The normal designation for lanes on divided highways is the quickest lane is the one closest to the center of the road, and the slowest to the edge of the road. Drivers are usually expected to keep in the slowest lane unless overtaking, though with more traffic congestion all lanes are often used.
When driving on the left:
• The lane configured for faster traffic is on the right.
• The lane designated for slower traffic is on the left.
• Most freeway exits are on the left.
• Overtaking is permitted to the right, and sometimes to the left.
When driving on the right:
• The lane designated for faster traffic is on the left.
• The lane designated for slower traffic is on the right.
• Most freeway exits are on the right.
• Overtaking is allowed to the left, and sometimes to the right.
Countries party to the Vienna Convention on Road Traffic have uniform rules about overtaking and lane designation. The convention details (amongst other things) that "Every driver shall maintain the edge of the carriageway appropriate to the direction of traffic", and the "Drivers overtaking shall do so on the side opposite to that appropriate to the direction of traffic", not minding the presence or absence of oncoming traffic. Allowed exceptions to these rules include turning or heavy traffic; traffic in lines, or situation in which signs or markings must dictate otherwise. These rules must be more strictly observed on roads with oncoming traffic, but still apply on multi-lane and divided highways. Many countries in Europe are party to the Vienna Conventions on traffic and roads. In Australia (which is not a contracting party), traveling in any lane other than the "slow" lane with a speed limit at or above 80 km/h (50 mph) is against the law, unless signage is posted to the contrary or the driver is overtaking.
Most areas in North America do not have any traffic rule about staying to the slowest lanes unless overtaking. In those areas, unlike many parts of Europe, traffic is allowed to overtake on any side, even in a slower lane. This practice is known as "passing on the right" in the United States (where it is common ) and "overtaking on the inside" and "undertaking" in the United Kingdom. In most countries, the inside lane refers to the fastest lane (the lane closest to the highway median), but in the United Kingdom, it refers to the slowest lane (the lane that is in fact outside).