However, the “strain” of the commuting experience from the perspective of the parents may also be seen as a stressor for the child. The strain of fatigue of the parent may encompass behavioral changes that constitute an objective stressor for the child. It should also be noted that the strain of commuting can involve behavioral changes of which parents have varying degrees of awareness. For example, if two parents are irritable from their long commute, but do not attribute this to commuting stress, they may offer the self-report that the commute has no adverse emotional impact on the family, even though behavioral changes may, in fact, cause strain for their children.

Salient Factors in the Stress-Strain Relationship for the Commuter

What then are the most important aspects of stress for the commuter? In what sense is commuting a strain? What are the constituent parts of commuting stress? Answering these questions will help identify the salient factors in the stress-strain relationship. In order to understand commuting stress we will consider both the objective and subjective aspects of the commuting experience in more detail.

Impedance

            Novaco, Stokols, and Milanesi (1990) formulated the concept of commute impedance, defining it as a behavioral restraint on goal attainment or movement. Impedance involves anything that impedes traveling to work such as distance, slow speed, or traffic congestion. It can also refer to subjective aspects of both stress and strain. In this regard, Novaco operationalized “subjective impedance” as an index of perceived constraints such as perception of the number of times brakes were considered necessary, slow-fast, stop-and-go ratings by the driver, and perceived surface street constraints. The distinction between objective and subjective impedance was clearly seen in the result that drivers tend to perceive their evening commute significantly different from their morning commute (Koslowsky et al., 1995).

            To illustrate this phenomenon we may imagine a female middle manager of a corporation who drives the same 28 mile route to and from her job. At both times of the day her commute takes roughly the same amount of time (40 minutes) and her drive is impeded by approximately three five-mile stretches of the road in which traffic slows to a crawl. Thus, for our hypothetical commuter, the objective impedance is virtually the same whether driving to or from work. But, she perceives the evening commute as involving more constraints (i.e., traffic jams). When she gets into her car to drive home, she is fatigued from the morning commute as well as the day at work. This fatigue, in turn, colors her perception of the actual, measurable constraints on the road (objective impedance). Her perception of the constraints is the subjective impedance. Thus, it is subjective impedance that is measured by commuter self-report surveys.

The Commuter’s Lack of Control

            Lack of control is one of several concepts from the general stress literature that can be used to understand commuting stress.   For example, two commuters may each travel the same amount of time to work. However, the first commuter has a shorter distance to travel but gets routinely stalled in traffic such that his shorter commute ends up taking as many minutes as the second commuter’s longer distance. The first commuter, stalled in traffic, is aware that his colleague can travel a longer distance in the same amount of time. This awareness appears to exacerbate the perceived lack of control in being stalled in traffic. This greater perceived lack of control adds to the subjective impedance of his commuting experience (Koslowsky et al., 1995).

Commute Time Variance and Predictability

            The difference between a “good day” of commuting and a “bad day” may be seen as the variance of the commute time and is more significant in causing stress than the average commute time. This is because a high degree of variance suggests a lack of predictability. The less predictable the commute time, the less the driver feels in control of the situation (Kluger, 1992; Koslowsky et al., 1995; Perlmuter & Monty, 1977). Thus, a longer commute where travel time is predictable appears to be less stressful than a commute where average travel time is shorter, but where the predictability of time spent on the road is much less.

Physiological Changes

            Control in the form of increased options is not always less stressful. Schaeffer, Street, Singer, and Baum (1988) examined the effects of morning rush hour commuting for single and carpool drivers and assessed the mediation of stress by the sources of control in the commuting situation. Among subjects traveling high impedance routes, stress reactions were reduced for single car drivers compared with those in carpools. Apparently, the passengers in the carpool experienced greater strain by virtue of their passive position (i.e., they saw the same obstacles of traffic as the drivers, but were not able to make decisions or exert control over the situation). The difference in control is largely perceptual, since the drivers may only be able to decide which lane to travel in or how much space to leave between cars.