The Speed Limit in Every City Should be 20 MPH

But that doesn’t mean simply changing numbers on signs. It should feel dangerous to go any faster than that.
20 mph speed limit road
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Screen Shot 2021-02-24 at 3
Moveable explores the future of transportation, infrastructure, energy, and cities.

In July 2016, the city of Edinburgh implemented a bold change. It lowered the speed limit on almost all of its roads from 30 mph to 20 mph that didn’t already have a 20 mph speed limit. The city center, main streets, and residential roads all became 20 mph zones. The only roads that retained 30 or 40 mph speed limits were in the city suburbs. 

At the same time, a group of researchers, including ones at the University of Edinburgh, formed a team called “Is Twenty Plenty For Health?” to study the impacts of the new 20 mph policy. The results all pointed in one direction: 20 mph is plenty. The zones with a reduced speed limit saw 371 fewer crashes per year, or 38 percent, including fewer crashes involving cyclists and pedestrians. On average, cars went slower. And, as a rule, people felt safer biking and walking. These results have been replicated in further studies since and most of London is now a 20 mph zone, too.


When it comes to urban travel, 20 mph is a kind of magic number. It is under most scenarios the natural limit of how fast people can move through dense urban areas at an average clip. The New York City subway, which can and will go 55 mph on long straightaways—like the run on the 2 or 3 line from Times Square to 72nd Street—travels at an average speed of about 17 mph when taking into account time spent at stops, slowing down for curves, and the occasional delay due to train traffic ahead of us (other systems go faster, but they tend to be ones with longer distances between stops serving primarily suburban commuters; but by way of comparison, the London Underground’s average speed is, you guessed it, 20 mph). The average urban biking speed is something like six miles per hour when factoring in stops, but closer to 11 to 18 mph when in movement. E-bikes—which have the potential to revolutionize urban transportation and already have in many global cities—typically have a top speed right around 20 mph.   

Top speeds and average speeds are, of course, different things, and each mode has its own safety implications depending on whether it has a dedicated path without obstruction or competes for space on busy urban roads. Perhaps it is just a coincidence that 20 mph is a kind of natural ceiling on average travel speeds in urban areas and also a speed at which most everyone feels safe regardless of what mode they or anyone else is using. Either way, the power of 20 needs to be taken seriously. 


A study out of the University of Surrey found cyclists are more likely to use roads where traffic travels at 20 mph or slower. Various slow streets programs around the world have found the same, that when cars are traveling slower than 20 mph, people feel comfortable cycling or walking on them, reducing the life-or-death need for separate infrastructure like protected bike lanes. The risk of death when struck by a vehicle traveling at 20 mph or slower is relatively low (it starts to dramatically increase around 25 mph). But, as Edinburgh found, it is also easier to prevent or avoid crashes from occurring at those speeds to begin with.

The problem is, while few cars in dense urban areas travel faster than 20 miles in an hour on average, many achieve speeds much, much faster for short periods of time to no one’s benefit. Multiple times a week, some driver will gun it to narrowly and dangerously pass me while I’m riding my bike only for me to roll up next to them a few hundred feet down the road at the next red light. (I used to wave at them with a smile on my face when I caught up to them in a friendly attempt to demonstrate passing me at high speeds has no benefit, but apparently the embarrassment and/or annoyance can make drivers so angry that they intentionally pass even closer when the light turns green.)

I do not blame drivers for their behavior, because I am occasionally a driver too. They (we) are encouraged to drive faster by the way the roads have been designed. For many decades, roads in urban areas were engineered to enable cars to go much faster than 20 mph, because that was supposed to be the whole point of cars. Two lanes became four, turning lanes were put in, and crosswalks were spaced further away so traffic would continue to freely flow. American cities in particular became re-designed to promote car usage as affluent residents fled for the suburbs and drove to work every day. For the past century, any suggestion that cars should be limited in speed in urban areas to 20 mph or less would have been met with derision, if it was deemed worthy of response at all.


The legacy of these road design changes are still visible today. An extreme but illustrative example is Park Avenue in Manhattan. Some people think it is named Park Avenue because it connects to a park somewhere. But it doesn’t. It is named Park Avenue because it was once a park.

Park Ave ca 1924-1927

Park Ave ca 1924-1927. Credit: George Rinhart / Contributor via Getty

Here is what that same spot looks like today:

Park Avenue 2021

Credit: Google Maps

As you can see, Park Avenue is not a park anymore. It is an eight-lane monstrosity with some flowers and a tree or two in the median, a sad reminder of what this glorious street once used to be, a place where people could stroll along fountains and flowers between skyscrapers. 

If you were to drive on Park Avenue today, you would experience two separate and contradictory emotions: That you should be going faster but also that there are too many damn people and cars in the way. 

The feeling that you should, somehow, be traveling faster is due to the road design, with as many lanes and as much space for cars as an interstate freeway. On one occasion, I experienced this feeling first hand. It was 3 AM, and I got a terrible migraine and had to take a cab home to Brooklyn to get medicine. In 2014, New York lowered the speed limit on most city streets to 25 mph. It also re-timed traffic lights so, if you go exactly 25 mph, you will hit nothing but green lights. My cab driver knew this and went precisely 25 mph. Without any traffic to slow us down, we cruised the five miles from 57th Street to the Brooklyn Bridge stopping only once to make a turn. And the entire time all I could think was, Why are we going so slowly? At 25 mph, Manhattan’s wide, expansive boulevards practically beg you to go faster. 


In most American cities, even the more transit friendly ones, it is quite common to come across a four-lane road where going 25 mph feels like you’re barely moving at all. This is intentional, as the road was designed for going much faster, perhaps 40 or 45 mph. As a result, urban roads are in a paradoxical state. They beg you to go faster than 30 mph, but traffic, traffic lights, and speed limits either prevent you from doing so or try to dissuade you with threats of fines or worse. It is like being offered a piece of candy and then slapped in the face when you try to take it. 

In recent years, some cities have made vague gestures towards acknowledging the safety problems of having vehicles travel that fast on city streets. Often, this is part of a larger “Vision Zero” publicity campaign in which a mayor declares an official goal of achieving zero traffic-related fatalities by some predetermined year, invariably after that particular mayor is term-limited. (I’m not talking only about former New York City mayor Bill de Blasio here, but I’m also not not talking about him.) Part and parcel of the American approach to Vision Zero campaigns is the wishful thinking that changing and enforcing speed limits will, on its own, make any dent in the rising number of people killed on American streets, even as roads continue to encourage drivers to go fast whenever they can.


This is where Edinburgh’s story gets a bit more nuanced. Because it did a lot more than change the numbers on some signs. At the same time, the city issued new street design rules including narrower lanes, new and more pedestrian crossings, wider sidewalks, more priority to cyclists, and removing center lines in 20 mph zones, among many other changes. All of these are proven methods for encouraging cars to slow down, to make drivers feel like they are risking their own safety as well as the safety of others by going any faster. 

You can see the impact of these changes not just by looking abroad, but also looking back in time. Let’s return to Park Avenue. In the old photo—which is undated but was taken sometime between 1924 when the Ritz Tower was built and 1927 when Park Avenue’s car lanes were widened for the first time—there are three narrow lanes, including one curbside parking lane, in each direction with a 40-foot linear park in the middle. In an environment like that, it would feel a lot less safe to drive any faster than 20 mph. But on today’s Park Avenue, with 12-foot wide lanes four abreast and no pedestrians to speak of in the median, it’s a speedway.

The city is making vague noises about returning Park Avenue to a semblance of its former glory, which is a step in the right direction. But this isn’t about one road. It is about the standard approach American cities take that results in a nonsensical policy of roads designed for travel much faster than anyone can actually go without risking their own safety or the safety of others. 

To be clear, if New York City declared tomorrow that the speed limit is being lowered from 25 to 20 mph, it would accomplish nothing. The point is not to set yet another bar drivers are incentivized to ignore (after all, everyone speeds). It is to help drivers feel uncomfortable going any faster in urban areas. The best way to accomplish that is to ditch the New Park Avenue design and return to Old Park Avenue. Cars will still get to where they are going in the same amount of time as they do now. But the journey will be better, and safer, for everyone.

Drivers may revolt at the idea of a 20 mph speed limit for cities, but if you sometimes drive in a dense, urban area like I do, ask yourself: When was the last time you actually traveled 20 miles in an hour without using a highway? What are you actually gaining by going 30 or 35 mph for a few tenths of a mile at a time just to wait at some lights longer? What if, instead of oscillating between going 35 mph or 0 mph, you were able to consistently travel 15 or 18 mph for prolonged periods? Would that be so bad? Maybe it would even be a little bit better.