Gridguide's purpose is to allow coordination between vehicles well beyond LOS/vehicle-based sensor range. If you've ever driven through a construction zone on the interstate, think about how one doofus braking too hard causes a ripple that magnifies back through traffic, sometimes culminating in someone getting rear-ended. Gridguide eliminates that. Under GG guidance vehicles maintain closer following distances at higher speeds than metahuman attention spans permit. Cars under GG guidance don't accelerate only to have to come to a stop due to a traffic light. They maintain steadier, more constant speeds. Consider in the real world cars average about 20kph in dense urban environments (lots of time stuck motionless in gridlock/red lights) whereas Gridguide guided traffic averages 80kph in the same conditions! (SR5, pg 200).
None of that means that off-grid drivers are necessarily dangerous, though I will concede that most people don't have the skill needed to safely drive in downtown without Gridguide, and that most people who do have that skill are riggers.
Your vehicle can get real-time status of at least the next three intersections (SR5 pg 421) and so your vehicle's speed can be tweaked to ensure you hit them all green. Assuming they even HAVE lights; imagine almost any traffic-depicting scene in a Sci-Fi movie... streams of traffic cross right through each other with no collisions as individual cars all pass through the gaps between cars in the crossed stream!
Rigger 3 mentions traffic lights as being something that Gridguide controls. Furthermore, the very example you bring up specifically says "next three traffic lights", not "next three intersections", so we can assume that they're still around. After all, you need them for pedestrians, and why bother spending money to tear down pre-existing infrastructure when you can use it as a redundant safety factor?
Think about that. You can just flip a sudden Yooie into oncoming traffic and so long as you warned GridGuide, and "like magic" the traffic just parts and gives you a lane.
She was a tow truck/recovery vehicle driver. Along with other first response vehicles such as police vehicles, firetrucks and ambulances, tow trucks and recovery vehicles are mentioned in Rigger 3 to have Gridguide priorities and privileges other vehicles don't. I don't think this is a good example to use.
And think about what that means if some of the oncoming traffic is NOT on GridGuide.
That is a question the designers and engineers of Gridguide have spent a lot of time thinking about. In that specific scenario, the u-turn is delayed until the off-grid vehicles have passed, much like if a pedestrian or large animal had wandered onto the road.
And if you go pulling extreme maneuvers while not on GridGuide
Overlooking the fact that only a privileged few are allowed to pull extreme maneuvers while on Gridguide, consider: what makes this dangerous? Is it because you're doing something inherently dangerous, or because you're doing it without Gridguide? I should think the former.
remember that vehicles under control of Gridguide are considered under the control of their Pilot program (SR5 pg 202). Even assuming everyone involved has perfectly good sensors working on the vehicles, most vehicles Pilot ratings don't go higher than 2, and that's not a lot of dice to succeed on a Crash test.
I would point out that the Maneuvering autosoft provided by Gridguide increases that dicepool significantly, but I feel it would detract from my previous point.
Anyway, this thread exists in part because I was the other partner in the OP's heated discussion. It revolved around whether or not it's reasonable for municipalities to require GridGuide participation/usage. Obviously it wouldn't be in places where GridGuide is not operational, natch. But in certain cases, sure it'd be a no brainer that Gridguide be mandatory and noncompliance could result in being stopped and ticketed.
Consider, for a moment, the humble seatbelt. It provides great safety benefits, has no real downsides other than personal mobility within your vehicle, and all you have to do to use it is put it on. Think about how you, the average driver, feels about seatbelts, and hold onto that feeling for a sec.
Now, think about all the benefits Gridguide offers. You don't have to pay for fuel, it's almost impossible for you to get into a crash, you get better insurance rates for using it, you get to your destination in good time and you can let the car drive itself if you want. For the law-abiding citizen, there are literally no downsides to using Gridguide, and you don't have to do anything to use it; in fact, you'd have to go out of your way not to use it! Considering how you feel about seatbelts, how do you think the average driver in 2080 feels about Gridguide?
I must think that it is the case that either:
A) Gridguide is so ubiquitous and beloved that no one has felt the need to make it mandatory or
B) Gridguide is mandatory in some areas for safety reasons, but it is so ubiquitous and beloved that not using Gridguide in a mandated area is an extremely rare crime on its own. As such, it's like seatbelt usage in that it's not something that the police are constantly on the lookout for; rather, dangerous drivers are arrested for driving dangerously, and failure to use Gridguide in a mandated area is slapped on top of their dangerous driving offenses. Wakshaani's comments seem to indicate that this is the case, meaning that you could get away with driving off-grid if you were skilled enough to do it safely.
Afterall, making any kind of turn or lane shift without being linked to GridGuide is in effect the same thing as doing it today without warning everyone around you by using your blinkers beforehand.
Let me explain why that isn't a valid comparison: the difference between turning with and without your blinker is how much time the driver behind you has to react to your turn. The difference between turning with and without Gridguide is whether or not the "driver" behind you has to react at all. Alright, maybe that makes off-grid driving sound worse, but it's not like people have stopped using their blinkers just because cars drive themselves now. A system like Gridguide would need to be built upon multiple redundancies for the sake of safety, and some of those redundancies would be the systems we use today. If an off-grid driver uses their signal lights to inform other vehicles of their actions and drives their vehicles in a reasonable manner, then Gridguide would be capable of accommodating them.
You're talking about so many things that I want to talk about. gah!
gridGuide(tm) isn't REQUIRED in many places but it's getting there. Some municipalities are starting to pass laws about requiring it in certain areas … the Downtown areas of major sprawls for instance, or Manhattan, but not so much the suburbs or smaller towns … yet.
Insurance companies are increasingly giving people a choice as well … pay a huge premium for "Bate hand driving" or get a car with GridGuide(tm) and get super-low rates since they won't crash. This leverage is causing more people to make the move.
There's also some movement on the priority scale (manual control vs Pilot vs remote control) and a few other things.
I'm *super* glad that anybody but me cares about this. 
As long as I have your attention, might I ask a few questions? First, somewhere on Reddit you stated that Gridguide, like Skyguide, provides Maneuvering and Navigation autosofts to the vehicles using it. You also stated that there are different levels of service to Gridguide, so they're not always going to be R6 autosofts. Could you clarify those levels of service? Are they based on what area you're currently in, what level of lifestyle you're living, or something else?
Second, I noticed that Rigger 1, 2 and 3 state that Gridlink physically cannot provide power to vehicles exceeding the speed limit (this is by design) and that sometimes during rush hour the Gridlink power grid overloads and crashes; is this still true in 2080?
Third, what is difference between driving off-grid and driving with a Gridlink Override? Obviously the Override lets you keep several benefits of Gridguide, but how do the vehicles around you react? Does a Gridlink Override provide the priorities and privileges granted to first responders, or at least some of them?
