Why should you bother looking at this complicated graph and text? Because it examines some of the factors that affect spot rates and the extent to which they are predictable and not.
Following on from my recent post on how the TEG Haulage Index from Transport Exchange Group reflects diesel price, I thought I’d have a look at how each of the Haulage & Courier indices are affected by various costs and indices. Unfortunately, because the TEG is so timely, we’re often waiting for other indices to come out after we know the TEG and there are always ‘other factors’, so (spoiler alert) a prediction using these indices isn’t possible!
So how do the TEG indices correlate to diesel prices?
Well, actually the Courier index correlates more closely to diesel prices (DESNZ mid-month pump price) with an R-squared of 0.54 compared with Haulage at only 0.26. Those figures are for the life of the TEG from January 2019 through to February 2025, but neither are great correlation. For those that don’t know what R-squared in Excel means, it looks at how far each spot is from the linear trend line. If the R-squared was 1 it would mean there was perfect correlation (all spots on the line), but if 0 it would mean the relationship was totally random.
Although we would expect diesel to affect spot rates, it’s doesn’t have as big an effect as some other things.
So what’s with the weird graph about traffic? And why are we interested in traffic levels?
We’re interested as traffic is a measure of demand for freight transport and introduces an element of seasonality, although demand could be limited by capacity, particularly for haulage. It’s worth noting that so far, the YoY rate of change of LCV traffic (mid Wed) has never been negative since DfT started publishing to measure the impact of Covid - it went to 0 back in June 2024 (so identical traffic levels to June 2023) but never negative.
What the graph is showing is how the TEG Courier index varies with DfT’s Light Commercial Vehicle traffic index for the Wednesday nearest to the middle of each month (Wednesday being less affected by bank holidays). So there *is* a spot for each month, but positioned on the X-axis by the traffic level and on the Y-axis by the TEG value for that month.
Continued below the graph...
The period included on the graph runs from June 2020 to February 2025 as the traffic index only started in 2020 as a response to measuring the impact of Covid and I’ve eliminated a couple of months at the start which were very affected by the first lockdown. Using the period shown on the graph results in an R-Squared of 0.73 for the TEG Courier versus LCV traffic levels. By contrast the TEG Haulage index versus HGV traffic is 0.41 for the same period, so less good correlation.
I’ve marked a few key dates on the graph: the start of the period and some of the outliers. Broadly, anything below the trend line has a lower price for a particular traffic level and everything above the line has a higher price for that traffic level, so it’s no surprise that some of the outliers on this graph are for 2022, when diesel prices were very high. And I’ve marked the most recent entry, February 2025, which is a bit of an outlier – you might have expected the Courier index to be higher for that LCV traffic level.
But vans are also used for other things – much more van use was related to trades (ie people using vans as mobile toolboxes for all sorts of equipment) than deliveries in 2019/20 – the most recent figures available from DfT. So it may have been the weather pushing LCV traffic levels up for other activities such as building and house repairs, with the Met Office reporting “an overall mean temperature above average for the month” for February, Scotland having above average sunshine and Hull getting to 17C on one occasion.
What about general inflation?
Of course, the relationship between traffic and prices is also affected by general inflation. The TEG Courier index has an R-squared of 0.75 when compared with the CPI All Items Index for the period January 2019 to January 2025. Haulage is 0.33, so again less correlation than Courier.
The relationship with this index will be a bit a bit circular – freight costs will be a factor feeding into inflation, but then freight costs themselves will be affected as wages go up and so on. Given the monthly rise and fall of the TEG (see the post I did back on 7 January 2025, further down this page), it’s interesting that the R-Squared for Courier versus CPI is as close as it is.
And a proviso: just because something seems to have some correlation, we still need to be careful that we don’t make an assumption about causation. Sometimes we can be pretty certain which is cause and which effect, but sometimes not. As an example, in 2020 after Covid lockdowns got started, it wasn’t low diesel prices that kept the haulage index down, but a reduced level of traffic (not just haulage!) that depressed the diesel price.
Obviously a variety of different factors affect the level of spot rates. You could look at retail sales, internet sales and construction activity, air cargo, job and vacancy levels, wages… and perhaps I’ll look at these in a future post, but the conclusion from above is that the Courier prices should be more explainable than Haulage rates, although it doesn’t always feel like that!
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