The Quality of a Car Journey: Evidence from Stated Choice Experiments
M Wardman, J N Ibáñez, ITS, University of Leeds, UK
Application of discrete choice modelling that addresses the relative disutility of time spent in different driving conditions as well as the fixed and duration related valuations of different types of infrastructure provision
The car accounts for the vast majority of personal travel in developed countries and its share of the market is significant and increasing relentlessly in the emerging economies.
The emphasis of major value of time studies in Western Europe, North and South America, Australasia and elsewhere has, quite understandably, tended to focus on car users? willingness to pay to save time as some generic good. In contrast, it is fair to conclude that more routine market research exercises in the public transport market have on a very regular basis investigated the sensitivity of public transport users to differing travel conditions, such as crowding and rolling stock type, that might influence the value of time and indeed a range of so-called ?secondary? factors, such as information provision, comfort and security that might impact on the quality of a public transport journey.
Whilst studies from the 1980s onwards have distinguished car travel time disutility according to whether it is spent in what might be termed congested or free flow conditions, there has not been to any great degree any further segmentation of these types of time. Indeed there has been a view that the discrete alternative of time spent in congested traffic is simply a proxy for unreliability.
Nor has there been a great deal of research into factors other than the degree of congestion that might influence the quality of a car journey.
This paper adds to the body of evidence in the area of the quality of a car journey. In particular it reports evidence derived from Stated Choice studies relating to two related sets of issues.
How does the value of motorists? travel time vary according to whether the time is spent in the following types of traffic:
? Free flowing: You can travel at your own speed with no problems over-taking
? Busy: You can travel pretty much at the speed limit, but you are forced to change lanes every now and then
? Light congestion: You can travel close to the speed limit most of the time, but you have to slow down every so often for no apparent reason
? Heavy congestion: Your speed is noticeably restricted frequent gear changes required
? Stop start: You are forced to drive in a ?stop-start? fashion
? Gridlock: You are only able to move at a crawl at best, and spend quite a lot of time stationary
Secondly, how do motorists value the following range of infrastructure and travel condition related factors:
? Proportion of HGVs on a route
? Information provision
? Lane width
? Number of lanes
? Presence of speed cameras
? Road surface
The analysis reported in this paper is based on a sample of over 1600 motorists making inter-urban journeys. Mixed logit modelling techniques have been used to allow for repeat observations and to test for the presence of preference heterogeneity.
Key findings that have emerged are that time spent in grid-lock conditions is valued most highly at around 80% higher than free flow time. The relativities for busy, light congestion, heavy congestion and stop-start are around 1.06, 1.12, 1.25 and 1.30. This is in the context of congested travel time typically being valued around 40% higher than free flow time.
The vast majority of the infrastructure and travel conditions variables had significant effects of the expected sign. For example, every 1% increase in HGVs increases the time coefficient by 0.43%, the movement to narrower lanes has a larger value than the movement to wider lanes, speed cameras, and the same effect is apparent for increases to 4 lanes or reductions to 2 lanes, whilst concrete surfaces and high-level jointed carriageways are particularly disliked.
Association for European Transport