This study aims at identifying the potential ways to increase the willingness to carpool, particularly in rural–urban travel settings, where there is no/minimal public transit service (due to low population density) and purchasing a personal vehicle poses a significant financial burden for many households. To do so, we used time flexibility, defined as the tolerance for increased commute time (which can happen because of re-routing and picking up others when carpooling), as a proxy to willingness to carpool. Using structural equation modeling and survey responses from about 1000 workers and college students living in a rural county in Central Pennsylvania, we analyzed the sociodemographic, attitudinal, and situational factors that can lead to higher time flexibility when carpooling. We also investigated whether people’s time flexibility changes when they are offered monetary incentives (in terms of travel costs reimbursement). The results indicated that being a driving fan and seeking privacy when traveling reduces time flexibility, while being conscientious about environment and health leads to higher time flexibility. Moreover, females, people who had inconvenient past carpool experiences, and those living closer (within 20 min of driving) to their workplace/college showed lower time flexibility. On the other hand, people with lower income and higher driving costs were willing to tolerate longer commute times if reimbursed for a portion of their travel costs. We also found that if there is no initial level of willingness to carpool, reimbursement offers cannot do much to sway people’s decisions.