Each year, the Greater Manchester Travel Diary Survey (TRADS) collects transport and travel information from every member (aged over four) of 2,000 households; respondents provide details about all the trips they make in a 24-hour period. TRADS is not an attitudinal survey, its focus is on the details of the trips and the characteristics of the people who make those trips.
The survey sample is designed so that each GM district is represented proportionately, based upon the demographics of the resident population. The survey programme covers the duration of a full year; surveys are in-field every day, excluding Christmas Day and any days after a bank holiday. The fieldwork period starts at the beginning of February and finishes at the end of the following January.
The data collected from 2,000 GM households equates to about 4,500 residents and between 7,000 and 10,000 trips. The survey collects information about trips including origins and destinations, travel times, method of travel used and journey purpose.
Prior to the pandemic our trip estimates were based on data collected over a three-year period, which provided confidence intervals of +/- 1% at the GM household level. At the district household-level the confidence intervals were +/- 3% to 4%. This was possible as people’s travel habits were relatively stable over the short-term. However, since the start of the pandemic in 2020, people’s travel habits have not been stable enough for this approach to be used, so our estimates are based on survey data from a single year.
The data is weighted/expanded to the GM population, based on district population by age and gender as well as Acorn Category. The survey weights are small, and the weighting efficiency is high. The weighting/expansion methodology from TRADS changed between 2019 and 2022 to better account for population growth. In 2019s TRADS data the population size for each district was expanded to the level recorded in the Census 2011. However, the data for 2022 is expanded to the 2021 mid-year population estimates (the latest estimate available at the time of weighting). This change has impacted some districts, like Manchester and Salford, more than others. The main impact is that in areas with significant population growth the estimated number of trips has increased despite the average trip rate per person decreasing.
The survey is delivered by a team of experienced interviewers who conduct face-to-face interviews. Prior to the pandemic the response rate was typically 50-60%. During the pandemic the survey methodology changed to a mixed methodology of recruitment via letter and interviews being conducted via telephone. This saw the response rate drop significantly. As restrictions on socialising eased, a mixed methodology of letter/phone and face-to-face was used, finally moving back to face-to-face interviewing in August 2021. The overall response rate in 2021 was 19%, but the response rate for face-to-face interviews was 43%.
The data include in this report includes estimates for the years 2019 and 2022. While the overall estimates at the district household-level have confidence intervals of +/- 8% to 7%, caution should be used when interpreting the sub-group estimates of commute trips, short-trips, age, and by hour and purpose. The confidence intervals around these estimates are much larger and the findings should be treated as indicative.
Where totals in tables don't sum to the figures in the table it is because the estimates are rounded to the nearest 1,000.