road design - environmental science & · pdf filefrom fhwa and state dots, also from...
TRANSCRIPT
Road Design
Susan Handy TTP Orientation Seminar
October 2012
Level Agencies Primary concern
Primary role
Federal FHWA FTA
National Highway System
Funding Policy
State DOT Highways outside metro areas
Planning Building Operating
Regional MPO Transit
Highways, transit within metro areas
Planning
Local Planning Public Works
Local streets
Planning Building Operating
Road Design in the U.S.
Manuals and Guidelines from FHWA and state DOTs, also from… AASHTO – American
Association of State Highway and Transportation Officials
ITE – Institute of Transportation Engineers
TRB – Transportation Research Board
Topics
• Network design • Facility design • Plus others
Network Design
• What are the two main purposes of streets/roads/highways?
• What’s the main difference between streets vs. roads vs. highways?
National Committee on Urban Transportation, 1958
City of Sunnyvale, 1957
ITE Street Layout Principles, 1984
City of Austin, Comprehensive Plan, 1994
Benefits of grid…?
• More direct routes – Less distance
• Less driving (?) – Less pollution, energy consumption, noise, etc.
• More walking/biking – More exercise, less weight, better health, etc.
– Better efficiency • Emergency response time • City services
Connectivity Measures
Source: Handy, Paterson, and Butler 2003
Source: Handy, Paterson, and Butler 2003
Source: http://www.fotosearch.com/photos-images/cul-de-sac.html
Berkeley Diverters
Source: http://www.ci.berkeley.ca.us/transportation/Bicycling/BB/BicycleBoulevardTreatments.html
Village Homes, Davis
Source: Google Maps
Davis Greenbelt System
Source: Google Maps
Houten, Netherlands
Source: Google Maps
Facility Design Responsibility Influence
Local Streets Cities and counties
ITE – Institute of Transportation Engineers
Highways and Freeways
State DOTs AASHTO – American Association of State Highway Officials
http://www.ite.org/bookstore/RP-011C.pdf
http://www.ite.org/bookstore/RP-011C.pdf
http://www.ite.org/bookstore/RP-011C.pdf
Source: http://www.ashland.or.us/Files/street%20standards_001.pdf
Source: http://www.ashland.or.us/Files/street%20standards_001.pdf
Source: http://www.ashland.or.us/Files/street%20standards_001.pdf
Innovations/Trends
• Traffic Calming • Skinny Streets • Road Diets • Complete Streets • Green Streets • Context-Sensitive Design • Others…
Traffic Calming
"Traffic calming is the combination of mainly physical measures that reduce the negative effects of motor vehicle use, alter driver behavior and improve conditions for non-motorized street users." - ITE Subcommittee on Traffic Calming
Speed Control Measures
Vertical Deflection Horizontal Deflection Horizontal Narrowing Other Measures
Speed Humps Traffic Circles Neckdowns Examples
Speed Tables Roundabouts Center Island Narrowings
Raised Crosswalks Chicanes Chockers
Raised Intersections Realigned Intersections
Textured Pavements
Speed Lumps *
Speed Cushion *
Split Speed Hump *
Volume Control Measures
Divertive, Restrictive Other Measures
Full Closures Examples
Half Closures
Diagonal Diverters
Lateral Shift *
Median Barriers
http://www.trafficcalming.org/measures2.html
Traffic Circles Roundabouts
http://www.trafficcalming.org/measures2.html
http://www.trafficcalming.org/measures2.html
Chicanes Neckdowns
Narrow Street Scenarios
http://darkwing.uoregon.edu/~cpw/projects/pdf/featured/tgm_2003/powerpoints/285,13,Narrow Street Scenarios
Narrow Streets
Canyon Rim Village, Medford
http://darkwing.uoregon.edu/~cpw/projects/pdf/featured/tgm_2003/powerpoints/366,11,Narrow Streets
Road Diet
Fifth Street Road Diet in Davis: Coming Summer 2013
Complete Streets
http://la.streetsblog.org/wp-content/uploads/2008/10_06/10_8_08_complete_streets.jpg
Marcy McInelly, SERA/Urbsworks
Green Streets
https://bookstore.transportation.org/item_details.aspx?ID=110
“Context-Sensitive Design”
Source: http://www.dot.ca.gov/hq/oppd/context/main-streets-flexibility-in-design.pdf
Riverfront Parkway and Downtown Streets, Chattanooga, TN
Image: City of Chattanooga and River City Company
Riverfront Parkway, Chattanooga, TN
“Before” Conditions
Image: City of Chattanooga and River City Company
Image: City of Chattanooga
Reconstructed Riverfront Parkway
Road Design Conundrum
Crash risks minimized but high speeds
Crash risks remain but low speeds
Parking
Parking Problems
• Minimum parking requirements for residential and commercial development, in zoning codes – Excess parking
• Free curbside parking in central business districts – Excess driving – “cruising” to find spaces
Parking Requirements
“Free parking isn't really free. In fact, the average parking space costs more than the average car. Initially, developers pay for the required parking, but soon tenants do, and then their customers, and so on, until the cost of parking has diffused throughout the economy. When we shop, eat in a restaurant, or see a movie, we pay for parking indirectly because its cost is included in the price of everything from hamburgers to housing. The total subsidy for parking is staggering, about the size of the Medicare or national defense budgets. But free parking has other costs: It distorts transportation choices, warps urban form, and degrades the environment.”
Source: http://www.planning.org/bookservice/highcost.htm
Traffic Management
• Approaches: – Traffic control devices to
regulate behavior – Roadway design to shape
behavior
• Goals: – Safety – Efficiency – Plus livability!
Source: http://mutcd.fhwa.dot.gov/pdfs/2003r1/pdf-index.htm
MUTCD Principles
• Purpose is “… to promote highway safety and efficiency by providing for the orderly movement of all road users… throughout the Nation…”
• “The decision to use a particular device at a particular location should be made on the basis of either an engineering study or engineering judgment…”
• Not a legal requirement • Not a substitute for engineering judgment
Speed Limits
• MUTCD section 2B-10 (update: 2B-13) requires that the numeric value be determined on basis of an engineering study. The following factors should be considered: 1. Road surface characteristics, shoulder condition, grade, alignment and
sight distance. 2. The 85-percentile speed and pace speed. 3. Roadside development and culture, and roadside friction. 4. Safe speed for curves or hazardous locations within the zone. 5. Parking practices and pedestrian activity. 6. Reported accident experience for a recent 12-month period.
For a discussion, see: http://www.motorists.org/speed-limits/safety-setting-limits
Level of Service TRB’s Highway Capacity Manual
LOS = f (volume/capacity) How to increase LOS?
Result: Massive Intersections
Next up: Pavements!