Now Reading: The Right Speed to Exit
-
01
The Right Speed to Exit
Q: When a freeway has an exit-only lane leading up to an offramp, what’s the speed limit in the exit lane? If the speed limit on the freeway is 60 mph, what speed should one drive in the exit-only lane?
A: Allow me to begin with a reminder that when the posted speed limit is 60 mph, that’s the maximum speed allowed by law. Even though every driver knows that, we often tend to drive as if the maximum speed is actually the required speed.
Instead, Washington’s law on speeding begins with the basic rule. It goes like this: “No person shall drive a vehicle on a highway at a speed greater than is reasonable and prudent under the conditions and having regard to the actual and potential hazards then existing.” If I lost you there, I’ll paraphrase. Drive at speed that’s safe for the situation, keeping in mind all the ways things could go wrong.
The speed limit part of the law comes next. Essentially, it says that there are some speeds that we know are not reasonable and prudent for a given type of road, so we’re setting a top end limit. The defaults in the law are 25 mph for city streets, 50 mph on county roads, and 60 mph on state highways.
As you read that, you probably thought of at least one road that doesn’t match those numbers. Not all roads are equal. A county road might be flat, wide, and straight with great visibility, or it might be steep, narrow and winding. A city street may need to change from 25 mph to 20 mph as it goes through a downtown district or a park with heavy pedestrian traffic. The law recognizes that the default settings won’t work on all roads and allows for adjustments, both faster and slower, to fit the road and surrounding environment.
Following that, we get to the part of the speed law that should answer your question. The posted speed limit on the freeway includes the exit-only lane. However, the last paragraph of the law lists some situations where drivers shall drive at an “appropriate reduced speed.” A couple things here: In the law, “shall” means it’s not an option – it’s required. And “appropriate” here means your speed should be consistent with the first part of the law, which you’ll remember means driving at a rate that is safe for the circumstances.
Now, the list. Drive at an appropriate reduced speed at intersections, railway crossings, curves, narrow or winding roadways, and when special hazards exist. That includes pedestrians, cyclists, weather, and road conditions.
A freeway exit probably means an upcoming curved offramp, along with other road conditions that may change as you transition from the freeway to the offramp. Offramps typically have an advisory speed posted on a yellow sign to let you know that you’ll need to slow down to a safe speed. Maybe you’ve heard that advisory speeds can’t be enforced. That’s true in a sense. However, if you disregard the advisory speed and end up crashing, you would have violated the first part of the speed law, because you didn’t choose a “reasonable and prudent” speed.
Considering all of that, the correct speed in an exit only lane, well, it depends. You’ll want to take into account the speed of the vehicles on the freeway, as slowing down too much too soon could cause a conflict before you reach the exit, as well as anticipate the changing conditions of the off-ramp. There isn’t a fixed number, but attentive driving and your good judgement should get you there.
Kary
Although I am sure there are some, off the top of my head I cannot think of a single freeway exit which is so poorly designed (or space limited) that it’s necessary to slow down before leaving the freeway. Unfortunately many people do slow down beforehand, which affects traffic on the freeway. That said, of course you might have to slow down early if there’s traffic backed up on the exit.
DOUG DAHL
As a general rule, I maintain my freeway speed until I’ve entered the offramp, for the reason you mentioned. However, I was thinking about your comment as I was driving home yesterday on I-5, and I can think of at least a couple exits that, while not absolutely necessary to slow down before leaving the freeway, would make some drivers uncomfortable if they didn’t.
At one exit I’m thinking of there’s a 20 mph cautionary sign and a ramp that drops down so you can’t see the curve ahead very well. I measured the distance from the beginning of the offramp to the curve on Google maps and it’s over 300 feet, so any vehicle should be capable of going from 60 mph to 20 mph in that space, but it feels like too-aggressive braking.
At my exit there’s a 40 mph cautionary sign and a visible curve shortly ahead. In my car I can maintain 70 mph into the exit, but I bet if I were in a full-size SUV it would feel too fast, because of how much speed you need to dump before you get to the 40 mph corner. I’ve noticed that at this offramp most drivers slow down a bit before the exit. Even if it’s a driver’s first time taking this exit they’ll probably slow down while still on the freeway because they can see how close the curve is on the offramp.
Now you have me wondering, so I did some deceleration calculations and looked up some numbers. The first off-ramp I mentioned would have a deceleration rate of about 3 meters per second squared. One chart I found suggested that 1.5 m/s2 is a desirable rate, 2.5 is comfortable, and 3.5 is a desirable maximum. The actual maximum deceleration rate for a car is 7.5 or more, so it’s not like you’re at any sort of danger zone at 3, but it’s getting into the area where it doesn’t feel right.
We tend to make decisions based on perceptions rather than reality, so I can see why a lot of drivers would slow down prior to reaching an onramp, even if they don’t need to. I hadn’t really thought about deceleration rates before, but after looking at it, and considering our perceptions, I now am going to be more intentional about my awareness of other drivers near offramps.
And I just wrote a response to your comment that’s almost as long as the original article. I need to learn to be more concise.
Kary
LOL on concise! Two related comments. 1. The size of vehicle would matter. 2. But it’s only likely vehicles that are larger than an SUV that would need to slow to the speed of the advisory sign. My truck and 20′ travel trailer are usually okay at 5 mph over the advisory.
Can you specify that 20 mph one so I can check it out? I’ve been trying to think of ones that are bad, but have been unable to come up with any other than the I-5 South at Union, but I think that’s an exit only lane, which doesn’t really count.
DOUG DAHL
The 20 mph exit is northbound I-5 at Lakeway in Bellingham, exit 253.
Kary
Using Google Streetview that does look nasty! And I’d add that with the curve/drop you can’t really see the number of stopped cars, which is probably the reason for 20 mph.
Seems like a rather make-shift exit too. It doesn’t even dump out on a major street. So it probably fits in both my poorly designed and space limited categories. I’m guessing taking out the motel would have been too expensive.