1. Introduction
The unequal wages of men and women have been the subject of an ongoing scientific debate. The gender wage gap (or gender pay gap) has declined over the second half of the twentieth century in many modern countries [
1], but this convergence has slowed down or even stopped over the past years or decades (for the USA: [
2]). In Germany, for instance, the pay gap between women and men has remained almost constant since the beginning of the 2000s. According to the Federal Statistical Office’s recent analyses, women in Germany still earn 20% less compared to men in terms of average gross hourly wages [
3].
Numerous studies have attempted to identify the possible causes of the gender wage gap. A variety of factors, like gender-specific areas of activities with regard to occupation and sector or gender differences regarding certain psychological attributes, have been considered as potential drivers of the wage differential between the sexes [
2,
4]. In Germany and other countries, however, a gap of around 10% remains after controlling various factors [
5].
Previous research suggests that a large part of the gender pay gap can be attributed to women’s wage and career penalties, which start to evolve with family formation [
6,
7]. The motherhood wage penalty (or motherhood wage gap) is a well-documented phenomenon in many countries [
8,
9]. Within the German context, career losses for mothers have been documented based on register and survey data [
9,
10,
11]. Various international comparative studies indicate that in Germany, the motherhood wage penalty is especially large. For instance, Gangl and Ziefle [
9] showed that the motherhood wage gap for West German women in the 1960–1969 birth cohorts was between 16% and 18%, while in the same cohorts for Great Britain and the US the gap was 13% and between 9% and 16%, respectively. When entering parenthood, women typically interrupt their careers for a while, and subsequently, reduce their activity level in the labor market to meet the increased domestic workload and emerging care responsibilities. Men’s time allocation, in contrast, is largely unaffected by the transition to parenthood [
12,
13,
14]. Accordingly, child-related employment interruptions, as well as subsequent changes to more family-friendly working conditions of mothers, were previously found to be crucial drivers of both the motherhood wage gap [
9,
15] and the gender pay gap [
16,
17].
One factor that has been occasionally examined in the context of the gender pay gap is commuting behavior, with mixed results [
18,
19,
20,
21,
22,
23,
24,
25]. These studies often take their starting point in the consistent finding that women, on average, have shorter commutes than men (for the USA: [
26]; for the Netherlands: [
27]; for Germany: [
28]). According to the household responsibility hypothesis, the unequal distribution of household and childcare responsibilities within couple-relationships in which women assume the main responsibility for housework and childcare is a major cause for these gender differences in commuting. At the same time, various studies have demonstrated that women’s commuting distances are especially short once they are mothers, while most studies did not find a negative effect of parenthood on commuting distance for men [
28,
29,
30]. In this context, it has been suggested that shorter commutes reflect a spatially more restricted labor market, which comes along with reduced opportunities to find high-paying jobs and undergo significant career progressions.
Even though the transition to motherhood appears to be crucial for the explanation of the gender pay gap, as well as for the gender commute gap, the association between the transition to parenthood, changes in commuting behavior and the motherhood wage gap has not been examined so far. Hence, we aim to analyze how child-related changes in commuting behavior contribute to the emergence of the motherhood wage gap. By focusing on the motherhood wage gap, we are able to study in more detail the phase of life around the event of childbirth and the mechanisms that might link the reduced willingness to engage in longer commutes with wage losses for mothers.
The present study pursues three major objectives: First, to research how the transition to parenthood is associated with changes in the commuting distances of men and women. Second, to examine whether reduced commuting distances of mothers are accountable for a part of the motherhood wage gap. Third, to analyze the mechanisms that might explain why reduced commuting distances come along with wage decreases for women. These mechanisms are derived from human capital theory and job search theory. The empirical analyses are based on data from the German Socio-Economic Panel study (GSOEP) that are analyzed within a fixed effects (FE) panel framework.
3. Data and Methods
3.1. Data
The empirical analyses are based on data from the German Socio-Economic Panel (GSOEP, version 34, SOEP, 2019, doi:10.5684/soep.v34.) that are analyzed within a fixed effects (FE) panel regression framework. The GSOEP is a representative longitudinal survey of randomly selected and yearly interviewed households in Germany, starting in the year 1984 [
67].
The analyses are restricted to the waves 2001–2017 as detailed information on commuting distances was not regularly collected until 2001. We focus on the transition to the first child and the associated consequences on male and female commuting behavior, as well as on female wage trajectories. The inclusion of higher parities would make the following analyses more extensive and complicated, and therefore, go beyond the scope of this paper. Accordingly, as soon as respondents report having a second child, their respective observations are excluded from the analyses (i.e., right-censored). Furthermore, since the effect of parenthood in the context of FE regressions is based on a before-and-after comparison, persons who already had a child at their first valid observation, as well as persons who provided only one observation, are excluded from the sample. In addition to our treatment-group (i.e., women and men transitioning to parenthood during the observation window), persons who remained childless (but were at risk of having a child) during their observation window were kept in our sample in order to obtain accurate estimates of age and period effects [
68]. To follow women and men during their fertility period, both remaining groups (i.e., the ‘treated’ as well as the ‘non-treated’) were restricted to the birth cohorts 1965–1994 and limited to the age of 18 to 49. Furthermore, we restricted our sample to persons who work at least 1 h per week, who are not currently studying (or attending general school), who earn at least one euro per hour and not more than 50 euros per hour, and whose commuting distance does not exceed the threshold of 149 km. We decided to introduce this upper commuting distance bound to reduce the risk of our results being affected by extremely long distances. Respondents with commuting distances of 150 km or more are often weekend (or weekly) commuters. The restrictions that this type of commuting imposes on family life can differ markedly from those imposed by daily commuting. After additionally dropping observations with missing values our sample finally comprises 41,111 observations (women—18,726; men—22,385) from 7183 persons (women—3294; men—3889).
3.2. Measures
Dependent variables. The dependent variable of the first part of the analysis in which we examine hypothesis 1 is the
commuting distance to the workplace in kilometers. As is usual in studies on commuting, the information on the commuting distance is
log-transformed to account for the right-skewed distribution of commuting distance [
22,
42]. For this, commuting distances of 0 kilometers were set to the value 0.1. The effect coefficients of such semi-logarithmic regression models reflect an approximation of the percentage change in the dependent variable when the independent variable increases by one unit [
69].
In the subsequent analyses of the motherhood wage gap, we deploy the hourly wages as the dependent variable. We calculate hourly wages by dividing the monthly gross income (in euros) by 4.35 times the reported actual weekly working hours. The wages were then deflated by the consumer price index (to 2010) provided by the German Statistical Office and finally transformed by calculating their natural logarithm (for analogous reasons as already discussed above).
Parenthood. The key biographical event in our study is the transition to parenthood (i.e., the birth of the first child). This event is indicated by a binary variable whose value changes from 0 to 1 when the first child is born (to determine birth events, biographical data on the birth of biological children were used). A transition to parenthood can be observed for 535 women and 863 men in the sample.
Explanatory variables for the motherhood wage gap. In our analyses, we pay special attention to the influence of child-related reductions in commuting distances on the motherhood wage gap and the underlying mechanisms. More specifically, our study aims to determine the effect of the
first substantial reduction of the commuting distance after the transition to parenthood. A reduction in commuting distance was considered substantial if it involves a reduction by at least a third of the previous distance (but was also at least 5 km). We have decided to introduce such a threshold to ensure that our variable mainly captures reductions that were actually intended to improve the compatibility of commuting and parenthood. In the course of robustness checks, we applied various other thresholds, but these did not lead to substantially different results (see
Section 4.5). Thirty-point-one percent (
n = 161) of all women who gave birth to a first child during the observation window reduced their commuting distance according to our criteria.
We included several variables with the aim to examine the link between commuting and maternal wage penalties. We used work experience, as well as firm tenure, to account for differences in human capital. For our measure of work experience, available information on the months spent in full-time and part-time employment was used and converted into a single indicator by summing up both variables. To account for the lower human capital accumulation in the context of part-time work, months spent in part-time were multiplied by 0.5 (i.e., down-weighted). In addition, we used firm tenure as a measure of firm-specific human capital. This variable is of particular interest in the context of this study as wage penalties, which are associated with a reduction in commuting distance, might be partly caused by the loss of firm-specific human capital and seniority after changing to a job closer to home.
We additionally examined a mechanism that can be derived from job search theory. According to this mechanism, wage losses are also caused by the restriction to the local labor market and the associated poorer chances of finding suitable, well-paid jobs. We tested this explanatory approach by investigating whether poor job matches resulting from distance reductions in commuting explain maternal wage deductions. To establish the
adequacy of the job matches we draw on the respondents’ corresponding subjective assessments (the wording of the item is: “Does this job correspond to the occupation for which you were trained?”). However, qualification mismatches might not be the only reasons why spatial restrictions lead to wage losses. Wage penalties can also arise if firms located in suburban labor markets pay less than firms in the central business districts [
23]. In this context, the findings of Lehmer and Möller [
62] indicate that
firm size plays a crucial role in explaining higher wage levels in urban compared to those in suburban areas. For this purpose, we deploy a variable that indicates the firm size based on six categories. Finally, we examined the possibility that reductions in the commuting distance are achieved by becoming
self-employed, which may often also lead to wage losses [
70,
71]. Findings show that self-employed persons have shorter commuting distances on average (for Germany see, for instance, [
51]).
Control variables. All regression models included control variables for partnership status (not living with a partner; cohabiting union; married), two regional indicators (living in Eastern Germany vs. living in Western Germany, as well as living in a rural region vs. living in an urban region) and the yearly GDP growth (in%) in order to account for period effects relevant to wages. Furthermore, all models included the age (and age squared) of the respondents. Such modelling enables us to assess the wage penalties after taking into account the age-related wage increases.
Table 1 presents a description of the sample differentiated by gender and parental status.
3.3. Analytical Approach
In our empirical analysis, we first tested the hypothesis that parenthood primarily restricts the commutes of women (hypothesis 1) by means of within-person fixed effects regression. For this, we estimated the effect of the transition to parenthood on the commuting distance differentiated by gender. Second, we investigate whether the reduction of mothers’ commuting distance is associated with wage losses and whether this restriction on mobility can (partly) explain the motherhood wage gap (hypothesis 2). Third, we analyzed the underlying mechanisms of this relationship. For this purpose, we first determined the wage penalties associated with a reduction of the commuting distance due to a job change. Then, we examined how the extent of wage disadvantages—resulting from switching to a workplace nearer to home—can be explained by loss of firm-specific human capital, by an increase in skills-related mismatches, or by moving to certain jobs (i.e., smaller companies and into self-employment).
We used linear fixed effects (FE) panel regression models [
68,
72], which are widely used in the analysis of the motherhood wage gap. These models estimated the effect of
x not by taking other persons as counterfactuals (between-comparison), but each person with him- or herself (within-comparisons). The advantage of this approach is that estimates are not biased by person-specific unobserved heterogeneity. Such a bias could, for example, arise if career-oriented women had a higher willingness to accept lengthy commutes and lower ambitions to have children than family-oriented women. In this case, the correlation between parenthood and commuting would at least partly be caused by the inter-personal variance regarding the career/family-orientation in the sample. As a result, our causal inferences can be made with less uncertainty.
5. Discussion
In this study, we investigated the assumption that the transition to parenthood negatively affects women’s commuting distance and that this reduction in commuting is associated with wage penalties during the transition to motherhood. We used data for the years 2001–2017 from the German Socio-Economic Panel Study as a basis for our analyses, which were carried out in a fixed-effects framework.
The analyses first demonstrated that the transition to (first) parenthood is associated with a significant decline in the willingness of women to commute longer distances (hypothesis 1). According to this, we find that starting a family leads women to reduce their commuting distance by an average of 33%. In contrast, the transition to fatherhood has no significant influence on the commuting behavior of men. A more detailed analysis of the negative effect of parenthood on the commuting distance revealed that the reduction primarily occurs once women return to work after parental leave and that this reduced commuting distance is then sustained over the long term. This is in line with findings showing that women’s job adjustments towards more family-friendly working conditions usually take place immediately after returning to work [
15]. Overall, our study thus supports the assumption that the spatial restriction of women, due to their higher responsibility for household and childcare within couple-relationships, is a major cause of the gender differences in commuting between men and women.
Subsequently, we investigated whether the restriction of spatial mobility for mothers is associated with wage penalties. For this, we first estimated the motherhood wage penalty, which amounts to −11.3%, without taking into account commuting behavior. However, for almost every third mother in our sample (i.e., 30.1%) a substantial reduction of the commuting distance (i.e., at least −33.3%) was observed after the transition to parenthood. Moreover, our analysis reveals that mothers who reduce their commuting distance after the transition to parenthood show an increased wage penalty (−18.4%) compared to those mothers that do not reduce their commuting distance (−8.7%). Our findings, thus, illustrate that 23% of the motherhood wage penalty is based on wage losses associated with corresponding reductions in commuting distance (hypothesis 2).
We finally examined various mechanisms that might explain why reduced commuting distances come with wage decreases for mothers. These mechanisms were derived from human capital theory and job search theory: The loss of (firm-specific) human capital, the loss of adequate employer-employee matches, the move to smaller firms, and the move to self-employment. For the subgroup of mothers who reduce their commuting distance by changing jobs, our estimates yield particularly high wage penalties of around −30%. In contrast, mothers who change their job without a reduction of commuting distance suffer only marginal additional wage penalties. Subsequent analyses showed that additional wage penalties for mothers who change to a job near their place of residence can be partly explained by the loss of firm-specific human capital. However, even after controlling for this factor, a significant wage penalty due to commuting remained. As our analyses further showed, this is largely due to mothers taking jobs that are less suited to their skills profile in favor of shorter commuting distances, and moving to smaller companies that tend to pay less than the larger companies that are further away from home. Changes into self-employment, which are accompanied by a reduction in the commuting distance, but at the same time are associated with wage losses, also appear to be a cause of the ‘spatial dimension’ of the wage penalty, but explain it to a much lesser extent.
In summary, the limitation of women’s commuting during the transition to first parenthood makes a substantial contribution to the emergence of inequalities between childless women and mothers in the labor market. If mothers (have to) change employers in favor of a shorter journey to work, this leads to a loss of firm-specific human capital and company seniority, which, in turn, leads to reduced wage gains and opportunities for career advancement. Moreover, the necessity and/or preference to find employment close to one’s home comes with a reduced job search radius that limits the choice of suitable and well-paid work opportunities. Since men are not affected by the career-related disadvantages of parenthood to the same extent as mothers, parenthood will also contribute to gender inequality [
8]. Our study clearly shows that parenthood does not restrict the spatial mobility of fathers to the same extent as that of mothers. Therefore, our results offer indications of the explanatory potential of the increasing gender differences in commuting in the context of parenthood for explaining the gender pay gap.
The evidence to date on the relevance of gender-specific commuting patterns for explaining the gender wage gap is mixed. Some studies conclude that gender differences in commuting can only explain a small part of the pay gap (for the US: [
18,
20,
21]; for Germany: [
22]). Other studies, however, find indications of a more substantial contribution. For example, Le Barbanchon et al. [
24], based on data from France, conclude that around 10% of the gender wage gap can be attributed to gender differences in the willingness to commute. Although the negative effect of children on women’s willingness to commute could be a mechanism for the motherhood wage penalty, which in turn is known to contribute to the gender pay gap (see
Section 1), the link between commuting and the motherhood wage gap is still almost unexplored. An exception is a study by Gutierrez [
23], based on data from the U.S., which found that sex differences in commuting patterns account for 10% of the gender wage gap among childless couples and more than 23% of the additional wage gap due to the birth of a child. Despite the differences in the country context and the statistical method used, our study also points to a relatively high relevance of commuting behavior. In
Section 4.5, we have discussed methodological reasons why the impact of commuting on the emergence of the gender pay gap may have been underestimated in some previous studies.
Our study has certain limitations that must also be addressed. Like other studies on the motherhood wage gap and its explanatory factors, we cannot exclude the possibility of endogenous selection bias. Consequently, it cannot be ruled out that women will become mothers more often if they anticipate a lack of career progression in the near future. By changing their focus away from the realm of the professional career towards home and children, these women might additionally have a high willingness to reduce their commutes. While we cannot rule out such anticipatory effects, it should be noted that the wage disadvantages associated with a reduction in commuting distance arise primarily after a change of employer, so that we consider the relevance for our findings to be limited.
Our study also offers a variety of starting points for further research. The link between commuting and the motherhood wage penalty is an important topic that deserves more attention. Future studies on the causes underlying the overall gender pay gap should also examine the role of mothers reducing their commuting distance. By additionally including higher birth parities, future studies could provide an even more detailed picture of the relationship between parenthood, commuting and wage disadvantages. Furthermore, it would greatly enrich the state of research if the associations shown here could also be investigated for other country contexts. In this regard, drawing on data from France, Germany, Spain and Switzerland, Rüger and Viry [
74] found that the relationship between fertility and commuting is shaped by national contexts. In addition, comparative studies showed that the factors influencing the motherhood wage gap vary between countries [
9].
As a final point, our results also have practical implications. They indicate the potential of two strategies, both of which could contribute to reducing wage disadvantages due to spatial mobility restrictions during the transition to parenthood. According to this, policies, on the one hand, could aim to support the spatial mobility of parents so that breaks in their employment histories are avoided. The expansion of a childcare infrastructure that is adapted to the needs of commuting parents is particularly promising in this respect. On the other hand, measures could be aimed at creating attractive job opportunities close to where families live, so that parents who reduce their commuting distance do not have to accept too great a loss of income in return.