sj-5112 intersection dimensions

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At-Grade Intersection Design

CE 453 Lecture 32

For a nice overview of intersection design, see

http://www.fhwa.dot.gov/environment/flex/ch08.htm

Objectives

Basic intersection dimensions

Turning templates

High-speed intersections Other considerations

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Design Vehicle

Source:www\fhwa\Flexibility inHighway Design - Chapter 8- FHWA.htm


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Curb Radius

Factors of influence:

Design vehicleIntersection angleApproach width and parkingChannelizationPedestriansAllowable speed reduction

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Curb Radius

Green Book minimums assume:

Turning Speed 10 mph

Vehicle properly positioned beginningand endVehicle doesnt cross inner edge of

pavement


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Radius Designs

Simple curve Low speed collector, local streets

Simple circle with taper 3-centered compound curve

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Curb Radius

General Guidance 10 to 25 ft. local 25 to 30 ft. collectors

30 to 35 ft. unchannelized intersections witharterials

Source: www\fhwa\Flexibility in Highway Design - Chapter 8 - FHWA.htm


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Minimize lane encroachment

R = 15 feet

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Simple Curve (passenger cartemplate)


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Simple Curve with Taper(passenger car template)

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Compound curves (passengercar template)


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Higher Speed Turns


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Intersection Design

Considerationsfor Pedestrians

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Provide median refuge to

provide crossing in stages

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Provision of crosswalks


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Intersections on High

Speed Rural DividedExpressways

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High speed expresswayintersections

Iowa DOT is building many ruralexpressways

At-grade intersections can be verydangerous Dont use traffic signals as a safety

measure (in most cases) - leave as 2-way stop or replace with interchange

There are alternate measures


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Alternate measures Double yellow center line and stop bars in the median

maintain and replace frequently More and longer left and right turn lane

Offset! Paved shoulders near the intersections "T intersections Offset "T" intersections

much fewer conflict points Restricted median allow lefts in and rights in and out

prohibit lefts out and cross traffic

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Alternate measures Education about proper process via media (print or

electronic) stop, look left only and enter into the median stop in the median

look right and then cross or turn left onto theexpressway Advisory speed limit 10-mph below the posted speed

Signs on both sides (where fast aggressive driversoperate)

In low volumes, traffic may not slow down In peak hours one slows everyone slows


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US 65 Bondurant Example

Speed study done before and after

Some problems with the speedplates

Intense enforcement during thebefore and after period

Data show promise

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Another idea median sign west on Boone

on US-30

Initially solar poweredstrobe light above the signto draw attention

was distracting to driverson US- 30

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Change Blindness A psychological phenomenon Lots of roadside items = ease of estimating speed Clean roadside = not so easy Gray/white/blue sky lots of glare Older drivers


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Overhead intersectionbeacons?

Recent research inMinnesota ineffective confuse motorists

(drivers may think theflashing red beaconmeans 4-way stop)

now removing over headflashing intersectionbeacons in favor of redbeacon on the stop sign

Another Idea

Overhead lighting

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Circular Intersections

Rotaries: large diameter > 300 ft, allowsspeeds > 30 mph with minimum horizontaldeflection of the path of through traffic

Neighborhood traffic circle: small diameter,for local streets, traffic calming

Roundabout

Yield control at each approach Separation of conflicting movements Speed < 30 mph (typically)

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DuPont Circle, Washington,

D.C. (Google Earth image)


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Urbandale

Image Google Earth

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A6 Motorway near Crooklands

Image Google Earth

sj-5112 intersection dimensions

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