In many parts of the world traffic is generally organized, flowing in lanes of travel for a particular direction, with interchanges, traffic signals, or signage at intersections to facilitate the orderly and timely flow of traffic. Traffic can be separated into vehicular, non-vehicular (bicycling), and Pedestrian classes of traffic. Vehicles of the same class share their speed limits and share easement with one another. Cooperative signaling arrangements can also be made with representatives of other classes of traffic.
Organized traffic typically reduces travel time. Though vehicles wait at some intersections, wait time at others is much shorter. Organized traffic degenerates to disorganized traffic with an unexpected occurrence, be it road construction, an accident, or obstructions in the road such as an animal, debris, or other objects. On particularly busy freeways, a disruption can persist until traffic thins. William Beaty observed persistent disruptions and named the phenomenon traffic waves.
Simulations of organized traffic frequently involve queuing theory, stochastic processes and equations of Mathematical physics applied to Traffic flow.
On roads that have multiple lanes going in the same direction, drivers may usually shift amongst lanes as they please, but they must do so in a way that does not cause inconvenience to other drivers. Driving cultures vary greatly on the issue of "lane ownership": on some countries, drivers traveling on a lane will be very protective of their right to travel on it while on others drivers will routinely expect other drivers to shift back and forth.
Different countries have different rules that establish who has the right of way, but a common pattern is for one of the roads (usually the smaller road) to have a marking indicating that it should "yield" to drivers on the other road. This can be in the form of a STOP sign, dotted lines painted on the pavement or other devices. Drivers approaching from the road with the STOP sign (or equivalent device) are required to stop before the intersection and only proceed when a breach occurs in the other road's traffic. Some countries also include pedestrian crossings near the STOP signs, and in this case the approaching drivers must also allow the pedestrian to cross the street before advancing.
Another way to resolve the right-of-way conflict is to establish a general rule such as the French prioritè-a-droit (priority to the right). This rule establishes that the right of way belongs to the driver who is coming from the right, and the driver coming from the left should yield to him. This rule is unambiguous, but may lead to some counterintuitive situations, such as in T-intersections, where, strangely enough, traffic going straight through the top segment of the T must yield to entering traffic that comes from the vertical leg of the T. [image] [image] In most modern cities the traffic signal is used to establish the right of way on the busy roads. Its primary idea is to give each road a slice of time in which its traffic may use the intersection in an organized way. The intervals of time assigned for each road may be adjusted to take into account factors such as difference in volume of traffic.
On roads with multiple lanes, turning traffic is generally expected to move to the lane closest to the direction they wish to turn. For example, traffic intending to turn right will usually move to the rightmost lane before the intersection. Likewise, left-turning traffic will move to the leftmost lane. Exceptions to this rule may exist where for example the traffic authority decides that the two rightmost lanes will be for turning right, in which case drivers may take whichever of them to turn. On certain parts of the world traffic will adapt to informal patterns that rise naturally rather than by force of authority: for example, in Brazil and elsewhere it is common for drivers to observe (and trust) the turn signals used by other drivers in order to make turns from other lanes. For example if several vehicles on the right lane are all turning right, a vehicle may come from the next-to-right lane and turn right as well, doing so in parallel with the other right-turning vehicles.
The actual appearance of pedestrian crossings varies greatly, but the two most common appearances are: (1) a series of parallel white stripes or (2) two long horizontal white lines. The former is usually preferred, as it stands out more conspicuously against the dark pavement.
Some pedestrian crossings also accompany a traffic signal which will make vehicles stop at regular intervals so the pedestrians can cross. Some countries have "intelligent" pedestrian signals, where the pedestrian must push a button in order to assert his intention to cross. The traffic signal will use that information to schedule itself, that is, when no pedestrians are present the signal will never pointlessly cause vehicle traffic to stop.
Pedestrian crossings without traffic signals are also common. In this case, the traffic law usually states that the pedestrian has the right of way when crossing, and that vehicles must stop when a pedestrian uses the crossing. Countries and driving cultures vary greatly as to the extent to which this is respected.
To enforce the speed limit, two approaches are generally employed. In the USA it is common for the police to patrol the streets and use special equipment to measure the speed of vehicles, and "pull over" any vehicle found to be in violation of the speed limit. In Brazil and some European countries, there are computerized speed-measuring devices spread throughout the city, which will automatically detect speeding drivers and take a photograph of the license plate, which is later used for applying and mailing the ticket.
Expressways usually have controlled entry and exit, that is, entering and leaving the expressway may only be done at specific points called entries and exits. Vehicles entering the expressway must yield the right of way to the vehicles already traveling on it.
Intersections have no signals or signage, and a particular road at a busy intersection may be dominant (that is, its traffic flows) until a break in traffic, at which time the dominance shifts to the other road where vehicles are queued. At the intersection of two perpendicular roads, a traffic jam results if four vehicles face each other side-on.