I've seen plenty of signs that say things like "Slower Traffic Keep Right," in fact some of them even threaten a fine if you disobey. So I think it is fair to assert that the US Department of Transportation recognizes that "fast lanes" are a real thing.

But isn't the speed limit still technically 55 (or whatever the limit is) for every lane? I mean, they would never put up a sign that said "Drunk Drivers Keep Left" or "Use Middle Lane if you have Jimmy Hoffa tied up in your trunk."

Are signs like these an acknowledgement that you are permitted, maybe even required, to speed?

  • 3
    It's the speed limit, not the minimum speed. Slower drivers can drive down the highway at 35mph unless a minimum speed is posted. It makes even more sense when some commercial vehicles are speed limited to 55mph, but the speed limit is 70.
    – Ron Beyer
    Commented Mar 1, 2019 at 19:37
  • 1
    Comment from the other side of the Atlantic: over here (Germany), you generally have to drive in the rightmost lane that is possible (i.e. we fill the lanes from right to left, if the right lane is empty, you have to move from 2nd lane into the right lane). And you're not allowed to take over on the right. Nevertheless, speed limit is usually equal for all lanes - so I don't see anything particularly incompatible in this combination. (In practice, slow lane forms on the right as trucks and trailers have lower general speed limits) Commented Mar 1, 2019 at 19:47
  • 1
    California specifically requires traffic moving slower than the normal speed of traffic moving in the same direction to be in the right-hand lane notwithstanding the prima facie speed limits. If you're slower than the surrounding traffic then you have to move right. In my experience, California drivers seem to be the worst at following this law. It reminds me of the question, "How can I be slower when everyone's behind me?" Most of the states that I've researched require slower traffic to move right if they're slower no matter the relation to the speed limit.
    – Dave D
    Commented Mar 1, 2019 at 21:38
  • 1
    The final question "Are signs like these an acknowledgement that you are permitted, maybe even required, to speed?" is a question about what the LAW is. This is on-topic here. Commented Mar 1, 2019 at 21:46
  • Fast v. slow lanes make more sense climbing a highway on a mountain with a high grade. Big trucks go slow uphill. They have to stay right.
    – ohwilleke
    Commented Mar 6, 2019 at 7:16

2 Answers 2


The US Department of Transportation does not "recognize" fast lanes, or have any limits on highway speed, which are determined by the states. Here is a resource on the various keep-right laws of the states. No state has a "fast lane" that allows speeds greater that the legal limit, nor does any state have a law requiring drivers to drive exactly the posted limit. Every state has some provision regarding slow-moving vehicles, and none frame the matter in terms of fast-moving vehicles. The legal convention is that slow-moving vehicles must be on the right, not the left. Some states have the restriction that you may not drive in the left lane except to pass, for example 625 ILCS 5/11-701(b), (d). You may drive in the left lane in Utah, but you must not impede traffic (which means you must move to the right). The signage depends on the laws of that state, and in all cases reflects laws against too-slow driving, and never approval of too-fast driving.

  • Some states are 'reasonable and prudent' states, like Texas. The speed limit isn't really a hard and fast absolute limit. It's just 'evidence' that it's not reasonable and prudent. The keep right laws usually DO NOT say keep right unless you're going the speed limit, in which case you're fine.
    – mark b
    Commented Apr 1, 2019 at 18:02

If "fast lanes" means "lanes for cars that are faster than most of the other traffic," then yes, fast lanes are legal.

But establishing them does not suggest you are permitted to speed; it merely acknowledges that some cars move faster than others and that slower cars impede the flow of faster-moving traffic. Preventing faster cars from passing slower cars creates traffic congestion, and traffic congestion increases the risk of injuries and property damage. The laws are meant to reduce the likelihood of those harms by managing the flow of traffic.

Of course, this doesn't necessarily have to involve speeding. If the speed limit is 70 MPH, a truck going 55 should move to the right if other cars are going 60.

But even if it is an acknowledgement of speeding, a law that acknowledges a crime by requiring others to help reduce the resulting harm isn't permission to commit the crime. A law requiring police to process rape kits isn't permission for you to rape anyone, a law requiring teachers to report child abuse isn't permission for you to beat your children, and a law requiring the government to prepare for a nuclear attack isn't permission to detonate a dirty bomb.

These are all just laws meant to help the government manage foreseeable problems.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .