Volume reports generally contain either one or two channels (also know as lanes or directions) of data. A variety of reports can be produced depending on the interval length (15 min., 60 min., etc) used and the number of channel in the file.
Generally, each report will provide interval totals per channel as well as overall totals. Multi-channel files also provide combined totals. Depending on the report, you may also see different percentage breakdowns. These list what percentage the given value is of an overall value, such as the Average Day (Mon. - Sun.) or Average Week Day (Mon. – Fri.).
Most volume reports also will list the Peak Hour (also referred to as Peak). This is the 60-minute period in which the most traffic was recorded on a specific day. The volume for that hour is also listed, along with the Peak Hour Factor (also known as PHF).
Peak Hour Factor
The Peak Hour Factor (PHF) is used to indicate how evenly the rate of flow of traffic is during the peak hour. For 15 minute intervals the equation for determining the PHF is: PHF = V/(4xV15)
Where V equals hourly volume (vehicles per hour) and V15 equals the maximum 15 minute volume within the hour.
The maximum value a PHF could be is 1.000, which would occur if the volumes in each 15 minute interval of the peak hour were equal.
The minimum value a PHF could be is 0.250, which would occur if the total volume for the peak hour occurred in only one interval.
Typically the PHF will fall into a range of 0.700 to 0.980. The lower the value, the higher the degree of variation in volumes during the peak hour.
Average Daily Total (ADT)
Most volume reports will provide the Average Daily Total (ADT) and Annual Average Daily Total (AADT) if they have been saved in the Header of the file. ADT is an average of volumes at a location for a period less than one year. AADT is an average for a full 365 days.
For the ADT, the program notes how many intervals of actual data there are. Say you had 2 complete days with 15-minute intervals, this would be 192. The program then notes how many intervals there are in a day. In this case, since the data is in 15-minute intervals, there are 96 in one day. The program then divides the number of intervals in a day (96) into the total number of data intervals (192) in the study for a figure of 2.00. The inverse of this number (1/2.00) is then used to create a factor of 0.5.
The program then adds all of the data in the study (for example, 20,000) and multiplies it by the factor created (0.5). This yields the ADT. (20,000 multiplied by 0.5 equals 10,000).
This formula can be used with anywhere from several weeks worth of data to an hour’s worth or less. Of course, the more data you have, the more accurate the ADT will be.
The AADT (Annual Average Daily Total) can be calculated from the ADT by applying a seasonal correction factor.
Speed reports provide vehicle volume data broken down into speed categories, or bins. Hourly Totals are provided, along with Daily Totals and Overall Totals. At the conclusion of the data, the Speed Statistics are given.
The speed statistics contain 4 separate percentile speeds, 15th, 50th (Median speed), 85th and 95th. A percentile speed is the speed below which the stated percent of vehicles traveled. This is the same as saying “85 percent of the traffic was traveling at this speed or slower.” The 85th percentile is often used to measure the maximum reasonable speed for the traffic, while the 15th is often used for the minimum reasonable speed.
This represents the largest number of vehicles traveling in a 10-mph speed range. For example, if the pace speed is 26 to 35, then you could say ‘More vehicles were traveling 26 to 35 mph than any other 10 mph speed range’. The Number in Pace gives the total number of vehicles that were in the pace speed range while the Percent in Pace gives what percentage this was of the overall data. The lower the percentage of vehicles in the pace speed range, the more widely dispersed the speeds in the study are.
Number and Percent Greater then XX mph
These values list the number of vehicle going over a certain speed along with the percentage of the overall data that number is. Usually the Speed Limit for the road is used, and is entered in the Report Details screen before the report is produced.
Class reports provide vehicle volume data broken down into class categories, or bins. Generally, the bins used are the FHWA Scheme F classifications. Hourly Totals are provided, along with Daily Totals and Overall Totals. At the conclusion of the data, the percentage each class is of the overall data is listed.
Gap reports provide the number of gaps that occurred in the traffic stream, broken down into gap bins, which are in seconds. The standard scheme is 0-4 seconds, 5-6, 7-8 … to 29-999.