Section 2 - Roadway Flashcards
ADT
Average Daily Traffic = total annual vol/365 days. Indicates general traffic volumes, but should not determine operating loads (Peak Hourly Volume is preferred but not all-inclusive)
DHV
Design Hourly Volume - approx. 15% more than ADT + represents vol. of traffic that is tolerable to avg driver
volume that each road can carry
DHV = AADT(k)(D)
k = percentage
D = direction
Avg Dims/Passenger Car, Standard
16’-8” L x 6’ w x 4’-6” h
Turning Radius = 24’
Avg dims/Passenger Car, Compact
14’-9” L x 5’-8” w x 4’-5” h
Turning Radius = 20’
Avg dims, Intercity Bus
45’-0” L x 9’ w x 14’-0” h
Turning Radius = 55’
Avg dims/City Bus
40’-0” l x 8’-6” w x 8’-6” h
Turning Radius = 50’
Avg dims/School Bus
39’-6” L x 8’ w x 8’-6” h
Turning Radius = 45’
Avg dims/Fire Truck
32’ L x 8’ w x 9’-8” h
Turning Radius = 50’
Avg dims/Trash Truck
28’-2” L x 8’ w x 11’ h
Turning Radius = 35’
Avg dims/Straight body Truck
17’-35’ L x 8’ w x 13’-6” h
Turning Radius = 45’
Avg dims/Conventional Semitrailer
55’-0” l x 8’ w x 13’-6” h
Turning Radius = 50’
Number of basic types of roadways
1 - Primary (Interstate)
2 - Secondary (Other Arterials)
3 - Tertiary(Collectors)
4 -Local
Freeway
The most rapid and largest volume through-traffic system across and between urban areas. Best characterized by its limited access and grade separated intersections. This includes
expressways and parkways. (typ. ROW = 120’+, 4+ lanes @12’ w)
Major Arterial
A through traffic system across and between urban areas. Allows direct access to adjacent properties, but is characterized by control of entrances, exits, and curb use. (typ. ROW = 100-120’, 4-6 lanes @ 12’w)
Collector Street
This provides for movement of traffic between major arterials and local streets with direct access to adjacent properties. Traffic control is usually provided by signals and stop signs on side streets. (typ. ROW = 60’, 2 (-4) lanes @12’ w)
Local Street
This provides for local traffic movement with direct access to adjacent properties and traffic control with stop signs (typ. ROW = 50-60 (up to 80”)’ w, 2 (up to 4) lanes @ 10, maybe 11’ w)
How does LA go about locating roads?
- traffic vols/type of road nec. to accomodate them
- PRESENT AND PROPOSED LAND USES + circulation routes (auto, pedestrians,bicycles, and any others)
- •TOPOGRAPHY, •SCENIC OPPORTUNITIES
- SAFETY
- RESPOND TO NATURAL FORCES AND FEATURES by respecting/accentuating quals of the landscape
Site Distance (roads)
Length of road clearly visible to driver, based on eye height (in a car, 3.75’ above road surface)
Calculation of
Perception/Reaction Distance
PR = 1.47(t)(V)
PR= perception/rxn distance in feet
t = perception + reaction time (2.5 sec = avg/typ)
V = initial velocity or speed in mph
Calculation of
breaking distance
d = V 2 /30f
where d = braking distance in feet
V = initial velocity or speed in m p h
F = coefficient of friction between tires and pavement
Calculation of
Total Stopping Distance
D = 1.47(t)(V) + V 2 /30f
where D = total stopping distance in feet
For example:
wet pavement will result in a greater total stopping distance due to the change in the coefficient of friction.
min spacing of intersections on an arterial road
800 ft
” levels of service” for transportation systems refer to
degrees of delay and congestion that would be expected during peak periods
levels of service
Level of service (LOS) is a measure used in the management of civil infrastructure to measure its ‘fit for pupose. LOS can also be used to analyze highways by categorizing traffic flow with corresponding safe driving conditions. The concept has also been applied to intersections, transit, potable water, sanitary sewer service, solid waste removal, drainage, and public open space and recreation facilities.
