Experimental Study of the Factors That Influence Driver Frustration on the A9(T) – a Stated Preference Approach

Experimental Study of the Factors That Influence Driver Frustration on the A9(T) – a Stated Preference Approach


Paul Murphy, AECOM, Joanne Casey, AECOM, Judith MacDonald, Transport Scotland


This paper outlines the results of a study for Transport Scotland to value driver frustration using an innovative Stated Preference survey, the results of which have been used to value time spent in different driving conditions.


In 2013 Transport Scotland commissioned TRL and AECOM to conduct an experimental study in order to improve its understanding of driver frustration on the A9(T) between Perth and Inverness in Scotland. This work built on a review of international literature in 2012 for Transport Scotland carried out by TRL. This found that while the notion of frustration on the road network is often cited and assumed, there is little empirical evidence to support its assumed impact.

This paper focuses primarily on the Stated Preference work that was carried out as part of an experimental study, although it does also draw on the parts of the experimental study that looked at driver frustration, in order to provide quantification of how drivers’ value driving in different traffic conditions linked to frustration.
There have been many attempts using Stated Preference techniques to quantify how drivers value time spent in congested conditions, for example, by valuing free flow and stop-start time. However, there is very limited research regarding how different driving conditions, for example, driving at less than one’s desired speed, being behind a platoon of traffic consisting of cars and HGVs and whether there is oncoming traffic, influences how drivers value their time.

An innovative Stated Preference survey was therefore designed and administered as part of the experimental study. The survey was based on variables thought to underlie driver frustration such as those listed above.
Data were collected from 183 participants on the A9 corridor who firstly took part in an experiment administered by TRL as a hall test using bespoke simulation clips of various driving scenarios to test the effect of several variables identified to be linked with driver frustration. In response to each clip drivers rated their level of frustration, task demand, feelings of risk and likelihood to overtake. After they completed this task they were then given a self complete Stated Preference survey questionnaire which asked them to trade off making part of their journey on a longer in distance (and journey time) free flow route compared with a shorter distance (and journey time) congested route.
From the Stated Preference models developed it has been possible to derive value of time multipliers, which may be taken as a proxy for frustration experienced by driving in different conditions. This was found to be influenced mainly by lack at being able to travel at their desired speed, but also by the number of HGV’s in the platoon ahead and whether or not there is oncoming traffic.

The experimental aspect of the survey also collected information on the level of driver frustration experienced in different driving conditions and an analysis of the frustration scores from the two approaches (experimental and stated preference) showed a very high and significant correlation between them (+0.95).

This work is unique and likely to be of international interest. The authors are not aware of any other Stated Preference research that has sought to value driver frustration in this way. In Scotland, it will enhance our understanding of driver frustration on the A9(T) and the network in general.


Association for European Transport