4. Layout of Signalised Intersections in MDCs 38
4.2. Separation of car and motorcycle traffic 40
4.2.3. Partial separation 43
4.2.3.2. Case of high motorcycle proportion 43
As presented in chapter 1 about the definition of MDCs, one sub-criterion is the motorcycle proportion in the traffic flow. It is called high motorcycle proportion if this proportion is higher than 50%.
• Traffic regulation
High motorcycle proportion on the road usually leads to a traffic situation with a low proportion of cars. On the road, a little number of cars means that the probability to appear long time gaps between cars is relatively high. It depends on actual car traffic volume. To save road space, motorcycles should be driven on car’s lanes between these long time gaps. Therefore, the mixed motorised traffic flows along the road will be operated. But, on the approach at the intersection, mixed traffic is partly separated as illustrated in Figure 30.
Chapter 4: Layout of Signalised Intersections in MDCs
Figure 30: Approach layout in case of high proportion of motorcycles
Thetraffic regulation is defined as follows: “If vehicles (motorcycles and cars) arrive at the intersection during the green time, they can successively pass the stop-line. If vehicles arrive at the intersection during the red time, cars must stop in front of their own stop-lines that are backward from the intersection, then motorcycle riders who are driving behind cars, have to decelerate and turn into the central lane in order to get in the head-start lanes. When the signal turns green, these motorcycles will first pass the stop-line and cars are followed”. The central lane is only used for motorcycles during the red time. If vehicles arrive at the intersection during the amber time, they can decide either to cross or to stop in front of their own stop-lines. To make the drivers comprehensively understood able about this traffic regulation, the central lane and the head-start area for motorcycles should be marked by dark-red colour.
• Advantages
+ Advantage of traffic safety
Compared to mixed traffic, critical collisions between motorcycles and cars on the approach and in the inner intersection areas will be reduced. When the green time begins, the phenomenon in which motorcycles flexibly manoeuvre and overcome cars is eliminated. Traffic process will be in order.
The opportunity for motorcycle riders to get in front of cars during the red time will abate their stress due to emission and weather conditions because unlike car drivers, the motorcycle riders are not shielded by an enclosed compartment.
By this approach layout, the leading green time for turning motorcycles can be applied. Hereby, the number of conflicts with crossing pedestrians is reduced.
+ Advantage of traffic flow quality
The waiting time will be shorter comparing to mixed traffic because with the same traffic volume on the approach, this traffic model gives a shorter cycle time. This is due to the saturation flow rate of this traffic model is higher than that of mixed traffic (note that mixed traffic flow is unstable, and see the section of the cycle time calculation).
+ Advantage of capacity
Because of higher saturation flow rate comparing to mixed traffic flow, this traffic model will give a higher capacity than that of the mixed traffic flow.
mixed traffic
Chapter 4: Layout of Signalised Intersections in MDCs
+ Does not much influence on the long-term plan for car-oriented layout
Because this approach layout is only applied in case of a high motorcycle proportion shared in the traffic flow, the central lane width for motorcycles accessing the head-start lanes should be designed as equally as 3.0 m. Therefore, it is easier to change this layout approach (see Figure 30) into the layout approach for car-oriented traffic by marking (see Figure 31). This will be implemented when the proportion of motorcycles is no longer high.
Figure 31: Car-oriented approach
• Disadvantage
The disadvantage of this layout approach (see Figure 30) is that right-turning and go- through cars have to share a lane because of the limitation of road space due to establishing the head-start area for motorcycles. However, this is acceptable because, in this case, car traffic volume is not very high.
• Conclusion
It is very suitable to apply this model of separation for the cases of high motorcycle proportion on approaches (higher than 50%).
• Dimensions of the head-start area
The width of the head-start lanes is designed based on the lane width that was presented in section 4.2.1. However, in some exceptional cases, the head-start lane width can be wider than the lane width on the road.
The length of the head-start lanes is designed based on the number of motorcycles arriving at the intersection during the red time. Firstly, the cycle time is calculated from traffic volume of motorcycles and cars (see section the cycle time calculation). Secondly, the green time is calculated for each phase. Finally, from the cycle time (tU), the green
time (tFi), and the amber time (tGi), the red time tRi is calculated by the following formula:
tRi = tU - tFi - tGi [second]
The average number of motorcycles arriving at the intersection during the red time is determined as follows:
Chapter 4: Layout of Signalised Intersections in MDCs
2
.
mc i mc Ri mc iw
q
l
=
[m]Where:
w
imc= the number of motorcycles that can stop in a row on the lane (normally,one motorcycle is fit to 1 m wide. Hereby,
w
imc can be understood as the width of the head-start lane, which is chosen as multiple of 1 m).2 is the length of the block for one motorcycle stopping [m].
Depending on motorcycle traffic volume on each lane, the length of the head-start lanes may be various as illustrated by following figures in which Figure 32 is applied when right- turning and go-through motorcycle traffic volume is high, and Figure 33 is applied when left-turning motorcycle traffic volume is high, and the width of the left-turning head-start lane can be 4 m or 5m. In both of Figure 32 and Figure 33, it is not necessary to locate the stop-lines equally on the car lanes as illustrated in Figure 30.
Figure 32: High traffic volume of right-turning and go-through motorcycles
Figure 33: High traffic volume of left-turning motorcycles
• Dimensions of the central lane for motorcycles
The length of the central lane for motorcycles
l
icaris designed so that the stopping cars donot prevent motorcycles from accessing the head-start area. Therefore, this length should be equal to the queue length of cars as computed according to HBS 2001 that was transferred to annex 3 of the draft of “Guidelines for Traffic Signals in MDCs”.
mixed
traffic
mc Ll
car Ll
mc Rl
car Rl
mc Lw
mc Rw
mc Tw
mc Rw
mixed
traffic
mc Rl
mc Ll
car Ll
car Rl
mc Lw
mc Rw
Chapter 4: Layout of Signalised Intersections in MDCs
As discussed above, the width of the central lane is designed as equally as 3.0 m. The central lane is also marked by red-dark colour, and its borders are designed depending on the route marking of the adjacent car’s lanes.