It is costly to provide full AP coverage on roads due to the limited range of radio transmission. To address this issue, whether a vehicle can complete all data transmission before it leaves an AP's coverage area becomes an essential topic in sparse WiFi deployment. This letter establishes an analytical model to estimate the session completion for sparse vehicular Internet access. We take various network parameters into consideration, such as the vehicle density, the bandwidth, the transmission range of an AP, and the data volume delivered in each vehicular session.