An Integrated Efficiency-Risk Approach in Sustainable Project Control

4. Integrated Efficiency–Risk Methodology with the Combination of Two EVM and CCM Techniques

4.2. The Integration of the Efficiency-Risk Control of the Projects by Managing the Schedule and Cost Buffers

Each buffer (schedule and cost) is divided into three equal parts of green, yellow, and red. The buffers can be in the green, yellow, or red zone in different stages of the project implementation based on progress and variance in terms of time and cost. Through the correct control of the usage of the two buffers in the project implementation (Table 2), the integration of the efficiency–risk control of the sustainable projects is conducted by managing the schedule buffer and the cost buffer.

Table 2. Project management by schedule and cost buffer.

Cost Buffer
Green	Yellow	Red
Follow schedule more quickly even if it leads to spending more cost.	Without extra cost, increase speed of project implementation by using of new techniques.	Follows more quickly and do non-critical activities in a cost saving manner.	Red	Schedule Buffer
Attention should be paid to the control of the project duration and it is not necessary to make corrective actions.	At remaining of project, continue same status of time and cost.	Keep speed in implementation of work with saving cost on noncritical activities.	Yellow
Do not need to make corrective actions.	Attention should be paid to the control of the project cost and it is not necessary to make corrective actions.	As far as possible, the value of the project is preserved and the costs are saved.	Green

Through Equations (6) and (7), the percentage of the cost buffer (P_C) and that of the work done based on cost (W_C) are calculated. The cost status of the project intersection of these two points is shown in Figure 4.

$\begin{aligned} &P_{C}=\frac{C V}{C B} \\ &\text { where } \\ &C B=\text { Cost Buffer } \end{aligned}$ (6)

$\begin{aligned} & W_{C} =\frac{E V}{B C A C_{0}} \\\ & where \\ & B C A C_{0} = Budget \, Cost \, At \, Complete \, regardless \, of \, cost \, buffer \end{aligned}$ (7)

Figure 4. Project control charts based on project progress (schedule or cost) and the buffer usage percent (schedule or cost).

The percentage of the schedule buffer (P_T) and that of the work done based on time (W_T) are calculated using Equations (8) and (9). The duration status of the project intersection of two points is presented in Figure 4.

$\begin{aligned} &E S_{T}=T+\frac{E V-P V_{T}}{P V_{T+1}-P V_{T}} \\ &S V_{T}=E S_{T}-A T \\ &P_{T}=\frac{S V_{T}}{S B} \end{aligned}$ (8)

$where$

$\begin{aligned} &T=\text { the time is that } E V \geq P V_{T} \text { and } E V < P V_{T+1} \\ &S B=\text { Schedule Buffer } \end{aligned}$

$W_{T}=\frac{E S_{T}}{B P D_{0}}$

$where$ (9)

$B P D_{0}= Baseline \, Planned \, Duration \, regardless \, of \, schedule \, buffer$