Experimental Study of the Factors That Influence Driver Frustration – a Stated Preference Approach – an Update

Experimental Study of the Factors That Influence Driver Frustration – a Stated Preference Approach – an Update


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


This paper outlines the results of a further study for Transport Scotland to value driver frustration. The results add new factors to an earlier study carried out in 2013 of which have been used to value time spent in different driving conditions.


This paper reports on further pioneering work carried out for Transport Scotland by AECOM and TRL on further attempts to value driver frustration. This builds on work reported here in 2014 (Experimental study of the factors that influence driver frustration on the A9(T) – a Stated Preference approach by Paul Murphy (AECOM); Joanne Casey (AECOM) and Judith MacDonald (Transport Scotland).
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 was little empirical evidence to support its assumed impact. The work carried out in 2013 provided quantification of how drivers’ value driving in different traffic conditions linked to frustration on the A9(T).
The same innovative methodology, as before, using a Stated Preference, was administered as part of the experimental study being carried out by TRL. Similar factors were explored again, namely 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. In addition the impact of Speed Cameras was also explored on the A9(T) and In order to widen the evidence base a similar survey to before, without Speed Cameras was also carried out along the A96(T) a rural route connecting Inverness, Elgin and Aberdeen.
Firstly, as before, respondents 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.
The survey was carried out at locations along the A9(T) and the A96(T) and whilst the route was not specifically mentioned to respondents, they were asked after the experiments about the frequency with which they use the two routes. The two routes have different characteristics and different traffic patterns so it was not known if the results would be similar across them.
Stated Preference models were developed for the independent data sets – A9 2013, A9 2015 and A96 2015. Following this, the models were tested for differences in scale and values between them and it was shown that pooling the data sets was appropriate. This provides a greater confidence in the results by providing a larger sample size and demonstrating a degree of transferability of the results between routes. This has produced Time Multipliers, which may be taken as a proxy for frustration experienced by driving in different conditions. This in turn is being used to monetise frustration impacts on the A9(T) and the A96(T) as part of the business case work for the dualling of both routes.
This work is innovative and likely to be of international interest. It enhances our understanding of driver frustration on the A9(T) and A96(T) and on the network in general.


Association for European Transport