One of the fundamental problems with transport planning in Australia is that politicians see it as demand-led, when basically transport systems are supply-led.

Demand-led thinking has them looking at congested roads and thinking “we need to build another one”.

Another one gets built, and it fills up. Rinse and repeat. (More people in cars = Bad outcome)

Or a train line is crowded and they put on more trains, and more people use them as well. Rinse and repeat. (More people in trains = Good outcome)

Supply-led is why they fill up. Provide options and people will use them. In general they’ll use the easiest/quickest option available. Built it and they will come.

This is how transport systems work: through induced demand.

It’s easy to see why demand-led thinking motivates action and funding. It’s very visible. Road congestion is obvious when you see it. Public transport crowding is obvious when you see it.

And it’s also easy to see why politicians feel they have to try and fix those issues. The problem comes in how they try and fix them: providing more of the same is not always the best answer.

A letter in The Age yesterday claims that if the West Gate Tunnel is built, “a great many west and north-west Victorian citizens travelling to the south and east of Melbourne will have significantly reduced travel times.”

Experience around the world shows this isn’t true. Travel times from road expansion don’t last — see Citylink Melbourne.

“But we have to drive!” they say. Yes, you have to drive because 80 years of investment in roads, with peanuts for alternatives has given you little choice. Every new investment in major roads makes this worse, and misses an opportunity to provide alternatives to give you choice.

The State Government could be funding Metro 2 (the rail tunnel linking Newport and Clifton Hill via Fishermans Bend and the City) and related projects such as fast frequent feeder buses, to massively boost public transport services from the west (alongside the logical, relatively small truck route they took to the 2014 State Election), but instead they now want the Transurban-led West Gate Tunnel.

Major roads are, by their very nature, inefficient. Vicroads data shows that lane occupancy is just 770 people per hour in AM peak, around 840 in PM peak — though this doesn’t show separate figures for motorways. For the sake of argument, let’s assume motorways are about double that, with 1800 — closer to a theoretical perfect driving scenario of a vehicle every 2 seconds.

Even 1800 is not very many people. If you try to solve congestion with another road, or more lanes, it doesn’t take many vehicles to clog it up again, and you’re back to square one.

Rail can’t move everything, but it’s far far more efficient for moving people, which is what accounts for most vehicles on the roads. Adding 1800 people is just two additional trains — about a 10th of the capacity of a rail line with old conventional signalling.

This means rail expansion is long-lasting. If managed well, extra tracks or a new line can handle huge numbers of people.

Roads get less efficient the more people use them: more space encourages more people, and congestion slows everybody down. If the response from government is more roads, we have a vicious cycle.

Public transport gets more efficient the more people use it: more passengers justifies more frequent services, which cuts waiting times and makes connections easier, and encourages more users. A virtuous cycle.

So the next time a politician talks about transport, consider whether they’re just bleating rhetoric, or they’re showing an understanding of how transport systems work.

We have to build more roads because people are driving! No, people are driving because we build more roads.

We have to build more roads because of population growth! No, we only have to build more roads if we want more people to drive. If you want them to walk/cycle/PT, then provide that instead.

This motorway will be city-shaping! Yes, but unfortunately the shape it will be is more car-dependent.

This motorway will be a congestion-buster! No, it will just generate more traffic. They always do.

More reading : I don’t think the debate should be about congestion. It shouldn’t even be about mobility. It should be about access to opportunity: jobs, education, amenity.

: I don’t think the debate should be about congestion. It shouldn’t even be about mobility. It should be about access to opportunity: jobs, education, amenity. The Sustainable Cities campaign (a joint project of PTUA and affiliated groups) has an event at 8am Tuesday at State Parliament — come along to hear about a broad community transport vision to provide Melbourne-wide sustainable transport options for the future. Update: see getonboard.org.au.

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