Modal Filters

Recently I've been thinking about how we make parts of our cities more and less attractive for non-automotive uses (and the inverse: how too often we prioritize cars). An important tool for that is the modal filter: a means of allowing one or more types of transportation through a certain point while stopping others, thus giving those types of transportation an advantage in navigating the city and making them (at least implicitly) more attractive.

Today I want to talk about why these can be good, but also how we actually use them not to help diversify our transportation portfolio but to advantage cars.

1. Modal filters work well with green space

One easy, common form of a modal filter that allows bikes and pedestrians through but not cars is: a park. 

Here's a simple example from the Somerville/Medford border in the Greater Boston metro:

The street is a T-intersection, but the pedestrians and bikes can slide right by the little playground and keep going. This does double duty as a modal filter and a chance to greenify/beautify the space and give people somewhere to entertain themselves. 

There are a lot of ways to make this very cute and very attractive. Any park can functionally be a modal filter, at least for pedestrians (and often bikes as well), and if you include green track trams, you can get transit through there as well.

2. Modal filters offer a solution other than parallel pathways

A modal filter, like the ones in Amsterdam, can naturally redirect car traffic. This creates less tension between modes of transportation than having them all jostle cheek by jowl.

To be fair, Amsterdam does that well too. 

Here we can see trams, car space, bike space, and pedestrian space. But because they all go the whole distance of what we can see, they have to cross each other for turns and jostle up against each other the whole way competing for space in the street width. A modal filter requires less space than this, and so can be a good way to separate modes without requiring fully separate paths for as much distance.

And of course, like Amsterdam, you could have both.

3. But the most common modal filter we use is pro-car

Shel Silverstein knew this before anyone: there's a modal filter Where the Sidewalk Ends. Or anytime you get on a highway, with those big signs that say no pedestrians or bikes allowed. Lots and lots of our American infrastructure uses modal filters to privilege cars, rather than to free us from their dominance. If you cannot go anywhere by anything other than a car practically, legally, or both, you have a modal filter that prioritizes cars. And this is all too common in our cities.

But the good news is this: the very frequency of this means we're actually very good at building modal filters, and very familiar with how they work. The next step is just to stop using them so much for cars, and put them to work for people.