Best of Blog: Ramp Metering

We are closing out the year with a Best of Blog collection containing our favorite posts from 2010. This piece, which was one of Ben's favorites, ran on February 3 under the title "Ramp Metering: An Unholy Alliance". The post examines how engineers and planners tend to agree on ramp metering, but for all the wrong reasons. It touches on the quasi-religious beliefs of each profession and, oddly enough, I remember a few angry emails in my inbox after this one ran. We'll see which profession emails me first this time around to inform me that I am ignorant. Send your emails to oleson@strongtowns.org.

Ramp Metering: An Unholy Alliance

When I was in engineering school we made fun of planners. They were out of touch, impractical, idealistic. When I was in planning school we joked about engineers. They were out of touch, unimaginative, rote. These two professions - planners and engineers - are two sides of the same coin, but their approach to solving problems and building communities could not be more different.

Straddling both of these professions (I am both a PE and an AICP), one thing I have always found revealing is how they both (generally) agree on ramp metering. Ramp meters are those mini traffic signals that queue vehicles as they enter the highway. Wikipedia explains their rationale succinctly.

Ramp meters are installed to restrict the total flow entering the freeway, temporarily storing it on the ramps, a process called "access rate reduction." In this way, the traffic flow does not exceed the freeway's capacity. Another rationale for installing ramp meters is the argument that they prevent congestion and break up "platoons" of cars.

The consensus on ramp meters is revealing because it exposes the general failings of each profession in their approach to our common problems of community-building.

In general, planners support ramp meters because they think single-occupancy cars are evil. There are likely some planners reading that sentence in recoil mode, but that is the reality. When we as planners can set up devices that make driving in a car more burdensome, we believe that somehow people will abandon their cars and move to high-density urban Utopias. At the very least, we can give preference to transit systems and people that carpool. Hopefully the "idiots" wasting time and money driving themselves solo to work in their SUV's will grow to understand the benefits of rideshare. And if not, at least they are being punished by having to wait.

In general, engineers support ramp meters because they believe it an ingenious way to solve traffic problems. With ramp meters, you can run more cars through the same pipe in less time. Cut overall travel time, improve safety and make efficient use of highway capacity. Get more out of your system without building any more costly lanes of traffic - it is a level of genius that would make any engineer proud.

Sadly, both professions are wrong about ramp meters.

And not just wrong in their motivation. Even if you hold their motives to be pure, ramp meters actually have the exact opposite result from what each profession is seeking. Let me explain.

In 2000, I was going to graduate school at the University of Minnesota, living in the exurbs and commuting in each day (my wife was driving an equal distance the opposite direction - young and no kids, all seemed fair). My commute was about 50 minutes. I never hit a ramp meter on my way in. I was too far out. But there as I drove by were the lines of cars queued up in the on-ramps, kindly allowing the traffic to flow.

That first semester, the State of Minnesota did a little experiment regarding ramp meters.Wikipedia accurately describes it as follows:

In 2000, a $650,000 experiment was mandated by the Minnesota State Legislature in response to citizen complaints and the efforts of State Senator Dick Day. The study involved shutting off all 433 ramp meters in the Minneapolis-St. Paul area for eight weeks to test their effectiveness. The study was conducted by Cambridge Systematics and concluded that when the ramp meters were turned off freeway volume decreased by 9%, travel times increased by 22%, freeway speeds dropped by 7% and crashes increased by 26%.

Despite the apocalyptic fears from my soon-to-be-planner classmates, their commutes were not snarled in congestion. They were mostly young, lived in the central urban area near campus and had short distances they needed to travel. Now they no longer had to sit at the ramp meters. Many actually indicated that their trip was quicker. 

But for me, those were eight weeks of hell. My 50 minute commute increased to two-and-a-half hours. I sat in congestion for endless stretches. And it is quite simple to understand why.

Before anyone from a first-ring suburb could enter the city, everyone living in the urban core needed to get to where they were going. Since they were uninhibited by metering, they owned the freeways. Once they reached their destination and parked their cars, those from the first ring suburbs could enter the city. The rest of us waited for them to clear out. Then the second ring could enter. Then the third ring. And finally those of us that lived in the exurbs could make our way into the city center.

Planners intent on punishing evil cars and their evil drivers with meters are doing just that. The only problem is, the closer to the city a driver lives, the more they are "punished". Ramp meters make those that live most efficiently - those closest to their place of employment, typically in higher density and in older neighborhoods - wait in favor of those that live the least efficiently. Not exactly what the planners had in mind.

For engineers, the model of efficiency - making better use of the highway capacity through ramp meters on the premise that it saves money - simply allows people to migrate to farther reaches of the system. Volume is up. Travel time is down. Speed is up. Great, but what isn't measured? Vehicle miles traveled. Sure, we may save some money by not having to build more lanes through the inner-ring, but now we have to build miles and miles of lanes in the second ring, third ring and the exurbs, not to mention the ramps, signals and other improvements that go along with that. Measuring the "results" of metering at the meter, engineers miss the overall impact their efforts have on the system. While congratulating themselves for saving millions, they are literallyinducing billions in new demands in other places.

If we are going to grow stronger as a country, we need more from these two professions. Planners need to get real. They need to embrace an approach that is more practical, more empirical and more refined than the simplistic (dare I say, elitist) line of thought that currently dominates the profession. Engineers need to embrace planning and a planner's approach to systems thinking. Building a better mousetrap is novel, but engineers need to ponder whether mice are really the problem and what the consequences of getting rid of them are. "Got hammer, find nail" is growing us into decline. We need to get smarter.

Ramp metering, and similar schemes, need to be replaced with a Strong Towns approach. The way to bring about a more efficient development pattern is not to try and "punish" the symptoms of bad development (talking to you, planners) but to instead stop subsidizing inefficiency. The way to get more out of our transportation system and reduce congestion is not more capacity (talking to you, engineers) but through strengthening neighborhoods and using mixed-use zoning to reduce trips.

Do more with less. Build better places. Stop sitting at ramp meters. That's Strong Towns.

Comments

[Ross Williams]

Chuck -

I am glad to read this. The burden of ramp meters is actually greater than you state. If you live in those inner city neighborhoods many trips are diverted onto local streets. The "time savings" on the freeway are offset by increased congestion on local streets.

The MNDOT study actually confirmed your point. People who lived close in had their travel times decrease, while people who lived in the exurbs had their travel times increase. The real issue is that ramp meters give priority to people who are on the freeway over people who are trying to get on it. So someone living in the central city where there are ramp meters has to wait for someone living in the exurbs, even if they are both headed to the same destination at the same time. This creates the paradox that the further you away you live, the quicker you will get to work once you get close to your destination.

I think there is at least one legitimate argument for using of ramp meters - the breaking up platoons of cars. That makes access safer for everyone and requires little more than a second or two delay between cars entering.

There are places where that is how almost all meters are used for that kind of queuing. But MNDOT is really using meters to benefit their preferred users. Which is the real issue of ramp meters, who gets the benefit, who bears the burden. MNDOT uses ramp meters to transfer the burdens of car dependent communities to people who live in traditional multi-modal neighborhoods, to the benefit of those who are car dependent. That makes sense for an agency which depends on increasing automobile use for its business model.

The argument about car pool lanes is actually different than you present. The question is whether you are serving people or vehicles. One way to reduce the need for new highway infrastructure is to use it more efficiently by putting more people in each vehicle. That also reduces other costs of transportation by reducing congestion, reducing the need for parking and making local streets more attractive for all modes of transportation. The idea is not to "punish" people for driving by themselves, its to make sure that they bear the burden for the benefits that their private vehicle provides. It makes sense to give priority to vehicles carrying two or more people over a vehicle that has only one person in it. That is not really an argument for using ramp meters to sort traffic, but that is one way to do it. But then you would put the ramp meters out in the suburbs where most of those people are getting on the freeway, not just in the inner city.

[Froggie]

I think both of you are missing some of the points. Consider for starters the crash rate reduction. That's significant, especially given the costs involved with crashes, between direct costs with the accident itself (police/rescue/medical/etc) and societal costs (increased congestion, time lost, environmental costs of the congestion). One could make the argument that those cost savings are higher than the costs incurred with people living farther out (i.e. the main argument of the article against ramp meters).

And the crash rate "increase" on the local streets is not enough to offset the significant crash rate reduction on the freeways....nevermind that freeway crashes have greater impacts overall than local street crashes.

Another thing to consider: we have *A LOT* of express bus usage in the metro. These buses benefit from less congestion on the mainline, allowing them to make their runs faster. And for those occasions when they're using the shoulders, breaking up the platoons coming down the onramp directly benefits these buses as they travel the shoulder through the on-ramp/merge area.

[Ross Williams]

Actually, there is plenty of evidence that there is no "crash rate reduction", if by that you mean fewer crashes even if you ignore the impact on local streets. The additional speeds and VMT generated actually offset any safety improvements you get.

"These buses benefit from less congestion on the mainline, allowing them to make their runs faster."

Again, given the increase in VMT that results, where is the evidence that ramp meters "reduce congestion"?

I think you missed a central issue. Who bears the burden and who gets the benefit. You induce traffic from the suburbs by giving it priority, then you place the burden that extra traffic creates on people who live close in by reducing their access to the freeway. If the strategy is to reduce the amount of traffic, the place to start is those suburban locations. Of course reducing traffic from the suburbs in order to preserve capacity for buses and people who live close to work does not serve the goal of increasing use of automobiles.