I see two likely types of ambush/roadblock being used in the SHTF world.
Predatory, and Defensive.
The Predatory road block has the same purpose as placing a snare on a game trail. It would be set up on a road near a camp by a 'raider' type person or group of people for the purpose of ambushing and robing travelers.
It would be monitored by at least one person with means to communicate to the others who would presumably be at nearby camp. As has been mentioned, its probably unlikely that a whole group of people would be able to man a ambush 24/7 for very long, but like a trap on a gametrail, it could be a low effort way to gather resources, for people inclined to murder and steal.
The second kind would be Defensive, placed on a road by people who have bugged in as a method of area denial to potential threats or competitors.
This would also be monitored but would only turn into an ambush if the travelers started to clear it or otherwise bypass. It would differ from a closed gate only that a gate obviously gives away that there is something to protect, while a possibly naturally downed tree has the chance to turn people back without revealing anything of value past that point.
For the traveler, in either scenario, its a high risk situation. A deliberately cut down tree likely means you will come under attack by whoever cut it down, wether it was for defense or predation when you try to clear it. Perhaps immediately, but very likely at least when you get out the saw.
However, the traveler presumably needs to get to wherever they are going fairly badly, or else they would not be on the road at all and turning back from every obstacle won't get you very far as without routine maintenance, most roads will pretty quickly end up naturally blocked.
I think it comes back to the idea that no matter what your doing, there is no way out of having to provide your own security. Anyone traveling will have to be able to do so in enough force to actively secure the area every time they stop.
Some kind of scouting ability will be extremely valuable. A classic 'stop, look, move' progression would be ideal. If for instance, you had a drone with a mile range, you could scout a mile a head, return the drone, move up to the last scouted position, make a secure stop, send the drone another mile ahead. This would be slow and tedious but high security usually is.
Alternatively, run a light fast scout vehicle ahead, something that is more likely to escape an ambush than your primary vehicle.
This has the obviously has the problem of, who do you get to scout?
Now, as for wether there will be people on the road.....yes. There will be.
Anyone with a full tank of gas will have 300 miles of range. Even with a half tank, 150 miles. That is a lot of travel distance. Those of us who have prepared......much much more.
After the worst of the crisis is over, at some point you will be venturing out.......but at that time, the risk will still be far above "normal", because the ROL will most likely still be absent.
Yep.
And there is really no period in human history without some form of extensive travel, even in periods we would consider WROL. Given millions upon millions of vehicles with probably millions of miles of fuel of various kinds above ground....vehicular travel seems very likely to continue in all scenarios.
What I think is likely is a return to various 'trade routes' of relatively safe, cleared roads with local 'powers that be' keeping them secure to encourage travel, and other, more dangerous back roads where people travel only in force.
Walking alone in the woods I think is the slowest, least useful and probably the most dangerous form of travel in most scenarios. This doesn't mean it won't happen, but it seems to have the least return on the risk. I think you are just as likely to run into someone else in the woods, as on a road, but in the woods you will only have what you can carry, and for a given distance, you will spend a lot more TIME out and exposed. Ten minutes on a road could be a full day on foot traveling in the woods. A three hour drive on less than a single tank of gas could be a month of travel and foraging for the person on foot, and could be a three hour trip with your entire group...on the way to return from barter town with 2000lbs of salted fish....or whatever.
The only time I think traveling on foot will be valuable, is when the only thing of value you have to transport is yourself, which in general, I do not think will require much travel.
If you don't have the budget for EVs, then pick your time of the day and other conditions (for your travel) that make preparedness by any potential ambushers likely to be poor........early AM, cold, raining, high wind (that suppresses vehicle noise), etc, etc
This was the first question I asked when I joined that 'other forum', what time of day is best to travel.
The answers that I got pointed towards after midnight, to before dawn as the period where there are the least "mark 1 eyeballs' open.
I think this is fine for foot travel.
For vehicle travel my opinion is the period before dawn when its just light enough to see, but before true dawn, and the period after sunset, before true dark.
I've observed that at those times, a careless driver can leave his headlights off and be very hard to see on the road from even 100 yards away, but he himself can see well enough to drive at highway speeds that he doesn't even realize his lights are off.