Description:
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://www.google.com/maps/@38.8276404,-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
Lab Tasks:
Field Observation
- 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
d2 in this analysis. The best way to approach this problem is to organize all information
in a table similar to Table 7.5.
a) What are the effective green time (g) and red time (r) for each phase?
b) What are the analysis flow rate for each lane group (from step 5)?
c) What are the g/C ratio, lane group capacity c, and volume capacity ratio X (please do
not confuse with flow ratio v/s (Y).
d) What are the average delay per vehicle for each lane group (d1)?
e) What are the average incremental delay per vehicle due to random arrival and
occasional oversaturation in seconds (d2)? In this study, we analyze LOS by
considering PHF. So T=0.25. We assume the intersection is pre-timed and take 0.5
for delay adjustment factor k. We assume the arrival pattern following Poisson
distribution and I=1.0. X is the v/c ratio for this lane group.
f) What are the lane group LOSs?
g) What are the average approach delays and approach LOSs?
h) What is the average intersection delay and intersection LOS?
Redesign the Intersection - As a traffic engineering, you are going to re-design the intersection using the procedure
in the textbook. First, apply the rules in the textbook to evaluate if a protected left turning
phase is warranted for the left turn movement for both the North-South and the East-West
directions. - You would follow the approach in Table 7.5. Assuming the saturation rate is 1800
veh/h/lane for through and right turning lanes and 1750 veh/h/lane for left turning lanes,
determine the flow ratio for all movements. - Assuming you do not change the phase plan, determine the critical lane groups and the
corresponding flow ratio. Calculate the optical cycle length with necessary assumptions
(ROUNDED UP to the nearest 5 seconds). Is it the same as the current plan? - Determine the effective green length allocation. Is it the same as the current plan?
- Following the same approach, evaluate LOS if the intersection was using your phase
plan. Summarize your analysis using a table similar to Table 7.5. Does it change the
LOS?
Discussions - What are the factors that may help to explain the difference in LOS by using the existing
plan and your phase plan?
Template for Lab Report
A standard lab report should include a brief discussion about the objective of your study and a
detailed description of your approach. In this study, you need to describe both the data collection
approach and the analysis method. The list of tasks serves as a template for analysis method. At
the end, you need to summarize your findings and discuss the significance of your study. In this
study, you are expected to answer the question in task 13.
To make the report more succinct, please use graphs and tables whenever it is possible.
Figure 2: Example of Observation Location
Sample Solution
Undoubtedly, migration leads to a loss of productivity and decrease in the labour force in the source economy. But remittances offset these losses in the long run. Households receive adequate sums of money, which leads to an increase in both consumption expenditure and investments, which in turn fuels the economy. Above this, emigrants are more keen on investing in new real estate, institutions, technology and better infrastructureâ education and healthcare facilitiesâ in their home countries. Remittances also substantially increase the inflow of foreign exchange and help tide over periods of income shocks for families. When the financial troubles are greater, remittances increase, and tend to decrease by a lesser degree during times of financial stability. In this way, it acts as a form of insurance and encourages activities that are imperative for long term economic growth (Collier 211). These activities include entrepreneurial ventures and better human capital development, factors that are key to increase the GDP of a country in the long run (Ratha). Trends over several years indicate that these foreign remittances actually exceed the sums received as portfolio investments and official development assistance, and are only second to foreign direct investments in low and middle income countries (Figure 2) (âMigration and Development Brief 30â). Remittances help maintain foreign exchange reserves in the country, which become vital for trade. Despite its advantages, a highly pressing issue that accompanies these remittances is the pressure it puts on economic inequalities within the source country. Migration in itself is a large investment, that only those who are relatively better off can make. This in turn means that remittances only reach the already well to do households, which increases the gap between the rich and the poor. Development activities fueled by remittances do provide greater employment, but this is rarely sufficient to narrow an already widening gap (Ratha). From the above discourse, stems certain socio-political consequences of migration. When oppressive political regimes and poor economic conditions overlap, emigration means the loss of those people who are affluent and have the influential positions in society. On the other hand, when these migrants return after receiving foreign education or understanding the economic and social systems of their host countries, they have the power of knowledge and new ideas. They can put this to use in their own countries by taking on new ventures and roles in top pos>
Undoubtedly, migration leads to a loss of productivity and decrease in the labour force in the source economy. But remittances offset these losses in the long run. Households receive adequate sums of money, which leads to an increase in both consumption expenditure and investments, which in turn fuels the economy. Above this, emigrants are more keen on investing in new real estate, institutions, technology and better infrastructureâ education and healthcare facilitiesâ in their home countries. Remittances also substantially increase the inflow of foreign exchange and help tide over periods of income shocks for families. When the financial troubles are greater, remittances increase, and tend to decrease by a lesser degree during times of financial stability. In this way, it acts as a form of insurance and encourages activities that are imperative for long term economic growth (Collier 211). These activities include entrepreneurial ventures and better human capital development, factors that are key to increase the GDP of a country in the long run (Ratha). Trends over several years indicate that these foreign remittances actually exceed the sums received as portfolio investments and official development assistance, and are only second to foreign direct investments in low and middle income countries (Figure 2) (âMigration and Development Brief 30â). Remittances help maintain foreign exchange reserves in the country, which become vital for trade. Despite its advantages, a highly pressing issue that accompanies these remittances is the pressure it puts on economic inequalities within the source country. Migration in itself is a large investment, that only those who are relatively better off can make. This in turn means that remittances only reach the already well to do households, which increases the gap between the rich and the poor. Development activities fueled by remittances do provide greater employment, but this is rarely sufficient to narrow an already widening gap (Ratha). From the above discourse, stems certain socio-political consequences of migration. When oppressive political regimes and poor economic conditions overlap, emigration means the loss of those people who are affluent and have the influential positions in society. On the other hand, when these migrants return after receiving foreign education or understanding the economic and social systems of their host countries, they have the power of knowledge and new ideas. They can put this to use in their own countries by taking on new ventures and roles in top pos>
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