Written Evidecen submitted by RAC Foundation (RSM0109)

Research note on callouts attended by RAC Breakdown on the English Strategic Road Network

Dr Ivo Wengraf, RAC Foundation

Introduction

This study is of callouts attended by RAC Breakdown (RACB) on England’s Strategic Road Network (SRN) over three years (2017, 2018 and 2019). The vast majority of callouts involved cars.

The definition of “on the network” used here is all breakdowns between 2017-01-01 03:22:00 and 2019-12-31 23:33:00, where the recorded location was closer to an SRN road (motorway or all-purpose trunk road) than any other road in the Ordnance Survey OpenRoads dataset.

This note excludes any Scottish, Welsh, Northern Irish and Republic of Ireland callouts in the RACB data and which might be in other analyses of motorway breakdowns.

It also excludes any RACB SRN breakdown event which failed to make it through the filtering process. This includes breakdowns: where the location is misrecorded; breakdowns at complex junctions; breakdowns at points where the SRN meets local roads; breakdowns marked as very close to nearby unconnected non-SRN roads; or anything that may result from errors in the OpenRoads data itself.

 

Different types of breakdown

The largest cause of breakdowns on the SRN is the category Wheels, Tyres & Punctures. This category includes fixing punctures (both with a motorist-supplied spare and without) and wheel damage (e.g., from debris or road condition). See bar chart below.

Across the study period, the largest category of breakdown cause was Wheels, Tyres & Punctures at 26.1%. The second largest category of breakdown cause was Engine Mechanical at 17.8%. The third largest category of breakdown cause was Engine Management at 7.8%. Running out of fuel accounts for 2.7% of all SRN breakdowns.

Road crashes (both injury and non-injury) account for 1.9% of all SRN breakdowns.

 

 

 

 

 

The following bar chart splits Motorway and A Road breakdowns and considers each type as a percentage of all breakdowns for that road type. There are some differences, most notably around wheel-related breakdowns and battery breakdowns, with Wheels, Tyres & Punctures accounting for 20.7% of all A Road breakdowns on the SRN, and 29.2% of all Motorway breakdowns.

 

 

 

Where breakdowns occur most

This section reviews the density of breakdown events across the network. For all breakdowns that could be matched to the Department for Transport’s AADF traffic data (99.9%), a mean number of breakdowns per road link were calculated across the study period. This was then compared to the vehicle miles travelled over an “average” (as per the AADF methodology, not a mean) day. This is a breakdown rate: allowing us to look at breakdowns relative to total traffic volumes.

To aid readability, these maps only show those links in the top 25% (3rd quartile and above) by breakdown rate.

It begins to demonstrate that there are significant spatial variations in the number of breakdowns by location when compared to overall traffic. In other words, the likelihood of breaking down is not uniform across the network. This is also apparent in particular breakdown categories.

For example, in the second map, motorway only breakdowns, we see that there are high rates of breakdowns in and around metropolitan areas where junction hopping might be common. Contrast this with the opposite picture for Cumbria where only one small stretch of the M6 has a high rate of breakdowns, suggesting that the vehicles using this route are typically on long-distance journeys they are well prepared to undertake: tyre pressures correct; adequate fuel; oil and water at the right levels.

In addition, the location of these breakdowns may also pose a greater or lesser safety risk, and may have a greater or lesser impact on the management of the network.

 

Firstly, breakdown rates on the SRN for all breakdown categories:

 

 

 

 

 

 

 

 

 

 

And then, for motorways only:

Secondly, the breakdown rates for Wheels, Tyres & Punctures:

 

And then, for motorways only:

And finally, for Out of Fuel breakdowns:

And, then for motorways only:

April 2021