An alluring image, produced by the NSW Department of Transport, was designed to promote the idea that trams – and public transport more generally – have a profound capacity to reduce congestion because too many of us travel alone in private cars.

It’s a powerful visual message and one that is easy to accept at face value. Except that if you pause for a moment and really think about it, there’s quite a bit wrong with this image.

For starters, the spacing of the imaginary cars in the image is excessive, while the occupancy of the imaginary tram is largely wishful thinking outside of the most congested of routes during peak periods. Occupancy of 100 per cent means a seat for every passenger, and 135 per cent is the DOT benchmark, above which passengers experience overcrowding. This benchmark is reached on some routes at the busiest of peak times, but outside this, public transport networks rarely average high occupancies across their operating hours. Neither, for that matter, do road networks operate at capacity around the clock, so the issue is really all about congestion at peak periods; or roughly four to six hours out of 24, five out of seven days.

Another weakness is that the car occupancy pictured is undercooked. Average private vehicle occupancy in Sydney is around 1.3 people per car, meaning there should be a two-passenger car for every two single-passenger cars. The image conforms to our perception that nearly every car on the road only has one passenger in it, but it doesn’t reflect reality all that well.

A further weakness is the implied suggestion that all the people in the imaginary vehicles are on the same route and going to mostly the same places as those in the imaginary tram. The image implies that mode of transport can serve the people in the top image just as well as those in the image below, but in so doing, it makes no reference to the reality that a fixed route mode of travel like a train or tram will serve mostly the people on that route, or who are prepared to travel to a station to access that route.

The private car, by contrast, has multiple routes open to it, which serve a much wider cross section of the community. The people in the imaginary cars in the image can all have very different destinations in mind, with multiple stops for varying reasons along the way (picking up kids from schools, grocery shopping et cetera).

But the biggest problem with the image is that it borders on propaganda. Paid for with our taxes, and produced by a government department, the image distorts the reality of public and private transport in order to promote an idea (the benefits of public transport to congestion). There is nothing wrong with this idea; indeed there is much that is right about it. But as long as we replace balanced, evidence-based public policy with propaganda, we run the risk of ill-informed debates and massive misallocation of resources which doesn’t reflect the needs or priorities of the majority. An informed public is at the heart of a democratic system.

There are many legitimate benefits of public transport in urban centres but those benefits surely do not need to rely on tricky advertising messages which distort the realities of both private and public transport. There are enough myths, fallacies and plain lies that do the rounds about private and public transport without the need for taxpayer funds to make the situation worse.