Stop Quoting the Congestion Cost Number as if It Were a Bill

Stop quoting the big congestion number as if it were a bill. It is a modelled estimate, and the people who build it would say so before you did.

Every few months a headline puts a dollar sum on traffic jams or road crashes, and the number gets passed around as proof that a city is failing. The sum is useful. It is also built on choices that rarely make it into the headline, and once you know what those choices are, you can read any cost figure in about a minute.

What the figure is, and what it is not

Federal and state transport agencies publish estimates of what congestion costs the economy, and the Bureau of Infrastructure and Transport Research Economics (BITRE) is a national source for congestion cost estimates. These are not totals taken from a ledger. Nobody receives a monthly invoice for being stuck on a freeway. The estimates are modelled: analysts compare how long trips take now with how long they would take under a chosen benchmark, then put a dollar value on the difference.

That already tells you three things. The result depends on the benchmark, because “avoidable” congestion is measured against a reference condition and a different reference gives a different number. It depends on the value placed on time, which is an assumption about what an hour of someone’s day is worth. And it leans on projections about future traffic, which are less certain than counts of what happened.

None of that makes the figure wrong. It makes it an estimate with a method behind it, and the method is where the argument belongs.

A test for any cost figure

When you meet a headline sum for congestion, crashes or anything similar, ask four questions of it.

1. What is counted? For congestion, published methods generally include time lost, extra fuel and vehicle running costs, and the added emissions from idling. Some leave the last of these out. Check the report, not the summary.
2. Compared with what? A cost relative to free-flowing roads is not the same measure as a cost relative to a realistic target. A bigger gap makes a bigger headline.
3. Whose time, and at what price? A figure that values every minute the same treats a delivery driver’s lost hour like a leisure trip’s. The assumption moves the result.
4. What year, and is it a forecast? A number that was an estimate for last year and a projection for ten years out should not sit in the same sentence.

If the source cannot answer those four questions, treat the figure as colour, not evidence.

Crash costs have the same problem, with higher stakes

Road crash cost estimates exist so governments can weigh a safety project against the money it would save. The usual approaches differ in a way that matters. One counts the economic losses: lost output, medical care, property damage and the administration that follows. Another tries to reflect what people would pay to avoid the risk of death or injury, which gives a larger figure because it places a value on life and quality of life that the narrower measure leaves out.

Neither is the one true figure, and a headline that does not say which approach it uses is hiding the single most important detail. A big crash cost does not mean a crash is only a financial event. It means an agency has chosen a method for comparing options, and the sum is a tool for that comparison, not a measure of grief.

What traffic management does, and what one number cannot show

Traffic management is the work of keeping vehicles, pedestrians and cyclists moving safely: signal timing, lane control, signage, incident response, and the temporary arrangements around roadworks and events. It is the reason the figures exist, since the cost estimates are used to decide where that work is worth doing.

The mistake in most coverage is treating the large national or city sum as a measure of how well traffic management is performing. It cannot be. One aggregate number mixes weather, population growth, road works, fuel prices, how many people work from home and how a city is laid out. A signal upgrade at one junction cannot be read off a citywide total. To judge whether a particular measure works, you want before-and-after data for that measure on that road, over a period long enough to cover the normal ups and downs.

The fair objection to all this is that big numbers matter politically. A large, round sum gets a project funded, and a project that gets funded may well save lives. That is a reasonable point, and it is the best argument for the figures. It is not an argument for reading them carelessly, because a number that wins a budget can still be a poor guide to which of two projects deserves it.

How to read the next headline

Read it the way an analyst would: find the report behind it, check which costs are counted and which are left out, note the benchmark and the year, and ask what the number is being used to justify. A congestion figure that is honest about its method is a fine thing to know. A congestion figure repeated without it is just a loud way of saying roads are busy, and if you want a way to judge how your own city is coping with that pressure, four measures for rating your own city is a good place to start.

Sources: Bureau of Infrastructure and Transport Research Economics, congestion and road crash cost publications (https://www.bitre.gov.au/resource/regions-cities/traffic-and-congestion-cost-trends-australian-capital-cities); Austroads, guidance on road safety and economic appraisal (https://austroads.gov.au); Australian Transport Assessment and Planning Guidelines (https://www.atap.gov.au/parameter-values/road-transport/4-crash-costs).