Introducción

Simons, Mason and Gardner (2004) adopted the OVE measurement from the Overall Equipment Effectiveness (OEE) metric. The OEE metric was historically used in the manufacturing industry to measure the effectiveness o f machines. It was developed by Seiichi Nakajima based on the Total Productive Maintenance (TPM) concept, (William, 2007). It focuses on eliminating six main classes o f equipment waste that can be categorised into downtime, speed and quality losses. Figure 6.1 is a diagram of the OEE tool illustrating the relationship between losses and the equipment performance as illustrated in M uchiri and Pintelon (2008).

Equipment timing The six big losess Perspective integrated

Loading

Figure 6.1: The OEE metric with 6 major losses in the equipment process

Muchiri and Pintelon (2008) differentiated between the effectiveness and efficiency measurement and concluded that the OEE metric is classified as a measure of effectiveness since it measures the actual performance against the expected performance o f the equipment, (ibid). It can be calculated based on the availability,

produce the product can be affected by idle time or speed reduction. The quality rate is determined by taking the defect and yield losses into account. This basic effectiveness measurem ent which is limited to measuring individual pieces of equipment, has led to the development o f improvement measurements which look at wider aspects, such as the total equipment effectiveness performance (TEEP), production equipment effectiveness (PEE), overall factory effectiveness (OFE), and overall asset effectiveness (OAE) (M uchiri and Pintelon, 2008).

Simons, Mason and Gardner (2004) expanded this performance measurement approach into the field o f logistics by using it to measure the total effectiveness o f a vehicle with a single measure. A similar concept to OEE is used where the availability, performance and quality are three main factors to calculate the new metric called Overall Vehicle Effectiveness (OVE). This performance measure, inspired by the lean thinking approach, is used to optimise the value adding activities and eliminate the non-value adding activities in road freight transport. W ith OVE, wasteful activities in the delivery process that can reduce the effectiveness o f a vehicle can be identified and eliminated. Simons, M ason and Gardner (2004) found that the value-adding activities in transport are affected by five main losses. These include the extra time used to load and unload a vehicle above the standard load time as well as the vehicle’s fill loss, speed loss and quality loss. The total performance is measured in terms o f an overall percentage and the identification o f the most important activity to reduce is given by the factor that has the lower percentage. The OVE metric uses weight- distance, as it is a common road-freight transport KPI, to evaluate the vehicle’s energy efficiency (Aylward and O ’Toole, 2007).

6.3.1 The availability rate

The availability o f the vehicle is the percentage o f the actual vehicle’s weight distance (after considering the loss time caused by the waste activities, such as excess loading time) compared to the planned weight distance as shown in equation (35) below:

, ... actual weight distance Availability ---

;---planned weight distance ⁽³⁵⁾

where the

(Actual weight distance) = (planned weight distance) — (loss weight distance) (36)

The planned weight distance and loss weight distance are calculated as follows:

Planned weight distance = Planned time (min) * optimal vehicle speed (km/min)

* vehicle capacity (weight) (37)

Loss weight distance = Loss time (min) * optimal vehicle speed (km/min)

* vehicle capacity (weight) (38)

Hence, equation (35) can be simplified as 1- loss time \

where the value o f loss planned time

time is supposed to be less than the value o f planned time. The planned time, o f course has to account for the statutory breaks during the journey.

Figure 6.2 is a diagram o f the OVE availability factor.

Planned weight distance

Actual weight distance Loss weight distance

<--- Availability --- ► Figure 6.2: OVE availability

6.3.2 Performance

The performance factor is evaluated by the capacity and the speed rate o f the vehicle.

The capacity rate is measured based on the total weight-distance carried by the vehicle to visit all delivery points against the actual weight distance as equation (39):

^ total weight distance carried . . . .

Capacity rate = --- (39)

actual weight distance

The total weight distance carried is calculated based on the total distance travelled and the weight carried by the vehicle along the trip, similar to the energy consumption calculation in equation (33), but the total weight-distance in this situation is determined without the vehicle un-laden weight as in equation (40) for the case o f direct delivery and equation (41) for multi-retailer scenario:

wd, = Wj * d 0 l (40)

(41)

The speed rate measures the average speed used by the vehicle compared to the optimal speed that is allowed for the vehicle as in equation (42).

n f

( » 'I

ii

M

/ =! V n

)

Speed rate = Actual average speed (km/min)

Optimal average speed (km/min) (42)

where

Actual average speed = Total distance travelled (km)

Travelling time (min) (43)

The travelling time is the actual time the vehicle spends on the route after taking into account the transport losses time such as the loading and unloading time from the whole replenishment planned time. As a result a lower actual average speed will occur if the lost time is low which will increase the travelling time value. Hence, the performance rate o f the vehicle can be computed by:

Performance rate = speed rate x capacity rate

A diagram o f OVE perform ance rate presented in Figure 6.3 below

(44)

Actual weight distance

Total weight distance carried Fill loss

Speed rate Speed loss

— Performance —►

Figure 6.3: OVE performance

6.3.3 Quality

The third factor that is important when evaluating the vehicle performance is the quality o f the output, w hich can cause additional losses, such as time delays and reductions in the total weight distance carried by the vehicle if any problem occurs along the process. For simplicity, the quality rate in the model is assumed at 95%, as this effect is outside o f the model boundary in this study.

6.3.4 OVE

The overall vehicle effectiveness can be computed by multiplying the percentages of availability rate, perform ance rate and quality rate as shown in equation (45):

OVE (%) = availability (%) * performance (%) * quality (%) (45)

A diagram o f these three factors with their wasteful activities is shown in Figure 6.4.

Some issues occur when using the OVE metric as some wasteful activities are incorrectly classified as value adding activities. The determination o f the optimal vehicle speed and quality level is a subjective measurement based on several factors.

However, it is not a m ajor problem as it can be overcome by making a clarification based on common logistics procedures and standard measurements, such as the national speed limit.

Planned w eig h t distance

A ctual w e ig h t d istance W eight distance lo ss

T otal w eig h t distan

N et w eight distance

V aluable Q uality lo s s w eieht distance

ce

S p eed lo ss

F ill lo s s

O V E = A v a ila b ility x Perform ance x Q uality

A vailability

Performance

Q uality

| = Effectiveness Loss

F ig u re 6.4: O V E diagram

A study by Simon, M ason and Gardner (2004) has revealed that the OVE metric raised a problem with regard to the round trip since the highest effectiveness occurred on trips with the highest weight-distance value. Therefore, Guan et al. (2003) suggested that the OVE metric should first determine the optimal route o f the vehicle before the OVE metric is used in order to achieve the correct optimal route decision.