The map simply shows it's not paved. But does that mean it's a decent dirt road that an ordinary car can handle, or is high clearance and/or 4x4 need? How would I go about finding out?
(Yes, this about the outdoors--I'm interested in the trailhead down the road.)
But does that mean it's a decent dirt road that an ordinary car can handle, or is high clearance and/or 4x4 need? How would I go about finding out?
You ask locals. It's the only way.
No map will tell you how frequently a road is maintained. Even maps that tell you whether you need 4WD or 2WD, as some road maps do, can at best tell you to what level it is maintained, but depending on conditions a rarely maintained road may still be 2WD-accessible. A road in Komi Republic (Russia) on which I took a mountain taxi to Europe's largest national park (Yugyd Va) is accessible by ultra-high-clearance 6WD ТРЭКОЛ only (averaging less than 20 km/h), but Google Maps and Openstreetmap will happily navigate people into getting stuck there (4 hours into our way back my driver tried to convince the driver of a SUV we met to turn around, as he wouldn't stand a chance). In Arizona (USA), after research online and emails to park rangers, we rented a high-clearance 4WD to get to the Whitmore Overlook but I still walked the last 10 km (we did make it to the Tuweap Overlook by car).
If you find a forum post describing the conditions 5 years ago, that's great, if you had been going there 5 years ago. Any weather event can change a 2WD-accessible road to a 4WD-only road or block the road completely. On rarely used roads, you may not find frequently updated information online. So you ask a local. In the United States you are lucky, as public areas are very well managed and there are always park rangers you can call or email (but even there I expect that for some roads the answer may be "we haven't been there since 3 years ago, so we're not sure"), and you'll have an adventure (take wilderness precautions). In Russia it may be harder. I didn't even consider doing my own driving to Yugyd Va, I booked transportation, and it was the right decision.
The easiest way is to just drive it. You need a "certain tolerance" for minor wear and tear and bumps to your car and some cars are better suited than others, but with a bit of patience and by taking your time you can pass by a lot of roads with a 2WD. For example I have a stick shift Civic, I'm quite happy going on lots of really bad roads here in BC.
Then again, if I had a brand new Tesla, I wouldn't be doing this.
Most of the time, our unpaved forestry service roads are somewhat OK to drive on with 2WD. Because we have a lot of recreational hikers, fishermen and hunters, we also have a local publisher that sells printed maps covering the whole province with a lot more info about road conditions than you would ever find in a normal road map. Could be you have something similar in your area.
Typically what will happen is that a road starts out OK and then gets worse as you go on. If it starts out bad, then it will almost never get better.
Hills or mountains are also an indication of possibly bad conditions. If your road crosses a lot of contour lines, not a good sign. With hindsight too: I've gone up roads where the Civic, being a 2WD, literally was sliding backwards from it being too steep. Obviously, that can be dangerous on icy terrain or near ditches. But another risk is if you do manage to go down, going forward, but that extreme slope traps when you try to make it back.
Err on the side of caution. And that, includes, as Chris has said, paying close attention to how difficult turning around would be. If you had to reverse, how long would that be? If it looks like it would be difficult to abandon and head back, head back sooner rather than later.
When you find that you are consistently going over your tolerance, punishing your suspension, finding unavoidable pot holes or snagging on stuff underneath, best to back off. Also, don't do this at night, you can't see potholes.
Still "4WD-needed" is a relative term, esp in individuals' feedback. Most of our $$$ 4WD hereabouts have seen much less unpaved road than my Civic and I've had people warn me off driving an unchallenging 30m to a camping spot because I wasn't in a 4x4. Someone who does a lot of backcountry told me modern SUVs can be crap too: often meant for trips to the mall, too many have insufficient ground clearance.
Alternatively, you could drive up a while and then proceed on a bicycle. Road bikes are totally out but a solid hybrid or mountainbike can easily handle much rougher roads than a car can. That might require you to split up your hike into 2 trips: 1 road recon, 1 actual hike.
But often trail reviews will include everyone's complaints about the access road. Trail reviews without them hint at a tolerable road.
Last, but not least. Depending on your location, winter may not be the best of time to navigate too much in the backcountry. Consider taking along a 406MHz band sat rescue beacon and stocking your car with some emergency supplies.
In fact, since you've mentioned Covid already: our local Search and Rescue group strongly recommends people not venture in difficult terrain right now. Rescue ops necessarily involve bringing a lot of people together.
Has the road been mapped by Street-view? If not does Street-view go along an intersecting road? If so you might be able to get some pictures of the start or all of the road respectively.
You can also look for commentary about the trail online or find local (to the area of the trail) hiking groups and/or 4WD groups that might have better knowledge.
In my experience there are no guarantees that any given road will be maintained to a standard that any car can pass, unless that road is a sealed and/or moderately trafficked road - ones with houses along them tend to be better maintained than ones in forested/wilderness areas.
In OpenStreetMap many roads have the key "surface". Its value should give a good idea of the road conditions.
Comparing satelite google view with a road you know and the road in question is the only way other than talking to someone who has been there, or going yourself. In the two roads you gave in a comment above, both to me look fine for a vehicle with reasonable clearance.
Signs that a road is out of use:
The resolution of these pix looks good enough that anything larger than 6" vertically should cast some kind of shadow.
Where there is a pic of a vehicle (at trail head) it's clear that the road is wide enough for two way traffic.
Consider this: 53.459683, -118.292208 This is the Rock Lake trail head at Willmore wilderness.
At one point there was coal mining in the park.
You can see the old road. It has numerous sections that are muddy for weeks after a hard rain. It crosses the creek about here: 53.471791, -118.342911. At that point you need a vehicle that can handle 12-18" of water.
So the trailhead road is easily handled by most cars. I've parked there several times in my Subaru.
The road beyond may get used once or twice a year by rangers, probably either coming with a 4WD pickup or a quad, or possibly pack horses. (It's nominally a horse park.)
But different terrain will make for different patterns. The Basin & Range country in the American southwest holds vehicle tracks for decades. Your best bet is to look at places on google satellite view and compare roads that you know are passible and roads you know aren't. You will occasionally get into a situation where you have to back up or 5 miles, but it will be an adventure.
Remember, any vehicle is an off-road vehicle if you don't care about it.
All kidding aside, OnX Offroad is a great app you can download that usually has trail conditions, accessibility, and closure info for a surprising number of trails and roads. Ranger stations are also a great resource, just pop in and ask, they're usually very friendly.
Just by looking at your average map there's really no way to know for sure. For a particular example you can look on google maps at Sedona, Arizona. If you zoom to the 1 mi scale you'll see Schnebly Hill Road going east, which looks like a reasonable way to get to the highway. In reality, even in good conditions you would want a 4x4 designed for trails to drive it. It's quite possible to slide off the road into a ditch in many areas. On the other hand, there's many dirt roads in Arizona which look identical to that road on the map and can be handled by basically any car.
You may be able to come to a determination based on satellite images of the road. In the case of schnebly hill road, it's popular enough that there are many videos on youtube of people driving it.
With a combination of Google earth satellite views, calTopo, and local govt aerial surveillance, I can get to a very high degree of certainty of the road condition. If you want to post the location, I can take a look at it and let you know what to expect.
Komoot may have the answer, if they know about that area and it's been classified well.
Here's an example (https://www.komoot.com/plan/tour/d09_WbV2ApJ0d8=FwgABLDx09EA/@-43.6021797,172.6347828,14z):
You should also take the posted gradient into account. 10% feels steep in a car, 30% is about as much as any average car can take on dry paved surface, and decreases when wet.
I have driven the route noted above years ago, and it absolutely required a 4WD in the upper sections. But the first section was just a hillside road, which deteriorated as you got higher.
