What’s the on-ramp speed limit and when does it kick in? Here’s a reasonable interpretation
Question: What is the speed limit on an on- ramp, and when and where does it change? Where I live there is a street that turns into an on-ramp. This street has a 30 mph speed limit on it. The highway has a 65-mph speed limit on it. When and where does that 30 end and the 65 begin?
Answer: My instinct is to say that on-ramps are part of the freeway infrastructure and subject to the same speed limits. But once you asked the question I realized that I couldn’t provide you with a law that led me to that conclusion. After searching through state law, the Code of Federal Regulations and the U.S. Department of Transportation’s Freeway Management and Operations Handbook, I still can’t provide a direct quote from the law. That’s not to say it’s not out there, but I haven’t found it yet.
Even without a reference to legal code, we have plenty of guidance on how to use an on-ramp, and that guidance makes some pretty clear implications about speed limits on ramps. The Washington Driver Guide states, “When you merge with traffic, signal, and enter at the same speed that the traffic is moving.” The Driver Guide goes on to say that on-ramps are for building up your speed to merge with traffic. It wouldn’t make sense, then, for an on-ramp to have a speed limit that’s any less than the posted limit on the freeway.
We can also conclude that freeway speed limits apply to off-ramps; the Driver Guide says that when exiting a freeway, drivers should not slow down until they’re on the exit ramp. For at least a little while, drivers should be traveling at freeway speeds on both on and off-ramps.
As to where that speed limit officially starts, I’ll make a couple of reasonable guesses. First, freeways and city streets are built by different people. There’s a good likelihood that when you approach an on-ramp, if you look carefully, you’ll see a change in the pavement between the city road and the freeway ramp.
Or you could just look at Google Maps, which shows freeway infrastructure as yellow roads and city streets in white. But I don’t think getting the “where” exactly pinpointed is actually that important.
While the section of the law on speed limits does include a few actual numbers, the overarching theme of the law is, to (very) loosely paraphrase, “drive at a speed that will avoid a crash.” If the freeway speed is 70 mph, but you can’t go faster than 40 mph through the curve in the on-ramp without grinding the side of your car on the guardrail, then for that stretch of the ramp the practical speed limit is less than 40 mph. There’s an expectation in the law that drivers will make safe decisions about their speed, regardless of the posted maximum limit. (It is a maximum, after all.)
Just to make sure I was on the right track, I asked a couple of transportation professionals in the fields of engineering and enforcement. They both described on-ramps as a tool to get up to speed so that you can safely merge. Understandably, they were more focused on safe behaviors than exactly where the line was between two speed limits. Regarding their use, one of them gave this analogy: “In the old Westerns, the hero never tried to board a train from his horse from a stop. He got up to and matched the speed of a train.” He didn’t say this next part, but I think it’s implied: merging properly makes you a hero.
This story was originally published March 15, 2021 at 5:00 AM.
