Comparison of capacity and trip length
In public transport, the mode capacity and route/trip length are the most important parameters to make it valuable for the planners and commuters. The frequency of buses is increased during peak-hour and buses with higher capacity such as articulated or bi-articulated buses are operated during peak hours. Similarly, during off-peak hours buses with low capacities are operated at a lower frequency to meet the demand to ensure optimal operation of the public transport system. However, in Karachi, the public transport modes (bus/chingchi) with fixed capacity are operated. The operators of public transport routes adjust the frequency of the bus/chingchi to meet the fluctuating demand. It is also observed that the operators purposely keep the frequency lower than the demand to ensure maximum profit, as there is no framework in place to ensure a certain level-of-service. Another important parameter associated with the mode of public transport is its PCE, especially when it operates in mixed traffic. Table 3 shows the capacities and PCE factors of the available modes of public transport in Karachi.
Table 3 shows that the capacity of bus service is highest among the existing modes of public transport, which is relatively higher as compared to other public transport, which are 75 persons per bus. Whereas, the capacity of a minibus is 40 persons and petrol operated bike-chingchi has the sitting capacity of 8 persons per vehicle.
The mode of public transport with the highest value of passengers per PCU should be preferred, as it is an indicator of optimal road space utilization. Figure 2 compares the values of passengers per PCU for different modes of public transport and it indicates that the bus has the highest number of passengers per PCU with 28 passengers per PCU. Chingchi has the least values of passengers per PCU, which is 16 passengers/PCU. The higher value of passenger per PCU also highlights the significance of having a proper public transport system, where more persons can be accommodated in less space in comparison with private modes of transport. Furthermore, this analysis also suggests that bus or any other mode with higher capacity should be used in urban public transport.
The data of route lengths for the selected routes were collected and the average route length is shown in Fig. 3. Chingchi is operated without approved routes and its operation on some major arterials is prohibited. Therefore, it operates mainly on collector roads with shorter routes. Thus, chingchi has the least observed route length with 12.87 km, whereas minibuses have the longest routes with around 49 km route length. Figure 4 shows the number of passengers served during a trip by different public transport modes. It indicates that, as expected, the number of passengers increases with the increase in trip length. Therefore, longer public transport routes are better for the transport system.
Comparison of fuel consumption and cost
The categories of PT modes for fuel analysis are more than the categories of PT modes used in previous sections, as minibuses and chingchi are operated on two different fuels. Bus and chingchi rickshaw only use CNG as fuel, chingchi bike uses petrol, and minibuses are operated on both CNG and Diesel. Fuel consumption for different modes on different fuel types is based on the survey data collected from drivers and operators of these modes. Estimated mileages in kilometre per unit of fuel are compared in Fig. 5 along with passenger kilometre per unit of fuel. Fuel consumption for petrol and diesel is measured in litters and CNG is measured in kilograms. Figure 6 compares the cost per unit distance and cost per passenger kilometre for available modes of PT in Karachi.
The comparison shown in Fig. 5 reveals that CNG buses consume the highest amount of fuel to travel a unit distance in comparison with other modes. The most fuel-efficient mode of PT is chingchi rickshaw which gives highest km per kg of CNG i.e. 18 km per kg. In terms of fuel efficiency measured in passenger-km per unit fuel, the most efficient PT mode is CNG minibus, whereas the least fuel-efficient mode is petrol chingchi bike.
Figure 6 shows that per kilometre cost of travel is highest for CNG bus and lowest for CNG chingchi rickshaw. However, travel cost per passenger kilometre is lowest for CNG minibus with PKR 0.56 Rs/passenger-km, and highest cost is estimated for a diesel-fuelled minibus with 0.81 Rs/passenger/km. This shows that for similar types of minibuses, the change of engine from diesel to CNG reduces the fuel cost for transportation by 30%. The cost for all other modes exists within this range.
Statistical analyses of the collected data were performed to determine if there is a significant relationship between fuel consumption and the type of PT mode. The outcome of one-way ANOVA analysis is shown in Table 4. The null hypothesis assumed that there is no association between fuel consumption/cost and the mode of PT. The results show that p value for one-way ANOVA between mode of transport and cost of fuel per km and cost of fuel per passenger kilometre is less than 0.001, which means that null hypothesis is rejected and alternate hypothesis is accepted. Thus, it can be concluded that there is a significant association between different modes of public transport and their cost of travel.
Comparison of energy consumption
The comparison for fuel consumed by different modes of PT is discussed in the previous section. Fuel consumption and energy consumption may be different, as the amount of energy produced by the combustion of the unit amount of different fuels may be different. Furthermore, the fuels in existing modes of PT are measured in different units, whereas the unit of energy consumption for all the fuels will be the same. The energy consumed in transporting a unit distance per person is estimated by multiplying the amount of fuel consumed per km per person with the energy produced by combustion of that fuel type. The data of the amount of fuel consumed per km per person was acquired in the survey from transport operators, which is presented in Fig. 5. The amount of energy produced by unit fuel combustion is taken from the available literature .
The comparison of energy consumption shows that the PT modes using high octane fuel are utilizing higher energy. Fuel types like diesel and petrol have higher energy contents in comparison with CNG measured in British Thermal Unit (BTU) . Figure 7 compares the energy computation for different modes of PT. It shows that the diesel-driven bus consumes the highest amount of energy per passenger-km. There is a significant difference in the amount of energy consumed by CNG-powered engines and petrol/diesel driven engines. CNG minibus has the least value of energy consumption, which is 8.9 BTU per passenger kilometre in comparison with 275.9 BTU per passenger kilometre for diesel minibus.
Statistical analysis of energy consumption per kilometre and per passenger kilometre, represented in BTU, shows that there is a significant association between modes of PT and energy consumption. The results of the one-way ANOVA are shown in Table 5. The P value for BTU per kilometre and BTU per passenger-km is less than 0.001, which shows that the alternate hypothesis may be accepted, indicating that there is an association between energy consumption and mode of PT.
Comparison of emission
The emissions from the transport sector are a major contributor to overall carbon-footprint. The emissions resulting from transport of persons can be reduced by increasing the share of public transport and reducing the dependency on private vehicles. Within various modes of public transport, the emissions are dependent on capacity and engine type of mode. This research also compares the emissions by different modes of PT in Karachi.
Actual emissions from a specific model can be accurately estimated using tailpipe emission analysis. Calibrated models exist for tailpipe emissions for different types of vehicles. However, there is no such data for the local modes of transport used in Karachi, as the emissions are affected by the type, age, maintenance and various operational parameters . Due to lack of existing emission factors for local transport modes, this study estimates the emissions based on the fuel/energy consumption data collected from the survey along with standard values of emissions per unit consumption of energy .
The comparison of emissions for different modes of transport measured in the equivalent of CO2 is shown in Fig. 8. Figure 8 shows a trend similar to the trend observed in Fig. 7. The emissions are directly dependant on the amount of energy produced during the combustion process. Results show that the highest emissions per passenger kilometre for travelling a unit distance are highest for the diesel-powered minibus. Similarly, CNG minibus emits the least CO2 during transport of passengers.
The amount of emissions per passenger per km is higher in diesel and petrol-driven PT modes as compared to CNG-driven PT modes. Results show that two types of minibuses with the same transportation capacity but different fuels (diesel and CNG) have significantly different emissions. Figure 8 shows that diesel minibus emits 1.557 lb of CO2 per km, whereas CNG minibus emits 0.0364 lb of CO2 per km, which is around 42 times. Statistical analysis of emission per kilometre and emission per passenger-km shows a significant association between PT modes and emissions from various available modes, as indicated by results of one-way ANOVA shown in Table 6.
Introduction and comparison of BRT system
The existing public transport system in Karachi is dominated by poorly operated and informal modes. The public transport operates without enforcement of any level of service criteria (time headways, punctuality, and seat/space availability) by the authorities. No bus schedules exist for any mode and route of public transport in Karachi and the entire public transport is operated on the principle of profit maximization by their operators. This results in continuously decreasing dependency on PT and more reliance on private vehicles, which leads to unsustainable transport system .
Finally, authorities have realized the significance of having a proper mass transit system and five Bus Rapid Transit (BRT) routes, as suggested by JICA Japan International Cooperation Agency, are being introduced in Karachi. The routes have been named as Green Line, Orange Line, Red Line, Blue Line, and Aqua Line. The infrastructure for Green Line and Orange Line BRT routes is under construction, while the other three BRT lines are in the planning phase. Green Line has a 25 km long dedicated bus-corridor with right of way category A. This section compares the BRT buses with the existing modes of PT to highlight the significance of the proposed mass transit system.
According to the official document, the fleet of buses for Green Line BRT will comprise of diesel-powered articulated buses with seating plus the standing capacity of 150 persons/bus [49, 50]. This research compares the attributes of the proposed diesel-powered bus with the existing modes of public transport. A CNG-powered articulated bus with similar capacity is also included in the analysis to compare the improvement in various operational parameters if a CNG operated bus would have been used instead of a diesel-driven bus.
The comparison of existing modes of PT with BRT is compared in Fig. 9. It shows that the BRT has a capacity of carrying 50 passengers per PCU, which is approximately twice the capacity of a bus. Thus, more passengers can be transported in comparatively lesser space with the introduction of BRT.
The data about the fuel consumption of the existing modes of PT was collected using the field survey. The fuel consumption of the proposed diesel bus is based on the data available from the official report [49, 50]. For comparative analysis, a CNG bus with similar capacity is selected. Figure 10 shows that passenger-km per litre of fuel is comparatively higher for diesel articulated bus than the CNG articulated bus. The passenger-km per litter for diesel articulated bus is 320, whereas for diesel minibus 133 passengers are transported per litre of diesel. Similarly, passenger-km per litter for CNG articulated bus is significantly higher than CNG minibus. This shows that a significant amount of fuel can be saved by the introduction of BRT and replacing the existing PT routes with articulated buses.
The fuel cost per km of travel and fuel cost per passenger kilometre is compared in Fig. 11. It shows that the fuel cost per passenger-km is lowest for diesel articulated bus, which is PKR 0.346 PKR per passenger-km, whereas the fuel cost for CNG articulated bus is 0.39 PKR per passenger-km. This could be the main reason behind the selection of diesel buses for Green Line BRT route. Furthermore, the supply of CNG is not consistent, as it suffers from a shortage of supply and closure on certain weekdays to manage the demand. However, using CNG is significantly environmental friendly. Figure 12 compares the energy consumed per passenger-km of BRT with the existing PT modes. The amount of energy consumed by diesel articulated bus is around seven times higher than the CNG articulated bus. The energy consumed per passenger-km for diesel articulated bus is significantly lower than current PT modes on diesel and petrol. Similarly, the CO2 emission per passenger-km is significantly lower for CNG articulated bus in comparison with diesel articulated bus.
The comparison of CO2 emissions from existing public transport modes and the proposed articulated buses for Green Line BRT is shown in Fig. 13. All the CNG fuelled modes have significantly lower emissions in comparison with petrol and diesel-fuelled modes. Furthermore, the diesel-fuelled articulated bus has less than half CO2 emissions per passenger-km in comparison with the diesel operated minibus. The comparison of the proposed diesel-fuelled articulated bus with the assumes CNG articulated bus shows that the emissions from CNG articulated bus are approximately ten times less than the diesel-fuelled articulated bus. This shows that emissions from CNG fuelled articulated buses are significantly lower and the environmental impact of Green Line BRT can be reduced by considering CNG fuelled buses.