If you haven't had the chance, check out saveourbridges.com. It's a simple but wonderful example of data journalism that shows both the effectiveness and the limits of opening up data.

Created by Barry Lepatner as a sort of online compendium to his book, Too Big to Fall, the site hosts a map of more than 72,000 bridges across America that the U.S. Federal Highway Administration has assessed as structurally deficient — in other words, bridges in poor condition that may not be able to support their intended carrying capacity. There are an additional 7,980 bridges that are "fracture critical," meaning there is no redundancy in the design. If a critical component breaks on one of these bridges, it will collapse.

And this, sadly, is precisely what happened on August 1, 2007, when a bridge in Minneapolis along the I-35W that was both structurally deficient and fracture critical collapsed during rush hour, killing 13 people and injuring 145.

Alarmed? You should be. If you are an American there is a very, very good chance there is a problematic bridge near you. If you aren't American, I wouldn't get too comfortable; you simply don't know if there's an at-risk bridge near you. The province of Quebec in Canada has experienced a rash of collapsing overpasses and crumbling infrastructure that has resulted in several deaths.

But saveourbridges.com doesn't just tell us about failing infrastructure, it is also an instructive window into the possibilities and limits of open data. Here are 5 lessons I've drawn from the site:

1. Open Data ≠ Relevant Data

Predictably, the saveourbridges.com map should never have been made. Lepatner gained access to the database while researching his book, but none of the data he refers to is available on data.gov, the place one would hope to find it. Indeed, even after a fair bit of digging, the data available on bridges from the Federal Highway Administration says little to nothing about the bridges' structural ratings. It is a sharp reminder that the critical data you would want a government to share is precisely the type of data they are likely not going to share.

Sadder still, Lepatner also got a snapshot of bridge quality data. This means that over time, the quality of this data will decline, and his map will decay in usefulness along with the bridges it charts. This serves no one.

2. Transparency is Helpful but it Can't Solve Every Problem

Lepatner has done worthwhile work trying to bring attention to the issue of crumbling infrastructure, and has gained some media attention. Of course capturing the attention of the US public is no small feat so I'm not sure I'd fault him for not gaining still more attention. But it is an important lesson in the limits of transparency. As I've written many times before, bringing transparency to an issue – in this case, showing people that the roads they drive on are unsafe – is rarely going to in and of itself lead to spontaneous change.

The data Lepatner has put together is fantastic, and arguably it's an important link in the chain between ideas and public policy – but it is not the only one.

3. Let others build (and have a call to action)

At no point on the site is there a call to action other than buying Lepatner's book. This is the single largest weakness of the website. There are so many things that could have been done with this data. I'd love to have seen a phone app that automatically emailed the relevant congressman and senator every time you drove over an at-risk bridge in their district. Or maybe a mashup of accident data with at-risk bridges (I suspect there is a correlation — old bridges are probably also less driver friendly). Or maybe an examination of the socioeconomic makeup of communities surrounding at-risk bridges. Could there be a link between poor infrastructure and marginalized communities?

I'd also love to have imagined the map served as the basis for hundreds of local news stories but sadly that does not seem to be the case. Part of this may be a result of the fact that many newspapers still are unwilling or unable to link to external websites. But it is also a sobering reminder of how hard it is to make any issue — data or no data — resonate, particularly if, despite being important, it is still somewhat mundane.

But a call to action around even some of this would have been interesting. Indeed, for a government keen on renewing US infrastructure and getting funding for shovel-ready projects, making this data available and encouraging people to use it might have been downright self-serving.

4. Lower Barrier to Entry

I think my favourite thing about saveourbridges.com is that it is a window into the lower costs of doing data journalism. I have no doubt that gaining access to this bridge data was not straightforward, but once he had it, finding ways to put it into Google Maps and build a website around it would not have been difficult. It still requires some skill and either resources or spare time, but the barrier to entry is falling. Thus, I hope that projects like saveourbridges.com could become more numerous as more people are able to explore critical issues.

5. These issues matter

I'm sure that some readers may believe that this issue is rather pedestrian – but that is exactly why I love it.

It is an everyday, boring issue, but it is one that matters. A lot. The vibrancy of many local economies and the safety of those communities depends on sound infrastructure. This is exactly the type of story that the media rarely covers, or only does so during a crisis. The opportunity to create sites that might even have continuous monitoring or engagement opportunities built into them strikes me as one of the exciting ways that technology might change the way the public engages with its government and some of the basic services it offers.

I know that saveourbridges.com isn't going to make the US's infrastructure a voting issue in a national election, but that would be a tall order for any project. But given the media attention it has received, there is some evidence to show that a well presented visualization of data can engage the public and help prompt a conversation on an important, if fairly mundane, issue. These are not terrible outcomes. I hope that we'll see more projects like saveourbridges.com in America and elsewhere.

Personal Democracy Media is grateful to the Omidyar Network for its support of techPresident's WeGov section.