The Zero Stoplight Paradigm

Stoplights are ubiquitous in our cities. They do their namesake: they stop traffic. Almost all busy city intersections of two perpendicular roads are controlled by stoplights. Left turns are quite costly in terms of accidents and delay. Left turn cycles must by their nature shorten the time allotted for straight through traffic which backs up more traffic in all directions which increases the need for the left turn cycle and so on. But the most time is spent stopped waiting for traffic on the intersecting road. Overpasses solve the problem nicely but are very costly. Although stoplights slow us down, causing us to waste fuel while backing up traffic into jams and snarls we put up with them because there is simply no cheap alternative. Or is there?

The obvious alternative to stoplights is the roundabout. Roundabouts connect two intersecting roads each supporting two-way traffic with a small counterclockwise one-way loop. Large roundabouts are common in European cities where drivers are familiar with them but they can be controversial in the USA where they are typically much smaller. A roundabout replaces an intersection by requiring traffic to slow down, then to get into the roundabout, yield and merge once then yield and merge again to get to out of the roundabout. These two yield and merges must occur in rather quick succession which can be tricky although the driver has the option once inside the roundabout to continue going round and round before exiting. People dislike them for these reasons and we know there are no more improvements that can possibly be made to the design of the roundabout because we haven’t seen any, or are there?

Usually only grass and trees live in the center of the roundabout. Using your imagination for just fifteen seconds right now, suppose the roundabout is greatly enlarged. And suppose instead of only trees and grass in the center, it contains a neighborhood or a section of a city. And now instead of calling it a roundabout, let’s call it a roundall. And suppose instead of four intersecting two-way roads along its outside perimeter, there are many. And imagine as you drive counterclockwise (CCW) around the roundall you occasionally see a one-way lane exit the roundall into the interior and occasionally you see a one-way lane joining the roundall from the interior. Now suppose this basic roundall topology occurs on a smaller scale within the roundall’s interior and again on a larger scale outside the roundall.

Since the roundall is much larger than the roundabout, and quite like a one-way version of a modern freeway, the roundabout problems of unfamiliarity and rapid yield-merges are both eliminated.

Using your further imagination, please envision a new type of roundall where the direction of travel is clockwise! Traffic on two-way roads outside the clockwise (CW) roundall would need to turn left to enter or exit the CW roundall. In order to avoid creating an intersection the two-way road would be split apart and rejoin itself in a loop that doubles as a merge-lane and an exit lane. All this is much like if not exactly like existing pavement already in place within our modern freeway system.

Now comes a key advance the roundall design can provide: Clockwise and counterclockwise roundalls can be directly connected to each other alternately such that two-way roads and stoplights would be together eradicated! A driver following roundalls that alternated CC and CCW would etch out one big S-shaped pattern after another. If the geography of a city dictated, the S-shape could be made taller or wider as needed by the local traffic patterns. For example my city is predominantly laid out north-south and so a taller S-shape would be suitable.

What you have just imagined is an area with smoothly flowing non-stop travel and a completely stoplight-free zone! But in order to get to someplace very nearby, it might be necessary to follow the loop and go out of your way a considerable distance. But so what if you have to travel a bit further if the time and fuel is the same or less? If you are navigating to a never-before visited location using visual reconnaissance, you would be in for some surprises and frustrations. All the more reason to upgrade your vehicle to include a modern GPS navigation systems like those in newer automobiles today.

Academic studies should begin investigating such properties of the roundall as average speeds , time to destination, accident rate, and number of lanes needed. A thorough computer Monte Carlo simulation should be performed comparing these factors for existing road designs against the roundall design. I bet 100$ that the roundall achieves higher speeds with comparable trip times and less pavement. Then the opportunity will exist for forward thinking city planners to adapt existing areas to the roundall or apply the roundall to new areas such that intersections are bygone, stoplights are bygone, fuel efficiency is increased, and even stopping is a rare thing until you reach your destination. And I can think of no better road design than one that completely eliminates intersections to turn over the navigation of our automobiles to a computer allowing drivers to relax while en route and finally be able to safely use those cell phones on the road.

Figure 1:

Roundall pattern with two possible routes in red and green: