Ephrem Woldetsadik

@02666435

9/16/2014

2014

Traffic Flow Study

Traffic Flow Study

Objectives:

The objective of this study is to conduct a traffic flow study at a location on a selected

corridor and compute the flow rate at the location for an hour.

Introduction/Background:

Traffic flow theory is expressed as numerical models that attempt to correlate

characteristics of traffic movement to each other and to essential traffic parameters. The science

behind traffic flow study was discovered by Bruce Greenshilds and the Yale Bureau of Highway

Traffic in the 1930s (1). The understanding of traffic characteristics has grown and became

beneficial for traffic engineers in developing roads, transportation plans, etc.

Traffic Flow is the study of the movement of individual drivers and vehicles between two

points and the interactions they make with one another. However, studying traffic flow is

difficult because driver behavior is something that cannot be predicted with one-hundred percent

certainty. Factors affecting traffic flow include geometric characteristics (length of the section,

free-flow speed, no. of lanes, lane width), traffic flow characteristics (volume, composition,

turning movements, driver behavior, etc.) and signal settings (cycle time, green times, phase

sequence, offsets) (2). Traffic flow characteristics consist of traffic speed, travel time, volume,

and density (1). These functions are the elements of planning, design and operation of roads and

highways and transport facilities. The relationship of flow, speed, and density help traffic

engineers in planning, designing and evaluating the efficiency of implementing traffic

engineering measures on a road or highway system. The basic for further analyses are data

collecting on several elements of traffic stream. One example of the use of traffic flow theory in

design is the determination of adequate lane lengths for storing left-turn vehicles on separate left-

turn lanes (1). The determination of average delay at intersections and freeway ramp merging

areas is another example of the application of traffic flow theory. Another important application

of traffic flow theory is simulation, where mathematical algorithms are used to study the

complex interrelationships that exist among the elements of a traffic stream or network to

estimate the effect of changes in traffic flow on factors such as accidents, travel time, air

pollution and fuel consumption (1).

Figure 1: Aerial View of Georgia Ave NW

Traffic conditions can range from almost free flow to highly congested conditions when

the roadways are jammed with slow moving vehicles. The basic variables that can describe the

existing conditions can be determined within a vehicles stream flow, concentration, and mean

speed. The fundamental relationship of these three elements can be used for several traffic

events. Consider the case of vehicles following each other on a long stretch of roadway.

Furthermore, assume that these vehicles are not required to interrupt their motion for reasons that

are external to the traffic stream, such as traffic lights, and transit stations. In this case of

uninterrupted flows the only interference that a single vehicle experiences is caused by other

vehicles on the roadway (1).

Scope:

The study was conducted on Georgia Ave NW between the intersecting roads of Howard

Pl NW and Barry Pl NW. This street is composed of 4 lanes, 2 northbound and 2 southbound.

The traffic flow study was performed on the 2 lanes southbound towards the intersection of

Barry Place NW and Georgia Ave NW. The location is surrounded with local restaurants, bus

stops, Howard University, college dorms, parking lots, Baseball Park, Banneker Recreation

Center, and 2 intersecting roads; Barry Place NW and Howard Place NW.

Methodology and Data Collection:

The flow rate data was collected on Georgia Ave NW

southbound towards the Barry Place NW for 30 minutes on

Thursday, September 4th from 8:30pm to 9:00pm. To

determine the flow rate, a tree was used as a reference point to

count the number of cars passing the tree within 30 minutes.

The tree location is shown on Figures 1and 2. Tally marks

were used to count the number of vehicles passing the tree

within the time frame. After 30 minutes, 262 vehicles passed

the reference point.

Reference point

Figure 2: Street View of Georgia Ave NW going Southbound

Reference point

Analysis of Result:

To calculate the traffic flow rate, the equationq=n /t , where q= traffic flow in vehicles

per unit time, n = number of vehicles passing some designated roadway point during time t, and

t= duration of time interval, was used (3). Theoretically, the flow rate can used to find the traffic

volume by multiplying the number of vehicles found in 30 minutes by 2 to determine the volume

for an hour.

Time (min) Vehicles(n) Traffic flow(q)

30 262 8.73

60 524 8.73

Conclusion/ Recommendations:

The traffic flow rate on southbound Georgia Ave NW between Barry Place NW and

Howard Place was computed to be 524 vehicles / hour.

References

1. McShane, William R., and Roger P. Roess. Traffic Engineering. 4th ed. Upper Saddle River

N.J.: Prentice-Hall, 2011. 107. Print.

2. Gartner, Nathan. "TRAFFIC FLOW CHARACTERISTICS IN COORDINATED SIGNAL

SYSTEMS." tft2010. Traffic Flow Theory and Characteristics Committee (AHB45) of the

Transportation Research Board, n.d. Web. 13 Oct 2014.

<http://www.tft2010.inrets.fr/papers/10-7-i4.pdf>.

3. McShane, William R., and Roger P. Roess. Traffic Engineering. 4th ed. Upper Saddle River

N.J.: Prentice-Hall, 2011. 107. Print.

4. Lecture 2- Traffic and Vehicle Characteristics, Dr. Stephen Arhin;

https://blackboard.howard.edu/bbcswebdav/pid-1579274-dt-content-rid-2690357_1/

courses/CIEG46501201408/Traffic%20and%20Vehicle%20Operating%20-%20Chapter

%202.pdf Accessed Sept. 13, 2014.

5. Valentin, Jan. "Traffic Flow Theory." Web. 15 Sept. 2014.

<http://d2051.fsv.cvut.cz/predmety/tren/trafficflow.pdf>.