Explaining how highways work is not always easy. We, drivers, typically view the world through our windshields and what makes sense from that perspective may not when considered from a broader system-wide perspective. For instance, ramp meters. WSDOT has utilized these devices to great effect throughout King County, for example. To the typical motorist, a ramp meter appears to just queue cars on surface streets, moving the backup from the highway to the local community. But to a transportation engineer, the process of controlling traffic flow makes all the difference between a highway functioning during the peak drive or failing.
So how do transportation experts explain complicated systems analysis in a way that makes sense to the rest of us?
Last September, Secretary Doug MacDonald announced the $1,000 Doug MacDonald Challenge, sponsored by the national Transportation Research Board, an organization with the National Academy of Sciences.
In his challenge, carried by the Seattle Times, Secretary MacDonald said he would give $1000 of his own money to the person who could best communicate to the public the concept of "through-put maximization," which means moving the maximum number of cars through a stretch of highway at the maximum speed.
After reviewing 258 entries, MacDonald selected Paul Haase, a Sammamish science writer with a thing for funnels, as the winner.
The Paul Haase solution
Haase suggested that anyone who has ever mixed up a recipe in the kitchen would understand traffic flow better through a simple experiment.
Here’s what you need to try this yourself:
- Two funnels
- Two liter-sized containers to place under the funnels
- One liter of rice
- One stop watch
To demonstrate his idea, Haase dumped one liter of rice all at once into the funnel and started the timer. Forty seconds (and several rice-sized traffic jams) later, all the rice was in the receiving container. Then, he took the same liter of rice, the same funnel and the same stop watch, but this time he poured the rice slowly and evenly into the funnel. Can you guess what happened? Twenty-seven seconds later, all the rice was in the receiving container. He shaved 13 seconds off his old time through gradual, controlled pouring.
The process of controlling the pour would intuitively suggest that the last "rice" in line was being slowed down. But in reality, that last "rice" in line actually arrived ahead of nearly all the rice that "jammed" the funnel during the uncontrolled pour.
What does this prove? According to Secretary MacDonald, it proves systems like ramp meters, which regulate traffic, save drivers time. It also proves future systems, like high occupancy toll lanes that use transponders to speed drivers through toll lanes, will make the most of our limited lanes.
We will continue to search for ways to talk about transportation systems. What do you think?