Florida Green Book & New TND Street Design Chapter

Billy Hattaway, PE, CNU

• Federal Highway Trust Fund – in the red as of September 2008.

• State transportation revenues also in big trouble….FDOT deferred $7 billion in projects

• Climate change

• Development on hold

“The Perfect Storm”

“The solution of the traffic problem is to be sought not so much by wider streets as by proper plan of the town.”

John Nolen, 1926

• Adopted by state DOT’s

• Reflects consensus of states on what constitutes good design practice

• Never intended to be used solely as a standard to base the design of every improvement on

AASHTO “Green book”

Flexibility in Highway Design - FHWA

• “… functional classification establishes the basic roadway cross section in terms of:

• lane width

• shoulder width and other major design features…”

• “The flexibility available to a highway designer is considerably limited once a particular functional classification has been established.”

Based on AASHTO criteria

• Florida roadways – focus on:

• Higher speeds

• Highway capacity

• Functional classification

• Rural & suburban

FDOT Plans Preparation Manual

A Typical State Arterial Highway

Miami, Fl

“Manual of Uniform Minimum Standards for the Design, Construction and Maintenance for Streets and Highways”

• Where does it apply?

• Local roads

FDOT “Green Book”

FDOT “Green Book”

• Based on AASHTO “minimums”

• County & City Roads – focus on:

• Highway capacity

• Functional classification

• Rural & suburban development

• Traffic calming & Residential Street (suburban) chapters added

TND Chapter

• Why is this chapter being included?

• Local governments want to encourage TND development patterns

• Context is needed to define when TND street design criteria is appropriate

• Criteria will reduce liability for all parties

Green Book Project Goals

• “Traditional” and “Conventional” characterdefined and differentiated

• Context and character for use of Traditional street design defined

A Introduction – TND vs CSDB Planning Criteria – Guiding principlesC Context – The TransectD Definitions – Teaching engineers a new languageE Land Use – Can’t get there without itF Networks – Power of the networkG Thoroughfare Types – Functional class vs MovementH Design Principles – Guiding principlesI Cross Section Elements – Defining the piecesJ Travelled Way - Designing the streetK Intersections - Focused on pedestrians

TND Chapter Content

The Context

Size neighborhoods for a 5-minute walk

Make blocks a walkable size:A fine grained network of streets & ammenities

Civic

Buildings

Neighborhood

Centers Parks and

Open

Spaces

Lane Width

• The normal range of design lane width is 9-12’

• Wider lanes are associated with higher speed roadways

• There is less direct evidence of a safety benefit associated with wider lanes in urban areas.

• Lane widths substantially less than 12 feet are considered adequate for a wide range of volume, speed and other conditions.

Lane Width

Driver Expectation

Design Speed

• Conventional practice is to design as high a speed as possible

VS

• Traditional practice is to design for the context and speed desired to support other modes

Design Speed

• Design speed is a selected speed used to establish geometric features of the street

VS

• Using the built environment to send the driver a clear message on how fast to drive

Pedestrian Fatalities & Speed

0

10

20

30

40

50

60

70

80

90

100%

Fa

tal to

Pe

de

str

ian

s

20 mph 30 mph 40 mph

Speed

Movement Type Design Speed Travel Lane Width

Yield Less than 20 mph 8 feet

Slow 20-25 mph 9-10 feet

Low 30-25 mph 10-11 feet

Lane Width:

Clear Zone:

• An obstacle free area that permits the driver to safely return to the roadway or bring the vehicle to a safe controlled stop

• Speed determines how much

Clear Zone

HorizontalClearance

• The focus of urban streets is provision for:

• Pedestrians

• Street furniture

• Landscaping

• In urban areas, 1.5’ minimum is for operational needs (car door conflicts), not safety.

Horizontal Clearance

Curb has no re-directional capabilities except at speeds less than the lowest design speeds used on the State Highway System.

“Barrier Curb”

• Driving through intersections is one of the most complex conditions drivers encounter

• 50 percent of fatal and non-fatal injuries to pedestrians occur at or near intersections

Intersections

Conflicts at a Four-Way Intersection

• Hazardous intersections

• High-volume

• High-speed

• Multilane

• Complex signal phasing

Intersection Safety

Typical State Road Intersection

Florida Green Book & New Urban Street Design

Billy Hattaway, PE, CNU bhattaway@vhb.com

Phone: 407.704.0782