Chart of the Day: Simulated Average Speeds Before and After 4-3 Conversions

Here’s a chart from a traffic engineering study (out of the University of Nevada*) that simulates the effects of 4-3 road diets on automobile speeds at stop sign controlled intersections.


The upshot of all this is that there are a lot of variables which enter into the picture when studying traffic impacts of 4-lane (Death Road™) vs. three-lane designs. For example: how many buses are there? What percent of the traffic is trying to turn left at two-way stop sign controlled intersections?

(The one thing that doesn’t enter into these LOS simulations, however, is pedestrian and bicycle traffic and/or safety concerns.)

There are a lot of different studies and arguments about the feasibility of 4-3 road diets, and at what point the tradeoff between safety and traffic speeds starts becoming one-sided. This kind of analysis is just one small piece of the puzzle.


*Note: I have no idea how peer-reviewed or thorough this study might be. It seems to have been presented at a convention-type thing in 2011.

Bill Lindeke

About Bill Lindeke

Pronouns: he/him

Bill Lindeke has writing blogging about sidewalks and cities since 2005, ever since he read Jane Jacobs. He is a lecturer in Urban Studies at the University of Minnesota Geography Department, the Cityscape columnist at Minnpost, and has written multiple books on local urban history. He was born in Minneapolis, but has spent most of his time in St Paul. Check out Twitter @BillLindeke or on Facebook.