Transport Behaviour and Public Transport Supply - ALTRANS (Alternative Transport Systems)
NERI Technical report, no. 320
Summary This report is part of the project ALTRANS - an alternative transport system. The main purpose of ALTRANS is to elucidate the possibilities of attaining an environmental improvement by transfer of motor traffic to alternative means of transport through a co-ordinated and intensified improvement of the public traffic.
The purpose of this report is especially to elucidate the importance of the service of the public traffic to behaviour in order to understand the possibilities of transfer of trips from car to public traffic.
The report is based on the continuous Transport Survey (TransportvaneUndersøgelsen (TU)). The survey shows the trips of the interviewed person on a chosen day, the trips being geographically located into zones. It also shows the means of transport, purpose of travel etc.
Furthermore the report is based on a geographical model - developed in ALTRANS. On the basis of timetables the model calculates the travelling time for each individual trip.
Chapter 1 offers a detailed summary (in Danish) of the report. Only the main features of the conclusions of the report are rendered below.
Assessment of the transport survey (TU)
The transport survey is based on a random sample of Danes between the age of 16 and 74. The random sample is being written down as to represent all of the population aged 16 to 74. The used method which consists of asking about transport behaviour the day before the inter-view, however means that the interviewed persons is not fully representative of all Danes. In several ways persons with special travel practices is not fully represented.
Viewed in the light of analyses of the method of interviewing and the composition of the outward and home journeys it is estimated that there is lacking travel activities corresponding to 4-5 percent of the person kilometres or approximately 1,5 kilometres pr person pr day. The share is very dubiously determined and it is recommended to continue the work on a clarification, among others through a few additional interview questions.
Moreover a comparison with the official statistic for person kilometres has been made. The conclusion to the comparison is that there seems to be a quite god accordance between the two methods of making up when considering the lacks in both of them. The difference of the two methods seems therefore not only to be due to errors and defects in the Transport Survey data, it also discloses problems with the register statement. The conclusion to the comparison seems to be that TU gives quite a true and fair view of the person kilometres in the 16 to 74 age group for all the means of transport that is used much in the survey (car driver, car passenger, bicycles and bus).
Travel time with public transport
The analyses have only been performed on 47 % of the trips. The greatest deficit is due to the fact that the model cannot calculate travel time for the internal trips in only one zone. Especially the small and medium-sized provincial towns which have many trips have not been sub-divided. Furthermore at the time of the calculation there were a good deal of data errors and defects in the model which, among others, meant that data for the local busses in 3 of the largest provincial towns lacked.
The analysis of the trips for which travel time can be estimated shows that the travel time with public transport for two thirds of these are between 1 and 3 times as long as the travel time by car with a top at about 2,2 times the travel time by car. Also considering the average waiting time the total time for travel by public transport is for the majority between 2 and 4 times the travel time by car.
At the same time it is concluded that the mobility is very unequally allocated. More than 20 % of all trips are so long that it would be desirable if they could be carried out with public transport. But these trips are in fact unable to be served. Of the remaining trips at least 90% takes twice as long time as a trip by car; sometimes even 3 to 4 times as long. In the villages 40 % of the trips cannot be made by public transport and 60 % of the rest have an average waiting time of over 1 hour.
The importance of the level of service to modal split
If the conditions between the total time usage on trips with public transport and by car becomes less than 2,5 - 3 the temporal relation only has small influence on the share of public transport. On the other hand if the conditions are good the public transport usage is strongly affected. For trips over 15 kilometres the share of public transport can reach well over 40 % if the service is optimal.
Also car owner-ship - first and foremost the number of households without car - is affected by the service of the public transport but the effect is substantially less than the effect on the share of public transport. If the service is reduced the number of cars will increase a little. On the other hand an improvement will hardly lead to fewer cars on short sight as people rarely give up cars they already possess.
Possible improvements of the
environment with public transport
Analyses show that busses and cars in average have the same environmental impact measured as CO2 emission pr passenger-kilometres while trains have a little lower impact. However, the impact varies depending on the part of the country and the time of the day. Especially at night the load factor of busses is low and consequently the emission pr passenger-kilometres becomes high.
The environmentally best reaction to this would be to replace large busses with smaller vehicles with adequate capacity. On many routes a medium-sized bus, here called midi-bus, would probably be viable. It will take an organisational effort by the bus companies but with the right planning it should be possible to realise a diversion of bus sizes beneficial to both the environment and the operating economy.
The environmental effect of the service improvements is elucidated with a calculated example of a doubling of the frequency for the public transport. The example shows that the elasticity on public transport is high - close to 1 calculated as the increase in person kilometres by public transport by an improvement of the total time usage on public transport trip compared to the time usage in car. On the contrary the elasticity for car drivers is only -0,14 and thus it is limited how many motorists can be moved to public transport.
The conclusion to the calculated example is that a general doubling of the frequency does not pay off in an environmental perspective and neither in an operating economic perspective. The results seems to show that it pays to improve the frequency on some sorts of trips, e.g. on long distances particularly if one increases the speed at the same time, and in the countryside if driving small public transport vehicles e.g. midibusses instead of 12 metre busses. The results of this simple calculated example contemplate that one seeks to find a planning that permits environmental gains also regarding improvements of the frequency. One merely have to be extremely determined as one has to obtain the same gain of time as in the calculations but with only one third as much extra driving.
The calculations are however very uncertain and a calculation in the geographic model would create a much safer basis for a conclusion.
Please site as: Christensen, L.. (2000): Transport Behaviour and Public Transport Supply - ALTRANS (Alternative Transport Systems). National Environmental Research Institute. 152 p. - NERI Technical Report no. 320. (online). http://faglige-rapporter.dmu.dk