Grid: consists of equally spaced streets or roads which are perpendicular to each other.
- Often used for its regularity, simplicity, and convenience.
- It simplifies the subdivision of land for both agriculture and urban use, alongwith providing a sense of orientation if not extended (vast) and sufficient landmarks are present.
- Grids can be used on sloped sites if carefully configured.
- Traffic flows can be controlled by increasing capacity in certain channels while decreasing them in others. This can direct heavier through-traffic to those channels that are capable of handling them.
- A grid system can lose its effectiveness with regard to circulation when its channels become congested. Usually before this point is reached, a freeway or expressway is introduced.
asphaltic concrete
Radial: directs flow to or from a common center, with straight channels of circulation radiating from this center point.
- This is the typical pattern created by traditional city growth outward (radially) from the original settlement.
- This usually causes the center point, where all channels converge, to become congested. This can be alleviated by creating “by-passes” that connect outlying hubs/radials thus allowing through traffic to avoid the congested area. As a result, a radio-centric pattern is created. This can also sometimes create concentric rings around the center.
Linear: of circulation connects flow between two points, either along a single line or along a series of parallel lines.
- Activities can be situated along the route or be routed into loops or branches on either side. Excessive traffic along the route could ultimately cause congestion.
- A drawback to this system is a lack of focal point and the on-and-off movements from the branches or activities can impede the flow of traffic. This can cause inefficiency and be hazardous to oncoming traffic.
- This type of system is useful for restricted sites such as a narrow valley between hills, or when parallel to existing infrastructure like a railroad, canal or freeway.
- Such routes lined with business are often called “strip commercial” developments. These businesses are often visually chaotic, very inefficient in terms of land use. They serve as good “incubator spaces”, Places for new businesses.
Curviniliear: responds to the topography of the land and aligns with natural contours.
- This system works best at small scales because the curving of the path reduces speeds.
- A network of curvilinear systems can conform to the natural topography of the landscape as well as be arbitrary. Most common to residential neighborhoods/suburbs.
- (PUD’s) employ this system for more interesting street layouts, better views, and site adaptability (topographic changes).
Vehicular traffic roads from lowest to highest
Local access streets < collector/ distributor streets < arterial streets < freeways
Freeways/ expressways/ motorways:
- designed to allow movement of large volumes of traffic between, around, or through urban areas.
- Velocity is reached because of high intervals between traffic interruptions (on- off ramps).
- All cross traffic is accomplished by overpasses and underpasses eliminating all grade level intersections which would impede traffic.
Arterial Streets/ highways:
- are continuous vehicular channels that connect with expressways by means of on-and-off ramps at carefully determined locations.
- These are typically two and three lanes wide in each direction.
- On street parking is prohibited
- Access to adjacent commercial property could be restricted
- Access to residential streets is allowed
- All crossings are controlled by traffic signals
- Typical speed limit is 35 mph
- Major intersections should be separated by at least 800’-0”
Collector-Distributor Streets:
- serve as the transition between arterial streets and the local access streets of a neighborhood.
- They provide access to adjacent residential properties
- They are usually discontinuous, thereby preventing through-traffic and reducing vehicular speed
- Curb-side parking is allowed but only at certain times of the day and may be limited or prohibited
- When collector streets intersect with arterial streets, traffic signals are used
- Local and collector streets are usually controlled by stop signs
Local access streets:
- provide access to low intensity uses fronting on them.
- They carry low traffic flows
- Such streets consist of loops and cul-de-sacs or combination of the two
- Unrestricted curbside parking
- Unlimited Pedestrian use
Depending on traffic intensities, the materials often used for paving and roads include (in order of preference):
- concrete
- asphalt concrete
- gravel
- decomposed granite
- stabilized soil
- graded and compacted earth shaped for drainage
When do intersections require traffic signals?
When intersection volume exceeds 750 cars per hour
Types of traffic control devices:
Stop signs
Traffic signals
Turning lanes
Islands
Medians
Grade separations
“cartridge drive”
-required when the amount of parking exceeds 400-500 cars,
aka distributor drive
For structured parking, ramps should not exceed
15% (speed ramp)
For slopes 10% or higher,
a transition of 8 feet on either side is required, the slope would usually be half of the actual slope of the ramp.
Ex. For a 10% ramp2 sections of 5% at 8’ long on top and bottom would be required
A ramped driveway exit rising up to a public sidewalk must have a transition section no more than —% so as not to obstruct the driver’s view of pedestrians
on the sidewalk ahead (the hood of the car)
5%
The area covered by a person is approximately —SF
3 SF
This is based on a shoulder breadth (width) of 24” and a body depth of 18” (adult male)
The U Value indicates …
…the speed of heat transfer
- a low value indicates slow heat loss or gain
- a high value indicates a rapid heat loss or gain
Freeboard
the distance between the water surface and the crest of the banks.
- this should be where the highest expected water level will be
- the freeboard should also be high enough to resist the highest wave action
aquifier
aka underground rivers or permeable materials through which water flows
-sand, gravel, sandstone, and some limestone are generally good aquifiers
Soil properties for which soil may be tested include:
- specific gravity: to determine void ratio
- grain size: (for granular soils) to estimate permeability, front action, compaction, and shear strength
- grain shape: to estimate shear strength
- liquid and plastic limits: (in cohesive soils) to obtain compressibility and compaction values
- void ratio: to determine compressibility
- unconfined compression: (in cohesive soils) to determien shear strength
Land adjacent to foundations require a ___% to channel water away from the building’s foundation
2%
a sheet flow system requires a ___% sloped grade
1/2% - 2%
The pipes of drainage lines are usually made of what?
- PVC
- Clay Tile
