The toll structure on Sydney's cross-city tunnel encourages drivers to behave in exactly the opposite way to the behaviour desired by the planning authorities.
Traffic in Sydney's CBD is a chronic problem, and never is it more so that during the peak-hour rush. To help alleviate that congestion, the cross-city tunnel was built to carry traffic under the CBD from Darling Harbour across towards Moore Park, and linking up with other tunnels to disperse that traffic east and west. Congestion makes life difficult for cyclists, pedestrians and those using public transport. It increases the noise levels, contributes to poorer air quality, and overall levels of stress. It's a significant problem and getting worse.
In order to reduce the congestion in the CBD, drivers need to use the tunnel. So our target behaviour is this: drivers travelling east-west (or vice versa) electing to take the cross-city tunnel instead of King St, Druitt St, Bathurst St etc through the middle of the city. In bypassing the traffic above, along with traffic lights, pedestrians, cyclists, intersections and the like, the tunnel offers a much faster journey across the city. In essence, the cross-city tunnel provides a premium service to the motorists of Sydney.
To help fund the construction of the tunnel the government - as has become common practice in recent decades - partnered with private enterprise. Also typical of such agreements is the introduction of a toll to help pay back the investment (at least from the private partners).
We therefore have a premium service (faster transit) attracting a service charge (toll). This makes great commercial sense. It is, at the end of the day, the way most businesses operate. We can impact demand (drivers using the tunnel) by tweaking the pricing - at least in theory.
Now let's take a look at this from a behavioural view. The behaviour we're attempting to encourage is the one attracting a charge. Alternatively, for no charge, I can continue behaving in my established routine. Yes, traffic is slow and painful, but the driver can estimate the time needed for the journey and plan accordingly. They are in a comfortable environment - their own car - where they have refreshments, entertainment, space.
Now, what if, during peak-hour, those charges were reversed? Instead of paying to use the tunnel, it is offered for free (since it is our best mechanism in reducing congestion and improving traffic flow). And instead of the CBD streets being free (which we're trying to discourage), a toll of $1 is charged on each of the entrances to the area.
Now at least we have aligned our charges with our desired behaviours. But let's take that a step further: have you tried to gain entry to the cross-city tunnel? It's actually quite difficult compared to heading up those CBD streets. So what if the traffic was actively channelled towards the tunnel, and the more difficult path was the one which takes you through the CBD? We have now also aligned our roads with the desired behaviour - providing easier access to the paths we're encouraging people to adopt.
For the government, they would need to adopt a different method of repaying the private investment in the road. Of all the problems facing Sydney, an innovative commercial arrangement would seem the easiest to resolve.
By aligning the tolls and the structures with the behaviours we wish to encourage, we are much more likely to see those behaviours in action. This is the lens that interaction design can bring to a project - any project - resulting in a much higher likelihood of success.