The discussion on cars circling to avoid parking fees (short-answer, they won't) leads to a few other interesting issues I want to cover.

• How to handle the "pick up rush" when thousands want to leave a place (like work, movies, schools, stadia or airports) at the same time
• Whether people will have their private cars go back home to park or serve other family members after doing the commute
• How we should manage the street parking and free parking in a city

Today, I want to talk about the pick up rush. Earlier, I covered what should happen with Lyft and Uber at airports to parallel what happens with taxi lines. Let's look at the evening rush hour and related situations.

As the work day ends, everybody wants to get home at roughly the same time. Some will do it in regular cars or on transit like today. Some will want robotaxi service. Some will want to take their private robocar home. And others will be open to self-driving transit forms which could come at a much reduced cost.

If we look at those in private robocars, robotaxis and regular taxis, we face the problem that there may not be enough "pick up curb" for all the people wanting pick-up. We see that at airports, which is why the "cell phone waiting lot" was created. Buildings have far less pick-up space than airports. We also see it at schools where most of the children are driven home by their parents.

The problem is people want to avoid waiting for long at the curb. They would rather summon their vehicle in advance, and have it waiting for them when they get there. This can quickly fill up the space. Most people will try to time it well, but many will signal for their car when they are almost ready to leave, and then be inaccurate in their estimate of when they would actually leave. Some will summon cars parked in cheaper parking 10 minutes away from their building, and thus have much more trouble matching arrival at the pick-up spot, though their phone will be aware of the approaching ride and giving the signal to get to the spot.

With robotaxis, we might imagine we can solve the problem with the "taxi line" concept. We certainly don't right now, as Uber/Lyft allocate a specific vehicle to a specific customer rather than having the next customer take the next available vehicle waiting in a line. We could try to implement a waiting area, but the problem is there can be 6 or 7 different services from Uber, another 5 from Lyft, and several other competing companies. Each class of service in theory needs its own line, and few curbs or even pick-up areas have enough room. The uniformity of taxis, allowing the line, is one of the few benefits of the way old taxis are regulated.

It's easier to do if the building has a parking facility. The facility can make sure there are enough spare spots in its parking lot for use as pick-up spots. But many buildings have only a little curb space in front of them, if that.

When it comes to private robocars, we have a bunch more questions. Each car is there for its owner and needs a place to wait if the owner is not there yet. If there is no place to wait, the car needs to go somewhere. If short term parking can be rented, that's OK, but if it can't, the car's only option is to keep driving -- which is going to increase congestion at the busiest time of the day. Indeed, it might start "circling" not because it does not want to pay for parking, but because there isn't any to be had.

Ideally, private robocars that parked nearby would not begin their journey until it was certain their owner was ready to get in. The question is, how would one enforce that? If you make a punishment for the car showing up and waiting, cars will just circle.

For private robocars parked more distantly, the owner will not be waiting when they summon. They will summon some time in advance of when they want to actually leave. The owner's phone will signal them when they must go down to the pick-up spot, but again, it's not easy to enforce violations of that. Cars won't have a "circle" command, but they will be commanded to travel to the pick-up zone for their owner, and if that zone is full, they will have no choice but to move on.

I can think of a few solutions, the most obvious of which is general road management and congestion charging that makes it expensive to circle. Even with the owner waiting, however, there may be times when no pick-up spots are free because volume of traffic is so heavy.

Designated pick-up locations

If you have used Uber/Lyft in certain towns like Las Vegas, or at airports, you learn they have designated pick-up areas. If you want to get picked up at a particular hotel, you must go to the designated area, you can't get picked up at side doors or on the street. Cities are already frustrated by Ubers blocking traffic to do pick-up/drop-off and are marking specific spots for this. This is likely to grow, possibly to the assignment of specific stalls for passenger exchange which are allocated at the busy locations.

Each building which is in a "congestion area" that needs a pick-up zone would have a computer to manage its pick-up spots. (Most probably they would just contract out to somebody else.) Cars heading for that building would, at the appropriate times, request a slot reservation, and an amount of time they might wait at the spot. The passenger's phone would also talk to this server to track how close the passenger is to the spot.

Here are some sample rules which might improve things:

• If a building's pick-up area never fills up completely, it sets its own rules -- it might not even have management software at all. Buildings would be encouraged to have sufficient amount of pick-up area. Pick up areas should ideally use perpendicular or parallel stopping stalls with a pass-through lane.
• If a private pick-up area fills up during a designated congestion period, such that cars can't go in, it must follow the rules of a "public pick-up area." Public curbside area is automatically under public rules at these times.
• In a congested public pick-up area, if an incoming vehicle gets within one minute of the area and the passenger is not closer in time to the pick-up area, the vehicle must find the closest parking and park there, and may leave once the passenger has arrived at the pick-up area. It may not divert back before it has parked, even if the passenger has arrived -- this is a penalty for summoning too early during a congestion period.
• If, under that rule a pick-up area still fills up, then no vehicle may be summoned except by a person already present in the area.
• If, under that rule a pick-up area still fills up, then the building must limit who can use the pick-up area until it doesn't. Others should be directed to a larger pick-up area (such as one in a parking garage.) Examples of restrictions might be allowing use of the internal area by the employee of the month, or by carpoolers or robo-transit riders, or the disabled, or top executives.

Cars doing pick-up would need to get permission to enter a pick-up area before accepting one as a destination inside a congested zone. Such permission would be granted by both the building manager (who might allocate who gets to use it) and or the city, which would manage pick-up zones on public streets.

In addition, buildings might work together, so that if one pick-up area is full and there are spots next door, vehicles go there and the passengers walk a short distance if able.

I am interested in contributions from readers on good solutions. Particularly ones that can work in a more distributed fashion with less central control. The above plans can actually be highly distributed, in that each building can manage its own zones, and each block can be managed mostly independently of the others, but it's still better if there can be an emergent system. The other open question is the best way to enforce any rules that are put in place.

Reader suggestions

Harvie Branscomb suggests an interesting idea for highly congested pick-up spots, namely enforced carpooling. If a taxi (or a private car) wants priority at the curb, require it to take other people who are waiting to a place along the way that is less congested or more spacious for them to meet their cars. People could insist on private pickup, but might have to wait. It would be nice to do this today for school pick-up, which is very crowded in the USA. But people are paranoid about their kids getting in the cars of others, even other parents.

Robotaxi or van away from work

One more extreme option is to discourage or disallow pickup by privately owned robocars in highly congested areas which don't have adequate pick-up spots for everybody. This is a variant of road metering, but it has a specific target.

The private robocar would park/wait outside the congested area, in a space which has ample nearby drop-off spots. Private owners would be required to take the next available robotaxi or similar to the staging area, where they would then quickly transfer to their private robocar. This is probably not needed for drop-off

Even better if the people take a group vehicle, such as a van, to the staging area. This is efficient and reduces congestion on the road. Indeed, a building or block might have specific designated staging areas. If every robocar owner in the building is heading to the staging area, it means you can fill a van quickly during peak demand times. This depends on how many directions of travel there are from the building, since people want a staging area along their route home. If there's only one direction, you could even have something larger than a van. It's essential the departures to the staging area are very frequent, to keep the convenience that led people to use a private car. Solo robotaxis of course would leave on demand and be almost as convenient has having your own car pick you up.

As an added benefit, the parking out at the staging area will be much cheaper than the CBD. Those who want the convenience of quick pickup by their car will need to park near their location -- and pay a premium for it. If your car parks close, it is not a problem to go down to the pick-up area and wait a short time for it to arrive.

When it's time to empty a stadium, the use of vans going to staging areas may be the only system that works. We can't have private cars and taxis all go up to the doors of a stadium when 40,000 people leave at once.

At the other end would be the use of robocar transit. In that article I outline a group transport option which works to frictionlessly put people together in vans on the shared parts of their trips. Such services could seriously reduce congestion, and thus it would make sense to give them priority at pick-up spots.

In the morning

As I noted, drop-off is a different story. Drop-off should always be quick, there is never any chance of the passenger not being present. It is still possible to overflow a drop-off area but it should usually not last for long. If it becomes a problem, a subset of the above techniques could be used. In addition, if a car approaches a drop-off area and there is no available space, it can just go do any other nearby area if the passenger is able to walk short distances.