در تقاطع سه راهی T شکل عموماً حق تقدم با چراغهای راهنمایی مشخص میشود اما در غیر این صورت قوانین ترافیکی حق تقدم را مشخص خواهند کرد.
A 3-way junction (or 3-way intersection) is a type of road intersection with three arms. A Y junction (or Y intersection) generally has 3 arms of equal size. A T junction (or T intersection) also has 3 arms, but one of the arms is generally a minor road connecting to a larger road.
Some T junctions are controlled by traffic lights, but others rely upon drivers to obey right-of-way rules, which vary from place to place. For example, in some jurisdictions, vehicles on the right always have the right-of-way (even at T junctions), while in other jurisdictions, vehicles travelling on the "through" road of a T junction have the right-of-way, meaning that vehicles approaching the "major" road must allow through traffic to pass before joining the flow of traffic.
In the People's Republic of China, going straight on red when approaching a T junction on the main road with the intersecting road on the left was permitted until the Road Traffic Safety Law of the People's Republic of China took effect on 1 May 2004.
In Taiwan (administered by the Republic of China), when at least two vehicles reach a T intersection without a working traffic light, the vehicle on the side road is to yield to any other vehicle straight on the main road. If two vehicles want to turn left, the vehicle on the left is to yield.
When one road at a 3-way junction has a higher traffic volume than the other (and particularly when the roads are perpendicular to each other), turns are characterized as "right-in", "right-out", "left-in" and "left-out". A turn "in" represents a turn from the major road into the minor road. A turn "out" represents a turn out of the minor road onto the major road. A 3-way junction allowing all four of these turns is characterized as "full-movement". These terms also apply to turns between roads and driveways.
An experiment was done[by whom?][when?] in Illinois, United States to allow going straight on red (like a right turn on red) when approaching a T junction on the main road, with the intersecting road on the left. It was a failure. However, at some T junctions where the main road includes at least two lanes on the side away from the intersecting road, the farthest (rightmost, in areas where traffic drives to the right) lane is given the right of way to proceed straight through the intersection at all times, denoted by a "green arrow" signal if a traffic light is installed at the intersection.
In such cases, often that lane is also specially delimited with pavement markings or other lane separation devices, to keep left-turning traffic on the intersecting road from colliding with traffic proceeding through the intersection on the main road. There are now safer variations of this, called continuous green-T (or seagull) intersections, that have a left turn lane off the main road either channelized or otherwise separated from traffic going straight, which allows for a traffic signal on only one side of the road.