Routine bus maintenance is crucial for the smooth functioning of an effective bus system. Preventive maintenance is defined as a servicing undertaken by technicians to maintain equipment in a satisfactory operating condition, to avoid failures or major defects (US Department of Defence, 2018). It helps anticipate and initiate repairs, improves safety, prevent service interruptions and critical mechanical failure on the road. Regular maintenance of bus fleets has the benefit of (National Academies of Sciences, Engineering, and Medicine, 2010):
- preventing mechanical failures
- achieving zero breakdowns during service
- reducing Green House Gas (GHG) emissions
- lowering fuel costs by improving fuel efficiency
- promoting passenger satisfaction and public
- improving occupancy rate, and
- increasing service life of buses
Preventive maintenance measures are usually conducted at fixed intervals. These intervals are based on legal requirements, the operating agency’s prior experience, manufacturer’s warranty requirements or merely borrowed from other agencies. The preventive maintenance interval suggested in the United States is 6,000 miles or about 10,000 kilometres (National Academies of Sciences, Engineering, and Medicine, 2010). In India, APSRTC (2016) reports doing the same within 9000 to 15,000 kilometres depending on the type of operation, age and model of the bus. Similarly, BMTC (2012) performs a docking preventive maintenance at a span of 20,000 kms. apart from the periodic 1 day, 2 days and 10 days maintenance. Apart from Preventive Maintenance Inspections (PMI), daily service line inspections are also undertaken. Through the case studies of WMATA and APSRTC, this article looks into the measures, needs and advantages of Preventive Maintenance.
CASE STUDY 1: Washington Metropolitan Area Transit Authority (WMATA): Use of AVM to optimize preventive maintenance
Metrobus service at Washington Metropolitan Area Transit Authority (WMATA) provides service in Washington DC. With a fleet of 1500 buses, WMATA covers an area of 1500 square miles. It serves a population of 3.4 million and logs about 134 million trips annually. As of 2010, the fleet also contains 460 CNG buses and 50 hybrid buses, with steps being taken to increase the number of low emission buses. WMATA has a preventive maintenance interval of 6000 miles (National Academies of Sciences, Engineering, and Medicine, 2010).
WMATA uses Automatic Vehicle Monitoring (AVM) system to support their preventive maintenance measures effectively. About half of their fleet are equipped with AVM and depots are equipped to download the service line data wirelessly when the bus enters the depots. Data on various components such as engine, transmission, heating, ventilation, air conditioning, door system, brake pushrod travel, etc. are monitored, recorded and reported on a daily basis. When specific parameters are over the critical range, the driver receives an alert immediately. The system also notifies the control centre and maintenance department about the flagged defaults. In other non-critical cases, an itemized report (annex 1) is generated to aid technicians to prioritize repairs. Technicians then schedule non-critical defects for maintenance at another time or during the next upcoming PM inspection (National Academies of Sciences, Engineering, and Medicine, 2010).
The benefits of preventive maintenance through AVM are as follows (National Academies of Sciences, Engineering, and Medicine, 2010):
- Senior technicians are able to conduct a trend analysis from the review of past issues. The trend analysis generates a work order on detecting the actions required to correct the defect. This relieves the technicians from diagnostics work.
- Fault detections are faster and more accurate
- Using AVM has enabled the collection of system components data on a daily basis, instead of PMIs of 10,000 kms. This regular check on components has helped prevent initial problems from growing into critical issues.
- Loaded with quality information and analyses, WMATA is able to request certain technical specifications while procuring new buses.
- The agency also uses the data to check for procedural compliance of drivers
- The agency is able to save money from warranty claims
CASE STUDY 2: APSRTC: Maintenance practices to maximize fuel economy
Improvement in fuel efficiency is another major benefit that stems from regular fleet maintenance. In 2015-16, 47 SRTUs reported that on an average they spent about 25% of their operating cost on fuel (Ministry of Road Transport, 2017). Therefore, even a small improvement in fuel efficiency significantly reduces the operating cost. The cost saved can be diverted into critical service repairs and improvements.
Andhra Pradesh State Road Transport Corporation (APSRTC) covers over 4.3 million kilometres and carries about 6.5 million passengers. As of 2015, it has 12,152 buses. In an effort to maximize the fuel economy and reduce GHG emissions, Energy Sector Management Assistance Program developed bus maintenance guidelines and implemented them in Hyderabad and Vijayawada in APSRTC in 2011. Some of the recommended course of actions include (ESMAP, 2011):
- management commitment
- setting fuel economy benchmark
- publicly communicating fuel economy results
- automation of data collection and analysis
- using data to refine preventive maintenance interval
- conducting two-tiered checks at the depot and central maintenance facility
- requiring mechanics to sign-off repairs
- conducting random and period checks of repairs
- having an independent QA/QC team
- retraining mechanics periodically
- Trainings for low performing drivers
- providing awards as incentives for technicians and drivers
A key recommendation was to conduct two-tiered maintenance checks that are well documented and standardized as operating procedure. Junior to mid-level mechanics can conduct the Tier 1 (Annexure 2) maintenance while Tier 2 (Annexure 3) maintenance needs to be done by well-trained senior mechanics.
The above recommendations were implemented and tested over a period of 10 weeks in 2011. Under APSRTC, 3 bus depots were chosen to do the field testing, namely Bharkatpura (BKPT) depot in Hyderabad, Governorpet1 (GVPT1) and Governorpet2 (GVPT2) in Vijayawada. In each of these depots, 10 buses and 20 drivers performing lowly on fuel economy were identified each month. Maintenance for low performing buses and trainings on good driving practices for the drivers was conducted to maximize the fuel economy (ESMAP, 2011).
Image 1: Maintenance facility of APSRTC Source: APSRTC, 2016
From the subset of buses that underwent maintenance, the results show that the maintenance had a positive and significant effect
on the fuel economy. Average fuel economy benefits range from 6 to 9 percent. Figure 1 shows the fuel economy improvements from repairs at Bharkatpura Depot in Hyderabad Older buses (>=4 years) appear to benefit more from the maintenance activities than newer buses (< 3 years) (ESMAP, 2011).
Figure 1: Percent fuel economy improvements from repair of buses at Bharkatpura Depot in Hyderabad.
Source: ESMAP, 2011
The trainings for drivers included instructions for best practices with on-road training. The design of the training accustomed the drivers with the local driving conditions. From figure 2, it is evident that on an average the fuel economy improvements from driver training were between 5 to 10 percent. Displaying the fuel economy’s information publicly made the drivers feel highly motivated. Awarding the mechanics and drivers for good fuel economy performance boosted their pride and their performance (ESMAP, 2011).
Figure 2: Percent fuel economy improvements from driver training in Vijayawada and Hyderabad
Source: ESMAP, 2011
Scaling up the results of figure 3 for the entire fleet of Hyderabad (3290 buses), the gain in fuel economy from maintaining old buses would be around 3% and from maintaining new buses it would be 2.1%. Similarly, the benefit of driver training for the entire fleet is estimated to be 2.7%. When extrapolating the results for both maintenance and driver training combined, the benefit from fuel economy is estimated to be 4.8% for the new buses and 5.7% for old buses (ESMAP, 2011).
Assuming 100 buses in a depot, the cost-benefit ratio of the recommended changes is 1.94 for new buses to 2.31 for old buses. The monthly cost of implementing all the recommended changes is estimated to be INR 1,46,651 per bus and the fuel savings per month is estimated to be INR 2,84,928 per bus for newer buses and INR 3,38,352 per bus for older buses. In Hyderabad alone, APSRTC can save about INR 95,40,000 per month by achieving a 5 percent improvement in the fuel economy (FE) (ESMAP, 2011).
Figure 3: Comparison of Average Fuel Economy
In WMATA, the availability of real-time data has equipped the agency to engage in preventive maintenance measures actively, thereby ensuring smooth functioning of the bus system in Washington DC. Through data analysis, the agency has developed a deep understanding of their priorities and specific requirements in buses. Flagged issues are dealt with at the earliest possibility, rather than allowing it to develop into a critical and more expensive problem to fix.
In APSRTC’s case study, test results from Hyderabad and Vijayawada reiterate the importance of preventive maintenance and onroad training of bus drivers to maximize on the fuel economy. With cost-benefit ratios of 1.94 for new buses and 2.31 for old buses, the recommended maintenance activities prove to be cost-effective for large operators with in-house maintenance capacity. These results would be more effective on considering the benefits from reduced GHG emissions and improved safety. The APSRTC case study has demonstrated that overall efficiency and safety improvements can be achieved costeffectively through maintenance activities.
The above recommendations for preventive maintenance are based on the assumptions that the depots have at least 70 to 100 buses, have an existing maintenance facility, has ability to conduct most of the maintenance activities in-house and has the capacity to train its drivers. These measures might be cost-intensive and challenging for informal bus operators who manage fewer routes with a smaller bus fleet. Yet, it is imperative for small-scale operators to plan and schedule their maintenance activities to benefit from improvements in fuel economy and improved safety.
Annex 1 – An example of a daily non-critical exemptions report generated
Source: National Academies of Sciences, Engineering, and Medicine, 2010
Annex 2: Tier 1 Checks At The Local Bus Depot To Improve Fuel Economy
Source: ESMAP, 2011
Annex 3: Tier 2 checks at the central bus maintenance facility to improve fuel economy
Source: ESMAP, 2011