The (then) Mobility and Inclusion Unit of the Department for Transport commissioned this research to inform a policy decision as to whether to,
- require buses that can kneel to do so at every stop, or;
- implement a policy whereby the bus kneels either on request from a passenger, or at the discretion of the driver.
This referred to the requirement for drivers to use a bus’s kneeling mechanism in order to reduce the gap between the vehicle’s first step and the kerb, at stops where passengers wish to get on or off the vehicle.
The objective of the trials was to evaluate the costs and benefits of requiring drivers of buses with a kneeling capability to kneel at every stop, instead of kneeling being a matter for the driver’s discretion, or on passenger request, which was the status quo. The trials were commissioned by the DfT to enable a possible change in regulations to be evaluated.
The research also looked at the possibility that extra time involved in the kneeling process may be offset by speedier boarding.
In order to provide the required information, the research required the collection of both cost data, and an estimate of the benefits of these two options for current and potential bus users. The assessment of the cost implications necessarily involved accurate measurement of a number of technical aspects, and initial discussions with operators shed light on what the important parameters were likely to be; these included:
- Stop dwell time effects;
- Fuel consumption;
- Additional wear on components.
The following aims of the pilots were clearly explained to each operator participating in the project,
- To set up trials involving two buses that eliminate, as far as practicable, the many variables that influences fuel consumption, so that the impact of the two policy regimes in question (i.e. compulsory and discretionary kneeling) could be studied in isolation. The crucial variables to keep constant were,
- The fuel consumption variances between the buses; here it was necessary to set base consumption figures before the trial began, which entailed capturing data without any change from the buses' usual routine;
- Driver influence. Given that a reasonable number of drivers were involved in the trial, it was expected that the combination of many drivers would balance out any driver-related differences over time;
- The route, which needed to be the same for each bus;
- Traffic & weather. These variables were controlled by ensuring that the two buses ran at very similar times on the same route, i.e. one behind the other in the schedule on the chosen route. Any roadworks or holdups of a short-term nature would therefore be similar for buses running consecutively;
- Passenger loading. Allowing for frequency of stops and passenger numbers. This factor was also controlled by the buses being scheduled to follow each another.
- To have a large set of pre-trial, or base, data (1 to 2 weeks)
- Bus 1 kneeling compulsorily for one week, and bus 2 in the same week and on the next scheduled run kneeling on demand;
- Swapping around in week 2, with bus 1 only kneeling on demand and bus 2 kneeling compulsorily with the same conditions.
The reasons for this process were,
- To set base fuel consumption data for each bus;
At the outset of the project, it was anticipated that a compulsory kneeling policy might have an adverse effect on fuel consumption, but this was not borne out by the data collected. In fact, some of the pilots showed increased kneeling to be correlated with more economical fuel consumption. Generally, though, fuel consumption figures were found to be very variable, with the two, for all intents and purposes identical, buses used in four of the six pilots showing opposite tendencies – i.e. one vehicle showing better fuel efficiency under compulsory kneeling, and the other being more fuel efficient during discretionary kneeling. Although, theoretically, there is no doubt that increased kneeling involved increased use of the compressor, and therefore, the use of marginally more fuel, the broad conclusion was that there was no conclusive evidence that a compulsory kneeling policy would increase fuel consumption, with frequency of kneeling being just one of a large number of factors which influence fuel consumption.
What did emerge as a major issue was the potential effect of kneeling on the buses’ compressors, in terms of both the peak temperatures that might result, and the additional wear & tear on important components. It is suggested that this is because compressors used in buses are primarily designed for use in trucks in the freight sector, which would put fewer demands on the compressor than frequently-knelt buses. For this reason, data gathered on compressor load cycles and compressor temperatures were extremely important. From discussions with vehicle and compressor manufacturers, it was learnt that there is a relationship between compressor load cycle and compressor life, and that this is not a linear relationship. One manufacturer indicated that a figure for total duty cycle of 67% might be a cause for some concern.
The Compressor Load Factor (CLF) is the proportion of the engine running time that the compressor is “on load,” as measured with a pressure probe, linked to a Black Box data recorder. The research in five of the trials suggested that an increase in CLF of 5% to 7% may be attributed to the increased levels of kneeling achieved. In the long term, high levels of compliance with, or enforcement of, the proposed compulsory kneeling regime could result in greater CLF increases. The variations between the peak and off peak CLF did not appear to be significant
Even though the CLF appeared to be influenced by factors other than the
A general problem encountered during the trials was the low compliance among drivers with instructions to kneel on a compulsory basis, in spite of prolonged efforts to improve compliance rates. This, however, provided insights into the limited extent to which drivers used kneeling mechanisms of their own volition. It suggested that initial compliance with mandatory kneeling may be poor and enforcement difficult. Also, if a rigorously enforced policy of compulsory kneeling were to be introduced, then the use, and potential wear & tear, of kneeling equipment would substantially increase, due to the considerable increase in the total amount of kneeling, from this low baseline.
The surveys generally revealed a high level of public support for kneeling buses in general, with in the region of 90% of respondents saying that they are a “good idea” or a “very good idea”. Interviews with management staff generally showed there to be a very positive attitude towards kneeling buses, with a clear appreciation that the ability of the vehicles to provide level boarding and alighting facilities might encourage more people to use buses. A common view, however, was that drivers are very capable of using their discretion and knowing when kneeling might be required at a stop, implying little or no appreciation for the fact that many disabilities are invisible, so that no driver can realistically be expected to adequately make such a judgement. Nevertheless, the view that the driver’s discretion is sufficient was shared by a substantial proportion of drivers who were interviewed.
Analysis of a large dataset of bus trips from the black box computers installed on the buses in each trial enabled the calculation of average stop dwell time, by dividing the length of time the bus doors were open by the number of times the bus doors opened. The analysis revealed that average stop dwell time for trips where the bus knelt at a high percentage of stops (over 70%), was 1 second greater than for discretionary kneeling (i.e. normal operation) in two of the trials (Cannock and Stratford), 2 seconds greater in one of the trials (Wakefield) and for two of the trials (Coventry and Putney) there was no difference in average stop dwell time between high frequency kneeling and discretionary kneeling. Such results seem to contradict the view of drivers and operator management staff interviewed during the project who perceived that kneeling at every stop would lead to a much greater increas