A 120mph robocar-mostly lane in the off-hours?
I'm here in Newport beach at the Transportation Research Board's conference on self-driving vehicles. Today in a pre-session there was discussion of pre-robocar technologies and in particular applications of "managed lanes" and what the might mean for these technologies. Managed lanes are things like HOV/carpool lanes, HOT (carpool+toll), reversible lanes etc. Many people imagine these lanes would be used with pre-robocar technologies like convoys, super-cruise, cooperative ACC, Bus Rapid Transit etc.
As I've said before the first rule of robocars is "you don't change the infrastructure." First you must make the vehicles operate fully on the existing infrastructure. And people are doing that. But we can also investigate what happens next.
Robocars as many envision them do not thus need dedicated lanes, even though some of the simpler technologies might. Earlier we talked about electrification which is a pretty expensive adaptation. Let's talk about high speed lanes.
Robocars (or any car) would be of much greater interest to people if they could go very fast in them. On one hand, the ability to work, read, watch video and possibly sleep in a robocar will mean to some that trip time is less important than comfort, and they might actually be happy with a slower trip with fewer disturbances. But sometimes a faster trip is very important, particularly on the long haul.
Today people are working hard to make robocars safe. Eventually they should be able to make them safe even at higher speeds, particularly on freeways that were designed for fairly high speeds. Even human drivers routinely see over 100mph on the autobahns of Germany. Problem is if you want to go 120mph outside of Germany , there's no road you can easily do that on. The other cars, going 65 to 80mph in the fast lane will get in the way, creating an uncomfortable ride and possibly dangerous situations.
Many of today's "managed lanes" are primarily for use in rush hour, from 5am to 9am and 3pm to 7pm. In other hours, traffic is very light. What if that special lane does not just become an ordinary lane after rush hour, but instead is converted to another special purpose. There are a lot of different technologies that might be able to become viable with such a lane.
The most interesting one to me is high speed. If the carpool lane switched to being the high-speed-car lane at 9:30am, I actually think a lot of people might very well delay their commutes and shift their hours. A one-hour commute at 8am or a 15 minute trip at 9:30am -- not a hard choice for many. And lots of people travel mid-day for various purposes.
The high-speed lane would actually mandate a minimum speed, perhaps 100mph when the road is clear. To get in this lane you would need a car that is certified safe at that speed or above. This might be a robocar, but it might also be a human-driven car with sufficient driver-assist technologies to certify it safe at that speed. The lane would probably only be open in good weather, and would probably revert to ordinary status in the event the main road got congested for whatever reason. Vehicles in the lane would have to be connected vehicles, ready to receive signals about changes to the dynamic status of the lane.
There probably would also be a requirement for efficient vehicles. Wind drag at 120mph costs 4 times as much fuel per mile as wind drag at 60mph. These cars would have to be highly aerodynamic designs. They might also be capable of platooning to further reduce drag, though you would want to wait a while to assure safety before platooning at 120mph. You might insist on alternate fuels or even that they be electric vehicles or other low emission vehicles. It doesn't matter -- I think there are a lot of people who would pay a lot of money to be able to go 120mph.
The lanes in general would need to be separated from the main lanes. Most carpool lanes are already like that, though most of the ones in the SF Bay Area are not this style. Ideally they would be the style that even has a special merge lane at the points where entry and egress from the main lanes are possible.
If such a program were a success we could see more. For example, one could imagine adding an extra lane to Interstate 5 in the California central valley and have it be a high speed lane most of the time. The planned California High Speed Rail, which probably will never be finished, is forecast to cost $68 Billion. 2 extra lanes on I-5 in the central valley south of Sacramento would cost well under a billion, and offer fairly high speed travel to those in the valley -- faster door to door than the HSR. And my calculations even suggest that aerodynamic electric vehicles would use less energy per passenger-mile than the HSR. (Definitely if they are shared by as few as 2-3 people or when designed for a platoon.) These teardrop-shaped cars would also be much more efficient than today's cars when they slow down and ply the ordinary highways and streets.
It is not trivial to go 120mph in a robocar though. Your sensors must be long range so you can stop if they see something. If you want to build infrastructure, here is where the road might have sensors which can report on road obstacles and other vehicles to assure safety. If you're building a whole high speed lane this is not an issue. The first rule of robocars is written to avoid needing new infrastructure to do ordinary driving and get most places -- not to prevent you from taking advantage of new spending that justifies itself.