Cross Sections CE 453 Lecture 22 Iowa DOT

Cross Sections CE 453 Lecture 22 Iowa DOT Design Manual Chapter 3 1

See also Iowa DOT Standard Plans 2

Objectives 1. Identify cross section components and design criteria See: http: //www. fhwa. dot. gov/environment/flex/ch 06. htm (Chapter 6 from FHWA’s Flexibility in Highway Design) 3

Cross Section Elements 1. Roadway 2. Median 3. Roadside Roadway Components 1. Travel Lanes 2. Shoulders 4 Source: http: //www. fhwa. dot. gov/environment/flex/ch 06. htm

Cross Section Elements 1. Roadway 2. Median 3. Border Roadway Components 1. Travel Lanes 2. Auxiliary Lanes 5 Source: http: //www. fhwa. dot. gov/environment/flex/ch 06. htm

Considerations for Design of Cross-Section n n Volume and composition (percent trucks, buses, and recreational vehicles) of the vehicular traffic likelihood of bicyclists and pedestrians using the route Flexibility in Highway Design Chapter 6 6

Considerations for Design of Cross-Section n n Climatic conditions (storage space for plowed snow, amount of rain) Presence of natural or human-made obstructions adjacent to the roadway (rock cliffs, etc) Type and intensity of development along the facility Safety of the users (speed of traffic) 7

Travel Lanes Function: guidance to drivers and vehicle support Pavement types: n high (modern standards), n intermediate (surface treatments), and n low (unpaved) 8

Travel Lanes Selection Criteria: n Traffic volume and composition n Soil characteristics n Past performance in area n Availability of materials n Energy conservation n Initial cost n Maintenance cost n Overall life-cycle cost 9

Cross Slope l l l Slope perpendicular to flow of traffic on tangent section Rural – normal crown – uniform slope from center to edge of pavement (cross slope break typically at centerline) Urban – parabolic shape (gutter capacity) 10

Cross Slope • • • Rate of Cross Slope = f(drainage, steering, and rollover or cross slope break) Drivers cross the crown line during passing maneuvers • Difficult to negotiate steep slopes AASHTO Recommends • High 1. 5 to 2% (0. 015 ft/ft m/m) • Intermediate 1. 5 to 3% • Low 2 to 6% 11

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Urban Cross-Sections 13

Urban Cross-Sections 14

HMA Cross-Sections 15

Drainage Considerations 16

Drainage Considerations 17

Roadway Component – Travel Lane Width Considerations • • • What is the impact of weather on cross slope design? Safety: Allow steering adjustment and lateral clearance Pavement edge crumbling (deterioration) less with wide lane Cost/Benefit (depends on traffic) Bicycle Use 18

Lane Width n n n n Limited by physical dimension of vehicles 12 ft desirable 11 ft acceptable in urban areas with restrictions 10 ft okay for low speed/urban roadways 9 ft – okay low volume rural and residential roadways 14 ft – shared outside lane with bike TWLTL 10 – 16 ft (3. 0 – 4. 8 m) Auxiliary 10 ft. (3. 0 m) or more 19

Shoulders • • Functions: Lateral Support Avoidance Space Emergency Stop Ped/Bike Use Turning/Passing at Intersections Mail Delivery, Buses, etc. Flexibility in Highway Design Chapter 6 20

Shoulders n n Should be flush with roadway surface Sloped to drain away from traveled way Should be stable enough to support vehicles in all kinds of weather w/out rutting Should be visibly different from traveled way 21

Shoulder geometry n n Paved/Unpaved (earth, turf, gravel) Graded and usable width depends on foreslope and rounding Consider function, safety, and capacity impacts Slope ¡ ¡ ¡ n 2 to 6% (paved) 4 to 6% (gravel) 8% (turf) Min. 2% + lane slope Max crossover 8%] Width 0. 6 – 3. 6 m (2 – 12 ft) 22

Source: A Policy on Geometric Design of Highways and Streets (The Green Book). Washington, DC. American Association of State 23 Highway and Transportation Officials, 2001 4 th Ed.

Curbs n n n Control access Control drainage Type used varies with location and design speed 24

Curbs 25

Curbs 26

Iowa’s Roadway-Related Fatal Crashes n 52% of Iowa’s fatalities are related to Lane Departure n 39% of Iowa’s fatal crashes are single-vehicle Run-Off-the-Road (ROR) crashes 27

Safety Investment Strategy n Candidate Safety Projects ¡ ¡ ¡ ¡ ¡ Paved shoulders Milled-in shoulder rumble strips 2 -lane shoulder widening High severity crash intersections High severity crash 2 -lane roads High crash curves Expressway intersections Centerline rumble strips Cross-median head-on crashes 28

4 Foot Paved Shoulder US 63 29

Milled Shoulder Rumble Strips 30

Median Function ► ► ► ► Separate opposing traffic Drainage Aesthetics Space for future lanes Recovery Access control Minimize headlight glare Flexibility in Highway Design Chapter 6 31

Median Types/Geometry Depressed (rural arterials, 6: 1 preferred, 4: 1 min) Raised (urban arterials) Flush (urban/sub. some rural) n n n ¡ ¡ Double yellow to limit access TWLTL Width is determined by n ¡ ¡ ¡ Function Safety Need for independent design Flexibility in Highway Design Chapter 6 32

Iowa DOT Urban Design Aids See http: //www. dot. state. ia. us/local_systems New Construction 33

Iowa DOT Urban 3 R* Guidelines See http: //www. dot. state. ia. us/local_systems 34 *Resurfacing, Restoration, Rehabilitation

Rural Design - New Construction 35