In my post from October 18th, I promised that in a future posting I would share some ideas I have about solutions to traffic congestion that might make you chuckle. Well, today is that day. In that post, I suggested that it might be possible to improve the capacity of highways through means other than simply adding more roads or widening existing ones. The way to do this was to address the two components of traffic flow, namely traffic density and average velocity. The previous article dealt with the issue of traffic density. Today, I’d like to discuss the speed component, and how we might be able to use technology to improve traffic flow.
Let’s say it’s a bright, sunny morning; there are very few cars on the road. You seem to have the whole road to yourself. How do you decide how fast to drive? If the posted speed limit is 65, you might figure you could get away with setting your cruise control at about 72 and be relatively safe from the State Patrol. You feel that you are driving safely: the road is dry, visibility is good, and there is little traffic. In fact, you might be able to drive for miles without even changing lanes.
Now let’s change the scenario: It’s still dry and sunny, and you’re still able to drive at 72 mph, but now the road is crowded with other vehicles, all moving at about the same speed. The highway is reaching its theoretical maximum capacity, which is that moment just before the density reaches the point at which cars are so close to one another that the slightest decrease in the speed of one car will result in a massive compression wave traveling backwards through traffic until the average velocity plummets to near zero. Here’s my question: What causes that one car to slow down so suddenly? It seems to me that if we were able to minimize such sudden decreases in speed of individual vehicles, we might be able to maintain a higher average traffic velocity and therefore a more efficient use of the existing roadway capacity.
So, here is my hypothesis: If we are able to reduce the number of lane changes of individual drivers, there will be fewer instances of other drivers having to brake to avoid colliding with these drivers cutting in an out of traffic. The reduced instances of braking will generate a smoother flow of traffic , resulting in higher traffic flow and fewer accidents. Stated another way, to the extent drivers keep to the same lane, overall traffic velocity will remain high enough to maintain an efficient traffic flow. Assuming this hypothesis is true, I believe the technology is available today to provide a solution.
Why do drivers change lanes? There really is only one reason: to overtake other drivers. Why would someone want to do that? There may be a number of irrational reasons (competition, a sense of superiority, etc.) and I’m certainly not qualified to go into the psychology of driving behavior. But the rational reason is simply that most drivers want to be able to travel at the speed they choose. If my “chosen” speed is 72 in a 65 mph zone, and the traffic is moving at 58, I will continue to change lanes to “get ahead” of slower drivers until I reach a point where I can drive, unhindered, at 72. Realistically, of course, this never happens if the traffic is very dense. Aggressive drivers who are constantly changing lanes never really manage to get to their destinations much more quickly than they would have if they had “gone with the flow”. But in the process, they create disruptions in the traffic flow that increase the likelihood of collisions and force other drivers to react to their behavior by making sudden braking or steering maneuvers.
Intelligent transportation system (ITS) technologies may be useful in gradually curbing excessive lane changing. Consider a stretch of interstate highway, slightly modified so that there are magnetic sensors placed at regular intervals along the lane markers. When a car makes a lane change and moves over one or more of these sensors, an on-board computer records the lane change; keeping a running total. The computer then calculates the number of lane changes per mile traveled. At the end of the year, during the car's annual safety inspection, the data in the computer are downloaded and sent to the state Department of Motor Vehicles. The lane-change per mile factor for that vehicle is then compared against values derived from a historical database of driving patterns. Excessive lane changers might be assessed a monetary fine or awarded negative driving points based on the past year's data. Gradually, either driver behavior will improve or such drivers will lose their licenses and be taken off the road.
The ITS-based solution I propose gets to the heart of the speed enforcement problem: Vehicle speed by itself is not the issue; it is speed relative to other vehicles. If I am a law enforcement officer, I am more concerned about the aggressive driver weaving in and out of traffic than the lone driver on a remote highway in Montana or Nevada who is driving above the speed limit.
For those who may be concerned that this proposal violates civil liberties or privacy, I will only offer that the license to drive a motor vehicle on public highways is a privilege granted by the state, not an absolute right. The state has a compelling interest in protecting its citizens and providing a safe driving environment for its licensed drivers. Collecting such data from a vehicle’s computer is no different than the collection of GPS location data by trucking companies of their drivers’ whereabouts. It is in the company’s interest to ensure its drivers stay on the route and are on time, and the acknowledgment of this data collection is a condition of employment.
We have reached a point in the development and management of our national highway system where we have to begin thinking creatively about solutions to traffic congestion and safety problems. If state departments of transportation knew it was possible to increase the traffic flow volume on a stretch of interstate highway without adding another lane, wouldn’t it be worth pursuing simply from a cost standpoint? If highway safety officials knew it was possible to reduce the number of accidents per highway mile and ease the jagged nerves of commuters at the same time through the use of ITS, wouldn't it make sense to investigate? The answer to both these questions is yes; and it will take real vision and bold action at the state and federal level if society is to get the most benefit from ITS.
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