Speed. Scale/design geometrics

Transcription

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4 Speed Scale/design geometrics

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6 Source: New Jersey DOT

7 15 MPH can mean the difference between crash avoidance and almost certain death

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12 Speed Complete Streets Scale/design geometrics

13 Source: AASHTO for flat urban/suburban roadways.

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27 Many overly wide roads could use a road diet

28 What saroaddiet? Classic road diet shrinks 4 lanes to 3 + bike lanes

29 Another road diet example Classic road diet shrinks 4 lanes to 3 + bike lanes

30 What else does a road diet do? Creates room for wider sidewalks

31 What else does a road diet do? An inexpensive tool for retrofitting existing streets

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35 X vs.

36 X vs.

37 Source; Converting four lane undivided roadways to a three-lane cross-section: Factors to consider. Iowa State University and Iowa DOT

38 Existing Proposed Stripe 4 bicycle lane Reduce travel lane width to 11 Eliminate offset (design speed =< 35 mph)

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40 Source: Highway Capacity Manual

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46 Oregon DOT

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49 Four-step travel demand model Microsimulation

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51 1 Design speed is 35 mph or less

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56 Horizontal clearance

57 Designers and the public should understand that, once a vehicle leaves the road, a crash or potentially serious encounter with the roadside may occur, regardless of the clear-zone width established by the designer.the selected clear-zone width is a compromise, based on engineering judgment, between what can practically be built and the degree of protection afforded the motorist. Limitations in available right-of-way, the location, frequency, and nature of roadside objects, or the presence of valued resources such as wetlands, or the need to provide for pedestrian or other activities may practically limit the clear-zone width.

58 Pedestrians feel exposed and vulnerable

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60 3 1.5 Source: AASHTO Green Book minimums

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64 Pedestrians Bicycles Cars, trucks, buses

65 Compact, low-speed, human scale Vs. high-speed, high-capacity

66 40% larger 120% larger

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70 Large radii 1. Increase crossing distance and 2. Make crosswalk & ramp placement more difficult

71 Effect of large radius on drivers They drive fast, ignoring pedestrians Tigard OR

72 Keeping it tight: Curb radius Effective radius is larger than built radius if travel lanes are offset from curb w/ parking and/or bike lane Oregon DOT

73 Keeping it tight: Curb radius On one-way streets, corners with impossible turns can have a very tight radius Impossible turn

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77 Must consider design vehicles, but don t choose larger vehicle than necessary

78 We shouldn t t design for the exceptional vehicle Moving vans use this street once or twice a year; hundreds of pedestrians cross every day Orlando FL

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87 Medians improve safety at driveways

88 Safety 30% potential increase in crashes 12% potential increase in crashes Lowest crash rate Safety issue becomes more pronounced at 24,800 to 28,000 AADT threshold Safety issue becomes more pronounced at 24,800 to 28,000 AADT threshold Mobility Highest delay Minimize turn movements (driveway consolidation) Least signal delay (storage) Must provide adequate storage Access Unrestricted access Unrestricted access Most restrictive Pedestrian safety Pedestrian must cross four lanes of traffic Widest crossing distance Center turn lane not a safe refuge Pedestrians cross two lanes at a time Raised median provides refuge

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90 Medians reduce crash risk for random mid-block crossings

91 Flush median is not much of a refuge

92 Flush median is not much of a refuge

93 Basic Principle Break long complex crossing into two simpler crossings

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99 2007 Alabama ASCE Summer Conference 148

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