By Charles Marohn/Minnesota Reformer
The following is an excerpt from chapter six of Confessions of a Recovering Engineer: Transportation for a Strong Town, the latest book in the Strong Towns series. It has been slightly modified for this space.
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.”
There is nearly total consensus among transportation professionals that ramp meters are a positive innovation. Even critics cede that ramp meters allow more efficient use of roadways. With ramp meters, more cars travel through the same lanes in less time. Ramp meters cut overall travel time, improve safety, and make efficient use of highway capacity.
Getting more out of existing transportation investments without needing to build any additional capacity is a level of genius that would make any engineer proud. Sadly, the professional consensus on the benefits of ramp meters is wrong. Understanding why will help us move beyond the fiction of models to an approach not dependent on traffic projections.
In 2000, I was going to graduate school at the University of Minnesota, living in the exurbs of Minneapolis and commuting to the university each day. My commute was about 50 minutes. I never hit a ramp meter on my way because I lived too far out, but there as I drove by were the lines of cars queued up in the on-ramps, kindly allowing me and the rest of the traffic to flow past.
During my first semester, the State of Minnesota did a little experiment regarding ramp meters. Again, Wikipedia accurately describes it:
In 2000, a $650,000 experiment was mandated by the Minnesota state legislature in response to citizen complaints and the efforts of state Sen. 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%.”
These results sound terrible and, in fact, the experiment is frequently cited as proving the validity of ramp meters. As an alternative, consider my experience as a participant in this experiment. Before the experiment began, nearly all of my classmates had apocalyptic fears about their commutes. They were mostly young and lived near the campus in the heart of Minneapolis. In class, they expressed their anticipation that their 20- to 30-minute commutes would take significantly longer without the meters. The opposite happened; without being forced to sit at ramp meters, they all reported much quicker commutes.
My experience was the opposite. The experiment was eight weeks of hell. My 50-minute commute suddenly 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, the freeways opened enough so that 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. Finally, after everyone closer in had arrived at their destinations, those of us who lived in the exurbs could make our way into the city center.
What shutting off the ramp meters did was effectively meter the highway itself. Instead of the city resident having to wait on a ramp for me to drive by, now I – the exurban dweller – had to wait for them.
With ramp meters, traffic volume is up, speeds are increased, and level of service is improved. The values transportation professionals care most about all trend in the right direction, but that leaves out a key part of the story. What ramp meters also increase is vehicle miles traveled. The engineer’s approach of making better use of highway capacity through ramp meters simply allows people to migrate to farther reaches of the system. Once again, the dynamic nature of traffic is not considered.
Whatever cost savings there are in getting more efficient use out of the existing roadway is more than offset by the miles of new lanes demanded in the second ring, third ring, and throughout the exurbs, not to mention the ramps, signals and other improvements that go along with them. Measuring the results of metering at the meter using the metrics that reflect their values, engineers miss the overall impact that their efforts have on the transportation system. While congratulating themselves for saving millions, they are literally inducing billions in new demand in other places.
Building more capacity is a fruitless endeavor. Reconfiguring our systems to make them more efficient in the limited dimensions that engineers find important is doing real damage to our cities, our families, and our economy. The only way to deal with congestion is to allow congestion to drive demand for local alternatives to auto trips. The only long-term way to address traffic congestion is to build alternative destinations locally. Shorter trips, or trips made by walking and biking, retain vehicles near their source and free up arterial capacity for others.
In this, congestion is an ally driving investment.
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Comments welcome.
Posted on September 13, 2021