A Junction Efficiency Metric: Vehicles Per Square Meter Per Minute · Josh Thompson

A Junction Efficiency Metric: Vehicles Per Square Meter Per Minute

September 2025

tag(s): mobility_networks • scooters • streets

Reading time: 19 mins

Article Table of Contents

Introduction

How To Calculate Vehicles per Square Meter per Minute

1. determine the size of the junction

2. do some vehicle counts (example from the 17th & Monaco junction)

2.1 the counts, examples & time lapse video

How I do the counts

animation of what 3x efficiency could look

Intersection Efficiency Comparison

Different ways the efficiency could be expressed

An audacious goal

Achieving a 400 square meter junction

Additional Reading

Footnotes

still sorta drafty, but also its entirely possible the point is easily apprehended, and I’m way over-explaining

Introduction #

Elsewhere, I’ve been referring to a ‘vehicles per square meter per minute’ calculation, when talking about junctions on mobility networks. The first place was this substack piece, A Pattern of Repair: The Traffic Bean, then again in depth in The Traffic Bean: An Idea Applied to 17th & Monaco.

Overall I’m arguing that the traffic bean concept is one or two orders of magnitude more efficient than a traditional american-style light-mediated junction. Those are big claims. This metric (vehicles per square meter per minute) is part of the math part of these claims.

Again, later, I did a demonstration on Downing, and addressed how by placing some cones, I got the junction size down by almost half, and the situation for everyone was dramatically safer/smoother.

Here’s a bit of an example of what we’re about to discuss: It’s possible that this single graphic perfectly encapsulates everything I’m trying to share in the following thousands of words:

See how those two shapes have different dimensions? and also specific, knowable dimensions? Now add the concept of ‘counting numbers of vehicles that can pass through the space in a given time’ and we have everything we need for a junction efficiency metric.

I’ve noticed wishing for better ways to calculate some of the stunning differences in efficiency of certain road junctions.

I’ve put this together partially by cutting the relevant pieces of other posts, and aggregating it here.

Having a metric like this allows someone to say something like:

configuration A gave 1 vehicle per 20 square meters per minute throughput. Configuration B gave 3 vehicles per 20 square meters per minute, and was preferable in many other ways, so we’re going with configuration B.

or:

the current junction moves .5 vehicles per 10 square meters per minute

It allows two different junctions, of different sizes, to be compared. If one junction moves 30 cars per minute, and a different design moves 45 cars per minute, which one is better? If the 2nd junction is twice the square meters of the first one, it’s less efficient per square meter, even though it moves more vehicles.

How To Calculate Vehicles per Square Meter per Minute #

every junction moves vehicles, and can move a certain number of vehicles through it, in a certain time, and that junction has a certain shape/area.

1. determine the size of the junction #

I think this is the easy part. Crack open Google Earth, and draw boxes around junctions. I’ve got a bunch of examples of other junctions here:

https://zoningverydifferentthanours.substack.com/p/traffic-congestion-as-solvable-part-510

There’s a few different ways a junction could be shaped. Everything is full of tradeoffs!

Consider reading that piece (or the entire series) as context for this junction efficiency metric.

It lets one say:

such-and-such junction is 290 square feet/26 sq meters, and such-and-such number of cars moved through it in five minutes. (3-5 minutes is probably the minimum time you’d want to do counts on a junction to get a per-minute time. One probably doesn’t need to count for a full hour to get an accurate time)

If a junction was 600 square meters, and in a 5 minute time at rough hour counted it as moving 150 cars, we could calculate it’s ‘vehicles per square meter per minute’ value. in this case, it would be:

v/m²/min =<br>150 vehicles / 600 sq meters × 5 minutes =<br>150 / 3000 = 0.05

thus, it could be expressed as:

.05 vehicles per sq meter per minute

or could be expressed in square meters per minute per vehicle:

1 vehicle per 20 m² per minute

Who knows yet what the actual values are we might see for a junction.

The expression seems reasonable enough, aids in reasoning about different junctions or plans. I think it might make more intuitive sense once we start looking at certain junctions.

2. do some vehicle counts (example from the 17th & Monaco junction) #

What do you think the value might be for the junction in question, in terms of vehicles per square meter per minute?

How many square meters do you think the junction is?

These are the two questions I posed in the above drone...