Transportation Planning

Question 1

What is the functional classification system for urban streets?

Answer 1

The functional classification system is widely used to define the traffic-carrying function of streets.

For urban streets, there are four classifications: (1) Principal Arterials, (2) Minor Arterials, (3) Collector Streets, and (4) Local Streets

Question 2

Who developed the Functional Classification System for Urban Streets?

Answer 2

The Federal Highway Administration (FHWA) developed the functional classification system in 1962.

Question 3

What is a “Principal Arterial”? (Functional Classification System for Urban Streets)

Answer 3

Principal arterials provide long-distance “trunk-line” continuous routes within and between urban areas.

Typically, but with some important exceptions, they carry high volumes of traffic at high speeds.

Examples include: Freeways, including interstates, are principal arterials.

Question 4

What is a “Minor Arterial”? (Functional Classification System for Urban Streets)

Answer 4

Minor arterials are the backbone of the urban street network.

Minor arterials are continuous routes through urban areas.

Minor arterials are designated as touring (i.e. U.S. or state-numbered) routes. They may be state, county, or city streets.

Question 5

For what percentage of street mileage and vehicle miles of travel do Minor Arterials account?

Answer 5

Accounting for only 10% of street mileage, Minor Arterials carry more than half of all vehicle miles of travel.

Question 6

What is a complication of the traffic function of Minor Arterial streets?

Answer 6

The traffic function of minor arterial streets is challenged because of their attractiveness as business addresses, an attractiveness fostered by the traffic function of the street itself.

Question 7

What is a “Collector Street”? (Functional Classification System for Urban Streets)

Answer 7

Collector streets are minor tributaries, gathering traffic from numerous smaller (local) streets and delivering it to and from minor arterials.

Seldom designated as numbered touring routes, collectors are usually city or county streets.

Most collectors are bordered by properties (both business and residential) with driveways to the street.

Question 8

What is a “Local Street”? (Functional Classification System for Urban Streets)

Answer 8

Local streets include all streets all streets not on a “higher” system. These streets may be short in length or frequently interrupted by traffic control devices (i.e. stop signs or signals).

Usually, local streets are city streets, and seldom are part of a numbered touring route. Local streets often have numerous driveways, as they are the addresses for most homes, as well as many nonresidential land uses (professional office, small industrial, churches) not requiring visibility to large numbers of passing motorists.

Question 9

For what percentage of street mileage and total vehicle miles of travel do Local Streets account?

Answer 9

Local streets comprise 90% of street mileage but carry less than 10% of the total vehicle miles of travel.

Question 10

Describe the typical travel distance(s) and speed(s) on local streets?

Answer 10

Travel distance on local streets is short, typically to the nearest collector street. Speeds are low (20 to 30 mph).

Question 11

What is “mobility”?

Answer 11

Mobility is the movement of through traffic with neither origin nor destination in the immediate area.

Question 12

What is “access”?

Answer 12

Access is the connection to immediately fronting properties.

Question 13

What street type offers high mobility and low access?

Answer 13

Arterial streets, located at the mobility end of the mobility/access spectrum, provide large amounts of service to through traffic, but little or no access to surrounding land.

Question 14

What street type offers high access and low mobility?

Answer 14

Local streets, located at the access end of the spectrum, provide unlimited access to adjacent properties, but little service to through travel.

Question 15

What street type offers a medium range of both access and mobility?

Answer 15

Collector streets are in the mid-range of the spectrum. They provide property access with mobility appropriate for connecting local streets to the higher-speed arterials.

Question 16

What is the “Lexicon of the New Urbanism” and how does it pertain to an emerging issue with the functional classification system of streets

Answer 16

There are several ongoing initiatives to combine the traffic functional classification of streets with their adjacent land uses to yield a more comprehensive array of streets. The “Lexicon of the New Urbanism” proposes a structure for accomplishing this.

Question 17

What is the context-sensitive design initiative?

Answer 17

The context-sensitive design initiative, sponsored by the Federal Highway Administration, urges state departments of transportation to make the road context an important part of road design.

Question 18

What are the spacing criteria for Principal Arterials?

Answer 18

Principal arterials should be located every three to four miles in urban areas.

Question 19

What are the spacing criteria for Minor Arterials?

Answer 19

Minor arterials should be spaced at around one mile intervals from other arterials (principal or minor).

Question 20

What are the spacing criteria for Collector Streets?

Answer 20

Collector streets should be spaced roughly one-half mile from arterials.

Question 21

What are the spacing criteria for Local Streets?

Answer 21

Local streets complete the network, with a block spacing appropriate to the land use–typically 300 to 500 feet in business districts and 250 to 600 feet in residential neighborhoods.

Question 22

What are the different local street network patterns?

Answer 22

• Grid
• Grid and squares
• Web
• Radial
• Curvilinear
• Irregular

Question 23

What is street connectivity?

Answer 23

Street connectivity can be defined as the quantity and quality of connections in the street network.

The purpose of the street network is to connect one place to another. The design of the street network determines how direct or indirect the connections are and governs the number of different paths that connect two places.

Question 24

What street network pattern typically provides high connectivity?

Answer 24

A traditional rectilinear street grid provides relatively direct connections and multiple routes and thus has high connectivity.

Question 25

What street network pattern typically provides low connectivity?

Answer 25

The curvilinear networks dominated by cul-de-sacs that are more typical of modern suburban subdivisions often provide relatively indirect connections and few routes and thus have low connectivity.

Question 26

Why have planners and public health officials expressed concern of low-connectivity networks?

Answer 26

Longer distances reduce the likelihood that an individual will travel to that destination or will choose to walk or bike. Thus, planners and public health officials have expressed concern that networks with low connectivity discourage walking and biking.

Question 27

Why have emergency service providers expressed concern of low-connectivity networks?

Answer 27

Emergency service providers have also expressed concern over low-connectivity networks, which may contribute to longer response times and limit the number of routes for emergency access or evacuation.

Question 28

How have a growing number of cities in the United States encouraged greater connectivity in the street network?

Answer 28

They have adopted street connectivity standards.

Question 29

What two techniques have cities employed to establish street connectivity standards?

Answer 29

(1) Block length requirements

(2) Connectivity indexes

Question 30

How are “block length standards” implemented?

Answer 30

Cities typically require a “maximum allowed block length” (measured as distance from curb face to curb face of intersecting streets) or a “maximum allowed intersection spacing” (measured as the distance between centerlines for intersecting streets).

Question 31

What is a “connectivity index”?

Answer 31

A connectivity index is the ratio of the number of links (street segments) to the number of nodes (intersections) in the network.

A higher connectivity index reflects a greater number of street segments entering each intersection and thus a higher level of connectivity for the network.

Question 32

What is “traffic calming”?

Answer 32

The Institute of Transportation Engineers (ITE) defines traffic calming as 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.

The American Planning Association (APA) describes traffic calming as a form of traffic planning that seeks to equalize the use of streets among automobiles, pedestrians, bicyclists, and playing children.

Question 33

What are some examples of traffic calming devices that control volume?

Answer 33

Forced Turns; Diagonal Diverters; Star Diverter; Forced-Turn Islands; Median Barriers; Half Closures or Semidiverters; Street Closures and Cul-de-Sacs.

Question 34

What are some examples of traffic calming devices that control speed?

Answer 34

Speed humps; Raised Crosswalks; Speed Tables; Raised Intersections; Textured Surfaces; Traffic Circles; Roundabouts; Realigned Intersections; Neckdowns; Chokers; Center Island Narrowings; Chicanes

Question 35

Traffic Calming Device: What is a “speed hump”?

Answer 35

Speed humps are raised humps extending across the road. ITE guidelines recommend they be 12 feet long, 3-4 inches high, and parabolic in shape, with a design speed of 15 to 20 mph.

Question 36

Traffic Calming Device: What is a “raised crosswalk”?

Answer 36

Raised crosswalks are speed humps with lat tops marked for pedestrian crossings. They bring the street up to the sidewalk level, increasing pedestrian visibility and safety.

Question 37

Traffic Calming Device: What is a “speed table”?

Answer 37

A speed table is a flat-topped, raised platform that is long enough for both wheels of a car to be on top of the table at the same time. Most speed tables are 3 to 4 inches high and 22 feet long in the direction of travel.

Question 38

Traffic Calming Device: What is a “raised intersection”?

Answer 38

A raise intersection is a flat-topped area that covers the entire intersection. They are usually raised to sidewalk level, approximately 6 inches. Approach ramps should not exceed a gradient of 16 percent.

Question 39

Traffic Calming Device: What is a “textured surface”?

Answer 39

Textured surfaces are usually used in conjunction with other traffic calming devices, but may be used alone.

Question 40

Traffic Calming Device: What is a “traffic circle”?

Answer 40

A traffic circle is a raised island located at an intersection around which traffic has to circulate. Yield signs are often placed on all four approaches. Traffic circles are used on residential streets in lieu of four-way stop signs.

Question 41

Traffic Calming Device: What is a “roundabout”?

Answer 41

Roundabouts are circular raised islands installed at intersections on higher-volume streets such as collectors and arterials and are often used in place of traffic signals of four-way stops. They require yield-at-entry design and must be well marked and visible. Roundabouts have been found to have significantly lower accident rates than signalized intersections with equivalent speed limits.

Question 42

Traffic Calming Device: What is a “realigned intersection”?

Answer 42

Used at T-intersections, these realign the straight approach into a curving street to slow drivers.

Question 43

Traffic Calming Device: What is a “neck down”?

Answer 43

Neckdowns are curb extensions at intersections used to reduce the roadway width. They are also called bulbouts, curb extensions, or intersection narrowings.

Question 44

Traffic Calming Device: What is a “choker”?

Answer 44

Chokers are narrowing devices similar to neckdowns. They are used at midblock to narrow the street and slow drivers.

Question 45

Traffic Calming Device: What is a “center island narrowing”?

Answer 45

Raised islands located along the centerline of the street narrow the travel lanes and slow drivers.

Question 46

Traffic Calming Device: What is a “chicanes”?

Answer 46

Chicanes are streets on which curb extensions alternate from one side of the street to the other, thereby creating s-shaped curves. They reduce both speed and volume. Design must prevent cut-through driving down the centerline. European manuals recommend shifts in alignment of at least one lane width.

Question 47

What are the basic steps in a traffic calming program?

Answer 47

(1) Identify the problem by residents or staff;
(2) Analyze the problem to verify and define it;
(3) Identify alternatives and techniques to address the problem;
(4) Select a plan or program with public input;
(5) Approve the plan by the majority of residents in the neighborhood and official governing body.
(6) Design, construct, and implement the plan; and
(7) Monitor, modify, and evaluate the results.