A traffic engineer
As a traffic engineer, you are assigned to evaluate the level of service of one intersection
near George Mason University Fairfax campus. The intersection is of Braddock Rd and the
Roberts Rd, and you can see the configuration of the intersection through Google Street Map
(https://email@example.com,-77.3008148,16.25z). One of your colleagues
went to the field and has collected the data using Jamar Counter (see Figure 2 at the end). The
data is summarized in Figure 1 below. Each arrow represents a unique turning movement (left,
through, and right) from each of the four approaches. For example, the south bound right has a
traffic volume of 97 veh/h.
Table 1 summarizes the current phase plan your colleague observed. It includes four phases
(E/W Left, E/W Through, N/S Left, and N/S Through) labeled in different colors. Although this
intersection is fully actuated and coordinated, for the practice, let us assume the current plan is a
fixed time plan with four phases.
Now, using this set of field data, you will first evaluate the level of service based on the current
phase plan observed by your colleague, and then resign it based on the Optimal Cycle length.
You will reevaluate the LOS under the new phase plan you design, and compare it with the
existing phase plan.
Figure 1: Traffic Data Collected at the Intersection.
Table 1: Current Phase Plan for the Intersection of Braddock Rd and Robert Rd.
Approach EB WB NB SB
Lane group LT T/R LT T/R LT T/R LT T/R
Effective Green (g) 12 133 12 133 15 34 15 34
Lost Time/phase 4
Total Lost Time 16
Cycle Length 210
- Assuming all traffic are passenger vehicles and the driving population are commuters,
convert the observed flow rate V into analysis flow rate v for different lane groups.
- Following the procedure of the textbook, evaluate the LOS of this intersection using
collected data. Assume the saturation rate is 1800 veh/h/lane for through and right turning
lanes and 1750 veh/h/lane for left turning lanes (or the lane shared by the through and left
turning movements). In this problem, we assume that there is no standing queue at the
beginning of the red phase and all traffic can go through the intersection within one cycle.
You may apply the formula on page 255 for calculating d1 and you also need to consider