Monday, June 28, 2010

Traffic engineering

Traffic engineering is a branch of civil engineering that applies engineering techniques to ascertain the safe and efficient movement of people and goods. It concentrates mainly on research and construction of the immobile infrastructure necessary for this movement, which includes roads, railway tracks, bridges, traffic signs and traffic lights.

Increasingly however, instead of building more infrastructure, dynamic elements are also introduced into road traffic management (they have long been used in rail transport). These use sensors to measure traffic flows and automatic, interconnected guidance systems (for example traffic signs which open a lane in different directions depending on the time of day) to manage traffic, especially in peak hours. Also, traffic flow and speed sensors are used to fish out problems and alert operator, so that the cause of the congestion can be determined and measures can be taken to minimize delays. These systems are generically called intelligent transportation systems.

The relationship between lane flow (Q, vehicles per hour), maximum speed (V, kilometers per hour) and density (K, vehicles per kilometer) is Q = KV. Observation on limited access facilities suggests that up to a maximum flow, speed does not decline while density increases, but above a critical threshold, increased density reduces speed, and beyond a further threshold, increased density reduces flow as well.

Therefore, managing traffic density by limiting the rate that vehicles enter the highway during peak periods can keep both speeds and lane flows at bottlenecks high. Ramp meters, signals on entrance ramps that control the rate at which vehicles are allowed to enter the mainline facility, provide this function (at the expense of increased delay for those waiting at the ramps).

Highway safety engineering is a branch of traffic engineering that deals with minimizing the frequency and severity of crashes. It uses physics and vehicle dynamics, as well as road user psychology and human factors engineering, to minimize the influence of factors that add to crashes.

Traffic engineering is closely associated with other disciplines:

* Transport engineering
* Highway engineering
* Transportation planning
* Urban planning
* Human factors engineering

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