Exploring crash statistics - an excellent interactive visualization

This series of interactive visualizations by the BBC is quite stunning. The first shows a map of fatal car accidents in the UK. For the area chosen you can see age, sex, and vehicle type breakdowns. Mouseovers show details of the accident as well as links to the news story about it.

The year slicer on the bottom is excellent, allowing you not only to quickly jump between years, but also to see how accidents vary over the months in each year. My only wish is that you could show the markers for all years, allowing you to better identify accident hotspots, and that they superimposed a line across years to show a trend of total accidents.

On another tab, they have the breakdown of accidents by time of day. The buttons on the side allow you to see the pie chart and time of day statistics by the category chosen. A pie chart is not my first choice here - a bar chart would be better, but you can click a section of the pie to show the time of day data by just that segment - mouseover the image below to see when young people kill themselves vs. the older population. I think the radial bar chart works very well in this case, especially with the radial gridlines.



In a previous career I was a consultant focusing on fatigue and safety, so these data are of particular interest to me - for example, if you select vehicles, then the pie segment for goods vehicles, you can see the spike in accidents at 4AM as truckers fall asleep at the wheel and crash. The only thing missing (which you rarely see in data like these) is normalization - the risk of driving in the early hours is so much greater than at other times of the day considering the amount of traffic. An excellent example of data visualization.

Safety critical interfaces

While the blog will focus on software, I will occasionally highlight good and bad interfaces elsewhere. Take a look at this picture of my current tester (you hold it near a wire and it beeps and flashes if the wire is live). The end of the tester turns to switch it on. Do you think it's on?

It isn't - it's actually rotated to the orientation where you can pop the cap off and change the batteries. But the cap doesn't pop off - it just sticks in this position until you wiggle it. To switch it on, you have to rotate it the other way, but this way it looks on, so if you weren't paying attention you could test a wire and assume that it's not live.

How should it be designed? Perhaps the cap should pop off as soon as you get it near the stop point - but that would be annoying as I'd be constantly picking up the batteries. Maybe the stop for the remove batteries should be beyond the 'on' setting, so at least you have to turn it past to screw up. Even better, there should be a completely different mechanism for changing the batteries (which you only have to do every few years...)

You'd be foolish to not check it's working by testing it next to a known live wire but people cut corners, work when they're tired, etc. This design is a safety hazard, but neither the manufacturers, insurers, or whoever tested it for its UL listing picked up on this.