24 Nov, 22 tweets, 7 min read
It looks like all of LA is on the 405 right now.

But...how many people is this? And, better yet, how many trains would it take to move them?

Let's do the math.

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We're looking at the interchange of I-405 and I-10 in Los Angeles, facing south.

When we zoom out, we see a full view of I-405 from Ohio Ave to Sepulveda Blvd, a distance of 5.8 miles, or ~30,500 feet.
The 405 is five lanes in each direction for this entire stretch, plus auxiliary (merge) lanes, so essentially 12 lanes across.

Some quick multiplication gives us 305,000' of through lanes and 61,000' of auxiliary lanes.

This is about 160(!) acres of space in total.
Now we need to get lane density. A good approximation for heavily congested mixed traffic is 40' per vehicle.

A passenger car is ~15', but you need space between cars, and some of the traffic is made up heavy trucks.

I also verified this by counting cars in the video.
Aux lanes tend not to be as congested, so we'll say that they have a vehicle every 80'.
Thru lanes:
305,000' * (1 vehicle/40') = 7,625 vehicles

Aux lanes:
61,000' * (1 vehicle/80') = 763 vehicles

Setting aside on/off ramps, that's a total of ~8,400 vehicles.
The FHWA assumes an average vehicle occupancy of 1.7 people per vehicle. Let's assume since it's the holidays that that's higher, and round up to 2.

So the total number of people actually traveling on the 160 acre stretch of roadway is...

And while that *sounds* like a large number, in transportation terms...it's really not.

A single very crowded BART car can hold about 200 people, or 2,000 people in a 10-car train.

Meaning we're looking at about 8.5 trains worth of people.
At peak capacity through the Transbay Tube (which connects Oakland and San Francisco), BART can move 23 trains per hour per direction, or one every 2 minutes 40 seconds.

This is a *theoretical* maximum of 46,000 per hour on a single line of track (actual ridership is lower).
The upshot:

Every single person on the 405 in this 6 mile length of 12-lane freeway could ride on one train line between West Oakland and San Francisco (the same distance) in about 30 minutes.
Note that that's everyone moving in both directions of freeway (12 lanes) fitting into 1 "lane" of train line.

But not only is the width needed only 1/12th as much, the length is also wildly different.

85 BART cars lined up would be about 1.2 miles long, or 1/5th the length.
Just to use another example, the Shinkansen (Japanese Bullet Train) runs 16 trains per hour per direction, with a capacity of 1320 people per train.

At full capacity, this many people could pass through in 48 minutes, everyone in their own seat.
All of this to say, cars (and the infrastructure to move them) take up a whole lot of space.

But *people* don't.

When we allow people to move in space-efficient ways, we will find that we don't have to devote truly massive amounts of space to our transportation system.

/๐งต
A couple more thoughts.

There is some confusion about one-way vs two-way travel, namely I compared 12 lanes of two-way cars vs one-way train throughout, which actually disadvantages the train.

Let's clear that up.
The Transbay Tube runs 23 trains per direction per hour.

Imagine that we have half of these 17k people on either side of the Bay, 8500 at West Oakland and 8500 and Embarcadero in SF.

A train comes every 2.6 minutes and each one picks up 2k people (or 1k more comfortably)
Assuming people are packing on the trains, every one of those 17k people is *on* a train in 11 minutes and to the other side of the Bay in 18 minutes.

More comfortably loaded, it's a total of 30 minutes to get everyone to switch stations.
Also, throughout matters, but so does speed.

How *long* does it take people to get from A to B?

We don't get to see the video long enough to judge speeds, but I'd guess ~12 mph.

At that rate, it takes 30 minutes to travel 6 miles, a distance that BART traverses in 7 minutes.
And as @SFBART points out, the Transbay Tube throughput is only going to increase.

Their ongoing Core Capacity Program will improve increase the number of trains from 23 per direction per our to 30 per direction per hour!

Some people are having a hard time with the use of thought experiments.

So, for the record, this *is not* a proposal to turn 6 miles of the 405 into a train line.

It is rather an illustration of the spatial efficiency of various travel modes.

And yes, for those wondering, this whole thread is indeed a long subtweet of Elon Musk and his breathless acolytes.

This thread would not be complete without @alon_levy's crayon map of LA rail.

Find the map here:

and the post about it here:
pedestrianobservations.com/2017/09/15/futโฆ
Pleased to see that my travel time estimate was pretty good.

Displeased to see that Google Maps is recommending that people whip through local streets instead of driving on the 405.

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# More from @WarrenJWells

23 Nov
This is almost *too obvious* to notice, but the reason that paint works to delineate lanes for cars is that drivers *carry their own physical protection.*

They don't need walls between them and other cars traveling in the same direction because their car has walls.
People on bikes carry no such armor, meaning paint and soft, plastic delineators do not...do anything.

If you don't feel safe in a paint-only bike lane, it's because you're not.
Because they don't carry it, bike users need their physical protection to be part of the built environment.

We need delineation that will *resist* incursion from cars.

This means k-rail, concrete, strong bollards, or putting the bike lane above the curb.
23 Nov
This is the first installment of #NorthBayNotes, Dispatches from Marin County by Bicycle.

The ongoing series will be things I notice, fun and frustrating, exciting and exasperating, while riding around the county I work in.
This is Nick. He rides an electric tricycle and told me he doesn't even need a car.

Many days he rides up to 20 miles, though the battery is good for 50+. He was generous enough to let me stop him and chat.
Work continues apace on the North-South Greenway Gap Closure project, a new bike/ped bridge over Corte Madera Creek that will replace the existing 4'(!) sidewalk.
22 Nov
Driving works best when only a few people are doing it.

But we've designed a system where driving is pretty much the only viable option.

Raise your hand if you see the problem here.
This is why so much NIMBYism is traffic-based.

People see the traffic we have today and imagine that twice as many people will mean twice the traffic, so they feel they have no choice but to say "no."
Because our traffic engineers have failed to design a system in which people can do anything other than drive, they (perhaps correctly, perhaps not) assume that anyone else coming to their neighborhood will drive as much as they do.
22 Nov
Personal confession:

One of the reasons am such a jerk about texting and driving is that, when I was 22, I totalled my car doing exactly that.

I've only told this to a couple people.
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This was in 2009, i.e. before smartphones.

I was going to frisbee practice and pulling up to a light. My phone buzzed with a text and, as I slowed down, I checked who it was from.

I thought I had space between me and the next car but I looked up just as I crashed into it.
Luckily I wasn't going that fast, maybe 8 or 10 mph. My airbags didn't even deploy. But it was still enough force to crush my car's radiator.

Thanks to forces beyond my control, no one was hurt.
12 Oct
On a zoom weminar hosted by @CalBike with renowned bike researchers John Pucher and @buehler_ralph on international international comparisons in biking!

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Here is the share of trips made by bike across North America, Europe, and Japan. Huge variation across countries, with English speaking nations lagging behind.
But these differences are not because those countries are more dense! In the US, our share of bikes used for even short trips are tiny!

Whereas in the Netherlands, nearly half of all 1-2.5 mile trips are on a bike.
12 Oct
6,000+ miles of riding over my three years in the Bay.

All my bikers out there, what do you notice?
Super true! SPA is a huge block hole my map. 9th St and California sort of work, but have their own issues (and no fronting commercial for me to actually use!)

I mean, this is the elephant in the room, right?

It's also so striking to see that we can get 2/3rds(!!) of the way there today. It's just not that far from Yerba Buena to Embarcadero, and yet it might as well be 1000 miles.