What are the rules for merging onto a US highway or Interstate from an on/off ramp when the highway is particularly busy? I am driving in Colorado.

This happened to me the other day, the highway was unusually busy and I slowed down to be able to merge with the almost stationary traffic. I was driving at 5-10 mph, waiting for an opening.

Meanwhile, someone pulled out of the highway and zoomed past me on the shoulder at an incredible 20 mph and honked his horn. I didn't want to cause problems for others so I followed him off the ramp and tried the same thing on the next, quieter, on/off ramp.

What do the rules say? Am I right to slow down? If traffic was at a complete standstill and I made it to the end of the ramp with no opening, should I stop and block the ramp, waiting for an opening? Or if things don't line up perfectly, is it my duty to miss my turn in order to aid traffic?

EDIT: This is the kind of ramp I am thinking of, I couldn't think of a better term than on/off but now 'continuous' comes to mind. enter image description here

  • Comments are not for extended discussion; this conversation has been moved to chat.
    – JonathanReez
    Commented Oct 22, 2017 at 19:56

5 Answers 5


Most, likely all, States require merging traffic yield. This is essentially the same a changing lanes.

Cloverleaf ramps, which is what you describe, can be tricky because you can get stuck between two rules, yielding and no stopping. So yes, theoretically, you may have to continue without merging if it cannot be done safely.

An officer or judge may not consider a traffic jam sufficient reason to stop and block even more traffic, and I would agree.

However, what usually happens is someone who is exiting slows enough to leave an opening for an entering vehicle or someone gives way (technically not yielding) to let a vehicle merge into traffic. Basically, it just sorta works out if everyone is courteous.

You were OK to approach slowly because the purpose of the ramp is to match the speed of oncoming traffic. The other driver was just impatient jerk.

  • Eh, I'm tepid on this answer. The yield is one of the more ill-defined rules in US traffic law and at least in my mid-western city it's been slowly disappearing for more forward-thinking traffic solutions. Ultimately, once a driver has established themselves in the highway lane (by beginning the merge), the car behind them is required to leave enough distance so as not to be at fault in a rear-end collision. "Failure to Yield" citations are typically reserved for left-hand turns in front of on coming traffic not for "bad merges".
    – user66434
    Commented Oct 20, 2017 at 12:45
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    OP isn't describing a cloverleaf interchange, just an on-off ramp, which every type of interchange has.
    – TylerH
    Commented Oct 20, 2017 at 15:42
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    @TylerH The difference is that the on and off ramps were the same ramp, so the OP was faced with yielding to traffic (ON) but also not stopping (OFF). Around here that's mostly clover-leaf type interchanges, the other interchanges have the on and off ramps separated. Commented Oct 20, 2017 at 17:13
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    @user3067860 I have seen many cases where there are simply multiple exits/entrances to the highway close together so the merging lane is simply a full extra lane that becomes turn-only when the next exit appears. This is sometimes the case on non-interstate highways when a town is accessible from the road across multiple stops.
    – TylerH
    Commented Oct 20, 2017 at 18:23
  • Yielding and stopping are not the same thing. You should be merging, and yielding and merging are not quite the same either. Normally when there's traffic contention a yield calls for a stop, and a merge does not and a stop really screws up a merge. People who stop at the bottom of acceleration ramps because of difficulty merging are scary and incompetent. Commented Oct 21, 2017 at 7:10

If you are moving at the flow of traffic trying to merge, you are doing your part.

The other guy was stuck in traffic going the same 10mph. He was hoping the weave lane would be wide open so he could use it to overtake main road traffic and speed to the next exit (or even merge back in near the end, the sneak!) He was sore because he couldn't - but them's the breaks. His crazed overtake on the shoulder was illegal and would have gotten him a $200 ticket if a cop had seen him.

Even if you weren't there, the exit lane isn't really intended for overtaking while exiting. Not least this would be passing on the right, which is illegal many places when done as an intentional act. You can kind of get away with it if you really are exiting.

Now there is discussion that merging at the last possible minute may be better... but that discussion may not apply to a weave lane since you'd be plugging up the works for all the "exit"ers.

  • We have a lot of these where I live and this is the best answer from my experience. Ultimately he has to wait for you no matter where you merge, start or end (as no matter what you have to merge in and you're in front of him). It will just be more frustrating for him the further down you are as he thought he had made it out of the backup by darting into the weave lane at the very start. A weave lane should match the speed of traffic. Commented Oct 20, 2017 at 18:43
  • @TemporalWolf - They'd have to cheat a lot less shoulder if you went all the way to the end and were also cheating a little bit at that point. That's what the honk was for. Because you were the one car in the way, and you could've been somewhat-half-not in the way. (waiting to merge is better, otherwise you screw everyone. +1)
    – Mazura
    Commented Oct 20, 2017 at 23:53

My driving instructor explicitly told me that, when one doesn't succeed in weaving from the acceleration lane onto the outermost lane, there is a difference between what one should do in theory and what one should do in practice. This applies to the situation where the enter lane ends and does not continue into an exit lane.

In theory, he said, one is supposed to stop at the end of the enter lane. This is very dangerous unless traffic on the motorway is very slow anyway, because other traffic trying to enter will try to go as fast as traffic on the innermost lane, perhaps faster in order to try to enter.

In practice, he said, the wisest thing to do in this case is to enter the emergency lane. This is prohibited, because it does not count as an emergency.

Faced with the choice between very dangerous and prohibited, I would choose the prohibited alternative. Fortunately, I've never experienced the situation in which I failed to merge with fast-flowing traffic, but I don't drive much.

But in your case the enter lane becomes and exit lane, so then you can safely exit the motorway and try again. Do not stop unless the highway is experiencing slow-moving/stopping traffic already. The on/off ramp is part of the motorway and stopping when others are doing 120 km/h (75 mph) is very dangerous.

  • 1
    Note that in the rare case where you cannot safely merge in the allotted space, you can always just not merge. You won't be going exactly where you wanted to go, but you'll be safe. This might happen 1 in 1,000 times, but it's always an option you should keep in mind. Being safe is more important that getting where you need to go quickly. Commented Oct 20, 2017 at 22:40
  • @DavidSchwartz That works when the enter lane becomes an exit lane (like in the question), but not in the normal enter lane.
    – gerrit
    Commented Oct 22, 2017 at 10:31

It doesn't sound like you did anything wrong. If you reach the end without being able to merge then you should take the exit. It shouldn't be too hard to come back to the same on ramp and try again with most interchange designs. Below is a real example, northbound on M23/37B entering Ann Arbor, MI one takes the exit/entrance shown below. This is one that stands out in my memory as having a rather short distance to merge/exit while being quite busy, and the exit ramp radius is quite tight so many unsuspecting drivers end up off the road in winter... The situation is the same going south on M23/37A, I'm just more familiar with the other way. What the other car did is almost certainly illegal, falling under reckless driving if nothing else, in most (all?) states using the shoulder that way is illegal. If there is an area with only shoulder between the on and off ramps then you should instead wait to merge, but here where on and off are not separated you should not stop. The other car should have waited behind you, regardless of whether you stopped or continued. Road rage is a serious issue in the US.

Google Maps image of M23/Washtenaw Ave interchange, Ann Arbor, MI

  • 4
    (1) IME, full cloverleafs like that are actually pretty rare, and (2) if you do miss your merge on this type of interchange, you have to do all four loops in order to try again, which is not what I would call "shouldn't be too hard to come back to the same on ramp and try again".
    – Martha
    Commented Oct 20, 2017 at 14:22
  • @Martha Yes, I don't see them often. I wouldn't take the cloverleafs to go back, I would probably left turn into the BP parking lot, turn around and right turn to go back. By not to hard to go back.... what I mean is that the exit and re-entrance are nearby and laid out such that you can find the way without a map. I am aware of a few highway exits that actually do not have a corresponding nearby entrance.
    – ttbek
    Commented Oct 22, 2017 at 7:23

The general consideration of merging onto any road, be it a highway or a regular street, is that if there are on-coming vehicles -> you have to let them pass. Your letting them pass means that you should not disrupt the traffic pattern i.e. making them slow down, change lanes etc. Your letting them pass may need you to simply slow down your vehicle or to bring it to a complete stop.

The Colorado DMV states that:

Merging: You must yield to all vehicles on that roadway. Do not merge if another vehicle must slow down for you.

Furthermore about high:

High speed roadways generally have acceleration ramps to give you time to build up your speed. When entering a freeway from an on-ramp try to increase your speed to match that of the freeway traffic. Do not merge into traffic until the solid white line has ended. Do not stop in the acceleration lane unless absolutely necessary. Remember, you must yield the rightof-way to the traffic already on the freeway.

  • Adjust to freeway speed in the acceleration lane.
  • Do not cross the solid white line.
  • Signal and move carefully into the freeway lane. enter image description here

And yes that the other driver did was wrong. Also in some states it's illegal to drive on the shoulder/emergency lane (i.e. lane to the right of the last lane) unless speficially mentioned what times of the day you can use them.

EDIT: Having a look at your picture gives more clarity. Usually interstates have a couple of miles distance between an entrance and an exit and people usually tend to merge way before the exit approaches. But in a situation where both of these points are so close, you might notice that once the merge lane starts the solid white line on your left will turn into a dashed line for merging traffic to cross over. After that it would go solid again for a short distance and then again dashed for exiting traffic to cross over. So the rule would be to merge or stop of you cannot merge before the dashed line turns solid.

If the line stays dashed the whole way, then it would create confusions during rush-hours/jams etc. and then you can use your best judgements only. I would stop a quarter mile before the exit with my signal on and wait for an opportunity to merge or some on car's front light flash as an indication that I can come infront of him/her.

  • 1
    Sorry, I don't think I was clear enough in my question, I'm specifically thinking about continuous ramps, where stopping will keep people from leaving the highway. I added an image for clarification.
    – Bazul
    Commented Oct 19, 2017 at 18:07
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    Isn’t the question asking about norms for when the traffic on the freeway is near stationary? Commented Oct 19, 2017 at 18:41
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    I think your advice to stop is very dangerous, on any kind of highway, unless traffic is stopped already.
    – gerrit
    Commented Oct 20, 2017 at 13:45
  • Where exactly are you? I have NEVER seen a case where the dashed line turns solid and then turns dashed again. And as others have said, you don't stop in the merging lane unless you really don't like your car and enjoy getting whiplash (or worse). Which hasn't stopped PennDOT from putting stop signs at the ends of acceleration lanes, but that's because PennDOT is insane.
    – Martha
    Commented Oct 20, 2017 at 14:16
  • We have several of these short weave lanes near me. Ultimately this business of where you pick to merge doesn't make a huge difference, but the general advice I'd give is earlier is better: They will have to wait for you either way, it's just the later they have to do it the more it seems like you're in the way. Commented Oct 20, 2017 at 18:23

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