Masurarea traficului

AADT reprezinta abrevierea de la Annual average daily traffic (= trafic mediu zilnic masurat pe durata unui an), este o untate de masura folosita in principal in planificarea si tehnologia transporturilor. Reprezinta volumul total de trafic de vehicole pe un drum sau o autostrada timp de un an si impartit la 365 de zile. AADT este o masura utila si simpla a traficului de pe un drum. Este numita uneori si ca "media zilnica a traficului anual".

Ce mai importanta folosire a AADT este pentru stabilirea fondurilor pe care le vor primi anumite zone pentru intretinerea si dezvoltarea acelor drumuri.

Pentru a masura AADT pe un anumit segment de drum, datele de trafic sunt colectate fie de un numarator automat de trafic sau pri angajarea unui observator pentru a inregistra traficul. There are two different techniques of measuring the AADTs for road segments. One technique is called continuous count data collection method. This is where sensors are permanently embedded into a road and traffic data is measured all 365 days. The AADT would be the sum of the total traffic for the entire year divided by 365 days. There is a problem with calculating the AADT with this method. The continuous count equipment is not operating for the full 365 days due to being shut down for maintenance or repair. A better calculation method is to average the daily traffic for each of the 12 months - MADT Monthly Average Daily Traffic - and take the average of the MADTs. This method is outlined in the [FHWA Traffic Monitoring Guide][1]. The continuous count method is costly. There are monthly maintenance fees involved and it is expensive to install and purchase the sensors. It can cost money to power the sensors if it is connected to the local power grid. It can cost money to maintain the communication connection whether it is a phone line or an IP address.

The alternative or second technique is called the short count data collection method also known as the coverage count data collection method. The AADT can be estimated with portable sensors that are attached to the road and record traffic data typically for 2 – 14 days. These are typically pneumatic road tubes although other more expensive technology such as radar, laser, or sonar exist. After recording the traffic data, the traffic counts on the same road segment are taken again in another three years. FHWA Traffic Monitoring Guide [2] recommends to perform a short count on a road segment at a minimum of every three years. After collecting the data with a portable traffic counter, the data is converted into an ADT - Average Daily Traffic. This would represent the average day of traffic for the month the data was recorded. Seeing traffic varies throughout the year, with it generally being low in the winter months and high during the summer months, the AADT is estimated by removing this seasonal bias by multiplying the ADT by the Monthly Seasonal Adjustment Factor. Short counts are taken either by state agencies, local government, or contractors. For the years when a traffic count is not recording, the AADT is estimated by applying a factor called the Growth Factor. Growth Factors are statistically determined from historical data of the road segment. If there is no historical data, Growth Factors from similar road segments are used.\n

Average summer daily traffic (abreviata ca ASDT) este o masura similara cu AADT. Metodele de colectare a datelor pentru cele doua sunt exact la fel, doar ca datele pentru ASDT sunt colectate doar in timpul verii. Masura este utila in zonele in care pe un anumit drum exista un volum semnificativ de trafic sezonier.