Question: Question 3): Peak Hour Factor. The Flow In Each 5-minutes Interval From 4:30 To 6 PM Is Given In The Table Below. Determine When The Peak Hour Begins And Ends. What Is The Peak Hour Factor 'PHF15min' For This Peak H. Between November and April, higher cost on-peak hours are weekdays from 5–9 a.m. You'll pay lower off-peak prices all other hours, including weekends and six observed holidays. New Year's Day (observed), Memorial Day, Independence Day (observed), Labor Day, Thanksgiving Day and Christmas Day (observed).
Peak Hour Volume, Design Flow Rate, PHF
It is commonly known in your area that the heaviest traffic flow rates occur between 4:00 PM and 6:30 PM. Your assignment for the day is to find the peak hour volume, peak hour factor (PHF), and the actual or design flow rate for an existing one-lane approach. To do this, you obtain a click-counter and position yourself at the intersection. For each fifteen-minute interval, you record the numbers of right-turns, left-turns, straight-through trucks, and straight-through passenger cars. Your tabulated values are as shown below.
Time Interval | Left Turns | Right Turns | ST Trucks | ST Cars |
4:00-4:15 | 5 | 10 | 6 | 30 |
4:15-4:30 | 6 | 15 | 8 | 26 |
4:30-4:45 | 4 | 7 | 10 | 35 |
4:45-5:00 | 7 | 16 | 8 | 40 |
5:00-5:15 | 10 | 13 | 6 | 49 |
5:15-5:30 | 9 | 12 | 12 | 55 |
5:30-5:45 | 14 | 15 | 8 | 65 |
5:45-6:00 | 12 | 12 | 10 | 50 |
6:00-6:15 | 10 | 9 | 8 | 39 |
6:15-6:30 | 9 | 12 | 4 | 30 |
If a truck is equal to 1.5 passenger cars and a right-turn is as well, and if a left-turn is equal to 2.5 passenger cars, then calculate the peak hour volume, peak hour factor (PHF), and the actual (design) flow rate for this approach.
[Solution Shown Below]
Solution
![Peak Hour 4 1 90 Peak Hour 4 1 90](https://image2.slideserve.com/4255670/inactivation-ratio-l.jpg)
The first step in this solution is to find the total traffic volume for each 15 minute period in terms of passenger car units. This is done by multiplying the number of trucks by 1.5, the number of right turns by 1.5, and the number of left turns by 2.5. Money pro 1 7 2. We then add these three numbers and the volume of straight-through cars together to get the total volume of traffic serviced in each interval. Once we have this, we can locate the hour with the highest volume and the 15 minute interval with the highest volume. The peak hour is shown in blue below with the peak 15 minute period shown in a darker shade of blue.
Time Interval | Interval Volume (pcu) |
4:00-4:15 | 67 |
4:15-4:30 | 76 |
4:30-4:45 | 71 |
4:45-5:00 | 94 |
5:00-5:15 | 103 |
5:15-5:30 | 114 |
5:30-5:45 | 135 |
5:45-6:00 | 113 |
6:00-6:15 | 90 |
6:15-6:30 | 77 |
The peak hour volume is just the sum of the volumes of the four 15 minute intervals within the peak hour (464 pcu). The peak 15 minute volume is 135 pcu in this case. The peak hour factor (PHF) is found by dividing the peak hour volume by four times the peak 15 minute volume.
PHF = 464 /(4 * 135) = 0.86
The actual (design) flow rate can be calculated by dividing the peak hour volume by the PHF, 464/0.86 = 540 pcu/hr, or by multiplying the peak 15 minute volume by four, 4 * 135 = 540 pcu/hr.
The peak hour factor (PHF) is the hourly volume during the maximum-volume hour of the day divided by the peak 15-minute flow rate within the peak hour; a measure of traffic demand fluctuations within the peak hour.
The peak hour factor is used in HCM capacity and level of service analysis to account for the variation in traffic volumes during the peak hour. Following is an example of how the peak hour factor is computed and how it might affect the final results of a capacity calculation.
The table below shows flow rates that were measured for four 15-minute time periods for each of the 12 intersection movements. Examination of this table shows that second time period, which begins at 4:15 pm, is the peak 15-minute period of the four that are shown here. The total flow for this time period is 4,220 veh/15 minutes, or 16,880 veh/hr. The average flow rate for the hour is 12,640 veh/hr; this is the sum of the total volumes observed during each of the four 15-minute periods shown below. The peak hour factor can then be computed as follows:
Peak Hour 4 1 90 Mph
PHF = (average flow rate)/(4*Peak 15 minute flow rate)
=12,640/16,880
Time period | Eastbound | Westbound | Northbound | Southbound | Total | ||||||||
LT | TH | RT | LT | TH | RT | LT | TH | RT | LT | TH | RT | ||
4:00 pm | 40 | 55 | 175 | 50 | 50 | 75 | 120 | 815 | 45 | 40 | 700 | 55 | 2,220 |
4:15 pm | 50 | 75 | 375 | 55 | 80 | 125 | 215 | 1,025 | 20 | 60 | 1,975 | 165 | 4,220 |
4:30 pm | 30 | 75 | 125 | 45 | 75 | 115 | 20 | 975 | 35 | 55 | 1,200 | 145 | 2,895 |
4:45 pm | 45 | 60 | 175 | 55 | 85 | 150 | 145 | 1,015 | 45 | 50 | 1,350 | 130 | 3,305 |
Peak Hour 4
You can see that the possible values of PHF can range between 0.25 and 1.00, inclusive. Higher numbers indicate a flatter peak. It is rare that PHF drops much below a value of about 0.70. In this case, the PHF of 0.75 is indicative of a very sharp peak for an urban environment, and is probably more characteristics of small towns and cities than larger urban areas.