffic lane, whichever is greater

▪ Height should not exceed 4 inches

Curbs



Curbs



▪ Curb/Guardrail Relationship (Sect 602.1.5)

▪ Face of MGS guardrail should be located within 6 inches behind the face of the curb; high-speed roadways, preferably located so the face of guardrail is at the face of the curb.

▪ If guardrail cannot be placed within 6 inches for speeds under 50 mph, then it should be installed well behind the 6 inch curb (4 to 12 feet)* to allow vehicle suspension to return to normal state

Curbs

* Applies to MGS Guardrail (new standard guardrail) and not Type 5 guardrail (old standard).

Refer to Section 602.1.5 for guardrail offsets when curb is used.



Curbs



▪ Operational Offset(Sect 600.2.3)

▪ Minimum offset of 1.5 feet (3 feet at intersections) is required behind the face of curb.

▪ This is necessary to:

▪ Improve driveway and horizontal sight

distance

▪ Improve travel lane capacity

▪ Reduce travel lane encroachments from

occasional parked or disabled vehicles

▪ Minimize contact with vehicle-mounted

intrusions (mirrors), car doors, and

overhang of turning trucks

Curbs



▪ Key Terms

▪ Clear Zone – The unobstructed, traversable area provided beyond the edge of the through traveled way for the recovery of errant vehicles. The clear zone includes shoulders, bike lanes, and auxiliary lanes, except those auxiliary lanes that function as through lanes

▪ Foreslope – The slope from the edge of the graded shoulder to the bottom of the ditch (also called fill slope)

▪ Backslope – The slope from the back of the ditch to the existing ground surface (sometimes referred to as the cut slope)

Grading and Sideslopes (Sect. 307)



▪ Key Terms (cont.)

▪ Non-Recoverable Slope – A slope that a vehicle can traverse, but it is generally too steep to allow the vehicle to stop or return to the roadway. Traversable non-recoverable slopes are between 1V:4H and 1V:3H and are NOT included in the specified clear zone distance.

▪ Recoverable Slope – A slope where a motorist may retain or regain control of a vehicle. Slopes flatter than 1V:4H are generally considered recoverable

▪ Critical Slope – A slope that is steeper than 3:1 on which vehicles are likely to overturn





▪ Recoverable Ditch – A rounded ditch having a radius of either 20 or 40 feet

▪ Normal Ditch – A trapezoidal-shaped ditch having a bottom width of 2 feet and a rounding of 4 feet

▪ Roadside ditches are generally

categorized as traversable or

non-traversable.




▪ Roadside Grading (Sect

307.2.1)

▪ Safety Grading – shaping of the roadside using 6:1 or flatter slopes within the clear zone area and recoverable ditches beyond the clear zone

▪ Used on interstates, other

freeways and expressways

Slopes (Sect. 307.2)



▪ Roadside Grading (Sect.

307.2.1)

▪ Clear Zone Grading – shaping of the roadside using 4:1 or flatter foreslopes and traversable ditches within the clear zone area

▪ Often used on high-speed rural

undivided facilities




▪ Roadside Grading (Sect 307.2.1)

▪ Common Grading – shaping of the roadside using 3:1 or flatter foreslopes and normal ditches.▪ Used on undivided facilities

where the conditions for the use of safety grading or clear zone grading do not exist.

▪ Designer should ensure that all obstacles within the clear zone receive proper consideration/protection




▪ Roadside Grading (Sect

307.2.1)

▪ Barrier Grading – shaping of the roadside when barrier is required for slope protection. Normally 2:1 foreslopes and normal ditch sections are used




▪ Section 601.1.1

▪ Objects, or hazards, that if struck by a vehicle

can cause serious injury or death and should

be protected within the clear zone

▪ Bridge piers and abutments

▪ Culverts, pipes, and headwalls

▪ Non-breakaway sign/light support; utility poles

▪ Rough slopes in cut sections

▪ Ditches where head-on impact is likely

▪ Bodies of water

▪ Retaining walls/MSE walls/noise walls

Obstacles



▪ Goal of a highway roadside safety device is to assist in providing a forgiving roadside for an errant motorist.

▪ Contains or redirects the vehicle away from the hazard

▪ Decelerates the vehicle to a stop

▪ Readily breaks away, fractures, or yields

▪ Allows a controlled penetration

▪ Allows a vehicle to safely traverse the feature

Roadside Safety Devices (Sect. 603)



▪ Longitudinal Barriers (Sect.

603.1)

▪ Function by containing and redirecting impacting vehicles

▪ Flexible Cable Systems **

▪ Semi-Rigid Barriers

▪ Type 5 and Type MGS guardrail

▪ Deflects up to 5 feet; provide enough

offset behind guardrail to obstruction

▪ Rigid Concrete Barriers

▪ Single slope barrier

▪ Portable concrete barrier

Roadside Safety Devices

** only used in Ohio to prevent cross-median crashes



▪ Longitudinal Barriers (Sect.

603.1)

▪ Steel beam guardrail post spacing influences the deflection distance

▪ Anchored concrete barrier is not intended to deflect; PCB is expected to deflect




▪ Long-Span Guardrail (Sect.

603.1.2.5)

▪ Requires 62.5 feet of MGS guardrail on both sides of the system

▪ All but the first 12.5 feet of an anchor assembly may be included in this value

▪ Deflects 8 feet; when over culvert, headwall should not extend higher than 2 inches above the ground line within this 8 feet

▪ Refer to SCD MGS-2.3

Roadside Safety Devices - Guardrail



▪ Guardrail Posts in Rock


Locations where motion of the posts may be restricted

Should use steel posts

Refer to:

Report TRP-03-119-03



▪ Blockouts

▪ Connector between the post and the face of guardrail

▪ Standard is 12 inch blockout for MGS guardrail

▪ 12 inch steel plate may be used for additional clearance; not recommended when:

▪ Post spacing is reduced

▪ Wooden posts are used

▪ Guardrail is adjacent to curb




▪ Anchor Assemblies (Sect. 603.3)

▪ End terminals along barrier; used to decelerate a vehicle to a safe stop or containing and redirecting the vehicle.

▪ Multiple types, based on need and function

▪ Refer to Section 603 and Standard Construction Drawings for when to use appropriate terminal assemblies and offset information




▪ Anchor Assemblies (Sect. 603.3)


Designers should consult the ORE approved products list for the most current information regarding proprietary safety devices.



▪ Design Considerations

▪ Barrier can impede sight distance, especially around driveways and approaching bridges

▪ Installing flared guardrail and

either terminating the end

outside of the clear zone or

burying it into a backslope to

avoid impacting sight distance




▪ Offset

▪ Face of guardrail should be placed 2 feet off of the edge of the paved shoulder

▪ Grading

▪ Grading in front of and underneath the guardrail should be relatively flat with minimal changes in the slope

▪ Use 10:1 or flatter slope from edge of shoulder to the face of guardrail –refer to SCD MGS-5.2/5.3




▪ Length of Need

▪ Tangent Alignments




▪ Length of Need

▪ Curved Alignments




▪ Design Considerations

▪ Make sure that the barrier is protecting something that is within the clear zone

▪ Guardrail can also be a hazard and should only be used where the results of leaving the roadway and overturning or striking a fixed object would be more severe than the consequences of striking the barrier




Roadside Safety Devices – Concrete Barrier



▪ Bridge Terminal Assemblies (Sect. 603.5)

▪ BTA Type 1 – commonly used to connect guardrail to concrete barrier or bridge parapet

▪ A single 10-gauge thrie-beam element may replace the nested 12-

gauge rail element

▪ BTA Type 1 Barrier Design – commonly used to connect barrier design guardrail or a Type 1 Impact Attenuator to a concrete median barrier

▪ BTA Type 2 – commonly used to connect guardrail to the trailing end of a concrete barrier or bridge parapet located outside of the clear zone of opposing traffic

Roadside Safety Devices – Bridge Terminal Assemblies



▪ Impact Attenuators

▪ Section 603.4

▪ Also known as crash cushions, used to shield motorists from rigid structures like bridge piers and end of concrete barrier

▪ 3 Types

▪ Type 1 – gating, re-directive, non-reusable

▪ Type 2 – non-gating, re-directive, re-usable

▪ Type 3 – low maintenance, re-usable, ideal

for use at locations of higher impact

frequency

Roadside Safety Devices – Impact Attenuators



▪ Design Considerations – Preferred

Order of Corrective Treatment

1. Remove the obstacle

2. Redesign the obstacle so that it can be safely traversed

3. Relocate the obstacle to a point where it is less likely to be struck

4. Reduce the impact severity by using an appropriate breakaway device

5. Shield the object

6. Delineate the object




▪ Key Terms

▪ Traveled Way

▪ Traveled Way Widening

▪ Graded Shoulder

▪ Treated Shoulder

▪ Clear Zone

▪ Foreslope

▪ Backslope

Module Review




▪ Traversable Slope

▪ Recoverable Slope

▪ Recoverable Ditch

▪ Normal Ditch

▪ Safety Grading

▪ Clear Zone Grading

▪ Common Grading

▪ Barrier Grading

▪ Roadside Safety Devices

Module Review

geometric review and design (grad) 5median width is 60-84 feet. 84-foot wide median allows for a...

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