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.
Posted on September 13, 2021