distributedlife

You’re driving along the road and you’re approaching an intersection. You’re at the point where if the light goes orange you’re unsure whether you should stop or continue through the intersection¹. We are making the assumption that you’re generally law abiding. The light turns orange and you’re still in this no-man’s-land.

If you leave it too late you could end up in the intersection; if you keep going then you may run the red-light.

To make it more interesting there is a red-light and speed camera; so you can’t speed up and you get fined if you don’t make it.

What do you do?

The issue is uncertainty there are too many variables to make an easy judgement call. Not all intersections are the same length, not all roads are at the same speed, you are not always going exactly the speed limit, you’re not always the same distance from the intersection when the light changes.

If you add additional factors like poor vision from eyesight, poor vision from bad weather or poor spatial skills it becomes even harder.

If you look at this problem as “should I keep going?” we can make a simple change that I think would remove the issue.

If you’re travelling at the speed limit there is a finite distance you can travel in the five seconds from when the light goes orange to when the light goes red.

If you travelling 80km/h then are moving at 22.2metres per second and if you’re travelling at 60km/h then you are moving at 16.6m/s.

If you have 5 seconds to cross the intersection then you are going to travel 111.1 or 83.3 metres respectively.

Now consider the example story and add a single orange line drawn across the lane at 110m from the far end of the intersection. If the light goes orange and you haven’t crossed the orange line then you are never going to make it. The decision is made for you. If you’ve crossed the line then you will make it and can continue at the speed limit.

The caveat is that all of these equations are based on the maximum speed of the road. If you’re travelling slower than the speed limit or there are poor conditions and you are outside the line you have more time to stop. If you’re inside the line then it comes back to the judgement call.

Some may argue that because it doesn’t solve the problem for all scenarios it won’t work or the government would get sued. The judgement call is the backup and is the current process. The orange line solves the problem in all scenarios where the driver is travelling at speed. In rainy or icy conditions it may even help drivers who are unsure whether their car will stop in time.

To me; all of this relates back to designing the User Experience and challenging the assumptions about what we think the user knows at the decision point. I feel we are often too focused on the outcome of a decision (user invokes behaviour) rather than the decision process.

If we’re in the mindset of “if the user wants to do X they can click here and if they want to do Y they can click there” or “if the driver wants to make it through they keep driving and if they want to stop they slow down” we need to take a step back and make sure the user can make the decision in time.

When you are next giving a user choice consider why and how the decision is made. It may be possible to better plan the flow so that no decision is ever necessary.

1. if you’re turning left you will be travelling at a lower speed and better able to stop [↩]