Based on the result, the average of headways from each cycle was calculated and the saturation flow was calculated using a given formula. The highest value of headway is 2. 93 seconds while the lowest value of headway is 1. 93 seconds. From the results obtained, it can be concluded that the saturation flow is influenced by the value of the headway.Introduction
Saturation flow rate is defined as the flow which can be obtained through a constant queue of vehicles and with 100 percent green time, often expressed in vehicles per hour of green (vphg). However, the definition of saturation flow has changed over the years by different researchers. The Highway Capacity Manual defined the saturation flow rate as the flow that can be accommodated by the lane in vehicles per hour lane, assuming that the green light phase is available to be approached, while the Canadian Capacity Guide for Signalized Intersections (CCG) described saturation flow as the discharge of the queue rate from the stop line of an approach line, expressed in passenger-car units per hour of green (pcu/hr green). Australian Road Research Board (ARRB) Report 123 however expressed saturation flow as the maximum rate of constant departure from the queue during the green light period, in through-car units per hour (tcu/hr).
Saturation flow is necessary in road traffic performance measurements of maximum rate of flow in traffic. Used widely in control and design of signalized intersection, saturation flow expresses the number of passenger car units (pcu) in a heavy flow traffic.
Saturation flow is affected by the proportion and type of vehicles on the road, making passenger car equivalents (pce) usually assigned to variety of categories of vehicle with the purpose of normalize the saturation flow to the common base of passenger car units per hour (pcu/hr).
The intersection before entering Universiti Malaysia Sabah was chosen for this study and the lanes selected was the road from Universiti Malaysia Sabah leading to Kota Kinabalu or Alamesra. Sample size should be around 80-150 vehicles.
The time selected to collect the data was done during peak hours, which in this case is around 4pm until 6pm. The weather condition was a little drizzle, but nothing too serious.
Stopwatch (with split timing functions).
Pen & Paper.
Camera (for recording purposes).
4 Study Procedure
Arrive at the intersection that needs to be surveyed and grab a spot that can easily observe the flow of cars passing the stop line.
As the traffic lights turn to green, the time taken for each vehicle’s rear wheels to cross the stop line was recorded. This will continue until the traffic light turns red again.
When the traffic light turns to red, the process is counted as one cycle.
Repeat step 2 until a total of 11 cycles are reached.
The recorded data was calculated using equation 1 and that is how the saturation flow or start-up lost times were determined.
Each of headway will give different value of saturation flow. The average of headways from each cycle was calculated. The saturation flow was calculated using equation 1 & equation 2. Based on the results obtained, the highest value of headway is from cycle 1 with 2. 93 seconds. Its saturation flow value obtained is 1228 (pc/h/l). Meanwhile, for the lowest value of headway is from cycle 10 which are 1. 93 seconds. Its saturation flow is 1865 (pc/h/l). With these results, the higher the value of headway the lower the value of saturation flow will be.
In this study, it was attempted to calculate the base saturation flow at Jalan UMS. This was accomplished using data collected from UMS to KK / Alamesra. From cycle 10, the mean headway was calculated as 1. 93 seconds. Consequently, the base saturation flow rate was found to be 1865 (pc/h/l). This shows the higher the value of headway the lower the value of saturation flow. The results found in this study will help local engineers to have better estimate of the capacity at the signalized intersections. Hence, this will benefit the road users as there will be less delay in traffic signals and they will reach their destination faster.