IN-PERSON Manchester Livable Cities

Abstract

UK transport planning is shifting from traditional ‘Predict-and-Provide’ methods towards ‘Vision-Led’, scenario-based approaches that acknowledge uncertainty in future travel. However, trip generation for new housing developments still assumes stable trip rates, which is the underlying principle in TRICS trip rates application, despite limited evidence that these rates remain valid amid post-COVID travel changes, remote working, and rising home deliveries. This study evaluates whether vehicle trip rates used in planning applications align with observed post-occupation travel across residential sites in the North West, Yorkshire and Humber. Preliminary results show that submitted trip rates slightly under-predicted observed vehicle trips in both AM and PM peak periods. Mean absolute error was 0.065 trips per dwelling in the AM peak and 0.079 trips per dwelling in the PM peak, with mean absolute percentage errors of 6% and 10% respectively. Errors varied with trip activity: Transport Assessments tended to overestimate trips at sites with lower trip rates and underestimate trips at sites with higher trip rates. A paired t-test however, found no significant AM peak difference between submitted and observed data, but a significant difference in the PM peak. Weighted calibration factors (AM = 1.083, PM = 1.115) were developed to align forecasts with observed post occupation behaviour. The influence of car ownership, dwelling numbers, bedrooms, and public transport accessibility on trip rates was also examined. The findings of this study suggest that fixed-rate trip generation assumptions may not always reflect observed behaviour, indicating that more locally calibrated or scenario-informed approaches could complement existing tools within planning policy and development management.