The Problem With Highway Lids And What Cities Should Do Instead

Henry Latourette Miller
8 min readMay 27, 2021
Photo by Benjamin Rascoe on Unsplash

One of the most impressive ideas for creating new green space where cars are dominant is also less effective and far more expensive than this simple solution.

The Problem

For decades America’s cities have tried to figure out what to do with urban highways. Many of those concrete gulches snaking across the cityscape were laid down in the mid-20th century, when city halls and state transportation departments had little to no concern for the damage they were doing to the host communities in terms of air and noise pollution, nor for the real estate sacrificed to a single use that mostly served suburban residents. With gentrification taking the place of white flight, and the idea of healing neighborhood wounds and accommodating pedestrians more prominent in the minds of planners, many cities are looking for ways to mitigate the negative effects of urban highways and get more out of the public space that was so undemocratically sacrificed for the sake of the automobile.

One simple solution to these problems has been around almost from the beginning: just put a lid on it. Highway “lids” or “caps” or “decks” are platforms built on top of highways that can host new uses, typically a park or public space. As far back as the 1970s cities and state DOTs have installed green space lids across the country, from Seattle to Dallas, Kansas City, Philadelphia, and Washington DC. They range from simple concrete covers carpeted with grass and playgrounds, to multilevel structures that also host arts institutions and commercial space.

Green space lids can be simple, but they are always expensive. In a story familiar to the cities that pick this solution, Chicago’s 24.5-acre Millennium Park, built over a railyard and car park, cost more than $490 million ($270 from taxpayers) and took six years to construct (four more than scheduled). This amounts to about $20 million per acre, which is especially outrageous when you compare it to the cost of building a surface park right across the street: the 25-acre Maggie Daley Park, which took only two years to construct and cost taxpayers $60 million, comes out to 2.4 million per acre. Prohibitive costs and a tendency to go way beyond schedule are often what shuts a lid proposal down, but this shouldn’t be the only or even the first reason. The truth is that in most cases green space highway lids are bad ideas that provide only a Band-Aid fix to a deadly problem along with a highly compromised new space.

First, let’s look at what all lids don’t do. If the noise and pollution highways create, along with the egregious amount of space they consume, are a problem, lids do almost nothing to fix it. Unless the lid is many hundreds of feet long, the toxic emissions from the highway are still coming out on either end of the new tunnel and wafting across the new park, or ball court, or playground. Even if it is an exceptionally long lid, the city has just spent a whole lot of money shielding one small area from some highway pollution while doing nothing for anyone who lives along a highway that likely stretches for miles and was deliberately built in low-income neighborhoods and communities of color. To make it worse, low-income residents who might have benefited from the new lid now face displacement as successful lids can shoot up surrounding property values.

When it comes to the noise, again, yeah, some people are protected, but it is worth noting that the main design conceit of all highways is to attract drivers and get cars on and off them as quickly and easily as possible. That usually means that urban highways are at the center of the city’s car traffic, and are surrounded by on-ramps, shoulders, and high-traffic streets. Lids alone do nothing to change this, and as long as there is a way to access the highway near the lid (as is the case with Dallas’ Klyde Warren Park), there will be highway noise in the neighborhood.

The same is true for the space highways consume: lids don’t return car-oriented land to the people, but only offer feeble disguises that come apart at the seams. A lid may create a small park and reconnect a street pattern in one neighborhood, but there are still miles of uncovered highway and highway-connected infrastructure that carry the exact same number of cars and take up the exact same amount of urban space as before. As lids alone do nothing to discourage driving and redeveloped public spaces are intended to attract new visitors, some lid projects, like the notorious “Big Dig” in Boston, are tied to the construction of new space for cars.

Which leads to the second problem with building a lid to create a new park: the spaces they introduce are poorly placed and highly compromised. It is important to remember that when mid-20th century city planners built highways, their primary objective was to move people by car from the suburbs to the commercial center as directly as possible. Only the very core of a city’s commercial center, where the wealthiest residents worked, would be spared from the destructive path of highways, which tended to blast through low-income communities with near zero regard for their existing street layouts or their social and economic fabric. Since then, and for all the obvious reasons, people and the places they like to spend time in have moved away from highways when they could. As a result, a green space on top of a highway is not guaranteed to be surrounded by local users who can easily access it, or any of the resources that contribute to a beloved local park, such as cafes, restaurants, and schools. Instead, you have built a green space that shares many of the same ills as highways: that is, disjointed from the local community and surrounded by car traffic and infrastructure.

None of this is to suggest that highway lids are never the right solution, and many successful lids have a few things in common: they are built in central, already walkable areas where they reconnect neighborhoods and services blown apart by the existing highway. In Boston, the Rose Fitzgerald Kennedy Greenway reconnects two halves of downtown split in the 1950s, making it easier for people who work in the office towers in the middle of the city to access the historic North End and vice versa. In America’s biggest and densest cities, highway lids like Seattle’s Washington State Convention Center become platforms for new, multi-story structures that capitalize on converting air to leasable square footage, making the cost of construction easier for city halls to stomach. It should be noted, however, that both of these projects have been controversial at different points in their timeline, with Boston’s Big Dig guzzling public funds during construction and Seattle’s Freeway Park suffering from a reputation for crime in the early ‘00s.

However, before considering the simple and handsome, if pricey, Band-Aid fix of highway lids, cities should acknowledge the actual problem: the existence of large, congested, loud, expensive to maintain, polluting, inefficient urban highways built by elitists who didn’t give a damn about the air we all breath or the neighborhoods the working classes and communities of color call home.

It is equally important to squash the mid-century myth that because urban highways allow for the movement of goods, they are good for the economy, and therefore good for workers and/or small business owners. By decentralizing cities and cutting through old neighborhoods, highways helped kill Main St. and made big-box stores built on cheap land at the fringes of a city possible. Despite relying on substantial public investment to build roads and utilities that can reach them while paying little in taxes, these big-box stores are now struggling to compete with goods delivery giants like Amazon, which thrives by adding more vehicles to already congested highways, shuttering the remaining small businesses, and paying its workers poverty wages.

Highways aren’t inherently good for the economy, but labor unions, healthy public schools, and a well-balanced transportation system are. Highways as we currently use them aren’t even that great for Amazon and the suburban communities they were designed to serve, when you consider that both of those entities are negatively impacted by the climate change disasters made worse by vehicle emissions. When it comes to escaping acidifying oceans, burning crops, and apocalyptic hurricanes: Jeff Bezos is going to need a bigger boat.

The Solution

Once we recognize this cycle of social, environmental, and economic doom that highways contribute to, it becomes clear that the goal shouldn’t be to disguise highways, but to make it easier for people to stop using them as often for everything we do.

One way to get people drive less is to look at far cheaper locations than above highways to add green and commercial space that can be accessed on foot, by bike, transit, or any number of less destructive modes of transportation than single occupancy vehicle.

Throughout the pandemic, cities across the country have sacrificed thousands of parking spaces and miles of driving lanes so that small businesses can add outdoor seating. In some cities, like Portland and Oakland, entire streets were blocked off to car traffic to make it easier to social distance and to give residents more space to recreate. While these moves have in no way been without complications or controversy- which often revolved around lack of input from communities of color- they were popular enough for Portland to try to make some of the changes permanent.

Instead of building inconvenient public spaces in uncomfortable places, we should be making our existing parks bigger and commercial areas more vibrant by removing cars from the street and filling the space they once occupied with new uses tailored to that community.

These uses might include food carts, or more athletic courts that can use the asphalt, or a Saturday market, or a new playground, or a tanning lounge on hot summer days. This new flexible space could be added to the spaces surrounding existing parks, where neighbors are already accustomed to reaching on foot, or to Main Streets that need a little extra boost to compete with the likes of Amazon and Walmart. Considering that personal use automobiles spend the vast majority of their existence not being used, and when they are being used they contribute to climate change and are overrepresented in deadly traffic collisions, literally any other use of our neighborhood streets would be an improvement.

A simple step like this could get the ball rolling in the effort to create a much more healthy relationship between American society and the automobile. As new local commercial, social, and recreational spaces replace car parking and driving lanes, picking a less harmful mode like transit or micromobility to get to where you want to go becomes more appealing. As fewer people require a 20 minute car read to access the services they need, highways will see fewer vehicles, thus reducing congestion, emissions, noise, and many of the other negative externalities that define America’s highways today. Lastly, rather than spending heaps of coin to build compromised real estate in poisonous air, we will be using cheap solutions to add to the spaces we already know we love.



Henry Latourette Miller

A writer and transportation planner based in Portland, OR.