The science of traffic | March 20, 2009 | Palo Alto Weekly | Palo Alto Online |

Palo Alto Weekly

Cover Story - March 20, 2009

The science of traffic

Don't blame the engineers: Human behavior is an equal cause of gridlock, experts say

by Nick Veronin

Peninsula commuters are no strangers to congestion, especially those living or working in Palo Alto. Whether heading to the North Bay from the suburban sprawl of San Jose, or south from San Francisco to a technology park in Mountain View, many drivers can recall — if not fondly — getting a very good look at the hulking, yellow-and-blue edifice of IKEA, as traffic on U.S. Highway 101 crawls past the University Avenue interchange.

Traffic jams, simply put, are a part of daily life in Silicon Valley, as are the questions they invariably raise, the most vexing of which — Just what in the world caused that gridlock anyway? — even gets traffic experts excited.

Take Mike Lepech, assistant professor of civil and environmental engineering at Stanford.

"You can get backups when absolutely nothing seems to have caused it," he said, acknowledging how frustrating, and common, the phenomenon is. Understanding why such jams accumulate, he said, is the key to preventing them, keeping drivers sane and getting people "home to their kids quicker."

"Driving is not rocket science," Lepech said, "but we do it so often that we tend to lose respect for what we are doing — hurtling ourselves at 75 miles per hour down the road." At that speed, and with the volume of vehicles found on a freeway such as 101, failing to understand one's role as a driver can contribute to dangerous road conditions and the very congestion people have so often cursed while staring up at the bold, serif font of that familiar Swedish furniture maker.

Lepech said it is just as important for individuals to understand how one car can adversely impact traffic flow as it is for transportation engineers to understand how to build more efficient road systems.

The most ostensible cause of traffic on 101 is population. The American Community Survey, an arm of the U.S. Census, estimated that roughly 2.6 million cars, trucks and vans hit Bay Area roads in 2007, ferrying commuters to and from their homes and offices.

According to Casey Emoto, deputy director of project development with the Santa Clara Valley Transit Authority (VTA), every day 150,000 to 200,000 of those vehicles use the stretch of 101 dividing Palo Alto from East Palo Alto.

Those numbers, Emoto said, have played no small part in prompting two projects, which aim to improve safety conditions and reduce overall congestion on 101 by adding additional infrastructure to a stretch of the freeway passing through Palo Alto.

The first is VTA's U.S. 101 Auxiliary Lanes Project, which aims to improve safety conditions and reduce overall traffic on the freeway between Highway 85 and Embarcadero Road. The $102 million project is funded in large part — $89.4 million — by Proposition 1B, which California voters passed in 2006. Another $17.3 million comes from the VTA Local Program Reserve Fund.

The project will widen the freeway to 10 lanes and will also widen ramps at each interchange of the 3.2-mile segment of 101. Once the project is completed, the rightmost lanes of both northbound and southbound 101 will be designated "auxiliary lanes," which will allow vehicles more time for merging onto or off of the freeway. It will also allow cars traveling from one interchange to the next to do so without ever entering the highway's main flow.

Planning began on the second project — metering lights — more than 20 years ago but has been held up by the red tape of regional governments ever since. According to Benjamin Edokpayi, the Caltrans public information officer for Santa Clara County, the project was first conceived in the '80s. During the mid '90s, metering lights were installed on all 101 southbound on-ramps, from the San Mateo County line all the way to De La Cruz Boulevard in San Jose, with the exception of the Charleston Road onramp in Mountain View.

However, city governments in Santa Clara County would not agree to the metering plan when Caltrans proposed to turn the signals on four years ago, Edokpayi said.

Since then, Caltrans, VTA, the Metropolitan Transportation Commission and cities in the county have been working together and the metering lights from Embarcadero Road to De La Cruz Boulevard are expected to be turned on the first week of April.

"Palo Alto commuters can expect their on-ramps to be metered before getting on the southbound 101 corridor in the evening commute," Edokpayi said. This, he hopes, will result in a less congested evening commute for drivers heading south.

According to Lepech, both measures should improve freeway safety and loosen gridlock.

"You're basically making the pipe wider from one exit to the next," Lepech said of the auxiliary lanes, comparing traffic to water flowing through a pipe.

"If you don't have a big enough artery to carry all the water needed, you have two options: increase the diameter of the pipe or increase the velocity of the flow. But this can't be done with freeway traffic. The last thing we want to do is put people closer together and have them go faster."

Fortunately, he added, the former option works like a charm.

On city streets, Lepech said, traffic moves in what are called "platoons," groups of cars that are stopped at each red light and then ushered through with every green. In this way, large blocks of traffic — or platoons — are moved around a city efficiently. But on the freeway, he said, a "platoon takes up the entire road" and is not broken up by traffic lights. If too many drivers attempt to enter a busy freeway, a platoon, which may stretch for miles, begins to slow and can ultimately come to a standstill.

The addition of metering lights will augment the lane expansion by forcing drivers to file onto the freeway in an orderly manner during peak traffic hours, Lepech said, ultimately increasing the fluidity of merging traffic through the Palo Alto stretch of 101.

The concept is simple enough. It isn't hard to understand why giving drivers more time to merge and allowing them to move from entrance to exit without disturbing the main body of freeway traffic will improve traffic flow. But Lepech and Emoto — along with Wolfgang Homburger, emeritus lecturer at U.C. Berkeley's Institute of Transportation Studies — say there is much more to traffic than what is revealed to the casual observer.

"Most drivers ... don't think about the underlying science (of traffic) any more than they think about the science of electricity when they turn on the TV," said Homburger, who served the institution from 1955 until his retirement in 1990.

The Institute of Transportation Studies, or ITS, opened its doors in 1948. Back then, it was called the Institute of Transportation and Traffic Engineering and was predated only by Harvard's Bureau of Highway Traffic.

Initial ITS studies, Homburger said, focused on traffic behavior and safety on streets and rural highways, characteristics of different paving materials, lighting of roadways and vehicle lights. As faster, more sophisticated automobiles were built and freeways were constructed, ITS' research kept pace to address evolving traffic concerns, such as those now being confronted on 101.

One of the most difficult things to account for scientifically is human behavior. In the case of the metering lights, Lepech said, they would be entirely unnecessary if everyone acted altruistically. "You should never have to use your brakes on the freeway, that's the whole point, right?" Lepech asked rhetorically. The problem is that drivers often do not move over when signs direct them to, but speed up to put themselves one or two cars ahead.

Erratic lane changes, short merges and selfish driving practices often cause what Emoto calls a "shockwave," a traffic phenomenon that isn't obvious at ground level but is clearly visible when watching traffic from above.

"Even if it's just tapping the brakes, it causes a cascading effect in the traffic behind you," Lepech said, describing how such a "shockwave" can form. "When the freeway is at, or near, capacity, if there is any perturbation in the flow — all of a sudden there is a reaction of a single driver — you end up with the first driver accounting for that perturbation and then, boom! It starts to go to the next person and the next person."

This "cascade" of brake lights, Lepech said, is often the root cause of those perplexing clots of traffic that seem to manifest from nothing and evaporate without explanation.

Homburger said that metering lights, by imposing controls on human behavior, can greatly improve a freeway's fluidity. Traffic flow on freeways increases with demand up to a certain point, or "capacity," he explained. Stop-and-go traffic is the result of a given freeway exceeding its capacity. By controlling the volume of traffic added to a freeway each hour, fluidity can be maintained.

"What you're trying to do is minimize the friction, the disturbances," Emoto added.

Drivers may not realize the amount of work — beyond simply erecting traffic signals — that goes into projects like these. Edokpayi said one of the biggest challenges of the metering-lights project was getting Caltrans, VTA and the Palo Alto city government on the same page. The auxiliary lanes project also had to be approved by the city and is currently open to public comment through March 27.

But in addition to the governmental logistics, there is also fine-tuned science working behind the scenes of all transportation projects. Homburger explained that there is a formula used to determine the appropriate time between red and green lights in freeway metering systems. Signal times are set by calculating the number of vehicles, per 5 minutes, that can be accommodated by a given freeway at a given on-ramp at a given time.

The southbound 101 lights have the ability to make such calculations in real time.

"The meters adjust rates to conditions on the freeway upstream of the on-ramp," Edokpayi said. "The rates at each of the on-ramps is part of a metering plan that looks at the whole freeway corridor."

It's food for thought for any frustrated driver impatiently waiting to get onto 101.

"By delaying you a minute or so at the ramp meter," Homburger said, "the total delay for all freeway users is substantially reduced."

Lepech said that sophisticated infrastructure, paired with technology and a better understanding of how traffic behaves, will not only lead to a safer commute, a healthier state of mind and a better family life. He also sees an opportunity to cut down on carbon emissions and conserve resources.

He and his colleagues look to a future where traffic control systems are smarter.

"Intelligent traffic," as he calls it, is the idea that with the aid of an extremely thorough system of fixed cameras, digital road signs and traffic signals that can be controlled in real time, the roads of an entire city or even county might move at optimum efficiency, as drivers are given up to the minute information and directed to take alternate routes when necessary.

Lepech admitted, however, that "the amount of data and the complexity of doing that is immense."

The biggest problem with such a system is that it could not simply be automated, he said. "People would have to make judgments about what is and what is not a situation that has to be dealt with."

The cost of staffing such an operation would be huge.

But even though such an intelligent system is currently out of reach, researchers at Stanford are currently working on transportation systems that seem more like science fiction than a practical solution. Lepech called them "adaptive cruise control" systems — the futuristic concept that cars might one day drive themselves with the aid of sensors in the road.

Until the day that such systems are implemented — if that day ever comes — and even with the improvements slated for 101, Lepech said there is no substitute for individual action. Knowing and avoiding the sorts of seemingly benign actions that can contribute to traffic jams is one thing drivers can do today to reduce congestion.

"Paver slowdown," he observed with a laugh, is both the easiest and hardest traffic generator to avoid. "No matter what happens, whenever someone drives by an asphalt paving machine, they slow down to 5 miles per hour to watch this machine that can lay down black asphalt."

Above all, he said, being safe and selfless on the road is paramount to keeping cars moving.

Staying focused on the surrounding road, obeying traffic signs promptly instead of waiting, and being sensitive to other drivers instead of only looking out for No. 1 all may seem to take longer in the short term, but in the long-run, everyone on the road will benefit.

"The biggest thing that impacts flow is traffic incidents, collisions," he said. "Keeping aware of the traffic conditions around you and practicing the same procedures you learned in drivers' ed — that's what keeps traffic flowing smoothly."


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