My mom always liked to say the speed limit is a limit not a goal.
Or, I should say, it’s more nuanced than that. By a lot. A lot a lot. But the basics don’t take long, so let’s dive in.
The thing about speed limits is that they are supposed to reflect the conditions, circumstances, and safety requirements of the road in question. You wouldn’t expect a long straight highway to have a 30MPH speed limit, because it’s obviously safe to go faster there. And I don’t think anyone would support a 100MPH speed limit in a school zone.
So: conditions, circumstances, and safety. These are all intertwined. The key is to know why they decided to put that speed limit on that street. Now I’ll run through the standard limits and what we should expect based on those numbers.
But before we start that, I want to mention special conditions. Bad weather absolutely has an impact on how safe roads are, and they largely negate those little white signs. If the rain or fog — or smoke in California — is so thick you can’t see 50 yards down the road, you should not be driving 65MPH no matter what the posted limit is. I’ll go into this in more depth when I write about driving in weather. For now, suffice to say that there can be really good reasons to drive below the limit as well. There are few hard and fast rules for driving that apply every single time (they exist! always wear your self-belt!); you need to be able to judge conditions for yourself.
Below 25MPH signs are uncommon, but they do exist. Usually these are special circumstances and you should at least start with the assumption that it might be 100% necessary to go exactly that slow! There’s a sign up at the dump, for instance, that says 7MPH. And, in that case, that’s pretty much the fastest you’d want to go in there.
25MPH is the standard speed limit for residential streets. This is the one standard limit I always keep to. You see, 25MPH is about the fastest you can go and still stop if a kid runs out in front of your car. Read that again. This is the fastest you can go on a residential street, period. It’s not only children! Grown adults will just wander into the street in a residential neighborhood. To say nothing of dogs off-leash! Keep it under the speed limit and keep a sharp eye out for animals and people to step in front of your car. This is also the speed at which you are most likely to encounter stop signs.
30MPH is largely a bullshit speed limit. It’s for 35MPH roads when the city needs that sweet, sweet traffic ticket revenue. Almost any street with this limit can be safely taken at 50 in terms of paving, turns, traffic lights, but not in terms of tickets you might get for going 20MPH over the speed limit!
35MPH is your standard business district road. There aren’t many houses on these streets, though there are often apartment buildings. You have to watch out for drivers entering or exiting large parking lots (such as those at grocery stores or Target), and you might have to slow down in a hurry. It can be safe to go quite a bit faster, but you still need to be on the lookout for parking lots and such.
40MPH is usually posted on a (business district) non-residential street with fewer large parking lots to go in and out of. However, it can have small businesses, ironically. These little parking lots aren’t as easy to see as you drive by, which has two ramifications. First, as you drive you may not be aware of someone wants to exit the lot and suddenly be in your way. And secondly, other drivers may not be sure where they are trying to go, so they may stop or slow unexpectedly.
45MPH You’ll see fewer buildings altogether at this level, and fewer cross streets. This is not a common speed limit for city streets. You can probably get up to 60 on these roads.
50MPH You very rarely see this in town, though I have. When it’s in town, the rules for 45 suit pretty well. If you are on a highway, it’s different; this is similar to 30MPH in that there is rarely a safety concern that justifies a speed limit lower than 60, or maybe even 70! Sometimes it is in place to gradually slow you down. 70 to 60 to 55 to 45 to 35 and there you are in town.
60MPH is honestly like 50, but from someone who cared more about your desire to drive fast.
65MPH Now we’re cooking! Any 65MPH highway in this country (assuming it’s in reasonably good repair) can be taken at 85, assuming good weather, etc.
70MPH is unfortunately the highest speed limit in this country. Same rules as 65MPH.
There are other speed-related signs and considerations.
Those yellow signs you usually see before a curve often have a number on it, but it is not a speed limit in the sense of white signs — or traffic tickets. It is the advised speed. I highly recommend against disregarding these signs altogether. You’d drive into a ditch at best the next time you went out. The key to those signs is, again, knowing why they are there.
In the mountains you might have a road with a 60MPH limit and then come across a yellow sign recommending 45MPH for an upcoming curve. Do you need to slow down to 45? Probably not. Should you slow down at least some? Probably. Another common place is on a freeway offramp, where you are often required to drive in a tight circle.
And the last common place you’ll see such a sign is before a speed bump. Speed bumps are a special case. Personally I don’t think they should be allowed to put a speed bump to slow you down below the speed limit, but they do. I’m sure you’ve noticed that they come in many shapes and sizes. If a bump says 5MPH you’d probably better slow all the way down to 5! But with the gentler 20MPH variety there is yet another consideration: The ground clearance on your car. I drive a Jeep Renegade and it’s got good clearance. I can take a 20MPH bump at 25 without any worries about the bottom of my car. Your average sedan can not. I’ll be going over Know Your Car in a later piece.
Allllllll this was a really long way to say that you should drive according to conditions, not numbers on a sign, always keeping in mind that your evaluation won’t impress a cop. And my mom? She likes to drive 40MPH regardless of what sign is posted. This, my friends, is not an improvement.