You may have heard of Bus Rapid Transit -- a system to give a bus line a private or semi-private right-of-way, along with bus stops that are more akin to stations than bus shelters (with ticket-taking machines and loading platforms for multiple doors.) The idea is to make bus transit competitive with light-rail (LRT) in terms of speed and convenience. Aside from getting caught in slow traffic, buses also are slow to board. BRT is hoped to be vastly less expensive than light rail -- which is not hard because LRT (which means light capacity rail, not lightweight rail) has gotten up to $80 to $100M per mile. When BRT runs down the middle of regular roads, it gets signal timing assistance to help it have fewer stops. It's the "hot new thing" in transit. Some cities even give it bits of underground or elevated ROW (the Boston Silver Line) and others just want to wall off the center of a road to make an express bus corridor. Sometimes BRT gets its own highway lane or shares a special carpool lane.

At the same time just about anybody who has looked at transit and the internet has noticed that as the buses go down the street, they travel with tons of cars carrying only one person and lots of empty seats. Many have wondered, "how could we use those empty private car seats to carry the transit load?" There are a number of ride-sharing and carpooling apps on web sites and on smartphones, but success has been modest. Drivers tend to not want to take the time to declare their route, and if money is offered, it's usually not enough to counter the inconvenience. Some apps are based on social networks so friends can give rides to friends -- great when it works but not something you can easily do on demand.

But one place I've seen a lot of success at this is the casual carpooling system found in a number of cities. Here it's very popular to cross the Oakland-SF Bay Bridge, which has a $6 toll to cross into SF. It used to be free for 3-person carpools, now it's $2.50, but the carpools also get a faster lane for access to the highly congested bridge both going in and out of SF.

Almost all the casual carpool pickup spots coming in are at BART (subway) stations, which are both easy for everybody to get to, and which allow those who can't get a carpool to just take the train. There is some irony that it means that the carpools mostly take people who would have ridden BART trains, not people who would have driven, the official purpose of carpool subsidies. In the reverse direction the carpools are far fewer with no toll to be saved, but you do get a better onramp.

People drive the casual carpools because they get something big for for it -- saving over $1,000/year, and hopefully a shorter line to the bridge. This is the key factor to success in ride share. The riders are saving a similar amount of money in BART tickets, even more if they skipped driving.

Let's consider what would happen if you put in the dedicated lane for BRT, but instead of buses created an internet mediated carpooling system. Drivers could enter the dedicated lane only if:

• They declared their exit in advance to the app on their phone, and it's far enough away to be useful to riders.
• They agree to pick up riders that their phone commands them to.
• They optionally get a background check that they pay for so they can be bonded in some way to do this. (Only the score of the background check is recorded, not the details.)

Riders would declare their own need for a ride, and to what location, on their own phones, or on screens mounted at "stops" (or possibly in nearby businesses like coffee shops.) When a rider is matched to a car, the rider will be informed and get to see the approach of their ride on the map, as well as a picture of the car and plate number. The driver will be signaled and told by voice command where to go and who to pick up. I suggest calling this Carpool-Rapid-Transit or CRT.

The pickup could be at a "stop" in the private ROW, but unless the road has room for such stops, they are actually quite expensive because you need the private section large enough to handle passing vehicles, pulling-off-vehicles and waiting passengers. This is one of the problems of BRT -- it needs to eat up a lot of the road to handle the stations. For a CRT pickup, the driver could leave the dedicated lane and pick up a passenger at any curb at all, as long as it's easy to enter and leave the lane. And if the system is working well, the driver will actually be able to do their 2-3 pickups before entering the lane at all, making no need for stations in many areas. You do need sections where the road is a bit wider to allow for entry and exit lanes for the dedicated lane, otherwise people would need to stop in the dedicated lane to wait for a spot to get out of it, which doesn't work -- but such spaces are also needed for BRT stations.

A CRT lane could be a single lane which changes direction at noon to cut in half the land needed. Commuters going in the other direction might be stuck with ordinary buses or CRT that doesn't get a dedicated lane. Encouraging reverse commute drivers to do CRT is much harder.

The CRT lane doesn't have to be walled off from the other lanes. To be cheaper, it could be virtual, with just overhead lights, and transponder readers and licence plate readers (violators only) to assure only those who have met the rules use the lane or pay a fine. When traffic is lighter, CRT drivers who have enough karma in the system could get access to the lane as a reward. Or it could revert to normal use. And yes, they could get some money, as paid by the passengers, but I think the real incentive would be access to a fast lane with a straight shot downtown.

My general feeling, however, is that you would have no money change hands either way. The driver would pay for any background check and transponders needed, but I doubt you would need to charge the riders. You would have a reputation system for both riders and drivers, as is already common in ride-share and carpooling apps.

There are of course privacy concerns here. I'm not fond of background checks, though nobody would be forced to do one. Some riders might insist on a driver with a check, others might not because it means a longer wait. Casual carpooling works with no checks or identity at all, other than perhaps remembering the plate on the car. It's not unknown in casual carpooling that women decline to get into a car with just a male driver and no 3rd passenger, or with 2 strange men -- they simply let the next person in line take the car. There actually aren't that many predators commuting in nice cars in the morning. This system also involves tracking the cars, so it should be done with a promise of erasure of the information after a few days. Same for the passengers. If no complaint report is filed, the system should forget about the trip. Pseudonyms could also be used for reputation.

And yes, carpools formed outside the system would not be allowed in the dedicated lane, at least not for free. To allow them would require enforcement which is expensive. The smartphone app system self-enforces. Enforcement is hard anyway, because a valid driver may be going solo, waiting for their first pickup. A pre-arranged carpool could be faked as people just carry 3 cell phones to look like one.

What's the robocar angle here? Two things.

First, early robocars might enjoy a dedicated lane with its more controlled environment. The owner could engage the robocar and let it worry about picking up passengers etc. while the owner just does their work.

Secondly, if a city still finds BRT a better plan than this, robotic driving of the buses has one big advantage -- you can probably pull off two-way bus traffic with mostly a single lane. To do this, you must track all buses, and if two buses are approaching one another, you adjust their speeds so they always meet up in a short wide passing-zone. They can still have human drivers but the speed must be set by the computer to allow this. You still need the passing zones but now you take only 2 lanes out of the main road anywhere. The route because either lane + parking, or double-wide passing zone. Mostly. Stations are still a problem. Rear-boarding buses would allow boarding in a single lane-width. If you can board the whole back width of the bus (thanks to a boarding platform which brings people to boarding height) you can do it pretty quickly. Or you might need stations for side boarding in some wide spots.

Some BRT designs want to run along the outside of the road rather than the middle. This solves the boarding problem but is meant for bidirectional lanes, and has a big problem with people wanting to turn right who have to cross the bus lane. Central transit lanes usually solve the left-turner problem by banning most left turns along the route until a place with a wide spot for such lanes can be found.