Not so long ago, it seemed that the hailing of a cab required long arms and a capacity to wave frantically to catch the eye of the taxi driver.

You would be standing at a curb and keep your cool while taxi after taxi seemed to entirely ignore your frantic motions. It was hard to discern why the cabs weren’t pulling over to pick you up. They were showing as empty and therefore ought to be avidly seeking a potential fare. Sometimes you would consider that perhaps they didn’t like the particular manner in how you waved your arms.

Maybe they thought you were overly excited and this was a worrisome sign by the taxi driver. Or they didn’t like the look of your seemingly crudely summoning tactic for getting a pickup. You see, there were lots of other potential cab seekers that had a more subtle approach. Some all-knowing people would nonchalantly do a once wave and that was all it took to get a cab to pull over. Others would merely nod their head or make a quick tip of their hat, as though these were secret signals in a private baseball game between a catcher and a pitcher.

Things could get really competitive at certain times of the day.

If it was rush hour, then all bets were off. There were tons of people fervently attempting to get cabs, all of them at the same time and all across the whole city. You pretty much had to hope for the randomness of the world to come to your aid. When a taxi perchance dropped off a rider at the very spot that you were standing, this gave you the top rights to commandeer the taxi and proclaim that it was yours for the taking.

Many movies and TV shows used to provide a gag whereby a taxi comes up to pick someone up, and then someone else darts into the cab instead. This was more than just a spate of humor. It happened. Quite often. Unless you took to mind the ever-present notion that possession is nine-tenths of the law, a nanosecond of a delay getting into a taxi could mean that an interloper would grab it and you would be left standing high and dry.

I remember getting into a cab at the airport and when I gave the hotel address for my stay, the cabbie gave me the most utterly disgusting of glances. He then explained that the hotel was less than a two-minute drive from the airport. His fare would be peanuts. Meanwhile, he had waited in an enormously long cab line while at the airport, and after dropping me at the hotel he would once again have to sit idly in that same darned line. In short, he emphatically told me that I just cost him nearly two hours of his available cab time, for pretty much nothing at all as a fare.

He pleaded with me to get out. The rules for the cabbies at the airport did not allow them to kick out a rider. It had to be the rider themselves that would decide to back out of a ride. He told me that he had a family and needed to support them. Get another cab, he exhorted. Just don’t force him to give me the dinky ride, for which he also suggested I could just walk from the airport and enjoy the fresh air, averting the need for a taxi altogether.

Anyway, the point is that even if you believe you had managed to snag a taxi, there was still a chance that it might get loose from your grip. Either the cab driver would not want you, or someone else might try to intervene and take your cab, sometimes offering a whale of a story.

I recall one time that I had just gotten into a hailed cab and a bystander tapped on the window. The person explained that they had been waiting for twenty minutes to get a cab. They had noticed me standing there too, though I apparently had only been waiting about ten minutes. The explanation turned into a morality play that I ought to voluntarily give up the cab since this other person had waited longer than me. It made no difference that the cabbie stopped in front of me. It made no difference that we were both humans. The key was that I had gone outside of my fair turn and had cheated this other waiting rider.

How about that?

On another occasion, I luckily hailed a cab and a person came running up to the vehicle. They offered me ten bucks if I would hand the taxi over to them. They were in a hurry and didn’t want to wait for a taxi. The logic was that time is money, as we all know, and so this potential rider was willing to pay me for giving up my cab and presumably giving up my waiting time. An interesting proposition. The taxi driver entered into the dialogue and pointed out that the ten dollars ought to go to the driver, or at least a cut of it ought to.

Hailing a cab while in the rain or snow was the worst.

There you are, standing out in the raw elements. The wind nearly blowing you over. Rain pouring sheets of water onto your head, or perhaps onto your umbrella or raincoat. If it was snow, you stood in the icy cold and kept moving your feet to keep the circulation going. An additional problem was that there seemed to be fewer cabs cruising around and thus the wait time was totally elongated.

In today’s world, there is a lot less handwaving hailing going on.

In lieu of wantonly hailing a ride, you usually pull up an app on your smartphone and use a ridesharing network or even a cab-hailing network to get yourself a ride. No need to stand around and try to spy on an available roaming vehicle. The computer systems do all that work for you. This is known as e-hailing.

On a digital map displayed on your smartphone screen, you’ll see various dots or tiny emoji cars that are moving around in your area. One of them will be usually chosen for you by the computer system, based on factors such as how close the roaming vehicle is, where you want to go, the type of vehicle preference you have, and so on. All you then need to do is wait for the arrival of the assigned vehicle.

No need to wave at anyone or anything.

That being said, upon the arrival of your assigned vehicle, sometimes you do need to wave or make a motion to ensure that the driver sees you. The map is oftentimes not precisely able to indicate where the passenger is standing. Plus, there might be a multitude of people waiting for lifts, perhaps having all gotten out of a theatre at the same time and now seeking rides home.

There is no doubt that merely requesting online to get a ride is a lot smoother than having to play the roulette wheel game of hailing on-the-street a prospective ride.

Besides the ease of no longer needing to make those waving motions, you also now have a somewhat ironclad guarantee that you will get a ride. In the case of standing around and hailing, you never really knew how long it might take and whether you would ever land a ride. That was the terrible uncertainty of it all. This could be especially on your mind if perchance caught in a bad part of town or rotten weather. Your mind was frantically praying for an available ride to come along.

Another nifty aspect about using an app to hail a ride is that you know beforehand the nature of the vehicle and the driver. You are usually presented with some info about the car that is coming to pick you up. There is also the name of the driver and their rating. This helps you to know whether the rider is presumably any good at providing rides.

When you hailed a cab at random, it was a wildcard as to what type of driver you might get. Some drivers were cautious and went relatively slowly, taking turns with great aplomb. Other drivers were like racecar drivers, zipping along. They wanted to get you to your destination as fast as possible, meaning that they then could seek to find their next paying fare that much sooner. More fares in a day were the mantra for making any money at this game.

Those that have never hailed a ride via the standing outside and waving method are at times aghast when they discover that this approach still exists. Many believe it was only something that happened during the times of the dinosaurs, and they assumed that since dinosaurs are extinct that presumably, the traditional method of hailing of a ride was certainly extinct too.

Well, sit down and prepare yourself for a bit of a shock, conventional hailing still happens.

There are though additional twists and turns.

In many locales, there are byzantine rules about which cabs or taxis can provide those impromptu derived rides. Depending upon various conditions, it could be that only e-hailing is legally allowed, per time of day or where you are in a city or town.  Anyone trying to do the street hailing has to be brazen to think that it will work since there are fewer and fewer chances of this being feasible.

Some sneaky riders will try to maximize their chances of getting a ride quickly by doing both the e-hailing and the stand-around techniques in unison.

They pull up the app for an e-hail and see what the wait time is like. They simultaneously stand out in the street and start waving at any seeming potential rides. If the wait time seems long on the e-hail, they will temporarily book it and then wait until the last allowed moment to drop it (before incurring any fees for doing so). During that interval, they will be stridently attempting to catch a ride via the waving method. Whichever approach strikes gold first is the winner in that momentary contest.

As they say, all’s fair in love and war.

Since we have been discussing cars and taxis, it makes indubitable sense to consider that the future of such vehicles will consist of self-driving cars. Be aware that there isn’t a human driver involved in a true self-driving car. True self-driving cars are driven via an AI driving system. There isn’t a need for a human driver at the wheel, and nor is there a provision for a human to drive the vehicle.

For my extensive and ongoing coverage of Autonomous Vehicles (AVs) and especially self-driving cars, see the link here.

Here’s an intriguing question that is worth pondering: Once self-driving cars are acting as robo-taxis and cruising around on our streets to do so, will you be able to hail one by hand or only via e-hailing?

Before jumping into the details, I’d like to further clarify what is meant when referring to true self-driving cars.

Understanding The Levels Of Self-Driving Cars

As a clarification, true self-driving cars are ones that the AI drives the car entirely on its own and there isn’t any human assistance during the driving task.

These driverless vehicles are considered Level 4 and Level 5 (see my explanation at this link here), while a car that requires a human driver to co-share the driving effort is usually considered at Level 2 or Level 3. The cars that co-share the driving task are described as being semi-autonomous, and typically contain a variety of automated add-on’s that are referred to as ADAS (Advanced Driver-Assistance Systems).

There is not yet a true self-driving car at Level 5, which we don’t yet even know if this will be possible to achieve, and nor how long it will take to get there.

Meanwhile, the Level 4 efforts are gradually trying to get some traction by undergoing very narrow and selective public roadway trials, though there is controversy over whether this testing should be allowed per se (we are all life-or-death guinea pigs in an experiment taking place on our highways and byways, some contend, see my coverage at this link here).

Since semi-autonomous cars require a human driver, the adoption of those types of cars won’t be markedly different than driving conventional vehicles, so there’s not much new per se to cover about them on this topic (though, as you’ll see in a moment, the points next made are generally applicable).

For semi-autonomous cars, it is important that the public needs to be forewarned about a disturbing aspect that’s been arising lately, namely that despite those human drivers that keep posting videos of themselves falling asleep at the wheel of a Level 2 or Level 3 car, we all need to avoid being misled into believing that the driver can take away their attention from the driving task while driving a semi-autonomous car.

You are the responsible party for the driving actions of the vehicle, regardless of how much automation might be tossed into a Level 2 or Level 3.

Self-Driving Cars And Hailing A Robo-Taxi

For Level 4 and Level 5 true self-driving vehicles, there won’t be a human driver involved in the driving task.

All occupants will be passengers.

The AI is doing the driving.

One aspect to immediately discuss entails the fact that the AI involved in today’s AI driving systems is not sentient. In other words, the AI is altogether a collective of computer-based programming and algorithms, and most assuredly not able to reason in the same manner that humans can.

Why this added emphasis about the AI not being sentient?

Because I want to underscore that when discussing the role of the AI driving system, I am not ascribing human qualities to the AI. Please be aware that there is an ongoing and dangerous tendency these days to anthropomorphize AI. In essence, people are assigning human-like sentience to today’s AI, despite the undeniable and inarguable fact that no such AI exists as yet.

With that clarification, you can envision that the AI driving system won’t natively somehow “know” about the facets of driving. Driving and all that it entails will need to be programmed as part of the hardware and software of the self-driving car.

Let’s dive into the myriad of aspects that come to play on this topic.

Assume for sake of discussion that self-driving cars are inevitably sufficiently able to drive around and at least achieve Level 4 capabilities (this means that there is a defined ODD or Operational Design Domain for which the autonomous vehicle is capable of driving within).

There is a hefty debate about whether individuals will be able to own and operate self-driving cars or whether only large companies will be able to do so. Part of the logic is that a self-driving car will need to be kept in tiptop shape else the AI driving system will not be able to safely provide rides. The assumption is that a company responsible for operating a fleet of self-driving cars is more likely to maintain and upkeep the autonomous vehicles than might individual owners do so.

I generally disagree with that contention and argue that we will indeed have individual ownership of self-driving cars, for various reasons that I have articulated at this link here.

Putting that whole brouhaha to the side, I think we can generally all agree that there will be self-driving cars offered on ridesharing or ride-hailing basis, regardless of whom the owner is. When you go to use an app to request a ridesharing lift, the odds are that the app will present you with one of two options, you can select a human-driven car or you can select a self-driving car. Some people will relish using a self-driving car, while others will eschew it and prefer instead to use a human-driven ridesharing car.

Each to their own preference.

Most pundits agree that self-driving cars will be on the go for much of their available traversal time. The nice thing about a self-driving car is that the AI driving system doesn’t need any rest, nor lunch breaks, or even bathroom breaks. The expectation is that self-driving cars will be able to be driving around 24×7, except for times when they need to refuel or need some maintenance or fixing up.

For an entity that owns a self-driving car, there is the opportunity to potentially make big bucks by this always on the move capability (and, without the labor costs of needing a human driver). For example, I assert that a person could own a self-driving car, have it take them to the office for a normal workday, and while at work the self-driving car is made available on a ridesharing basis. The person then has the self-driving car take them home after work, and for the rest of the night, the self-driving car continues making money by providing more lifts. In short, their self-driving car makes money for them when they otherwise don’t need it.

Without getting mired into any messy arguments, the emphasis is that a self-driving car can be a ridesharing or ride-hailing vehicle and provide rides to those making such a request. That seems abundantly clear-cut and inarguable.

The question we are considering herein is the matter of how to request a self-driving car for those that are seeking a lift.

We can already assume that the most likely approach consists of app-based e-hailing.

Either the company operating the self-driving car will provide a dedicated app for this purpose, or might list the self-driving car on some existing ridesharing network. If they list via a network, the odds are that a cut of the fare is bound to be required (i.e., a split between the operator of the self-driving car and the network operator). Ergo, the chances are that the operator of the self-driving car would prefer that people use the specialized app and not have to split any fees.

It is a tradeoff of course, as to whether the dedicated app will ensure enough use of the self-driving car versus being listed on a ridesharing network.

Will a self-driving car be occupied at all times while on a ridesharing basis with a passenger inside the vehicle?


There will be times during which the self-driving car will be absent of a passenger. It could be that the self-driving car is doing delivery of a package, thus, there isn’t a person inside the autonomous vehicle. Other times the self-driving car might be making its way to a requested lift and is empty until it reaches the person seeking a ride.

One other possibility is that there aren’t any ride requests at the moment and so the conundrum of what to do with the self-driving car then logistically arises. Do you opt to park the self-driving car at some locale, and have it wait for a requested ride? That might not be as advantageous as having the self-driving car roaming around, for which it might be in a better place when a request occurs.

The operator of a self-driving car will need to make this balancing act decision. In some instances, it might be better to park the self-driving car, while in other instances it is more prudent to keep it underway. A variety of factors come to play.

All told, we can seemingly agree that there will be times at which self-driving cars will be roaming empty of any passengers and awaiting a request for a ride. I’ve suggested that this might become quite prevalent, see my analysis at this link here.

We are now at the moment of truth.

Should a self-driving car that is acting in this robo-taxi manner be able to pick up passengers that might undertake a traditional hailing gesture, or will self-driving cars only be summoned via e-hailing?

My claim is that we potentially could have self-driving cars programmed to handle the streetwise hailing approach.

This probably though will not occur at first. The mainstay will be the e-hailing avenue. Once that has become firmly established, I believe we will see some self-driving cars that are adjusted to be responsive to street-level hailing. This will primarily be due to competitive forces that require self-driving car operators to increasingly find ways to outshine their competition.

Now, it could be that the human drivers take the same stance too.

In other words, if self-driving cars start to become commonplace on ridesharing networks, the question naturally comes up about how human drivers will remain competitive. Assuming that a self-driving car is less expensive to use and that it won’t have the human foibles of driving, the logical progression is that riders will aim to select a self-driving car over a human-driven car (all else being equal, as it were). A means for a human driver to remain competitive would be to offer something that the self-driving cars aren’t offering, namely the traditional street hailing approach.

Let’s dig briefly into the complications of having a self-driving car attempt to perform the conventional hailing method.

As mentioned earlier, a person seeking a ride is customarily expected to make a motion that will serve to relatively definitively indicate that they are seeking a ride. This usually consists of waving an arm, along with perhaps looking directly at the targeted cab or taxi, and possibly pointing at the cab too. All of this is intended to catch the attention of the human driver.

Self-driving cars will be outfitted with a variety of sensors, including video cameras, radar, LIDAR, ultrasonic units, thermal imaging, and so on. Via the use of techniques such as Machine Learning (DL) and Deep Learning (DL), the data from those sensors is computationally analyzed and various patterns are being scanned for.

In theory, the image processing of the video camera’s live stream could be used to try and detect a person that seems to be hailing the self-driving car. It would be easiest if the person had some special token or signal that was known for this purpose, such as a special flag or even just a specific gesture. But this might be a bit much for people to keep with them or have to know, so we’ll assume that the traditional waving motion is the preferred method per se.

Admittedly, a person could be simply waving at a friend across the street, or perhaps swatting at a buzzing bee. It will be hard to discern with absolute certainty that the person is hailing the self-driving car. You could make the same case for human taxi drivers too, namely that they do not know for sure that a person is doing a hailing action. The context of the moment and the movements of the potential rider have to be carefully combined to reach such a conclusion.

Okay, so trying to spot a person seeking a ride that is doing a streetwise hailing will be somewhat computationally tough to do, but not insurmountable. There will be instances of an AI driving system skipping past the person due to the lack of detecting that a hailing activity was underway. There will also be instances of mistakenly coming to the person to provide a ride when they were not genuinely in the act of hailing a ride.

We can also assume some dolts will just for kicks decide to falsely attempt a hailing to see what the self-driving car will do.

In the case of a human taxi driver, the driver would likely be irked at the jokester and provide a rather stern talking to (or worse). One supposes that the AI driving system could send the video to a remote agent for review, and if the trickster is seen to have been playing false games, perhaps there would be some means of legitimately issuing a ticket or something along those lines (unfortunately, that could be a slippery slope too).


Flagging down a self-driving car that is being operated as a robo-taxi is not likely in the cards for the near-term, but certainly can be envisioned for the future.

This is going to be tricky to program.

Nonetheless, it is possible.

We will likely initially have disgruntled indications of situations that the AI driving system that went right past someone and ignored them. Similar to how there have been concerns about human taxi drivers that cherry-pick whom they will pick up, we would need to test and validate that the AI driving systems do not have any built-in patterns of biases (see my column for coverage on this and other AI Ethics issues).

There won’t be much cause to out-the-gate have self-driving cars operate in this manner. The easiest approach entails doing e-hailing. Given that the AI developers already have their hands full as they aim to just get self-driving cars to safely go from point A to point B, the notion of including a conventional ride-hailing capability is ostensibly considered an edge or corner case. Those edge or corner cases are ranked as low priority and construed as outside the core of what needs to be developed.

Besides hand waving, perhaps we can program the AI driving system to detect a ride-hailing gesture such as a quick wink of the eye. Imagine though how confusing that might be when the self-driving car is going down a crowded street of pedestrians.

I know, maybe we can use mind-reading instead. If a person merely thinks about needing a lift, the AI driving system can make use of that type of hailing. As you likely know, the desire for mind-reading computers is right up there with the aspiration for autonomous vehicles (see my coverage).

Just don’t read whatever else is in our minds, and stick with the earnest and singular desire of hailing a ride.

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