TRICS® - Understanding Transport Development

TRICS enables its users to undertake calculations, using a number of calculation parameter options, to ascertain potential levels of trip generation for a user-defined development scenario.

What are trip rates?
Trip rates show the number of traffic/people movements in and out of a development (or an average of a number of developments within the same land use category), for a given trip rate parameter factor. For example, when trip rates are calculated by Gross Floor Area (GFA), they are shown per 100m2 of GFA. Using this factor, users can apply trip rates to potential developments, and are encouraged to achieve a balance between their selection criteria and the size of their selected data sample to achieve this aim.

How are they calculated?
Trip rates are calculated as follows:
Mean average trip rates are calculated when there are at least 2 surveys included in a selected list (trip rates for an individual site can also be calculated). The calculation process consists of 3 parts, and these apply to every hour of the survey duration, for arrivals, departures and totals counts:

i  Obtaining mean trip rate parameter figures

ii  Obtaining mean traffic/people count figures

iii  Calculating trip rates from the result of (i) and (ii)

(i) Obtaining mean trip rate parameter figures
Surveys at sites that have the necessary data available for a particular hour (those that include arrivals and departures count data for that time period) are used throughout this procedure. The GFA (for example) figures of the sites are added up, with the total GFA then divided by the number of surveys used, to produce the mean trip rate parameter figure (mTRP).

(ii) Obtaining mean traffic/people count figures
The same surveys used in stage (i) are also used in stage (ii), those being surveys that include arrivals and departures count data for a particular hourly period. The ARRIVALS figures from the selected surveys during the hourly period are added up, with the total number of ARRIVALS then divided by the number of surveys used, to produce the mean ARRIVALS count figure (mARR). The same process takes place for DEPARTURES and TOTALS (mDEP, mTOT).

(iii) Calculating trip rates from the result of (i) and (ii)
To calculate the mean ARRIVALS trip rate for a particular hour, the following equation is worked out:

(mARR / mTRP) X 100

This calculates the mean trip rate per 100m2 of GFA, and this figure is then shown on the trip rate calculation screen. The calculations for DEPARTURES and TOTALS are similar, as shown below:

DEPARTURES = (mDEP / mTRP) X 100 TOTALS
= (mTOT / mTRP) X 100

This calculates the trip rate per 100m2 of GFA for a particular hour. Note that the calculation factor (100m2 in the case of GFA) varies, depending on the trip rate parameter used (e.g. PER 1 EMPLOYEE, PER 1 HECTARE, PER GOLF COURSE, etc).

NOTE: The trip rate parameter weighting factor: Care should be taken when compiling a list of surveys, as including a site (or sites) containing a much higher or lower trip rate parameter value than the rest of the selected set may lead to average trip rate figures being "weighted" more towards such sites. Comparisons between mean trip rate figures and the median figures in corresponding rank order lists (see below) can sometimes show a difference, as no "weighting" can occur when calculating a rank order list from each individual survey.

Trip rate graphs can also be viewed after calculations have been made. Graphs are a much more visual way of representing trip rate data, and are used to identify percentages of trips per hour as a proportion of the whole survey, as well as show periods of peak trip activity.

Trip rate rank order lists can also be calculated. A rank order list shows the trip rate value (either arrivals, departures or totals) for each individual survey included in the original trip rate calculation, with the survey with the highest trip rate shown at the top of the list. Rank order list trip rates are calculated for a given time period or the busiest time period for each individual survey in a selected set. This is a good way of comparing trip generation at different sites in a selected set, and for spotting any "weighting" factors amongst the selected surveys.

Note that from TRICS® version 4.5 onwards, trip rates for multi-modal surveys can be calculated for car occupants, public transport users, bus passengers, train passengers, coach passengers, pedestrians, and total people, as well as the standard vehicles count which is present in all TRICS® surveys. Also note that for surveys where OGV, PSV, Pedal Cycle and Taxi counts are available, trip rates can also be calculate by these.