Highway Design 5510 - Midterm 1 - Michael Shea
ADT (Average daily traffic)
• #Veh. in a time period (both directions) / time period - Time period measured in days - Averaged >= 2 days
Traffic Volumes Concepts
• AADT (Average annual daily traffic) • ADT (Average daily traffic) - #Veh. in a time period (both directions) / time period - Time period measured in days - Averaged >= 2 days • Design year and traffic projections • Design hour volume • PHF (Peak hour factor) • Design level of service
Difference between urban and rural areas
• Travel patterns, land use, road density and their relationships to functional class all differ between the two areas • separate functional classification system for rural and urban areas
Function is defined by:
• channelization of trips (Hierarchy of classification directly related to hierarchy of trip distance) • character (or proportions) of service
design
• v. To devise with a specific function or end; to draw the plans for • n. A preliminary plan or sketch; a set of drawings that guide the making or production of something
Section 4(f) of DOT Act, 1966
- Establishes protected land • Public parks, recreation areas, wildlife & waterfowl refuge, historic sites • It must be publicly owned (except historic sites), open to the public , its major purpose must be recreation, it must be significant as a park or recreation area - No project that uses these lands will be approved unless there is no other prudent alternative and harm to used property is minimized
Design Control Factors: Driver
Addressing variability in driver performance: • Information handling, expectancy, performance • Comfort • Adaptation and safety
highway
Any publicly-maintained roadway that is open to the use of the public for purposes of vehicular travel, including the entire area within the right-of-way More commonly used for facilities characterized by higher speeds, fewer turning conflicts and smaller numbers of non-motorized users
Collectors
Directly serves small towns; connects small towns to arterials; "accumulates" volumes from local roads
MEF (Monthly expansion factor)
MEF = AADT / (ADT for that month)
Fun Acronyms
NIMBY = Not in my back yard CAVE = Citizens against virtually everything BANANA = build absolutely nothing anywhere near anything
PVC station = ??
PVC sta. = PVI sta. - (L/2)
PVT el. = ??
PVT el. = PVI el. + (G2 * (L/2))
High/Low Point = ??
High/Low Point = K * |G1| = [G1 / (G1-G2)] * L
degree of curve (degrees) (Horizontal Curve)
D = 5729.58 / R or D = 18,000 / (pi)(R)
"As intended" Speed relationship
Design speed is outside of observed operating speeds with the speed limit on the upper end of the observed speed range
Access
The ability to approach a desired trip destination: • Ability to directly approach • Needed at both ends of any trip • Providing access decreases mobility!!
unbalanced lateral acceleration
The acceleration/force that acts on vehicles traveling through a horizontal curve. This is what the occupants are feeling, although it is actually higher due to vehicle body roll angle af = (fs)(g) - af = lateral acceleration (ft/s^2) - f = coefficient of friction - g = gravity (32.2 ft/s^2)
Uniform cross slope
The point where the superelevation of the outside edge equals the normal crown
Full Superelevation
The point where the whole road is sloped at the design superelevation
mobility
The quality of being able to move about freely: • Ability to move efficiently and comfortably • Often measured by speed and travel time • Important to longer trips
Method 5
Used for: All Rural Highways, Urban Freeways, High-Speed Urban Streets (50 mph and higher) Use table 3-8 through 3-12 in Green book
National Environmental Policy Act (NEPA), 1970
1. Applicable to decisions that involve Federal funding/permitting • States have adopted similar processes otherwise 2. Assessment of environmental impacts • Direct effects, indirect effects 3. Systematic, interdisciplinary approach
Rural Functional classification system
1. Principal arterials • interstate highways • other freeways and expressways • other principal arterials 2. Collector roads • Major collector roads • Minor collector roads 3. Local roads
Urban Functional classification system
1. Principal arterials • interstate highways • other freeways and expressways • other principal arterials 2. Minor arterial streets 3. Collector streets 4. Local streets
Design Level of Service (LOS)
A quantitative stratification of a performance measure or measures that represent the quality of service, measured on an 'A' through 'F' scale (with 'A' representing the best-operating conditions, F representing the worst)
Middle Ordinate (ft) (Horizontal Curve)
A straight line from the midpoint of a chord to a point on the arc. The middle ordinate is perpendicular to the chord. M = R ( 1 - cos I/2)
Design Controls
Factors that are fixed outside the design process but may dictate the result.
Directional, Design Hour Volume (DDHV)
DDHV = (AADT)(K)(D) - D = proportion of peak hour traffic traveling in peak direction
Design Criteria
Factors by which the adequacy of a design is assessed.
Free-flow, lowest possible volume
Measure speeds of vehicles with >5-10 second lead headway - Measure speeds of vehicles when flow <200 pc/hr
When does Green Book criteria become 'minimum' requirement?
On National Highway System • New Construction • Reconstruction • Maintenance States may adopt own standards that are different than Green Book for these project types, but the state standards must at least meet Green Book "minimums."
Design Year
Road improvements not based on current volumes (based on future volumes) - typically 20 years from project let date (when bid to perform the work is accepted)
Design vehicles
Selected vehicles with representative weight, dimensions, & operating characteristics
locals
Serves individual farms and other individual, rural land uses
Functional Classification
The class, or group, of roads to which the road belongs Characterize roadway by the position in the transportation network and type of service being provided. (freeways, collectors, locals, etc.)
AASHTO Design Vehicles:
a. Passenger cars b. Buses c. Trucks (i.e. interstate semitrailer WB-67) d. Recreational vehicles (i.e. Motorhome and boat trailer MH/B)
Profile view
a drawing that shows an object as though you were looking at it from the side (vertical alignment)
Plan View
a view of an object as projected on a horizontal plane.(bird's eye view / Horizontal alignment)
Selecting a Design Vehicle
consider the largest design vehicle that is likely to use that facility with considerable frequency... ...or a design vehicle with special characteristics appropriate to a particular location in determining the design of such critical features as radii at intersections and radii of turning roadways.
Ball Bank Indicator
instrument installed in a vehicle to measure side friction demand while traversing a horizontal curve.
AADT (Average Annual Daily Traffic)
is the amount of traffic on a roadway in a 24 hour period, averaged over a year. - #Veh. in a year (both directions) / 360
Tangent runout
length of roadway needed to accomplish a change in outside lane cross slope from the normal cross slope to zero (flat) and vice versa
Peak Hour Factor (PHF)
measure of the fluctuation in traffic flow during the period of analysis. PHF = [V / (4*(V_15))] - V = Volume [#veh.] - V_15 = Peak 15 min. count [#veh.]
85th percentile free flow speed
most frequent measure used for design speed (85 percent of drivers at or less than)
Volume
number of vehicles (or persons) passing a point during a specified time period [Vehicles]
Flow Rate
rate at which vehicles (or persons) pass a point during a specified time period less than one hour (usually 15 minutes), expressed as equivalent hourly rate [Vehicles / hr] or [vph]
Basic horizontal curve equation
relates friction, superelevation, the radius of the curve, and speed together
Speed zones
shall only be established on the basis of an engineering study that has been performed in accordance with traffic engineering practices. The engineering study shall include an analysis of the current speed distribution of free-flowing vehicles. Should be within 5 mph of the 85th percentile speed of free-flowing traffic
Stopping sight distance (ssd)
simplified formulas
Sight distance (SD)
the distance along a roadway throughout which an object of specified height is continuously visible to the driver
Passing Sight Distance (PSD)
the distance required for a driver to complete normal passing maneuver required at frequent intervals on two-lane, two-way roads Eye Height = 3.5 ft object Height = 3.5 ft
Cross Section
the intersection of a three-dimensional figure and a plane (cutting the road along traveled path to show edge, center line, super elevation, shoulders)
Sub-deflection angle (degrees) (Horizontal Curve)
the total angle of change since the PC. Sub-Def. Ang. = (s)(D) / 200 s = distance from PC to current angle (used mostly to manually layout a horizontal curve from the PC - we use GPS coordinates now)
This course focuses on...
• Geometric design criteria and relationships • Driver considerations • Operational considerations • Safety considerations
Vehicle Characteristics that Influence Design include:
• Physical dimensions (length, width, height) • Turning characteristics • Weight • Horsepower / Vehicle performance
PVT station = ??
PVT sta. = PVC sta. + L
Movement Hierarchy (6 stages):
(Hierarchy based on volume) • Main movement (freeway) • Transition (exit ramp) • Distribution (Principle arterial) • Collection (Minor arterial) • Terminal Access (collector) • Park at origin/destination
Long chord (ft) (Horizontal Curve)
- In the elements of a circular curve, it is a straight line distance connecting PC to PT C = 2(R)*sin(delta/2)
Design Criteria Factors
-safety -efficiency -driver comfort -aesthetics -construction cost -future maintenance activities
"classes of action" allowed under NEPA
1. Class I - Environmental Impact Statement (EIS) is prepared for projects that would cause a significant adverse effect on the environment. 2. Class II - Categorical Exclusion (CE) is prepared for projects that would cause minimal social, economic, or environmental impact. 3. Class III - Environmental Assessment (EA) is prepared for larger-scale projects that do not meet the requirements for a CE or those for which the significance of the environmental impact is not clearly established. If the environmental analysis and inter-agency review during the EA process find that a project would have no significant impacts on the environment, a Finding of No Significant Impact (FONSI) is issued. If the review finds that the project would have significant impacts, an EIS must be prepared.
Environment
1. Social • Community life • Cultural enrichment • Ecological health • Economic prosperity • Equity & Justice • Personal health • Social interaction 2. physical 3. natural
Design Control Factors
1. Terrain/environment 2. Traffic 3. Drivers 4. vehicle type • Motorized • Non-Motorized 5. Other (financial, regulatory, etc.) 1. Principal arterials • interstate highways
Design Speed Selection
1. urban areas: • The selected design speed was often equal to or 5 mph higher than the anticipated posted speed limit across terrain types and functional classifications. 2. Rural Areas: • The selected design speed was nearly always 5 mph higher than the anticipated posted speed limit across terrain types and functional classifications. designers generally select design speeds that are within the range of anticipated operating speeds, regardless of terrain or functional class.
30 HV
30-hourly volume greater than that shown
Daily Volume Projections
AADTfuture = AADTcurrent * (1 + i)^n - i = growth rate [decimal form] - n = number of years from "current year" to design year (AADTcurrent may be counted or estimated)
cumulative distribution function
CDF = (Count so far) / (total count)
Context Classification
Characterize roadway by the surrounding environment and how the roadway fits into the community (rural vs urban)
Design Hour Volumes (DHV)
DHV = (AADT)(K) -K = proportion of design year AADT (actual or estimated) occurring in design hour -Rural areas: 18% > K > 12% (15% is typical) -Urbanized areas: 12% > K > 8%
Design Control Factors: Adaptation & Safety
Define safety by crash frequency (number of crashes for some time period) and crash severity (injury resulting from those crashes) ΔSeng = (1 + f)*(ΔSact) • ΔSeng = change in safety expected based on engineering and human factors principles • ΔSact = actual change in safety observed • f = driver feedback parameter that captures the degree to which drivers respond to the change
Highway and Street Design
Determine physical appearance of a highway or street in three dimensions
Tangent length (ft) (Horizontal Curve)
Distance from PC or PT to PI T = (R)*tan(delta/2)
Arterials
High-capacity urban road, primarily designed to deliver traffic from collector roads to freeways (Directly serve trips between cities and larger towns)
What establishes the general character of a highway, more than any other design consideration?
Horizontal and vertical alignment
(PC = ??) & (PT = ??)
PC = PI - T PT = PC + L
PVC el. = ??
PVC el. = PVI el. - (G1 * (L/2))
street
Same definition as a highway More commonly used in built -up areas and characterized by: -lower speeds -Wide range of traffic and volumes -Narrower lanes -Frequent intersections and driveways -Significant non -motorized traffic and more surrounding businesses and houses
National Highway System
Serve major centers, destinations, facilities • Meet national defense requirements • Freeways and other arterials (150,000+ miles) • May include collector if on Strategic Highway Network (STRAHNET) and a "connector"
Super elevation
The banking of a curved section of road to help overcome the effects of centrifugal force e = 100tan(alpha) Limited by: Climate, presence of slow-moving vehicles, area type (urban, rural)
Horizontal sight line offset (HSO)
The distance between the driver's line of sight along the roadway ahead on a horizontal curve and a sight obstruction on the inside of the curve
External Distance (ft) (Horizontal Curve)
The distance from the mid-curve to the PI E = R { [1/cos(delta/2)] - 1 }
Stopping Sight Distance (SSD)
The distance needed by a driver to bring his/her vehicle to a safe stop, given roadway grades, surface conditions and operating speeds required at all points on all highways Eye Height = 3.5 ft object Height = 2.0 ft Sum of: (1) the distance traversed by the vehicle from the instant the driver sights an object, and (2) the distance needed to stop the vehicle from the instant brake application begins.
Rate of vertical curvature (K)
The horizontal distance required for a 1% change in slope on vertical curve [ft / %] K = L/A
Superelevation revolved around the Inside edge
The inside edge gets assigned the elevations that the center line has. Then, the elevations of the CL and Outside edge are calculated with the superelevation at the stations
Normal Crown (NC)
The slope of the road before any superelevation occurs
operating speed
The speed at which drivers are observed operating during free-flow conditions.
True
True or false: A bicycle should be considered as a design vehicle where bicycle use is allowed on a highway.
Design Speed
a selected speed used to determine the various geometric design features of a roadway. should be logical with respect to topography, anticipated operating speed, the adjacent land use, and the functional classification
Method 2
Used for: Low-Speed Urban Streets (45 mph and lower) because of - the need to meet the grade of adjacent property - surface drainage considerations - the desire to maintain low-speed operation - frequency of intersecting cross streets, alleys, and driveways. when calculated required superelevation is less than the normal crown (i.e. ed < NC), the full superelevation will be set as the NC (Table 3-13b in green book)
Can f be "negative"?
Yes, If superelevation is significant and speeds are slow, vehicles would have a tendency to want to slide to low point of traveled way (imagine driving slow on a professional racetrack), so friction would point towards the outside of the curve. We try to avoid this (as drivers would have to steer towards the outside of the curve)
Decision Sight Distance (DSD)
distance needed for a driver to detect an unexpected condition in a roadway environment, recognize its potential threat, select an appropriate speed and path, and initiate and complete complex maneuvers required at complex locations Eye Height = 3.5 ft object Height = 2.0 ft Sum of (1) distance traversed by the vehicle during 'pre-maneuver,' and (2) the distance traversed by the vehicle during 'maneuver.'
Superelevation runoff
length of roadway needed to accomplish a change in outside lane cross slope from zero (flat) to full super (and vice versa)
Running Speed
the speed at which an individual vehicle travels over a highway section. The running speed is the length of the highway section divided by the running time for the vehicle to travel through the section.
Remove Adverse crown (RC)
when one side of the road is at NC and the other is horizontal (outside edge and Center line have same elevation at this station)
Rural Highway Network functional relationships
• Specific traffic generators more difficult to identify because of overall high intensity of land use and travel • Spacing becomes a much more important consideration in defining a logical street network
Highway design references used:
• The Green Book (AASHTO) • Highway Capacity Manual • Highway Safety Manual (AASHTO) • Manual on Uniform Traffic Control Devices (FHWA)
