Travel plans can be required for new or expanded buildings as part of the process of land use planning and approval. The purpose of these plans is to manage car use of future building occupants and support access by more sustainable forms of transport. Although the effectiveness of travel plans is generally well established at preexisting sites, there is very little evidence of the impacts when they are applied to new developments, particularly residential sites. In response to this situation, a series of multi modal person trip counts and parking surveys was undertaken at four case sites (residential developments with travel plans) and four control sites (similar residential developments without travel plans) in Melbourne, Australia. Results indicated that the average weekday (7:00 a.m. to 9:00 a.m.) mode share for car driver trips was 14 percentage points lower at the case sites than at the control sites. The findings also highlighted issues with relying solely on comparisons with secondary data sources, such as published vehicle trip generation rates and regional travel survey data, to assess travel plan effectiveness. Such reliance was shown to lead to an overestimation of travel plan impacts because of inconsistencies in the geographical locations and data collection periods of the secondary data sources. This finding highlights the importance of using suitable control sites to account for such factors. Further work is needed to strengthen the evidence base through evaluating travel plans at other residential developments and also accounting for residential self-selection effects.