Application to MDCs 101 

5.5.3.1. Setting values for determining the intergreen time

Going from the geometry elements of the intersection in MDCs, especially the positions of the stop-lines for motorcycles and cars as illustrated in Figure 74 below:

Figure 74: The intergreen time in MDCs

Some traffic models were already introduced in chapter 4 depending on the intersection layout. However, to analyse for determining the intergreen time, all these traffic models in MDCs can be generally summarized as shown in Figure 74. It means that either a motorcycle or a car can be the clearing vehicle or the entering vehicle. However, during the red time, cars must stop in front of their own stop-line, and motorcycles have an opportunity to move up and stop in front of their own stop-line ahead.

According to the German method, individual elements for determining the intergreen time in MDCs must be analysed clearly as follows:

a. Crossing time

In the critical case, the stop-line of cars is referred for determining the intergreen times. Because the speed limit vzul at traffic signals for car traffic in MDCs is the same as in

Germany, the crossing time value can be taken from RiLSA edition 2009. These crossing time values are still safe for motorcycles because the speed limit of motorcycles is lower

Car + Mc Motorcycle Se2 So lfz Mc + C ar M oto rc ycle Car + Mc Motorcycle Mo tor cyc le Mc + C ar Se1 S1

Chapter 5: Calculation of Signal Program Elements for MDCs Intergreen time

b. Clearance time

As discussed above, the clearance time is determined by the formula:

r r r

v

s

t

=

= so + lFz as shown in Figure 74. While the basic clearing distance so is fixed by the

geometry elements, the fictitious length of vehicle lFz can be either of car or of motorcycle.

It is assumed that lFz of car is 6 m, of motorcycle is 2 m, the clearance time tr of the car

will be longer than that of the motorcycle in case of the same clearing speed vr (because

the fictitious length of the car is longer than that of the motorcycle). Hereby, the calculation of the intergreen time for car is longer than for motorcycle. Therefore, in order to make it simple, the fictitious length of vehicle is always chosen as equal as 6 m for determining the intergreen time in MCDs.

Now, the clearing speed vr in MDCs has to be analysed. Since the speed limit in MDCs in

Vietnam are stipulated as high as 40 km/h for motorcycles and 50 km/h for cars inside densely populated areas, it is still reasonable to assume the clearing speed vr of 10 m/s

(36 km/h) for straight-on cars, and of 7 m/s (25,2 km/h) for turning cars as introduced in the German method. However these values are too high for motorcycles because vzul of

motorcycles is lower. It means that, in practice, if a straight-on motorcycle is clearing at a speed of less than 36 km/h, it cannot clear the conflict area before the entering vehicle comes up. This can definitely occur when the speed limit at traffic signals for motorcycles is as high as 40 km/h (very close to the value of 36 km/h). Therefore, the clearing speed according to the German method must be reduced for MDCs due to vzul of motorcycles is

lower. If the speed limit at traffic signals for motorcycles is 40 km/h, it is reasonable to assume the clearing speed vr of 8 m/s (28.8 km/h) for straight-on motorcycles and of 5

m/s (18 km/h) for turning motorcycles. Obviously, these values are still safe for cars because the speed limit of cars is 50 km/h. In addition, these values of the clearing speed are also reasonable according to the investigation under mixed traffic conditions at Daewoo intersection in Hanoi (see Annex B).

c. Entering time in MDCs

As shown in Figure 74, in the critical case, the stop-line of motorcycles is referred for calculating the entering time because the stop-line of motorcycles is closer to the conflict point than that of cars.

Now, the entering speed ve has to be discussed. As discussed in the German method for

the entering time, the entering speed in RiLSA 2009 is set at 40 km/h. This value shows that, in practice, if the vehicle is entering the stop-line at a speed of more than 40 km/h, the high risk of accident may happen because this vehicle will reach the conflict point before the clearing vehicle comes up. Therefore, the higher the value of entering speed is set in the guidelines, the safer the traffic process in practice is, and of course the longer the intergreen time will be.

In MDCs, there is no red-and-amber signal as in Germany. Hereby, the value of the entering speed may be lower than 40 km/h. However, in respect of safety, the value of 40 km/h for the entering speed is still safe for both cars and motorcycles (note that vzul of

Chapter 5: Calculation of Signal Program Elements for MDCs Intergreen time

cars is 50 km/h, vzul of motorcycles is 40 km/h). Therefore, this value should be kept the

same as in RiLSA.

Finally, from the referred stop-line for motorcycles in Figure 74, and the entering speed of 40 km/h, the entering time is determined by the following formula:

40

*

6

.

3

s

t

=

5.5.3.2. Cases for determining the intergreen time in MDCs

Since MDCs did not have special traffic situations as in Germany, especially situations of trams, the following cases for determining the intergreen times in MDCs are recommended:

Case 1: Straight-on vehicles are clearing, Case 2: Turning vehicles are clearing, Case 3: Cyclists are clearing,

Case 4: Pedestrians are clearing,

Case 5: Buses are clearing with and without stop before the intersection.

These cases will be presented in detail in the draft of ‘’Guidelines for Traffic Signals in MDCs’’ (see Annex A).