# Traffic Volume

Traffic Volume Study: The term traffic volume study is also known as traffic flow survey or simply the traffic survey. It is defined as the procedure to determine mainly the volume of traffic moving on the roads at a particular section during a particular time. A volume is basically a number of vehicles or persons passing a point during a specified time period which is usually one hour but maybe less than that. It means during a period of time, it may be fifteen minutes, it may be half an hour, it may be even sixty minutes or one hour and how many vehicles or persons are passing a point during that particular time period is known as volume. Traffic volume study is used for traffic planning of a particular road or area. The traffic stream composition of a particular road can be known from traffic volume study.
It is denoted as ‘q’, also called the traffic flow, which represents the no. of vehicles crossing a section of road over a unit period of time at any selected period. Unit is vehicles/hour or vehicles/day. The calculation is important for traffic planning, operation, and control.
Methods- Manually or using mechanical counters( Pneumatic hose, magnetic detector, or radar detector)

## Presentation of different Traffic Volume data

Pedestrian Volume Counts: Volume counts of pedestrians are made at locations such as subway stations, mid-blocks, and crosswalks. The counts are usually taken at these locations when the evaluation of existing or proposed pedestrian facilities is to be undertaken. Such facilities may include pedestrian overpasses or underpasses. 6. Periodic Volume Counts: In order to obtain certain traffic volume data, such as AADT, it is necessary to obtain data continuously. However, it is not feasible to collect continuous data on all roads because of the cost involved. To make reasonable estimates of annual traffic volume characteristics on an area-wide basis, different types of periodic counts, with count durations ranging from 15 min to continuous, are conducted; the data from these different periodic counts are used to determine values that are used to estimate annual traffic characteristics. The periodic counts usually conducted are continuous, control, or coverage counts.
Average daily traffic or ADT, and sometimes also mean daily traffic, is the average number of vehicles two-way passing a specific point in a 24-hour period, normally measured throughout a year. ADT is not as highly referred to as the engineering standard of AADT which is the standard measurement for vehicle traffic load on a section of road, and the basis for most decisions regarding transport planning, or to the environmental hazards of pollution related to road transport. Annual Average Daily Traffic (AADT): Annual average daily traffic, abbreviated AADT, is a measure used primarily in transportation planning and transportation engineering. Traditionally, it is the total volume of vehicle traffic of a highway or road for a year divided by 365 days. AADT is a useful and simple measurement of how busy the road is. Newer advances from traffic data providers are now providing AADT by side of the road, by day of the week, and by the time of day. Passenger Car Equivalent (PCE): Passenger Car Equivalent (PCE), is a metric used in Transportation Engineering to assess traffic flow rate on a highway. A Passenger Car Equivalent is essentially the impact that a mode of transport has on traffic variables (such as headway, speed, density) compared to a single car. Highway capacity is measured in PCE/hour daily. Passenger Car Equivalent is also sometimes used interchangeably with Passenger car units (PCU).

Annual average daily traffic (AADT) – It represents the average 24-hr traffic volume for 365-days. It includes seasonal variations also.
As the name suggests it is average daily traffic or in other words the number of vehicles per day. To find out the average number of vehicles per day, the traffic volume should be recorded for some days so that the average can be taken. If traffic volume is recorded for all the 365 days of the year the average daily traffic volume obtained is called Annual average daily traffic (AADT).

Average Daily Traffic (ADT) – It is the average 24-hr volume taken for a minimum of 7-days. It includes the daily variations of traffic like Market days etc.
This is also average daily traffic which is obtained by recording traffic volume of a few days (less than a year). Generally, traffic volume counts are carried out for 3 to 7 days. So, when volume counts are carried out only for a few days the average daily traffic volume obtained is called simply average daily traffic or ADT.Traffic census on non-urban roads is generally carried out twice in a year by taking direction-wise count for a 7-days period, once during the peak traffic season and once during the lean season.

Traffic flow maps– In the traffic flow map representation, the traffic volume or flow is represented by thick lines along the route. The thickness of these lines (to any desired scale) represents the traffic volume. More the thickness more is the traffic volume and vice versa. This representation gives an idea about the traffic volume distribution along the road, at a glance.

DF (Daily Factor)

Seasonal factor –

ADT = Traffic volume count x DF x SF

Annual average daily traffic (AADT)=ADT x DF x WF x SF Where SF = Seasonal factor

Thirtieth highest hourly volume- Plot between hourly volume and no. of hours in a year that traffic volume is exceeded. It is the hourly volume that will exceed 29 times in a year. It is the traffic volume for which design is considered.