KEY CONCEPTS
• Surveyed respondents determined their value of travel time when driving themselves versus other means.
• Respondents achieved a 13% reduction in value of travel time when using a ride-hailing service that grew to 45% when reminded they can multitask. 
• Respondents were not as comfortable using a driverless ride-hailing service.

As technology changes continue to improve the drivability of an automobile, we consumers now have more choices for how to get from Point A to Point B. New propulsion systems are under development such as lithium-ion batteries, and electronics are increasingly being used to automatically adjust the temperature in the automobile to meet our preferences.

These improvements have led to the use of a greater number of automobiles on the roads, particularly in urban environments, increasing the prospects for congestion (see Figure 1). One particular challenge as a driver is to figure out a way to move through an intersection without being held up by a red light.


Figure 1. A new study determined that drivers facing more congestion on highways are wiling to use ride-hailing services as long as the vehicle uses a driver. (Figure courtesy of the University of Washington.)

A previous TLT article (1) discussed a newly developed Green Light Optimal Speed Advisory system that used a series of mobile phones placed on the windshield by drivers to enable users to adjust the speed of their automobiles to pass through intersections. An additional benefit of using this system in urban environments was a 20% increase in fuel economy.

The number of choices for consumers to get to a specific destination have increased with the proliferation of ride-hailing services (RHS) and the prospect that driverless vehicles may become commonplace in the near future. These factors have increased the choices consumers have to determine the value of travel time (VOTT). 

Don MacKenzie, associate professor of civil and environmental engineering and also the leader of the Sustainable Transportation Lab at the University of Washington in Seattle, Wash., says, “VOTT can really be called the cost of travel time. This term basically reflects the monetary value of time spent traveling in an automobile. Included in the cost is the time taken away from productive tasks, as well as the burden of stress from driving.”

Past work has been conducted to evaluate how consumers feel about being driven by another individual or how using a self-autonomous vehicle will impact VOTT. MacKenzie says, “These studies indicated that VOTT was significantly lower if individuals did not drive the vehicle because they could multitask, which could involve working or doing leisure activities such as reading and listening to music.”

MacKenzie and his colleagues conducted a new study that is differentiated from past work by asking respondents to determine their VOTTs when driving themselves as compared to being driven by other means. He says, “Our approach was to ask individuals about their preference in using a RHS versus driving themselves. We randomly assigned respondents with using a human-driven RHS or a driverless RHS. Our initial hypothesis before the study was that people do not trust the technology used in driverless vehicles.”

Discrete choice model
The researchers provided respondents with the challenge of taking a 15-mile commute. Individuals were asked to select between driving themselves or one of four options that included a regular human-driven RHS, driverless RHS, regular human-drive RHS with explicit mention of multitasking and driverless RHS with explicit mention of multitasking. 

MacKenzie says, “We prepared a full factorial experimental design that contained a total of 81 stated preference scenarios. Our respondents were arbitrarily assigned to one of four choice set groups and given six choice scenarios randomly selected from the 80 scenarios. Attributes provided to the respondents included travel time, travel cost and wait time.”

A U.S. national online crowd sourcing platform known as Mechanical Turk was used to recruit respondents. MacKenzie says, “Mechanical Turk is a widely used platform that enabled us to easily recruit more than 500 respondents to participate in the study. We obtained over 90% valid responses. One concern, though, is that Mechanical Turk tends to overrepresent younger and highly educated people.”

A discrete choice model was used to evaluate the results. MacKenzie says, “We used this variation of a linear regression model to determine the relationship between two variables. In our case, we used it when the outcome variable is not continuous but gives the respondent the choice of Option A or Option B.”

The study results indicated that RHS enabled respondents to achieve a 13% reduction in VOTT. This figure grew to 45% when the respondents were reminded that using a RHS will enable them to multitask. In contrast, respondents were not as comfortable using a driverless RHS. The VOTT for this situation was 15% higher than if an individual drove a personal car.

MacKenzie says, “We are not sure about the reasons for why a driverless RHS would increase VOTT. It is possible that respondents are not comfortable using driverless vehicles because this technology is relatively new and most individuals are not familiar with it. With the future growth of driverless technology, it may be worth revisiting this study in the future to assess if there is a change in VOTT.”

MacKenzie envisions expanding work in the future to a wider range of variables. He says, “We are considering the possibility of using a different commute length and also having respondents consider traveling for a different purpose other than commuting.”

Additional information can be found in a recent article (2) or by contacting MacKenzie at dwhm@uw.edu. 

REFERENCES
1. Canter, N. (2011), “Better driving decisions = improved fuel economy,” TLT, 67 (11), pp. 10-11.
2. Gao, J., Ranjbari, A. and MacKenzie, D. (2019), “Would being driven by other affect the value of travel time? Ridehailing as an analogy for automated vehicles,” Transportation, 46 (6), pp. 2103-2116.